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Concrete maturity

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Title:
Concrete maturity the combined effects of temperature and time on early-age strength development
Creator:
LaCome, Matthew L
Publication Date:
Language:
English
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90 leaves : ; 28 cm

Subjects

Subjects / Keywords:
Concrete -- Effect of temperature on ( lcsh )
Concrete -- Curing ( lcsh )
Concrete -- Testing ( lcsh )
Concrete -- Curing ( fast )
Concrete -- Effect of temperature on ( fast )
Concrete -- Testing ( fast )
Genre:
bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

Notes

Bibliography:
Includes bibliographical references (leaves 89-90).
General Note:
Department of Civil Engineering
Statement of Responsibility:
by Matthew L. LaCome.

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Source Institution:
|University of Colorado Denver
Holding Location:
|Auraria Library
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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
45210648 ( OCLC )
ocm45210648
Classification:
LD1190.E53 2000m .L33 ( lcc )

Full Text
CONCRETE MATURITY: THE COMBINED EFFECTS OF
TEMPERATURE AND TIME ON EARLY-AGE STRENGTH
DEVELOPMENT
by
Matthew L. LaCome
B.S., Walla Walla College, 1996
A thesis submitted to the
University of Colorado at Denver
in partial fulfillment
of the requirements for the degree of
Master of Science
Civil Engineering
2000


This thesis for the Master of Science
degree by
Matthew L. LaCome
has been approved
by

Judith J. Stalnaker
John R. Mays
4-26,-00
Date


LaCome, Matthew L. (M.S., Civil Engineering)
Concrete Maturity: The Combined Effects of Temperature and Time on Early-Age
Strength Development
Thesis directed by Assistant Professor Kevin L. Rens, P.E.
ABSTRACT
This thesis discusses the concept of concrete "maturity". It begins by looking
at the history and early theories of how the combined effects of temperature and time
affect concrete strength. The result of continued research on the subject has led to
several forms of non-linear equations, which help predict the early-age strength of
concrete. These equations are defined and discussed briefly. The maturity method
was incorporated into an American Society for Testing and Materials (ASTM)
standard method, C 1074-87. This standard is introduced and one of the main
limitations of the current standard is explained. The results of a survey sent to the
fifty Departments of Transportation (DOT) across the nation are presented. Several
of the written comments are evaluated. The thesis explains how the maturity concept
can be used as a Non-Destructive Evaluation (NDE) method to prevent certain types
of concrete failures. Also, two case studies are presented to explain how the concept
can and has been used in a forensic investigation. A research pilot study to


investigate certain aspects of the concept was conducted as part of the research. The
objective of the pilot study was to determine the point in time when temperature no
longer affects the long term, ultimate strength of concrete. The procedure and results
are presented. The thesis concludes with a summary and final recommendations for
future research in the area of concrete maturity.
This abstract accurately represents the content of the candidate's thesis. I
recommend its publication.
Signed
Kevin L. Rens
IV


DEDICATION
I dedicate this thesis to my loving wife, Marilyn and all my other family
members whose continuous encouragement kept me going towards this goal.


ACKNOWLEDGMENTS
I would like to first thank God for giving me the strength each and every day
needed to complete this project. Next, I would like to thank Professor Kevin Rens,
P.E., chair of my thesis committee, for his unending support and guidance.
Throughout the project, Prof. Rens taught me, not only with words but by example to
strive towards excellence. I would also like to thank Prof. Rens for allowing me to be
in charge of the project from beginning to end. This was a great learning experience.
I want to also thank the other faculty on my thesis committee, Professors Judy
Stalnaker and John Mays.
I need to also acknowledge several students, who helped me a great deal in
performing the 1999 pilot study. First, Adam Blankespoor who helped me a great
deal in mixing, testing, and recording all the data for the pilot study. Without Adam's
diligent work, the pilot study would not have been completed. Also, Myron LaCome
and Elie Humamji, who both helped out with the exciting work of mixing the
concrete batches by hand. I would like to again mention Prof. Rens, because he also
got in there and helped out with the hard work of mixing concrete and preparing the
samples for the pilot study. Finally, I would like to thank the University of Colorado
at Denver for the financial support provided to complete the pilot study. Without it,
we would have been hard pressed to finish the work.


CONTENTS
Figures ................................................................ x
Tables ................................................................. xi
Chapter
1. Introduction ........................................................ 1
1.1 History ............................................................ 1
1.2 Purpose ........................................................... 3
1.3 Scope ............................................................. 4
2. Theoretical Maturity Functions ..................................... 6
2.1 TTF Maturity Index ................................................ 6
2.2 EA Maturity Index ................................................. 7
2.3 Simplified Rate Constant Equation ................................. 9
3. ASTM Cl074 Standard Procedure....................................... 11
3.1 Introduction ............................................................ 11
3.2 TTF Maturity Index Procedure ........................................... 12
3.3 EA Maturity Index Procedure ............................................ 14
3.4 ASTM Cl074 Limitations ................................................. 14
4. 1998 Department of Transportation Survey................................. 17
4.1 Introduction ...................................................... 17
4.2 Purpose
17


4.3 Questionnaire Results
18
4.3.1 Tabulated Responses ................................................. 18
4.3.2 Written Responses ................................................... 21
5. Using Maturity as a "NDE" and Forensic Tool ...................... 23
5.1 Introduction .......................................................... 23
5.2 Using Concrete Maturity to Prevent Concrete Failures ............ 23
5.3 Using Concrete Maturity in Forensic Engineering ................. 24
5.3.1 Case Study #1: Hypothetical Example ................................. 24
5.3.2 Case Study #2: Cooling Tower Failure at Willow Island, WV ........... 27
5.4 Summary .............................................................. 30
6. 1999 Research Pilot Study .............................................. 31
6.1 Introduction .......................................................... 32
6.2 Purpose .............................................................. 33
6.3 Experimental Testing Procedure ....................................... 34
6.3.1 Phase 1 Constant Curing Temperatures .............................. 35
6.3.2 Phases 2 Through 5 Step Function Curing Temperatures .............. 36
6.4 Data Analysis ........................................................ 39
6.4.1 Strength vs. Time Data .............................................. 39
6.4.2 Rate Constant vs. Temperature Relationship .................... 40
6.4.3 Strength vs. EA Maturity Index ...................................... 40
viii
6.5 Results
40


6.5.1 Results From Phase 1 .............................................. 40
6.5.2 Results From Phases 2 Through 5 ............................. 43
6.6 Errors .............................................................. 48
6.7 Pilot Study Summary and Recommendations ....................... 49
7. Summary, Conclusions and Recommendations ............................. 50
Appendix
A. 1998 Questionnaire .................................................. 53
B. Willow Island Cooling Tower Failure ........................... 60
C. 1999 Pilot Study Data ............................................... 66
References .............................................................. 89
IX


FIGURES
Figure
1.1 Typical Strength vs. Time Curves for Concrete Cured at Different 3
Temperatures
3.1 Typical Maturity-Strength Relation ............................... 13
3.2 Typical Temperature-Time Curve for Field Cured Concrete .......... 15
6.1 Dry Gravel Being Weighed ......................................... 32
6.2 Finished Mix ..................................................... 33
6.3 Phase 2 Curing Temperatures ...................................... 37
6.4 Phase 3 Curing Temperatures ...................................... 38
6.5 Rate Constant vs. Constant Temperature ........................... 42
6.6 Phase 1 EA vs. Strength for Three Constant Temperatures .......... 42
6.7 Ultimate Strength vs. Time in Cold Prior to Warm ................. 44
6.8 Ultimate Strength vs. Time in Warm Prior to Cold ................. 45
6.9 Ultimate Strength vs. Time in Hot Prior to Warm .................. 46
6.10 Ultimate Strength vs. Time in Warm Prior to Hot .................. 47
B.l Temperature Variation Used to Cure Test Specimens ........ 63
B.2 Compressive Strength vs. Maturity TTF............................. 64
x


TABLES
Table
4.1 Results of State Highway Agency Questionnaire ....................... 19
6.1 Concrete Mix Proportions ............................................ 34
6.2 Phase 1 Strength-Age Data ........................................... 41
6.3 Ultimate Strength vs. Time in Cold Prior to Warm .................... 43
6.4 Ultimate Strength vs. Time in Warm Prior to Cold .................... 45
6.5 Ultimate Strength vs. Time in Hot Prior to Warm ..................... 46
6.6 Ultimate Strength vs. Time in Warm Prior to Hot ..................... 47


1.
Introduction
Maturity is defined as the combined effects that temperature and time have on
concrete strength gain. The product of temperature and time is incorporated into a
maturity index, and the maturity index is then related to the strength gain of concrete
in the form of a hyperbolic curve. Utilizing the concept allows construction tasks,
such as form removal and load application, to be performed on a more efficient time
schedule.
During the past fifty years, there have been numerous studies contributing to
the continued development of the maturity concept. One of the most significant
developments took place in 1987 when the American Society for Testing and
Materials (ASTM) first published the standard method C 1074-87 titled, Standard
Practice for Estimating Concrete Strength by the Maturity Method. This was a
major step in gaining acceptance as a viable non-destructive testing method that could
be used in the field to estimate the in-place strength of concrete. Since then, there has
been a growing interest in the maturity concept and how it can be utilized in the
concrete industry.
1.1 History
Maturity was first defined in the early 1950s as the combined effects that
temperature and time have on strength gain of concrete (Saul, 1951). It is well
documented that as concrete ages it continues to gain strength. This is the basis for
1


the seven and twenty-eight day cylinder testing. The effect that temperature has on
concrete, however, is less understood. During the early part of this century, research
was conducted on the effects of curing temperatures. McDaniel, (1915) found that
the same concrete cured at different temperatures would develop strength at different
rates. Later, Wiley, (1929) stated that the higher temperatures produced a faster rate
of strength gain. About twenty years later, McIntosh, (1949) attempted to develop a
way to predict the strength gain of concrete for different curing temperatures, but it
wasnt until Saul, (1951) that a single term, which he called maturity, was introduced.
Since then, it has been found that the effects of temperature on concrete strength gain
are most profound during the early-age of the concrete (Carino, 1981; Barnes et al.,
1977; Tashiro and Tanaka, 1977). These studies indicated that the early-age
temperature not only affects the rate of strength gain, but also the long-term, limiting
strength of the concrete. This is important because the same concrete cured at
different temperatures will develop different limiting strengths. Figure 1.1 shows two
typical strength-versus-time curves, for the same concrete cured at different
temperatures. It is clear from Figure 1.1 that the curing temperature affects both the
early-age strength gain as well as the limiting strength of concrete (Carino, 1981).
The concrete cured at the high temperature gains strength faster initially. Flowever, at
some point in time the strength of the concrete cured at the low temperature will
surpass that of the high temperature cured concrete. Ultimately, the concrete cured at
the lower temperature will reach a higher limiting strength than the concrete cured at


Time (hours)
Figure 1.1 Typical Strength vs. Time Curves for
Concrete Cured at Different Temperatures
the higher temperature. As stated above, research has shown that the early-age
temperatures have the most influence on the rate of strength gain, as well as the
limiting strength. It is during this early-age period when heat, produced by the
chemical reactions taking place, is most significant. It is also the period when the
concrete develops strength at the fastest rate.
1.2 Purpose
The purpose of this thesis was to investigate several aspects of the maturity
concept. This includes the following:
3


