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Skip to main content. Log In Sign Up. In the present study, an extensive test program is conducted to measure and compare the heat of hydration obtained from both calorimeter and ASTM C test methods. A statistical analysis is performed to evaluate the variations of the test data.
The results indicate that the isothermal conduction calorimeter method is a more reliable, less time-consuming, and less labor-intensive method than the ASTM C test method. The heat of hydration at 3 days showed the least variation in all calorimeter tests. These suggest that ASTM shall consider adopting the isothermal conduction calorimeter method for measuring the heat of hydration of cement.
The 3-day heat of hydration value can be used for specifying the limit of heat release for type II cements. Such testing shall not be used for acceptance or rejection of the cement, but results shall be reported for informational purposes. The research work in this paper is intended to develop some supplementary information, which may be useful for current ASTM standard development efforts.
The main objectives of this paper are to Manuscript received February 5, ; accepted for publication August 28, ; published online October No further reproductions authorized. Experimental Program Materials All cement samples used in this test program were from commercial sources.
In order to have represen- tative data, cements produced at various locations on different production dates were selected for evalu- ations. The chemistry, Blaine fineness, and mineral compositions of these cements are summarized in Table 1. Testing Techniques ASTM C method —This test method determines the HoH of hydraulic cement by measuring the heat of solution of the dry cement and the heat of solution of a separate portion of the cement that has been mixed with water and hydrated to a specified age; the difference between the heats of solution of dry cement and hydrated cement is the value of HoH for this cement at the specified age.
The heat of solution of hydrated and unhydrated cement is determined through many steps involving tedious preparation of hydrated cement sample, the use of chemical agents, and v186 skills of wet chemistry.
TAM Air is an eight-channel isothermal heat conduction calorimeter. The energy change during hydration is collected and registered by an automated data acquisition program.
The energy value is based on the unit weight of cement mass. The sample preparation, testing conditions, and procedures for the calorimeter test are summarized in Table 2. Before calorimeter tests were conducted for data collection and data analysis purposes, a series of test procedures was examined with the objective of selecting a standard operating procedure for testing. These include the following: The EM procedure involves mixing cement paste outside the calorimeter for certain amount of time and then transferring the paste to the testing vial for data collection.
In this testing procedure, the HoH is not counted during the period of EM. A modified mini-electrical drill mixer was chosen for IM procedure.
The IM was conducted by pre-loading cement material into the testing vial and then injecting water into the sample vial followed by mixing action. The HoH was simultaneously collected during the mixing operation. These tools and subsequent procedures were used throughout this program. The objective was to evaluate the sensitivity of the heat release signature to the EM time.
This is particularly true during the early stages of cement hydration and strength development. The objective of the strength test was to establish a strength database and compare the strength development with the heat release. The detailed descriptions of the procedures are listed in Table 3.
During this period, any lumps in the cement paste were broken down. Three different intense mixing times of 45, 75, or s were evaluated.
ASTM C, Test equipment Controls
For each mixing procedure, tests were conducted in pairs. The heat release values are summarized in Table 4. With 45 s of intense mixing, the heat release at 30 min and 24 h is slightly lower than the heat release with the asfm two longer intense mixing procedures of 75 and s.
This was likely due to the insufficient mixing time to disperse c168 cement particles. The highest heat release is from 75 s of the intense mixing procedure. The longest intense mixing time of s also reduced the heat release.
This is probably caused by the loss of the hydration heat during the EM time. It is interesting to note that the heat release variation among the different intense mixing times mainly occurred during the first 30 min of cement hydration. The heat release from 30 min to 24 h for 75 and s of intense mixing time remains the same. Figure 1 shows the actual hydration profiles of the cement pastes with different mixing procedures.
The heat release rates during the first 30 min are illustrated in Fig. Relatively large variation was observed during this period. However, all heat release rates returned to approximately the same baseline after 30 min. This indicates that hydration is stabilized from the rapid initial heat release in the early minutes. The heat release variation was also reflected in the cumulative heat release as shown in Fig.
By and large, no significant variation can be seen regardless of the intense mixing duration. Aastm total heat release profiles shown in Fig. This difference in the total heat release largely originated from the early period as shown in Table 4.
Regardless of the variation in the early minutes, the final total heat release at 24 h did not appear to be significantly different. Therefore, for the purpose of standardizing the mixing procedure, 30 s of premixing followed by 75 s of intense mixing was used throughout the rest of this study.
Zstm Mixing versus External Mixing There is a strong interest in the technical community to understand the HoH variation when the cement and water are mixed inside of the aetm vial of the calorimeter versus the procedure when it is mixed externally prior to transferring the paste into the testing vial.
The argument has been largely focused on the unknown amount of heat not accounted for when the EM method is used. Extensive asgm were conducted to compare the heat release changes between IM and EM methods. In addition, statistical evaluation was also conducted on the heat release data collected from both mixing methods.
In general, most of the heat loss takes place in the first 30 min. The heat loss at the early ages is mostly related to the unaccounted heat release before the cement paste was loaded into the test vial. This trend is graphically shown in Fig.
EM shows a lower standard deviation than the IM. This measure is wstm useful parameter for comparing the degree of variation from one data series to another, even if the means are drastically different from each other.
ASTM C186 – 17
From Table 5, it can be seen that the variation in CV is very high in the first 30 min and is drastically reduced to the lowest level from 1 to 3 days. There is a slight up-trend in CV at 7 days. The CV trend is also graphically shown in Fig. In general, the variation in EM is slightly lower than the variation observed asstm IM.
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This c1186 largely due to the exclusion of heat release during the EM period. The heat release in the early minutes is highly variable; hence, its exclusion helps improve the statistical variances.
A total of 17 cements were tested in this program. The Atm procedure with 30 s premixing and 75 s intense mixing time was used. HoH values obtained from both calorimeter and the ASTM C methods, along with the strength results at various ages, are summarized in Table 7.
The difference in HoH values is not understood at this point. However, it is important to point out that the calibration process of the calorimeter could potentially affect the heat value. Asttm calorimeter instrument used in this work was calibrated in the absence of f186 material.
As previously stated, when cement v186 mixed with water, HoH represents the progress of cement hydration, which in turn dictates cement strength development. The relationship of HoH of cement and strength development has been studied by many scientists and engineers. The degree of relative relationship is used to assess the relative reliability of HoH obtained from the calorimeter and ASTM C methods. The 1- 3- and 7-day strengths were used for establishing correlation with 1- 3- and 7-day HoHs obtained from the calorimeter test.
The R2 at 3 days is 0. This may be attributed to the following: Therefore, the EM method is preferably used as a standard mixing procedure. Standard cement may be recommended for users to calibrate the calorimeter instruments.
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