Chemical shrinkage, 1.25

Once the temperature and degree of cure can be predicted throughout the material during cure, the nonmechanical loadings (thermal expansion and chemical shrinkage) can be obtained. With this knowledge in hand the residual stresses can then be analyzed. 

The final transverse chemical shrinkage strain is and ach is the degree of cure when chemical shrinkage is complete. The parameters c, and c2 are empirical constants obtained from chemical shrinkage characterization tests. In most cases occh can be approximated as the degree of cure at gelation. 

Minimum water/cement ratio for complete hydration chemical shrinkage... 

Neither entropic, nor chemical shrinkage are exported to be very sensitive to the small amount of comonomer present. More probably, the greater plasticization by the larger comonomer molecules enhances the elongation in the thermoplastic phase, thus reducing the apparent shrinkage. 

Figure 22. Cement chemical shrinkage. (Reproduced with permission from reference 5. Copyright 1991 Schlumberger.)...

Figure 23. Cement pore pressure declines due to gellation (self-supporting column) and chemical shrinkage. It occurs simultaneously with the maximum of the hydration exotherm, and if gas is present, it is at this stage gas will penetrate into the cement. (Reproduced with permission from reference 5. Copyright 1991 Schlumberger.)...

Chemical Shrinkage of Pastes Made with Shrinkage Reducing... 

Keywords Shrinkage reducing admixtures, chemical shrinkage, cement pastes, compressive strength. 

In order to evaluate de delay of hydration due to the presence of SRA, the degree of hydration of cement pastes with SRA is analyzed, using the chemical shrinkage test, for two different cements and three polymers. The compressive strength of mortars was also used as an indirect method of estimation of relative degree of hydration. 

Fig. 2 show the chemical shrinkage results for cements A1 and Se. As can be seen, the values are not too different when adding the SRAs. However, small changes are noticeable, which depends on the type of cement and on the type of SRA. To put that into evidence. Fig. 3 show individually the chemical shrinkage of reference paste and SRA paste. In this figure is evident the higher influence of SRA on pastes with cement Se. 

Comparing the chemical shrinkage of the two reference pastes, without SRA, the values of cement Se are higher than the correspondent ones of cement Al, at the same age, which is in... 

Figure 2 Chemical shrinkage of pastes made with cement A1 and cement Se...

It is recognized that chemical shrinkage is an indirect measure of the degree of hydration [9], However, in this case same assumptions should be made to use the chemical shrinkage as indicator of hydration rate of cement pastes incorporating SRA, which may be summarized in the following the volume decreases is only dependent on the reaction rate the reaction with water of the different anhydrous compounds of cement occur at the same rate and the density of combined and gel waters do not change in the presence of SRA. 

The assumptions may not be consensual, but serve as a basis for the following analysis. The final chemical shrinkage. Vs, when the hydration is complete, may be estimated by the equation 3 [10],... 

Fig. 6 shows the compressive results of the eight mortars. The results also indicate less influence of SRA S on the performance of the material, which may be related with degree of hydration. The relative influence of the three SRA on chemical shrinkage and compressive strength was similar for pastes made with cement Se. Compressive strength results on pastes made with cement A1 also... 

The influence of SRA products in chemical shrinkage of pastes depends on the cement used and on the type of polymer, and no systematic tendency was observed. However, the values obtained in this study generally indicate a small reduction of chemical shrinkage when using these polymers, mainly at early age. 

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