Determine if and to what extent the maturity concept is being applied in
the field
Explain how the concept is a valid non-destructive evaluation (NDE)
method and forensic investigation tool
Conduct a pilot study to try and estimate the time when temperature no
longer affects ultimate strength
Investigate a new procedure to utilize the maturity concept in the field
1.3 Scope
This thesis covers several topics, which help fulfill each purpose. In order to
determine if the concept is actually being utilized in the concrete industry several
meetings were held at the Colorado Department of Transportation (CDOT) in the
spring of 1998. Also, a survey was sent to each of the fifty state transportation
departments (DOTs). A comprehensive literature review was performed in order to
gain a better understanding of the concept. During this review, it was learned that the
maturity concept is a valid NDE method and forensic tool. Finally, a pilot study was
conducted at the University of Colorado at Denver, during the summer of 1999. The
purpose of the pilot study was to estimate the point in time when temperature no
longer affects the ultimate strength and also to investigate an alternate procedure to
the current ASTM C 1074 standard.
The thesis consists of seven chapters. Chapter 2 discusses the theoretical
basis for the current maturity index-strength functions. It is necessary to begin with a
4


review of the theory to help gain a better understanding of the concept. Chapter 3
takes a look at the current ASTM C 1074 standard method and one of the main
limitations of the ASTM method. Chapter 4 describes the DOT survey and the
results. A major portion of chapter 4 considers the written responses submitted by
some of the DOTs. Chapter 5 describes how the maturity concept can be used as a
NDE method to help prevent certain types of concrete failures. It also discusses how
the concept can be used in a forensic investigation. Chapter 6 explains in detail the
pilot study, which was conducted as part of the overall study. Chapter 7 begins with a
summary of the thesis and then gives some final conclusions and recommendations
for future research work in the area of concrete maturity.
5


2.
Theoretical Maturity Functions
In order to begin to understand the maturity concept a brief explanation of
several widely accepted maturity index functions is necessary. There are two
separate functions defined in the current ASTM C 1071-93 standard. These are the
Temperature-Time Factor (TTF) maturity index and the Equivalent Age (EA)
maturity index. The TTF index is the preferred method in the U.S. and the EA index
has gained wide acceptance in Europe (Carino, 1984). Research has shown that the
EA index is a more accurate representation of the relationship between temperature
and rate of strength gain (Carino, 1984). Numerous modified functions have been
considered. One such modified function is a simplified EA index, which simplifies
some the computations (Carino et. al, 1992). The next three sections will discuss the
two main maturity index functions as well as the modified EA function presented by
Carino et. al, (1992). Other modified functions are out of the scope of this thesis.
Carino et. al, (1992) is a good source to learn more about these functions.
2.1 TTF Maturity Index
The TTF index was developed during the early 1950s. It has also been called
the Nurse-Saul equation, named in part for the primary researchers who developed it.
Saul introduced the term maturity to define the combined effects that temperature
and time have on concrete strength (Saul, 1951).
6


The TTF is currently defined in ASTM C 1074-93 as:
M(t) = X (Ta T0)At (2.1)
where: M(t) = TTF at age t, (C-hours),
Ta = Average concrete temperature during time interval, (C),
T0 = The datum temperature at which cement hydration stops, (C),
At = Time interval, (hours).
This TTF is essentially the same term that Saul defined as maturity.
The fundamental basis of the TTF is based on the assumption that the rate of
strength gain is linearly related to curing temperature (Carino, 1984). It has been
shown, however, that a linear function does not adequately define the relationship
between temperature and the rate of strength gain (Freiesleben-Hansen and Pedersen,
1977; Carino, 1984). It has been shown, that a more accurate relationship is produced
by a exponential model, which is the basis of the equivalent age method (Carino,
1984).
2.2 EA Maturity Index
The EA maturity index was originally based on the Arrhenius equation. This
equation was first introduced in 1888 by Svante Arrhenius to explain why chemical
reactions do not happen instantaneously when reactants are brought together, even
though the reacted form is at a lower energy state (Brown and LeMay, 1988). The
rate that a chemical reaction takes place is directly related to temperature. This can
be explained by what happens in a molecular system during a chemical reaction. In
7


the system, molecules are in constant motion, and energy is transferred between them
as they collide (Brown and LeMay, 1988). These collisions cause some of the
molecules to eventually gain enough energy to form reactants at the lower energy
state (Carino et al., 1992). Adding heat to the system increases the molecules kinetic
energy, causing more molecular collisions. This results in more molecules gaining
enough energy to form reactants at a faster rate (Carino et al., 1992). A term called
the rate constant defines this rate at which the chemical reaction takes place for a
specific constant temperature. The Arrhenius equation defines the rate constant as a
function of constant temperature as:
k = Ae_E/RT (2.2)
where: k = Rate constant, (K),5
A = The frequency factor of molecular collisions,
E = Activation energy, (J/mole),
R = Universal gas constant, (8.314 J/K-mole),
T = Absolute temperature, (K).
A complete review of how this equation is implemented into the EA maturity index
can be found in Carino et al., (1992). ASTM Cl074-93 defines the equivalent age
index as:
~Q(y~)
te = YJe At (2.3)
where: te = Equivalent age at a specified temperature Ts, (hours),
8


Q = Activation energy divided by the gas constant, (K),
Ta = Ave. temperature of concrete during time interval, (K),
Ts = Specified temperature, (K),
At = Time interval, (hours).
The complexity of Equation (2.3) has lead to investigations for the
development of other functions that share the improved accuracy of the equivalent
age function, but are easier to work with (Carino et al., 1992). One of the simplest
and most accurate functions was developed by Carino in this same 1992 paper.
2.3 Simplified Rate Constant Equation
It has been documented that the relationship between the rate constant and
constant curing temperatures can be defined with a much simpler equation than the
Arrhenius equation (Carino et al., 1992). In this same paper, Carino defined the
relationship between the rate constant and constant temperature as:
Using the simplified rate constant equation, the equivalent age maturity index
becomes:
(2.4)
where: k = Rate Constant, (C),
Ao = The value of the rate constant at 0 C, (C),
B = Temperature sensitivity factor, (C_1),
T = Concrete temperature, (C).
te = I eB(TTs) At
(2.5)
9


This simplified equivalent age index equation compares well to other proposed
maturity functions in its accuracy and simplicity (Carino et al., 1992). Due to the
simplicity of Equation (2.5), it may become a more accepted approach in the future.
The simplified equivalent age index equation along with the current equations
found in ASTM Cl074 provide methods that can be used for estimating in-place
concrete strength. These methods, however, have certain limitations that must be
considered when they are to be used. One of the more important limitations will be
discussed in the next chapter.
10


3. ASTM Maturity Functions
It is standard practice for any type of material testing to follow an ASTM
standard. This allows for a consistent testing procedure, which is important when
comparing results. This chapter discusses the ASTM standard Cl074 titled,
Standard Practice for Estimating Concrete Strength by the Maturity Method.
3.1 Introduction
In recent years, the maturity method has become a well-recognized way to
monitor the in place strength gain of concrete. As mentioned previously ASTM
established a standard method for utilizing the concept with the introduction of
Cl074-87. It has been updated to Cl074-93 but is essentially unchanged. The
standard was based largely on the paper published by Carino (1984). It has given the
construction industry a standard procedure for developing a maturity index-strength
relationship in the lab and then implementing the developed relationship in the field.
In the ASTM standard, there are two separate functions given to develop a
relationship between maturity and strength. The first one is based on what is
considered to be the traditional method and is based largely on the work of Nurse,
(1949), Saul, (1951), and Bernhardt (1956). This method incorporates the maturity
index described previously as the TTF. The second method uses the previously
described EA maturity index.
11


3.2 TTF Maturity Index Procedure
The procedure given in ASTM C 1074-93 for developing the relationship
between the TTF and concrete strength follows several basic steps. By recording the
temperature history of concrete as it cures, values of the TTF can be calculated. In
the ASTM procedure, temperatures of cylinders cured in the lab are recorded over a
period of twenty-eight days at specified time increments. These temperatures are
then used to calculate values of the temperature-time function. During this same
twenty-eight day time period, compressive strength tests are performed on the
cylinders at specified ages. After the testing is completed the values of the TTF are
calculated for each of the times when compressive strength tests were performed.
The strength values are then plotted against these TTF values. The TTF can then be
related to strength to develop a hyperbolic curve. Using regression analysis, a
hyperbolic equation can be developed for the maturity index-strength curve (Carino,
1984; Carino et al 1992).
Once the curve is developed, it can be used to predict strength gain
development for the same concrete mix placed in the field. This is accomplished by
first recording the temperature of the field concrete at specified time intervals. Then,
calculating the value of the TTF at the specific test times. Commercial maturity
meters are available that automatically calculate and record the values of the
temperature-time factor at specific time intervals. Once this value is obtained, it is
plotted on the pre-established strength versus TTF curve to determine the strength at
12


that specified time. A typical strength versus TTF curve is shown in Figure 3.1. It is
important to note that initially the concrete gains strength quickly and then slows
down until it theoretically reaches a final ultimate strength. The full procedure can be
found in ASTM C 1074-93.
It is worth mentioning that the datum temperature term T0, in Equation (2.1) is
usually assumed to be a constant value of-10C. This is generally not a valid
assumption, since the datum temperature will vary with concrete mix design, and this
assumption can lead to less accurate strength prediction results (LaCome et al., 1996;
Carino, 1984). The Appendix to ASTM C 1074-93 provides a method for
13


developing the datum temperature for a particular mix design. The explanation of
this procedure is out of the scope of this paper, and the reader is directed to the
ASTM Appendix as well as the paper published by Carino (1984) for a full
description. Carino also gives a thorough derivation of the equations used to develop
the hyperbolic curve relationship between the temperature-time factor and strength.
3.3 EA Maturity Index Procedure
The procedure in ASTM C 1074-93 for developing the relationship between
equivalent age and concrete strength is the same as for the temperature-time function.
The only difference is that the recorded temperatures are used to calculate equivalent
age values, rather then the temperature-time-factor. The activation energy, Q, in
Equation (2.2) is a function of concrete design mix, similar to the datum temperature
in Equation (2.1). A procedure for estimating the activation energy can also be found
in the Appendix to ASTM C 1074-93. Again, the reader can find description of the
procedure in (Carino, 1984).
3.4 ASTM C 1074 Limitations
One of the major limitations of the current ASTM standard is that it does not
consider the effects of early age temperature on the limiting strength of concrete.
This limitation is directly stated in Cl 074-93 section 5.3 (2) as, the method does not
take into account the effects of early-age concrete temperature on the long-term
ultimate strength. Another significant limitation of the ASTM standard and of most
research in the area of maturity is that the sample concrete cylinders, or mortar cubes,
14


are cured at constant temperatures. This is a significant limitation because all
concrete in the field cures at a variable temperature. Concrete placed in the field
reaches a maximum peak temperature during its early-age and then drops down over
a period of time (Johnson et al., 1996; LaCome et al., 1996). An example of a typical
temperature-time history curve for concrete placed in the field is shown in Figure 3.2.
This temperature-time history was recorded from a 5'-0 thick concrete mat foundation
(LaCome et al., 1996). It is important to note the distinct peak temperature that the
concrete reaches and the short amount of time it takes to reach it. It is during this
100
15


stage, when the temperature of the concrete is changing rapidly, that the concrete is
gaining a large amount of strength.
The effects of early age temperature on strength gain and on the maturity
concept continue to be studied. As the maturity concept continues to gain acceptance,
more research is necessary to improve upon the current methods.
16


4. 1998 Department of Transportation Survey
Since the publication of the ASTM Cl 074 standard, the interest in the
maturity method continues to grow. The use of the method in actual field
applications is in several key areas including the transportation industry, cold weather
concrete placement, and post-tensioning applications. The transportation industry has
utilized the concept to a large extent in the area of fast-track paving. The objective
of fast-track paving construction is to complete the project in a short time frame,
allowing traffic back on the highway quickly. This is coupled with the need for
providing a safe and durable road. Numerous studies have been performed in an
attempt to implement the maturity concept successfully.
4.1 Introduction
Due to the increasing use of the maturity concept by the transportation
industry, a questionnaire was developed to gain a better understanding of the current
trends. The results of the questionnaire define several key factors, which explain how
the transportation industry currently utilizes the concept as well as what some of the
current difficulties and limitations are with the current methods being used.
4.2 Purpose
During July 1998, a questionnaire was developed and sent to each of the fifty
state highway agencies in the United States. The purpose of the questionnaire was to
develop a better understanding of how the maturity concept is currently being utilized
17


in the transportation industry. This was important because even though the concept
has been utilized in other construction projects, (LaCome et al., 1996; Johnson et ah,
1996), the transportation industry has been very interested in utilizing the concept
during fast-track projects. A copy of the complete questionnaire and cover letter
can be found in Appendix A.
4.3 Questionnaire Results
The response to the survey far exceeded the expected rate of return. Eighty-
eight percent of the surveys sent out (44 surveys) were completed and returned. This
high rate of return, along with the responses given, suggests that there is a significant
interest in the maturity concept. The results of the survey show the current trends of
the transportation industry in regard to the maturity concept.
4.3.1 Tabulated Responses
The first question was directed at finding out how many research departments
in the DOTs are familiar with the maturity concept. Of the forty-four departments
responding, over ninety- five percent are familiar with the concept. This is a
significant finding. It shows that the majority of departments do know about the
concept and how it can be utilized in the field. However, some of the other responses
indicate that even though the DOTs are familiar with the concept, a relatively small
percentage are actually utilizing it in the field. Table 4.1 gives a breakdown of the
questions asked and the responses.
18


Table 4.1 Results of State Highway Agency Questionnaire
Question %Yes %No %Total
Are you familiar with the concrete maturity concept? 95.2 4.8 100
Have you, or the Department of Transportation you work for, ever utilized the maturity concept? (i.e. for particular jobs, or in the actual specifications for fast track paving) 57.1 42.9 100
Are you familiar with the current ASTM standard method Cl074-87, used for developing the maturity-strength relation curve? 73.8 26.2 100
Have you ever used the ASTM method or asked that it be followed in the project specifications? 35.7 64.3 100
Are you aware of the limitations of the current ASTM standard method Cl074-87? 50 47.6 97.6
Have you, or the department where you work, ever tried to modify the ASTM method in order to overcome certain limitations? 16.7 83.3 100
Would you think research in the area of early-age temperature and its effects on the maturity-strength relation is applicable? 69.1 11.9 81.0
Do you feel a modification to the current ASTM standard, that would remove certain limitations, would be beneficial? 40.5 14.3 54.8
Would you, or anyone else in the department, be interested in learning more about the maturity concept and how this proposed research project will attempt to remove some of the limitations of the current ASTM standard method C1074-87. 71.4 21.4 92.8
Another question asked if the respondent was familiar with the current ASTM
standard method C 1074-93. Seventy-four percent of the respondents are familiar
with the current ASTM standard. Even though ninety-five percent are familiar with
the maturity concept, significantly less are aware that there is an ASTM standard
method to follow. This suggests that there is a need to establish a more unified
network of transportation departments in which current practices and standards can be
19


introduced and discussed. With todays technology, it is feasible that an internet web
site could be developed for the sharing of information between state DOTs.
The percentage of departments actually utilizing the maturity concept in the
field is just over fifty-seven percent, but only thirty-five percent of respondents have
ever followed the ASTM Cl074-93 method for developing the maturity-strength
relation. These are important findings because nearly all of the respondents are
familiar with the concept, but only half of them have actually utilized it in the field,
and only a third have followed the ASTM procedure. This implies that many of the
departments are not comfortable utilizing the concept, and even fewer are
comfortable with the current ASTM procedure. These points are justified by several
comments made by respondents. These comments can be found in Appendix 1.
Regarding questions aimed at future research in the area of concrete maturity
and improvements to the current practices, sixty-nine percent of the total respondents
thought that research in the area of early-age temperature and its effects on the
maturity index-strength relation would be applicable. Forty percent felt that a
revision to ASTM Cl074-93 was necessary to remove the limitations surrounding
early age temperatures. Finally, seventy-one percent were interested in finding out
more about the ongoing project mentioned in the cover letter and requested that more
information be sent to their offices.
It should be noted that the percentages described above and shown in Table
4.1 include only the data in which respondents answered yes or no. There were
20


instances where respondents either left the question blank or input a I dont know
response. The effect of such responses is seen by the total yes/no percentages not
being equal to one hundred.
From the results, several key points can be made. These are:
The majority of DOTS across the U.S. are familiar with the maturity
concept
There is a significant interest in the concept
Only a limited number of departments use the current ASTM method
More research is necessary to improve upon the current methods being
utilized
As part of the questionnaire, a request for comments was made in regard to
the maturity method. Several key responses were made and a discussion of these key
comments is important to explain the current trends in the transportation industry. A
complete list of all the comments submitted can be found in Appendix A.
4.3.2 Written Responses
The written responses were categorized into three main groups. These were:
Comments Regarding Past and Current Investigations into the Maturity Concept.
Comments Regarding the Current Limitations of the Maturity Concept.
Comments Regarding Current Use of the Concept in Field Applications.
A total of seventeen respondents commented on their experience with and knowledge
about the maturity concept. These comments provided an important insight into the
21


current trends of the transportation industry in regards to maturity. Several comments
were made in regards to past and current investigations that the departments were
involved in. These investigations included using commercially available "maturity
meters to determine the opening times on a concrete paving project".
One of the most significant comments, made by several DOTs, was that the
maturity concept is being used in the field, but without following the ASTM C 1074
specification. Another comment was that the current methods of developing the
maturity-strength relationship are cumbersome and not always practical. One
respondent said, "The Procedure to calculate the datum temperature and activation
energy found in the Appendix to ASTM C 1074 is tedious and may not be practical".
Other comments pointed to the current limitations of the ASTM C 1074 specification
that produce inaccurate results. One respondent went as far as to say, "Using the
Nurse-Saul equation has inherent error built in with using a standard datum
temperature".
The results show that the maturity concept is well known in the transportation
industry. There is also a growing interest in how the concept can be utilized,
especially in fast-track paving projects. Unfortunately, the current ASTM method has
not gained wide acceptance. As discussed previously, the current ASTM standard
method is limited in its applications. In order to overcome these limitations and
improve upon the current method more research is necessary.
22


5. Using Maturity as a "NDE" and Forensic Tool
5.1 Introduction
The application of construction loads on insufficiently cured concrete is
responsible for many injuries and deaths each year (Feld and Carper, 1997). These
types of failures are well documented and widely discussed yet such accidents
continue to occur (Feld and Carper, 1997). Failures of this nature could be prevented
if safety procedures, including evaluating in-place strength by using the maturity
method, were implemented.
5.2 Using Concrete Maturity to Prevent
Concrete Failures
Section 3.2 described the ASTM Cl 074 standard method of developing the
relationship between maturity and strength gain. Once the maturity-strength
relationship is properly developed for a given concrete mix, the relationship can be
used to estimate the in-place strength gain of the concrete as it cures in the field. As
stated previously, this relationship between the maturity index and strength is
represented with a hyperbolic curve.
By recording the in-place temperature after the concrete has been placed, the
maturity index can be calculated for the field-cured concrete. Then the in-place
strength can be estimated using the pre-developed curve. Maturity can be extremely
helpful in monitoring the strength gain of concrete placed during the cold winter
23


months. Tracking the temperature of concrete is vital when heating applications may
be necessary (Johnson et al., 1996). By monitoring the concrete temperature during
cold weather, one can determine as to when and to what extent heating is required.
Other preventative measures that can be accomplished by using maturity include
premature form removal and load application. However, there is still the potential for
failures to occur even if the maturity concept has been utilized. When this happens,
the maturity concept can be a useful tool in the forensic investigation.
5.3 Using Concrete Maturity in Forensic Engineering
In cases where a concrete failure has occurred, maturity can be a helpful tool
in determining the strength of the concrete at the time of failure. Even if the maturity
procedure was not originally followed during a project, it may be possible to estimate
the concrete strength at the time of failure using the concept. The following two case
studies describe how the concept could be utilized during a forensic investigation.
Case study #1 is a hypothetical example of how the maturity concept if used on a
project prior to the failure can be used in the post-failure investigation. Case study #2
describes a real life failure that took place where the maturity concept was
subsequently used to help estimate the concrete strength at the time of failure.
5.3.1 Case Study #1: Hypothetical Example
5.3.1.1 Introduction
The following hypothetical example explains how the maturity method, if
utilized during construction, could be used in a failure investigation. It should be
24


noted that this is a simple example only and the actual investigation would be more
complex.
5.3.1.2 Background
A 6" elevated slab was constructed during the winter. The contractor hired a
consulting firm to implement the maturity concept in compliance with the design
engineers specification for cold-weather concrete work. Before concrete was placed
in the field, the consulting firm collaborated with the ready-mix manufacturer to
develop the maturity index-strength curve shown in Figure 3.1. A temporary shoring
system was constructed to support the new slab until the concrete gained adequate
strength to support its own self-weight and a construction live load of 25 psf. Using
general ultimate strength design equations, it was calculated that the concrete
compressive strength needed to be a minimum of 2,100 psi. to support these loads.
When the slab was poured, thermocouples connected to a commercially
available maturity meter were inserted into the slab at several pre-determined
locations to monitor the temperature and calculate the TTF maturity index. During
the first three days after concrete placement, the average temperature of the slab, Ta, =
5 C. Assuming a datum temperature, T0, = -10 C. and using the TTF maturity index
equation (Equation 2.1), the maturity meter calculates a maturity index = 45 C-days.
Referring to the maturity index-strength curve (Figure 3.1), the concrete compressive
strength was estimated to = 2,200 psi. At this time it was decided to remove the
temporary shoring. Shortly after the shoring was removed, the slab collapsed.
25


5.3.1.3 Investigation
During the preliminary investigation, the investigating consultant determined
the following facts:
6 Slab with #3 bars @ 12 o.c. self wt. = 150 pcf *(0.5) = 75 psf
f c = 4,000 psi
fy = 60,000 psi
The slab was designed as a simple span one-way slab with a span = 11 -6
Two days after the slab was poured, with the shoring still in place, a load of
construction materials was placed on the slab. This was estimated to = 50 psf,
which was double the original design load.
5.3.1.4 Analysis
The following is a summary of the calculations performed using the
information given above:
The distance to the centroid of the steel, d, was estimated to = 4.3
Analyzing a l-0 wide strip gives the factored load,
wu = 1.4x(75+50)/1000 = 0.175 k/ft.
Mu = wu12/8 = 0.175* 11,52/8 = 2.89 ft.-kips
= OAsfy
f <0
d-~
v 27
(5.1)
a =
AJy
0.85.f\b
(5.2)
26


where: 0=0.9 As = 0.1 lin.2 fy = 60ksi d = 4.3
f c = 2.2ksi (at the time of failure) b = 12
Solving Equation (5.2) gives: a = 0.294
Plugging this into Equation (5.1) gives: OMn = 2.05 ft-kips
5.3.1.5 Conclusions
Based on the self wt. = 75 psf; this additional dead load = 50 psf; and the
estimated concrete strength of 2,200 psi, the simplified design analysis shows that the
design moment, OMn, is less then the factored moment, Mu. The ratio of Mu/OMn =
1.41. This estimates the concrete was overstressed by 41%, which resulted in the
ultimate failure of the concrete deck.
5.3.2 Case Study #2: Cooling Tower Failure at
Willow Island, WV
5.3.2.1 Introduction
The Willow Island concrete cooling tower failure is considered one of the
most catastrophic construction failures in U.S. history. The failure was the result of
inadequate concrete strength gain (Lew et al, 1982). The report titled, "Investigation
of Construction Failure of Reinforced Concrete Cooling Tower at Willow Island,
WV", was issued by the National Bureau of Standards (NBS), now the National
Institute of Standards and Technology (NIST) (Lew, et. al, 1982). This report
describes in detail how the cause of failure was determined. A short summary of the
report is given in the next section.
27


5.3.2.2 Background
On April 27, 1978, the second of two natural-draft hyperbolic concrete
cooling towers collapsed. At the time of failure, the tower was being constructed
using a patented lift form technique. A five-foot vertical lift of concrete was placed
each day and a new lift was started the next day. At the time of failure, 28 lifts had
been placed and the 29th lift was underway. All fifty-one workers working on the
scaffolding were killed.
53.2.3 Investigation
As part of the complete investigation conducted by several agencies, including
the NSB and the Occupational Safety and Health Administration (OSHA), a
comprehensive laboratory testing and analysis procedure was followed. In order to
perform a complete analysis of the concrete, the strength at the time of failure had to
be estimated. This is where the maturity method was utilized to help with the
investigation.
Since the maturity method had unfortunately not been utilized prior to the
failure, it was necessary to establish a temperature time history of the concrete that
failed. This was accomplished by obtaining temperature data from an airport located
near the construction site. Due to the tower shell walls being relatively thin (8"), the
air temperature was used as an approximate concrete temperature. The temperature
time history curve is shown in Figure B.l in Appendix B. This figure gives the
temperature time history for the time period between when lift 28 began up to the
28


failure. It also shows the approximate temperatures used for curing samples of the
concrete in the lab. It is important to note that during the night after the 28th lift had
been placed prior to the failure the temperature dipped to around 40 F. This
indicates that the rate of strength gain of the concrete during the cold night was
slowed.
Once the temperature-time history had been approximated, the maturity-
strength relationship was established. Figure B.2 shows the maturity- strength curve
developed for the concrete mix used in the tower. Using the maturity-strength
relation, the strength of the concrete at the time of failure was estimated to be 220 psi.
A more in-depth discussion of the cooling tower failure is given in Appendix B.
5.3.2.4 Conclusions
After a complete analysis of the tower structure, it was determined that the
most probable cause of the tower collapse was due to the inadequate strength gain of
the concrete placed in lift 28 (Lew, et. al, 1982).
This case study illustrates how the changing temperatures can substantially
affect the rate of strength gain in concrete. It also shows that if the maturity concept
had been used on the cooling towers during construction this dramatic failure may
have been prevented.
29


5.4 Summary
Case studies 1 and 2 illustrate the potential use of the maturity concept in a
forensic investigation. It should be noted that it is not always necessary to have
utilized the concept prior to the failure occurring as illustrated in case study #2.
The next chapter discusses a pilot study performed to investigate the effects of
curing temperatures on the maturity index-strength relationship and develops an
alternative procedure for utilizing this relationship.
30


6.
1999 Research Pilot Study
In order to begin quantifying the effects of early-age temperatures on the
maturity concept, the point in time when temperature no longer affects limiting
strength must be determined. Once this time is known for different curing
temperatures, the limiting strength can be predicted for other temperature conditions.
This makes it possible to know the limiting strength at early-age. By knowing the
limiting strength early on, the relative strength concept can be utilized to predict
early-age strengths of the concrete.
Previous work by Carino (1981) attempted to determine this point in time for
a mortar mix with a w/c ratio of 0.43. The procedure followed in this 1981 project
allowed mortar samples to cure at a maximum (32C) and minimum (5C) constant
temperature for different amounts of time. The samples were then brought to a
constant average room temperature (23C) for the remaining test period. The amount
of time that the samples were allowed to cure at the maximum and minimum was
based on initial and final set times. These set times were determined using the pin
penetration method (Carino, 1981). Unfortunately, the procedure was unsuccessful
and the time at which temperature no longer affects the limiting strength was not
observed. The main reason the procedure failed can be attributed to the assumption
made that initial and final set of mortar influences the time when temperature no
longer affects limiting strength. The results from the 1981 study show that
31


this is not the case and initial and final set do not directly influence the time when
temperature no longer affects limiting strength (Carino, 1981).
The 1999 pilot study followed a procedure different then the one followed by
Carino, (1981). The main differences between the two procedures are the times for
which the samples are kept at specified test temperatures and the range of constant
test temperatures used. A more complete explanation of the procedure will be given
in section 6.3.
6.1 Introduction
In the spring of 1999, a research pilot study was initiated at the University of
Colorado at Denver to investigate the early-age temperature effects on the maturity
concept. During the summer of 1999, over 250 concrete cylinder samples were
mixed, formed, cured, and tested for compressive stress. Figures 6.1 and 6.2 show
some of the work in progress.
Figure 6.1 Dry Gravel Being Weighed
32


Figure 6.1 shows the dry aggregate being weighed prior to mixing with the other dry
components. Figure 6.2 shows the concrete after thoroughly mixing in the water.
Some of the 4" x 8" cylinder molds can be seen at the top of Figure 6.2.
6.2 Purpose
The purpose of the study was to investigate the effects of early-age
temperatures on concrete maturity and try and determine the time at which
temperature no longer affects the limiting strength of concrete. This is a necessary
first step in addressing the previously mentioned limitations of the ASTM procedure.
33


6.3 Experimental Testing Procedure
After careful consideration, the EA maturity index was chosen as the preferred
index to be used in the study, since it has been proven to be more accurate than the
TTF index. Also, since Equation (2.4) is much easier to work with it was substituted
for Equation (2.2) in the EA method.
The entire testing procedure used a standard 4,000 psi concrete mix design
with a w/c ratio = 0.537. No special additives or admixtures were part of the mix
design. Table 6.1 lists the proportions of sand, aggregate, and water that were used
for the design mix.
Table 6.1 - Concrete Mix Proportions
w/c Gravel (lbs.) Sand (lbs.) Cement (lbs.) Water (lbs.)
0.537 295 211 108 58
Five separate phases were developed to accomplish the purpose. Phase 1
consisted of curing samples at three different constant temperatures. This phase was
conducted to develop the relationship between the rate constant, k, and curing
temperature, T. This relationship is defined by Equation (2.4). Phases 2 through 5
used the same three curing temperatures as phase 1. However, in phases 2 through 5
the samples were cured at one of the constant temperatures for specified amounts of
time and then moved to a different temperature. A more complete explanation is
given in section 6.3.2.
34


During each phase, a specified number of concrete cylinder samples (4 -
diameter, 8 long) were molded out of a batch of hand mixed concrete. The cylinders
were cured in limewater baths at the specified temperature for the particular phase.
Compressive tests were performed on sets of three samples at specified test
times. The average of the three compressive strengths and the average of the time
when tested was used as the data point for each test. The specified test times for
phases 1, 4, and 5 were: 0.75 days, 1.75 days, 3.75 days, 6.75 days, 12.75 days, and
27.75 days. The specified test times for phases 2 and 3 were: 1.75 days, 3.75 days,
6.75 days, 12.75 days, and 27.75 days. The reason that the 0.75 test was omitted
from phases 2 and 3 was that the concrete in these two phases had not reached
adequate strength at the 0.75 test time. These specified test times were established to
investigate the affects of temperature over a wide range of time.
Due to the need to utilize all the equipment to the fullest capacity, mainly the
curing chambers, and to cut down on the amount of lab time, some of the phases were
performed concurrently.
6.3.1 Phase 1 Constant Curing Temperatures
Phase 1 was set up to test samples cured at three different constant curing
temperatures. Three temperatures were used to cover a wide temperature range and
also to determine the relationship between the rate constant and temperature for this
specific concrete mix. The temperatures used were low (10 C.), medium (20 C.),
35


and high (32 C.). The main goal of phase 1 was to establish the temperature-
sensitivity factor, B found in Equations 2.4 and 2.5.
6.3.2 Phases 2 Through 5 Step Function
Curing Temperatures
Phases 2 through 5 were developed to try and determine the point in time
when temperature no longer affects limiting strength. Each of these four phases had
specific temperature-time histories established to investigate a wide range of curing
conditions.
Phase 2 began with placing a set of samples in the cold-water bath (10 C.).
At the first specified test time of 0.75 days, a sub-set of samples were moved to the
warm water bath (20 C.) The remaining samples were left in the cold bath. No
compressive testing was performed at this initial test time for this phase since a
compressive test had already been performed at this test time during phase 1. At the
next specified test time of 1.75 days, another sub-set of samples were moved from the
cold to the warm water bath. At this time, a set of three samples from the first sub-set
placed in the warm bath at 0.75 days were tested for compressive strength. Figure 6.3
shows the step function temperature-time curves used to cure the samples in phase 2.
One can see at the third test time of 2.75 days, another sub-set of samples were
moved from the cold to the warm water bath. At this time, three samples from each
of the previous two sub-sets were tested for compressive strength. This process was
repeated for the 6.75 and 12.75 day test times. At the 27.75 day test time, three
36


samples from each of the five sub-sets that had been moved from the cold
to the warm water bath were tested for compressive strength. Due to the samples
Phase 2 Temperature-Time Histories
Time, t (days)
Figure 6.3 Phase 2 Curing Temperatures
initially being cured in the cold temperature bath and then sub-sets of samples being
moved into the warm bath during phase 2, the phase was given the name "Cold to
Warm".
The remaining phases 3, 4 and 5 were carried out following the same steps as
described for phase 2, except that the two curing temperatures were varied. Phase 3
initially had samples placed in the warm bath and then at each of the first five test
times, sub-sets of samples were moved to the cold temperature bath. This led to phase
37


3 being called the "Warm to Cold" phase. Figure 6.4 shows the step temperature-time
histories used in phase 3.
Phase 3 (Warm to Cold) Temperature-Time Histories
Time, t (days)
Figure 6.4 Phase 3 Curing Temperatures
Phases 4 and 5 looked at the other end of the temperature range with 4 being
"Hot to Warm" and 5 "Warm to Hot". The temperature-time histories used in phases
4 and 5 were similar to those shown in Figures 6.3 and Figure 6.4. One of the
limitations faced during the project was the monitoring of cylinder temperatures. Due
to the lack of funding available for the project, only the water bath temperature was
monitored and controlled. It was assumed that the concrete temperature would be
38


very close to the water temperature. This limitation and its effects on the test results
will be further discussed in the errors section 6.6
6.4 Data Analysis
The data analysis was performed following a procedure similar to the one
outlined in Carino et. al, (1992). Once all the testing had been completed for all five
phases, the data was analyzed for the following:
Strength vs. Time
Rate Constant vs. Constant Temperature
Strength vs. Equivalent Age Maturity Index
6.4.1 Strength vs. Time Data
The strength vs. time data was analyzed using the "Linear-Exponential"
equation (Carino et. al, 1992). This equation is given as:
where:
S = S
1 + k(t-t0)
(6.1)
s Strength at age t, psi
Su = "Limiting or Ultimate" strength, psi
k = Rate Constant, day'1, and
to = age at start of strength development
This equation is based on a linear relationship between the inverse of strength and the
inverse of time and was established using constant temperatures (Carino, 1984).
39


Using Equation (6.1), the best-fit parameters, Su, k, and to can be determined by least-
squares regression analysis on each set of data. The regression analysis for this study
was performed using the commercially available numerical analysis software
package, "KaleidaGraph", developed by Synergy Software (version 3.0.9, 1997).
6.4.2 Rate Constant vs. Temperature Relationship
Once the strength vs. time data is analyzed and the rate constant, k, is known
for different curing temperatures, the relationship between the rate constant, k, and
temperature, T can be established. This is performed in accordance with the
procedure used in Carino et. al, (1992). Again, using regression analysis, Equation
2.4 is used to determine this relationship and to establish the temperature-sensitivity
factor, B.
6.4.3 Strength vs. EA Maturity Index
After establishing the temperature-sensitivity factor, Equation 2.5 was used
along with the temperature-time histories to develop the relationship between strength
and maturity. In Equation 2.5, the term, Ts, represents a specified base temperature.
An average room temperature of 23 C. was used as the specified base temperature
for this study.
6.5 Results
6.5.1 Results From Phase 1
Following the procedure described in section 6.4, the data for each of the three
curing temperatures were analyzed. Table 6.2 shows the results of this analysis. The
40


complete set of data for phase 1 can be found in Appendix C. Two items should be
Table 6.2 Phase 1 Strength-Age Data
Temperature Su k to
(C.) (p.s.i..) (day'1) (days)

10 7441.5 0.2508 0.627
20 7660 0.4397 0.318
32 7241 0.6326 -0.119
mentioned in regard to Table 6.2. First, the value of Su for the low temperature is less
then that of the warm temperature. This goes against what was discussed in section
1.1 where it was suggested that the low temperature Su would be higher then the
warm temperature. One possible explanation for this is that the low temperature
concrete was not given enough time, 27.75 days, to surpass the warm temperature
concrete.
Another interesting result shown in Table 6.2 is that the to value for the hot
temperature is negative. Since this is a time in days, it is unreasonable to have a
negative value. No explanation is available to explain this. After determining the
information in Table 6.1, values of the rate constant, k, were plotted against the
constant temperatures, T, to develop the temperature sensitivity factor. Figure 6.5
shows the plot of rate constant vs. temperature. Regression analysis was performed
on Equation (2.4) which gave a best fit curve shown in Figure 6.5 and a value for the
temperature sensitivity factor, B, equal to 0.038. Using this value for the B-factor and
a specified temperature of 23 C, equivalent ages were calculated for each of the test
41


Rate Constant, k, vs. Temeprature, T
Temperature, T ( C .)
Figure 6.5 Rate Constant vs. Constant Temperature
times for all three constant curing temperatures. The result of this was the three
curves shown in Figure 6.6.
42


6.5.2 Results From Phases 2 Through 5
In order to determine the time when temperature no longer affects limiting
strength, sample cylinders in phases 2 through 5 were cured at a specified initial
temperatures, and then moved to a different temperature at each test time as described
in section 6.3.2.
Phase 2 (Cold to Warm) considered samples initially placed in the cold water
bath and then sub-sets of samples were moved to the warm bath at the specified test
times. Using regression analysis on Equation 6.1, the strength-age data was analyzed
to determine the ultimate (limiting) strength for each sub-set of samples. Table 6.3
shows the results of this analysis.
Table 6.3 Ultimate Strength vs. Time in Cold Prior To Warm
Time in Cold Prior to Warm (days) Ultimate Strength (p.s.i.)
1.75 7921.8
3.75 8471.6
6.75 8889.8
12.75 8239.4
27.75 7441.5
Plotting the ultimate strength versus the time spent in the cold-water bath produced
the graph in Figure 6.7. As can be seen in Figure 6.7, no obvious correlation was
produced from this data. It would seem from previous discussions in section 1.1 that
the longer a sub-set of samples stayed in the cold bath prior to the warm, the higher
the ultimate strength would be.
43


Ultimate Strength vs. Time in Cold Prior to Warm
Time in Cold Prior to Warm, t (days)
Figure 6.7 Ultimate Strength vs. Time in Cold Prior to Warm
In fact the ultimate strength from the samples cured in only the cold bath for the
entire test cycle should be greater then any of the sub-sets that were cured in the cold
bath for various amounts of time. This was not the case, and some of the possible
reasons will be discussed in sections 6.6 (Errors) and 6.7 (1997 Pilot Study Summary
and Recommendations). Phase 3 (Warm to Cold) followed the same procedure as
phase 2. The results of the regression analysis on Equation 6.1 are given in Table 6.4.
The ultimate strengths were plotted versus the time spent in the warm bath. This plot
is shown in Figure 6.8.
44


Table 6.4 Ultimate Strength vs. Time in Warm Prior To Cold
Time in Warm Prior to Ultimate Strength
Cold (p.s.i.)
(days)
1.52 6994.5
13.65 6713.9
6.53 6896.5
12.77 7318.2
27.78 7660
Ultimate Strength vs. Time in Warm Prior to Cold
Time in Warm Prior to Cold, t (days)
Figure 6.8 Ultimate Strength vs. Time in Warm Prior to Cold
Again, there was no apparent correlation between the time spent in the warm bath and
the ultimate strength. The results for phases 4 (Hot to Warm) and 5 (Warm to Hot)
45


are shown in Tables 6.5 and 6.6. Figures 6.9 and 6.10 show the plots of ultimate
strength versus time in initial (Hot-phase 4; Warm-phase 5) water bath.
Table 6.5 Ultimate Strength vs. Time in Hot Prior To Warm
Time in Hot Prior to Warm (days) Ultimate Strength (p.s.i.)
0.73 7514.1
1.74 7022.5
2.73 6854.3
6.74 6945.4
13.73 7182.1
27.74 7241
Ultimate Strength vs. Time in Hot Prior to Warm
Time in Hot Prior to Warm, t (days)
Figure 6.9 Ultimate Strength vs. Time in Hot Prior to Warm
46


Table 6.6 Ultimate Strength vs. Time in Warm Water Prior To Hot
Time in Warm Prior to Hot Ultimate Strength
(days) (p.s.i.)
0.80 7172.7
1.52 7408.8
3.65 7868.2
6.53 7497.8
12.77 7690.1
27.74 7660
Ultimate Strength vs. Time in Whrm Prior to Hot
Tine in Warm Prior to tit t (days)
Figure 6.10 Ultimate Strength vs. Time in Warm Prior to Hot
47


Now that all the plots have been presented, it is interesting to note the
similarities between phases 2 (Cold to Warm) and 5 (Warm to Hot), and phases 3
(Warm to Cold) and 4 (Hot to Warm). It appears from all four figures, that there is an
optimum curing temperature for this particular concrete mix to reach the maximum
ultimate strength. This optimum temperature seems to depend on whether the
samples were placed in a cooler temperature first then moved to a higher temperature
at the specified test times. Even though the ultimate strength did not quite stop being
affected by temperature, by projecting the pattern observed it does appear that it may
have reached this point given more time. This in fact brings up a proposed project
that may be able to show this and observe the time when temperature no longer
affects ultimate strength. This future study will be further discussed in section 6.7.
After analyzing all the data, areas where possible errors may have affected the
results were considered.
6.6 Errors
There were several areas in the research program that could have contributed
to errors in the data. These included:
Lack of consistent water temperature monitoring.
No monitoring of actual concrete temperatures
Certain variables from the equations used in the analysis, such as Equation 6.1,
were estimated using regression analysis techniques and there is always a factor
of error with this type of analysis.
48


6.7 1999 Pilot Study Summary and Recommendations
The purpose of the 1999 pilot study was to investigate the effects of curing
temperature on long-term, ultimate strength. Also, an attempt was made to determine
the time when temperature no longer affects ultimate strength. It is obvious from
Figures 6.7 through 6.10 that curing temperature has a significant affect not only on
the ultimate strength but on the initial rate of strength gain.
The actual time when temperature no longer affects ultimate strength was not
observed. However, it is the opinion of the research team that given a longer test
period up to 56 days, this time would be seen. A future project could look at the same
mix design or possibly a high early-strength mix. A high early-strength mix would be
affected by temperature over a different period of time then the mix used in this
study. It seems like the time to reach a constant ultimate strength should be less for
the early strength mix.
49


7. Summary, Conclusions, and Recommendations
The purpose of this thesis was to investigate the concept of maturity. The
areas that were considered included:
The historical background and theory behind maturity
Current standard practices
To what extent the maturity concept is actually being utilized in the field
Less known applications including "NDE" techniques and forensics
A pilot study to investigate the effects of different curing temperatures on
strength gain and maturity
The results of this investigation lead to some final points that should be made. These
are:
The maturity concept was first introduced in the 1950's. Even though the
effects of temperature were being studied as far back as 1915.
The actual quantitative theory behind maturity began in the 1970s and the
current equations being used today were developed in the early 1980's.
Even though the ASTM incorporated a method for utilizing the concept in the
field, there are important limitations that must be considered. One of the main
limitations is that the current method does not consider the effects of early-age
temperature on concrete strength gain.
50


The industry using the concept most frequently is the transportation industry.
However, there are several applications including slip-form construction, pre-
cast, and large cold weather projects that have began to utilize the concept to
some extent.
In the transportation industry, over ninety-five percent of the respondents to a
nation-wide survey of state transportation departments were familiar with the
concept of maturity. Over half had already utilized the concept on a project.
Nearly seventy percent think research in the area of maturity would be
beneficial. The complete discussion of the results is given in Chapter 4 and
the entire questionnaire can be found in Appendix 1.
There are other applications less known that should be considered for
maturity. Chapter 5 considers the concept as a viable "NDE" technique that
can prevent failures in early-age concrete due to inadequate strength gain.
Also, two case studies were presented to illustrate the potential usefulness of
the concept in a forensic investigation. These two case studies are perfect
examples, where if the maturity method had been incorporated as part of the
project specification, the resulting failures may have been prevented.
The results of a 1999 pilot study to investigate the effects of early-age
temperature on maturity show that the rate of strength gain early on is greatly
affected by the temperature during this time. The long-term, ultimate-
strength, of the concrete is also affected by the early-age temperatures. It
51


appears that for the mix used in the pilot study there is an optimum
temperature between the cold (10C.) and the warm (20C.) temperatures used
that would produce the maximum ultimate strength. An exact time at which
temperature no longer affects ultimate strength was not observed, but
Future studies of maturity are necessary to continue to gain understanding as to the
underlying reasons why temperature affects concrete strength gain and maturity.
52


Appendix A: 1998 Questionnaire
July 8, 1998
Dear Director of Research,
The attached questionnaire has been sent on behalf of the University of Colorado
Denver Campus, which is currently developing a research project under Professor
Kevin L. Rens, Ph.D., P.E. and Matthew L. LaCome, a graduate student pursuing his
M.S. in Civil Engineering Degree. The research project being developed deals in the
area of concrete maturity and its relation to strength gain. The questionnaire is
intended to help gain a better understanding of how the concept is being utilized in
the field and to determine specific needs of those utilizing it. The project team is
sending the attached questionnaire to all the Departments of Transportation around
the country in order to gain a better understanding of how the concept is being used in
the transportation industry. The goal of this project is to gain a better understanding
of the effects of early-age temperatures on the maturity strength relationship,
ultimately proposing a change to the current ASTM standard Cl074-87. A copy of
the current standard has been included.
Your response to this questionnaire will be greatly appreciated. Please respond by
August 3, 1998 with the self addressed stamped envelope that is enclosed. If you
have any questions or comments in regards to the questionnaire or the project itself,
or if you would like more information about the project, you may contact Dr. Rens or
Mr. LaCome at the following:
Kevin L. Rens Ph.D, P.E. Matthew L. LaCome
Phone: (303) 556-8017
Fax:(303) 556-2368
e-mail: krens@carbon.cudenver.edu
Phone: (303)937-1745
Fax:(303) 843-2416
Thank you for your time and consideration.
Sincerely,
Kevin L. Rens, Ph.D, P.E.
Assistant Professor
Civil Engineering Dept.
Matthew L. LaCome
Research Assistant
Civil Engineering Dept.
53


UNIVERSITY OF COLORADO AT DENVER
CIVIL ENGINEERING DEPARTMENT
DENVER, COLORADO
Questionnaire Concerning Concrete Maturity and How It Is Utilized In The
Transportation Industry
Organization
Address
Name _____________________________________
Title
Are you familiar with the concrete maturity concept?
Yes No
Have you, or the Department of Transportation you work for, ever utilized the
maturity concept? (i.e. for particular jobs, or in the actual specifications for fast track
paving)
Yes No
Are you familiar with the current ASTM standard method Cl074-87, used for
developing the maturity-strength relation curve?
Yes No
Have you ever used the ASTM method or asked that it be followed in the project
specifications?
Yes No
Are you aware of the limitations of the current ASTM standard method Cl 074-87?
Yes No
54


Have you, or the department where you work, ever tried to modify the ASTM method
in order to overcome certain limitations?
Yes No
Would you think research in the area of early-age-temperature and its effects on the
maturity-strength relation is applicable?
Yes No
Do you feel a modification to the current ASTM standard, that would remove certain
limitations, would be beneficial?
Yes_____ No_____
Would you, or anyone else in the department, be interested in learning more about the
maturity concept and how this proposed research project will attempt to remove some
of the limitations of the current ASTM standard method Cl 074-87?
Yes No
If you answered yes to the last question, please send a written request with the
completed questionnaire or contact one of the people listed on the cover letter.
Please add any additional comments in the space provided below.
Thank you for taking the time to go through this form. In so doing, you have helped
the research team develop a better understanding of how the concept is being utilized
across the nation in the transportation industry. Please feel free to include any other
information that you would like. The results of this survey will be forwarded to you
as soon as possible.
55


Comments Regarding Past and Current Investigations into the Maturity
Concept
The maturity meter was used to determine the opening times on a concrete paving
project in Fillmore County, Minnesota. The Iowa State transportation
specification was used and beams were tested rather then cylinders. The
limitations in section 5.3 of ASTM Cl074 are not significant to the use described
in section 5.1.
Louisiana is currently evaluating the maturity concept. The purpose of the
evaluation is to determine if the maturity concept will help the contractor predict
the proper timing for joint sawing.
Planning and Research has copies of the following reports completed in 1985 and
1988 respectively in relation to Concrete Maturity. Early Strength of Concrete
TRC-98, Principal Investigator Dr. Tom Parsons, Arkansas State University,
Jonesboro, Arkansas and Early Age Concrete Testing by a Modified Pull Out
Test, also by Dr. Parsons.
Our experience with the maturity meter is limited to two projects: the SPS-2
section we constructed for SHRP and a section of pavement containing slag
cement which was constructed for the FHWA TE-30 project investigating high
performance concrete. The FHWA did the testing on the SHRP project and Dr.
Shad Sargand, from the Ohio University, did the testing on the TE-30 project.
The Pennsylvania Department of Transportation has some experience with the use
of a concrete maturity meter for the prediction of concrete strength.
Unfortunately, the equipment and software that was tried was difficult to use and
concrete producers were unfamiliar with the technology of maturity. As a
result, the technology could not be validated. A final report of the trial use of
maturity will be written sometime soon. The department is still very much
interested in the use of maturity technology to determine concrete strength. The
departments Bureau of Construction and Materials is moving forward with an
initiative to purchase a few maturity meter systems, possibly from various
vendors. These systems will be given to a few of our Districts in an effort to
further evaluate the technology through documented field trials.
The Texas Department of Transportation is currently evaluating the test method
through a research study sponsored by the Texas DOT and being conducted by
the University of Texas at Austin under the direction of Ramon L. Carrasquill,
Ph.D., P.E. Part of this research involves the use of maturity meters on the North
56


Central Expressway project in Dallas, currently under construction. Based on this
work, the Texas DOT and the researchers are developing a test method that
simplifies the ASTM C 1074 procedure. The state of Iowa has done a
considerable amount of work using the maturity concept on pavements.
Comments Regarding the Current Limitations of the Maturity Concept
The bottle neck of implementation of the maturity concept is clearly not the
ASTM C 1074-87. A state agency has to do the homework first before
applying this concept in the field. This is the primary reason. The homework is
very tough to do. It may include reviewing numerous mix designs, hydration
analysis, fatigue testing, etc. However, with the A + B bid system, the industry
will try to push this concept harder. Indianas DOT has one research project
with Purdue University about this maturity concept.
Using the Nurse-Saul equation has inherent error built in with using a standard
datum temperature
Our specifications already include the use of the maturity meter for measuring the
early strength of concrete for early strength concrete patching, however, we were
never able to make a good correlation between maturity and strength. With the
assistance of the FHWA and the SHRP manual, we again endeavored to draw a
correlation between strength and maturity. We were unable to do this and the
FHWA conducted further research on the problem and it was concluded that
strength and maturity do not have a relationship for concrete pavement patches
that gains strength at an early age. High early heat of hydration is the reason that
it doesnt work for patching. We know that the technology does work; it just
doesnt work for patching materials. However, we did find success in using
match-cured cylinders such as sure-cure molds with high early strength
concrete materials.
In routine field operations it is not always feasible or practical to allow 28-days to
establish the calibration curve (strength-maturity relationship) and to establish it
under laboratory conditions.
The procedure to calculate the datum temperature and activation energy found in
the Appendix to ASTM C 1074 is tedious and may not be practical. Is there a
quicker way to obtain these values?
57


Comments Regarding Current Use of the Maturity Concept in Field
Applications
New York States Department of Transportation routinely uses the maturity
concept for early age concretes which contain chloride accelerators or non-
chloride accelerators for rapid repairs. Two problems exist which limit the use of
the maturity concept for daily use:
1. Manpower/equipment is not sufficient to perform lab testing for every
concrete mix combination available, prior to field use.
2. Although concrete may achieve design strength at an early age, the
concrete is still green and subject to damage. The maturity concept
allows use of concrete at the earliest possible time, which could result
in damage, other then strength, which could affect long term
durability.
West Virginias Department of Transportation uses ASTM C 918 extensively.
This procedure removes most of the concerns or limitations of C 1074.
We have used maturity meters on a limited basis, primarily on thin bonded silica
fume modified concrete overlays.
In Illinois, the concrete maturity concept is useful for determining when to begin
sawing operations. To use concrete maturity to estimate strength is risky, since
air content will vary and can have a significant impact on strength. The
department relies on a portable beam breaker for field strength. Another
disadvantage for the concrete maturity concept, is the cement shortage. This has
caused ready mix producers to frequently change sources, which will require the
concrete maturity to be re-established.
The Maine DOT used the maturity meter in 1989 to evaluate the effects of cement
contents and silica fume on the early age temperature gains of four separate
mixes. These tests were not conducted in accordance with ASTM C 1074-87.
We are interested in any further research on this subject.
The New Jersey DOT has used the Maturity concept on the following three
research projects to date:
Development of a Fast Track Concrete for pavement slab replacement
Fast Track Concrete Follow-up Study
Development of a Concrete Maturity Protocol and Specification for NJ
58


The maturity method was used in the first two studies to provide an opening-to-
traffic criteria for the fast track repair work. This has led to three construction
projects in which fast track concrete has been specified. The third project is an
ongoing study to develop a tool for the Department and contractors for estimating
in-situ strength of mass concrete in structures (abutments, columns, gravity walls,
decks). The Department currently owns a Humbolt maturity meter and we are
evaluating a laboratory meter developed by the NJ Institute of Technology (Dr.
Ansari) and a Smart Reader developed by ACR Systems to record concrete
temperatures in the field. We found the maturity meter and the maturity concept
to be a valuable tool for our fast track concrete work.
59


Appendix B: Willow Island Cooling Tower Failure
Concrete Strength Testing (Lew et. al, 1982)
After the collapse, a laboratory test program was initiated to determine various
strengths and stiffness values of concrete. Included were tests for compressive
strength, pullout bond strength and modulus of elasticity.
Test specimens were prepared and cured in an environmentally controlled chamber.
Temperature in the chamber was controlled to simulate the temperature conditions at
the Willow Island site over the 24-hour period immediately prior to the collapse. The
chamber temperature was controlled using the data obtained from the Parkersburg
airport, which is located about 5 miles (8 km) from the Willow Island site. It should
be noted, that the airport is situated at an elevation of about 170 ft. above the Ohio
River on which the tower was situated. The temperature variation prior to the
collapse based on the airport data and the temperature variation used for curing of
concrete specimens are given in Figure A2.1.
The following tests were performed:
1) Compressive strength test of 6 x 12 in (150 x 300 mm) cylindrical
specimens.
2) Bond strength tests using 8 x 8 in (200 x 200 mm) cylindrical pullout
specimens.
While several series of compressive tests were made to examine the strength gain
characteristics, only one series was carried out for the pullout bond tests. For the first
24-hour period after casting, all specimens were subjected to a simulated field
temperature condition as described above. Thereafter, the specimens were cured at
55 F (12.8 C). For 28-day test, a separate set of three compression specimens were
cured at 73 F (22.8 C). The actual temperature of the concrete was recorded
periodically by means of a thermocouple inserted in a 6 x 12 in (150 x 300 mm)
cylinder. The specimens cured in the chamber were tested at 0.5, 1, 2, 3, 5, 7, 14 and
28 days.
60


Compressive Strength (Lew et. al, 1982)
The compressive tests were performed according to the procedure described in
ASTM C 39. Figure A2.2 shows the results of the compressive strength tests in
which the compressive strength is plotted against the maturity of the concrete.
The NBS test data, plotted as squares, are shown in the figure along with the results
of compressive tests carried out by the Ohio Valley Testing Laboratory (OVT) and
the Pittsburgh Testing Laboratory (PTL), plotted as triangles, and the field test data of
6 x 12 in (150 x 300 mm) cylinders for the lift 28 concrete,, plotted as circles. The
test specimens used by the Ohio Valley Testing Laboratory and the Pittsburgh Testing
Laboratory were made on May 2, 1978, at the Willow Island site using the concrete
delivered by the concrete supplier. These specimens were field cured for the first 24-
hour period and thereafter, in 70 F (21.2 C) lime water. The specimens prepared at
the time lift 28 was cast were kept at the base of the tower for the first 24 hour period
and subsequently, moved to a 70 F (21.1 C) fog room.
The next section does not come out of the NBS report. It illustrates how the maturity
method was utilized to estimate the in-place strength of the concrete at the time of
failure.
Maturity Calculations
The NBS investigation chose to follow the TTF maturity procedure discussed in
section 2.1 of this thesis. In order to estimate the in-place compressive strength of the
concrete using this method, Equation (2.1) was utilized. By summing the product of
temperature and time from the time the pour ended until the time of failure, the TTF
is calculated using Equation (2.1). The calculations using Equation (2.1) are
illustrated below:
M(t) = £ (Ta T0)At (2.1)
where: M(t) = TTF at age t, (C-hours),
Ta = Average concrete temperature during time interval, (C),
T0 = The datum temperature at which cement hydration stops, (C),
At = Time interval, (hours).
T0 is assumed to = -10 C = 14 F based on the ASTM Cl074 default.
Figure A2.1 shows the temperature-time history used for the calculation of the TTF.
The summation of (Ta T0)At is assumed to began at the time when the pour of lift 28
61


ended. This was approximately 4:00 p.m. on April 26th. The first value of Ta used
was 57 F. The first value of At = 2 hours. Plugging in these values for Ta, T0, and At
into Equation (2.1) gives:
M(t) = (57 14)*2 = 86 F-hours = 3.58 F-days.
Repeating this calculation for the remaining temperatures steps shown in Figure A2.1,
gives a total TTF of:
M(t) = (57-14)*2 + (53-14)*4 + (48-14)*4 + (42-14)*4 + (46-14)*4
= 618 F-hours = 26 F-days.
The TTF calculated in the NBS report was 43 F-days. The reason for the TTF value
calculated above is different then the one published in the NBS report can be
attributed to the two assumptions of T0 = 14 F, and the time at which the summation
of temperature-time products began. Using the TTF value of 26 F-days, the strength
can be estimated using Figure A2.2. It is estimated to be roughly 160 p.s.i. The
NBS report estimated a compressive strength of 220 p.s.i. This 220 p.s.i. vaulue as
the compressive strength used in the analysis of the tower failure.
62


63


Os
£*.
MPa


Appendix C: 1999 Pilot Study Data
Strength and Age Data For
Constant Cold Temperature = 10
Time, t Strength s
(days) (p.s.i.)
0.753
1.625
3.719
6.597
12.875
27.697
343
1302
3242
4485
5841
6317
C.
Ultimate Strength,
(Psi)____________
7441.5
S
u Rate Constant,
__ (days'1)
0.25082
y= m1*(m2*(m0-m3))/(1+m2*(m...
Value Error
ml 7441.5 313.67
m2 0.25082 0.037143
m3 0.62703 0.1 1482
Chisq 12925e+05 NA
R 0.99778 NA
Equivalent Age, te
(days)____________
Relative Strength, S/S
U
0.459
0.990
2.265
4.018
7.841
16.868
0.046
0.175
0.436
0.603
0.785
0.849
k
*Note: The equation shown in the box above as:
y = ml *(m2*(m0-m3))/(l+m2*(m0-m3))
represents Equation (6.1) in the Kaliedagraph numerical analysis program. The
variables: mO, ml, m2, m3 represent the variables in Equation (6.1) which are
estimated using the regression analysis tool in Kaliedagraph. The box shown in the
table represents the results of this analysis.
65


66


Strength and Age Data For
Constant Hot Temperature = 32 C.

Time, t Strength, s Equivalent Age, U Relative Strength, S/Su
(days) (P s i.) (days)

0.726 2481 1.023 0.343
1.736 3991 2.447 0.551
2.733 4705 3.853 0.650
6.736 5704 9.495 0.788
13.729 6524 19.353 0.901
27.739 6920 39.102 0.956


Ultimate Strength, Su Rate Constant, k
(P s i.) (days'1)

7241 0.63263



y= m1*(m2*(m0-m3))/(1 + m2*(m...
Value Error
m 1 7240.9 138.64
m2 0.63263 0.079662

m 3 -0.1 187 0.12815
Chisq 48152 NA
R 0.99827 NA





67


Strength and Age Data For Cold to Warm

1.5/10/20

Time, t Strength, s Equivalent Age, te Relative Strength, S/Su
(days) (P si.) (days)

0.753 343 0.459 0.043
1.625 1302 0.990 0.164
3.744 4378 3.339 0.553
6.625 5419 5.909 0.684
12.885 6354 11.492 0.802
32.878 7152 29.323 0.903


Ultimate Strength, Su Rate Constant, k
(P s i.) (days'1)

7921.8 0.34169



y rm
Value Error
ml 7921.8 510.95
m2 0.34169 0.085429
m3 0.71631 0.15361
Chisq 5.405e+05 NA
R 0.99289 NA



68


Strength and Age Data For Cold to Warm

3.5/10/20

Time, t Strength, s Eguivalent Age, te Relative Strength, S/Su
(days) (p.s.i.) (days)

0.753 343 0.459 0.040
1.625 1302 0.990 0.154
3.719 3242 2.265 0.383
6.545 5311 5.837 0.627
12.781 6564 11.399 0.775
31.656 7194 28.233 0.849


Ultimate Strength, Su Rate Constant, k
(p.s.i.) (days'1)

8471.6 0.239


y = m1*(m2*(m0-m3))/(1+m2*(m...
Value Error
m 1 8471.6 587.35
m2 0.239 0.057299
m3 0.68384 0.19206
Chisq 4 8929e+05 NA
R 0.9938 2 NA




69


Strength and Age Data For Cold to Warm

6.75/10/20

Time, t Strength, s Equivalent Age, te Relative Strength, S/Su
(days) (P s i.) (days)

0.753 343 0.459 0.039
1.625 1302 0.990 0.146
3.719 3242 2.265 0.365
6.597 4485 4.018 0.505
12.792 6524 11.409 0.734
32.76 7434 29.217 0.836


Ultimate Strength, Su Rate Constant, k
(P si.) (days'1)

8889.8 0.18414



y mi V 111^1
Value Error
ml 8889.8 454.83
m2 0.18414 0.030586
m3 0.59723 0.16442
Chisq 2.2338e+05 NA
R 0.99717 NA




70


Strength and Age Data For Cold to Warm

13.75/10/20

Time, t Strength, s Equivalent Age, te Relative Strength, S/Su
(days) (P s i.) (days)

0.753 343 0.459 0.042
1.625 1302 0.990 0.158
3.719 3242 2.265 0.393
6.597 4485 4.018 0.544
12.875 5841 7.841 0.709
32.892 7123 29.335 0.865


Ultimate Strength, Su Rate Constant, k
(P si.) (days'1)

8239.4 0.19856


y = m1*(m2*(m0-m 3))/(1+m2*(m...
Value Error
ml 8239.4 142.26
m2 0.19856 0.011481

m3 0.57366 0.05562

Chisq 23796 NA

R o CD CD CO 35 NA




71


Strength and Age Data For Warm to Cold

1.5/20/10

Time, t Strength, s Eguivalent Age, te Relative Strength, S/Su
(days) (P s i.) (days)

0.799 1321 0.713 0.189
1.521 2697 1.357 0.386
3.979 3707 2.423 0.530
6.635 4529 4.041 0.648
12.851 5359 7.826 0.766
27.667 6335 16.849 0.906


Ultimate Strength, Su Rate Constant, k
(P s i.) (days'1)

6994.5 0.27974


y= m1*(m2*(m0-m3))/(1+m2*(m...
Value Error
ml 6994.5 485.37
m2 0.27974 0.086309
m3 -0.23354 0.39244
Chisq 2.6348e+05 NA
R 0.992 NA




72


Strength and Age Data For Warm to Cold

3.5/20/10

Time, t Strength, s Eguivalent Age, te Relative Strength, S/Su
(days) (p.s.i.) (days)

0.799 1321 0.713 0.197
1.521 2697 1.357 0.402
3.646 4471 3.252 0.666
6.642 4994 4.045 0.744
12.861 5757 7.832 0.857
27.677 6452 16.856 0.961


Ultimate Strength, Su Rate Constant, k
(p.s.i.) (days'1)

6713.9 0.54741


- y = m1*(m2*(m0-m3))/(1+rr 2*(m...
Value Error
ml 6713.9 212 42
m2 0.54741 0.093952
m3 0.33421 0.11854
Chisq 1,0582e+05 NA
R 0.99717 NA





73


Strength and Age Data For Warm to Cold

6.75/20/10

Time, t Strength, s Equivalent Age, U Relative Strength, S/Su
(days) (P s i.) (days)

0.799 1321 0.713 0.192
1.521 2697 1.357 0.391
3.646 4471 3.252 0.648
6.531 5638 5.825 0.818
12.871 5789 7.839 0.839
27.684 6598 16.860 0.957


Ultimate Strength, Su Rate Constant, k
(P s i.) (days'1)

6896.5 0.58697


- y = ml *( m2*(m0-m3))/(1 + m2*(m...
Value Error
ml 6896.5 244.56
m2 0.58697 0.11344
- m3 0.40205 0.12032
Chisq 1,5157e+05 NA
R 0.99633 NA




74


Strength and Age Data
For Warm to Cold
12.75/20/10
Time, t
Strength, s
Equivalent Age, te
Relative Strength, S/Su
(days)
(P-si)
(days)
0.799
1321
0.713
0.181
1.521
2697
1.357
0.369
3.646
4471
3.252
0.611
6.531
5638
5.825
0.770
12.771
6534
11.390
0.893
27.69
6658
16.863
0.910
Ultimate Strength, Su
Rate Constant, k
(P-si)
(days'1)
7318.2
0.5147
y= m1*(m2*(m0-m3))/(1 r-rr^'im...
Value Error
ml 7318.2 203.19
m2 0.5147 0.073756
m3 0.37906 0.096409
- Chisq 93777 NA
- R 0.998 NA
75


Strength and Age Data For Hot to Warm

0.75/32/20

Time, t Strength, s Eguivalent Age, U Relative Strength, S/Su
(days) (p.s.i.) (days)

0.726 2481 1.023 0.330
1.726 3502 1.539 0.466
2.742 4083 2.445 0.543
6.745 5241 6.016 0.697
13.726 6102 12.242 0.812
27.75 6853 24.749 0.912


Ultimate Strength, Su Rate Constant, k
(p.s.i.) (days1)

7514.1 0.31758


- w rwl */ irO*/W) (1+m2*(m...
y 1111 \
Value Error
ml 7514.1 178.96
m2 0.31758 0.041942
m3 -0.89277 0.23007
- Chisq 36027 NA
R 0.99868 NA








76


Strength and Age Data For Hot to Warm

1.75/32/20

Time, t Strength, s Eguivalent Age, U Relative Strength, S/Su
(days) (p.s.i.) (days)

0.726 2481 1.023 0.353
1.736 3991 2.447 0.568
2.75 4395 2.453 0.626
6.753 5335 6.023 0.760
13.743 6016 12.257 0.857
27.757 6822 24.755 0.971


Ultimate Strength, Su Rate Constant, k
(p.s.i.) (days'1)

7022.5 0.52895


y=rri1*(rr21(rrCkr8))/(1-tiT2\m..
V9u= Error
ml 7C225 337.13
m2 0.52895 0.16651
rrB -0.39191 0.40162

Ctisq 2.2838e+05 m

R 0.99017 NA




77


Strength and Age Data For Hot to Warm

2.75/32/20

Time, t Strength, s Equivalent Age, te Relative Strength, S/Su
(days) (P s i.) (days)

0.726 2481 1.023 0.362
1.736 3991 2.447 0.582
2.733 4705 3.853 0.686
6.76 5374 6.029 0.784
13.75 5956 12.263 0.869
27.76 6850 24.758 0.999


Ultimate Strength, Su Rate Constant, k
(P s i.) (days'1)

6854.3 0.68765


v = m1*(m2*(m0-m3h /(1+m2*(m...
Value Error
ml 6854.3 340.69
m2 0 68765 0 23729
m3 -0 14178 0 35218
Chisq 3.033e+05 NA

R 0.98713 NA





78


Strength and Age Data For Hot to Warm

6.75/32/20

Time, t Strength, s Eguivalent Age, te Relative Strength, S/Su
(days) (P s i.) (days)

0.726 2481 1.023 0.357
1.736 3991 2.447 0.575
2.733 4705 3.853 0.677
6.736 5704 9.495 0.821
13.757 6293 12.269 0.906
27.767 6703 24.764 0.965


Ultimate Strength, Su Rate Constant, k
(P s i.) (days'1)

6945.4 0.74581


y = ml *(m2*(m0-m3) )/(1+m2*(m...
Value Error
ml 6945.4 81.751
m2 0.74581 0.060693
m3 -0.029081 0.073988
Chisq 19118 NA

R n NA




79


I
Strength and Age Data For Hot to Warm

13.75/32/20

Time, t Strength, s Equivalent Age, U Relative Strength, S/Su
(days) (p.s.i.) (days)

0.726 2481 1.023 0.345
1.736 3991 2.447 0.556
2.733 4705 3.853 0.655
6.736 5704 9.495 0.794
13.729 6524 19.353 0.908
27.774 6850 24.771 0.954


Ultimate Strength, Su Rate Constant, k
(p.s.i.) (days'1)

7182.1 0.65668



y = m1'(m2*(m0-m3))/(1+m2*(m...
Value Error
ml 7182.1 125.14
m2 0.65668 0.076012
m3 -0.094339 0.11458
Chisq 40544 NA
R 0.99852 NA





I
80


Strength and Age Data For Warm to Hot

0.75/20/32

Time, t Strength, s Eguivalent Age, U Relative Strength, S/Su
(days) (p.s.i.) (days)

0.799 1321 0.713 0.184
1.753 3413 2.471 0.476
2.75 4215 3.877 0.588
6.752 5349 9.518 0.746
13.753 6280 19.387 0.876
27.757 6991 39.127 0.975


Ultimate Strength, Su Rate Constant, k
(p.s.i.) (days'1)

7172.7 0.58899




y = mV (m2*(m0-m3))/(1+ m2*(m...
Value Error
ml 7172.7 276.3
m2 0.58899 0.12144
m3 0.38371 0.14127
Chisq 2.1575e+05 NA
R 0.99495 NA



81


Strength and Age Data For Warm to Hot

2.75/20/32

Time, t Strength, s Equivalent Age, U Relative Strength, S/Su
(days) (p.s.i.) (days)

0.799 1321 0.713 0.168
1.521 2697 1.357 0.343
3.646 4471 3.252 0.568
6.766 5318 9.538 0.676
13.767 6602 19.406 0.839
27.774 7212 39.151 0.917


Ultimate Strength, Su Rate Constant, k
(P s i.) (days'1)

7868.2 0.36601



y = ml *(m2*(m0-m3))/(1 +m2*(m...
Value Error
ml 7868.2 238.19
m2 0.36601 0.052 2 32
m3 0.20266 0.12841
Chisq 95479 NA
R 0.99814 NA




82


Strength and Age Data For Warm to Hot

6.75/20/32

Time, t Strength, s Eguivalent Age, te Relative Strength, S/Su
(days) (P s i.) (days)

0.799 1321 0.713 0.176
1.521 2697 1.357 0.360
3.646 4471 3.252 0.596
6.531 5638 5.825 0.752
13.774 6213 19.416 0.829
27.788 7082 39.171 0.945


Ultimate Strength, Su Rate Constant, k
(P si.) (days'1)

7497.8 0.45337


y = m1*(m2*(m0-m3)) /(1+m2*(m...
Value Error
ml 7497.8 204.93
m2 0.45337 0.062208
m3 0.31607 0.10413
Chisq 87816 NA
R 0.99819 NA




83


Strength and Age Data For Warm to Hot

13.75/20/32

Time, t Strength, s Equivalent Age, U Relative Strength, S/Su
(days) (P s i.) (days)

0.799 1321 0.713 0.172
1.521 2697 1.357 0.351
3.646 4471 3.252 0.581
6.531 5638 5.825 0.733
12.771 6534 11.390 0.850
27.795 7065 39.181 0.919


Ultimate Strength, Su Rate Constant, k
(P s i.) (days'1)

7690.1 0.43387



y= ml *(m2*(m0-m3))/(1+m2(m.
Value Error
ml 7690.1 79.838
m2 0.43387 0.021923
m3 0.31275 0.038848
Chisq 12395 NA
R 0.99975 NA



84


Data Sheet for Cold to Warm

Time Cold Bath Warm Bath Test #1 (lb) #2 (lb) #3 (lb)
0 51 18 0

1.5 36 27 3A/1.5/10 16000 15850 15000
3B/1.5/22 32900 33650 32900

3 24 30 3A/3/10 37900 40600 41500
3A/1.5/10/3/22 54900 54500 53400
3B/3/22 55200 55600 55500

7 12 24 3A/7/10 54100 55250 57500
3A/1.5/10/7/22 66000 70550 65500
3 B/3/10/7/22 65000 66500 66500
3B/7/22 70100 69400 70800
3B/7/10 (cal) 53600 54600 53300
3A/7/22 (cal) 68450 66750 68100

13 6 15 3A/13/10 72000 72850 73100
3A/1.5/10/13/22 79000 76900 81400
3B/3/10/13/22 81600 82000 81600
3B/7/10/13/22 79900 82500 81300
3B/13/22 81600 81500 81000

32 0 0 3A/33/10 83250 86100 82600
3A/1.5/10/33/22 88700 90200 88500
3B/3/10/32/22 87500 89950 91500
3B/7/10/33/22 92000 93500 92500
3/13/10/33/22 86600 91200 88500
3B/33/22 88000 92000 89750
85


Data Sheet for Warm to Cold

Time Warm Bath Cold Bath Test #1 (lb) #2 (lb) #3 (lb)
0 42 12(cold)

0.75 42 9(cold) 3/0.75/10 3500 3400 3800

1.5 30 9(cold)
12(1.5)

3 21 9(cold) 3/1.5/20/3/10 47500 45000 45000
9(1.5)
9(3)

7 12 9(cold) 3/1.5/20/7/10 55600 55000 57900
6(15) 3/3/20/7/10 62250 62600 61200
6(3) 3/7/20 cal 64000 60800 65600
6(7)

13 6 9(cold) 3/1.5/20/13/10 68200 66000 65600
3(1.5) 3/3/20/13/10 70900 72000 71900
3(3) 3/7/20/13/10 69500 73500 73000
3(7) 3/13/20-cal 77400 78000 75000
3(13)

28 3 6(cold) 3/1.5/20/28/10 78900 78500 79200
3/3/20/28/10 78600 81000 81400
3/7/20/28/10 80700 84300 81500
3/13/20/28/10 83200 83550 82000
3/28/20 cal 90100 89900 87000
3/28/2010 77700 78600 79600
86


Data S hieet for Hot to Warm Test

Time Hot Bath Warm Bath Test #1 (lb) #2 (lb) #3 (lb)
0 63 0 0
9(warm)

0.75 45 15(0.75) 3/0.75/32 30000 30600 30700
9(warm)

1.75 30 12(0.75) 3/1.75/32 50000 51100 47100
12(1.75) 3/0.75/32/1.75/20 42400 43000 44400
9(warm)

2.75 18 9(0.75) 3/2.75/32 58600 58250 58300
9(1.75) 3/0.75/32/2.75/20 50100 51100 50500
9(2.75) 3/1.75/32/2.75/20 53900 57050 52500
9(warm)

6.75 9 6(0.75) 3/6.75/32 69200 70500 73100
6(1.75) 3/0.75/32/6.75/20 64300 64900 66150
6(2.75) 3/1.75/32/6.75/20 65800 66500 66600
6(6.75) 3/2.75/32/6.75/20 68500 71050 60800
6(warm) 3/6.75/20 65550 67100 67400

13.75 3 3(0.75) 3/13.75/32 80650 81300 81750
3(1.75) 3/0.75/32/13.75/20 76800 73150 77850
3(2.75) 3/1.75/32/13.75/20 74350 73850 76350
3(6.75) 3/2.75/32/13.75/20 69850 74800 77650
3(13.75) 3/6.75/32/13.75/20 80000 78900 76100
3(warm) 3/13.75/20 77150 76750 73700

27.75 0 0 3/27.75/32 83250 87400 88000
3/0.75/32/27.75/20 85000 85700 85400
3/1.75/32/27.75/20 84950 85100 84900
3/2.75/32/27.75/20 85450 84000 86550
3/6.75/32/27.75/20 86550 84100 79800
3/13.75/32/27.75/20 84500 84000 87500
3/27.75/20 85950 91500 85500
87


Data Sheet for Warm to Hot

Time Warm Bath Hot Bath Test #1 (lb) #2 (lb) #3 (lb)
0 54 0 0

0.75 36 15(0.75) 3/0.75/20 15700 17450 14400


1.75 24 12(0.75) 3/0.75/20/1.75/32 42200 40600 43650
12(1.75)


2.75 15 9(0.75) 3/0.75/20/2.75/32 52200 52400 52050
9(1.75) 3/1.75/20/2.75/32 47050 47600 51900
9(2.75)


6.75 g 6(0.75) 3/0.75/20/6.75/32 69000 61000 69400
6(1.75) 3/1.75/20/6.75/32 69100 67400 67500
6(2.75) 3/2.75/20/6.75/32 67100 65900 65250
6(6.75) 3/6.75/20 58600 61550 60100


13.75 6 3(0.75) 3/0.75/20/13.75/32 78600 78400 77500
3(1.75) 3/1.75/20/13.75/32 76900 78750 81950
3(2.75) 3/2.75/20/13.75/32 81800 83400 81450
3(6.75) 3/6.75/20/13.75/32 77500 76000 78500


27.75 0 0 3/0.75/20/27.75/32 86900 87400 87000
3/1.75/20/27.75/32 85300 85600 87550
3/2.75/20/27.75/32 91000 91400 87250
3/6.75/20/27.75/32 87500 87750 89500
3/13.75/20/27.75/32 86400 89600 88100
3/27.75/20 84400 85000 82500
88


References
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Maturity Methodf Annual Book of ASTM Standards, Vol. 04.02.
ASTM Cl074-87, Standard Practice for Estimating Concrete Strength by the
Maturity Method, Ann ual Book of ASTM Standards, Vol. 04.02.
Barnes, B. D., R. L. Orndorff, and J. E. Roten, Low Initial Temperature Improves
the Strength of Concrete Cylinders, Journal of the American Concrete Institute, Vol.
74, No. 12, December 1977, pp. 612-615.
Bernhardt, C. J., Hardening of Concrete at Different Temperatures, Proceedings of
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Copenhagen, Denmark, 1956, pp. 18.
Brown, T. L. and LeMay, H. E., Chemistry: The Central Science, 4th Edition,
Prentice Hall, 1988, pp. 494-498.
Carino, N. J., Temperature Effects on the Strength-Maturity Relation of Mortar,
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Carino, N. J., The Maturity Method: Theory and Application, Cement, Concrete,
and Aggregates, CCAGDP, Vol. 6, No. 2, Winter 1984, pp. 61-73.
Carino, N. J., K. I. Lawrence, and J. R. Clifton, Applicability of the Maturity
Method to High-Performance Concrete, National Institute of Standards and
Technology, NISTIR Report No. 4819, May 1992.
Feld, J. and Carper, K. L., Construction Failure, 2nd Edition, John Wiley and Sons,
Inc., 1997
Freiesleben Hansen, P. and Pedersen J., Maturity Computer for Controlled Curing
and Hardening of Concrete, Nordisk Betong, 1, 1977, pp. 19-34.
Johnson, G. L., Farrell, C. W., Hover, K. C., In-Place Temperature Recording for the
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89