In this work, the roles of curing temperature on the mechanical performance and microstructure of cement paste/mortar modified by VAEC dispersible powder are reported. The experimental results show that as compared with mortars cured at standard condition, the strengths of mortars cured at 60 degrees C are enhanced, whereas the 100 degrees C curing temperature makes a side effect. The formation of carboxyl-containing substances is facilitated at elevated temperatures and meanwhile the pores are refined and the thickness of polymer film is reduced together with the pores in the polymer film are increased. These alterations are responsible for the changes of mechanical performances. (C) 2021 Elsevier Ltd. All rights reserved.

The present study reports the influence of defoaming agent (DA) on the mechanical performances and pore characteristics of cement paste/mortar in presence of ethylene and vinyl acetate copolymer (EVA) dispersible powder. To make a comparative investigation, two various types of DA including silicone and ether DA are introduced. Fluidity, air content, volume density and strengths experiments are performed to evaluate the development of workability and mechanical performances. The hydration kinetics, phase composition and pore structure are characterized by isothermal calorimetry (ICC), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and mercury intrusion porosimetry (MIP) techniques. The experimental results indicate that the initial fluidity is increased with addition of EVA, while it is decreased with the content of defoaming agents. The DA enhances the development of strengths and volume density of hardened paste/mortar in presence of EVA. The fact that EVA participates in the chemical reaction and promotes the formation of carboxyl-containing substance (e.g. calcium acetate), ettringite and calcium hydroxide can be found. MIP results shows that the porosity and more-harmful pore are increased with the incorporation of EVA. DA significantly reduces the porosity and quantity of more-harmful pore, contributing to the higher mechanical properties. This study can be viewed as a valuable reference for the improvement of pore structure by using DA in the EVA modified cement-based materials.

It is still uncertain whether polyacrylamide polymer powder can restrain the cracking of cement mortar in the plastic period and the mechanisms, which are responsible for this role, still need to be systematically clarified. Thus the different contents of the polyacrylamide polymer powder were mixed and various pastes with polyacrylamide were prepared. The cracking behaviors and water evaporation losses of mortars were evaluated. The bleeding percentages, chemical shrinkages, ions concentrations, ultraviolet visible spectra and the characteristics of hydration heat liberations of cement pastes with polyacrylamide polymer powder were investigated to carry out the insight into the role of polyacrylamide polymer powder on the cracking of cement paste in the plastic period. The experimental results indicate that the polyacrylamide polymer powder improves the mortar resistance to the cracking in the plastic period. It decreases the water evaporation loss and bleeding percentage. But it enhances the chemical shrinkage and the increased chemical shrinkage is mainly attributed to the role of polyacrylamide polymer powder on the promotion of cement hydration in the tested ages, especially in the initial fast reaction and the first deceleration periods. The existence of the intermolecular hydrogen bonds is the main reason for lowering the water evaporation loss and bleeding percentages. Acting forces from the intermolecular hydrogen bonds may be additional contributor to the improved resistance to the cracking of cement mortar in the plastic period. The results from this work will provide a reference for the alleviation of the plastic cracking of cement based paste.

This work investigates the synergistic utilization of EVA, TEA and C-S-Hs-PCE as admixtures in Portland cement. The alteration of hydration process is measured by isothermal calorimetry (ICC) and the effects of admixtures on mechanical properties are evaluated by the development of strengths and apparent density. The mechanism of admixtures acting in cement is revealed via XRD, FT-IR and TGA techniques. Results show that the fluidity of fresh cement paste is significantly improved with the addition of EVA, TEA and C-S-Hs-PCE, and consequently to the increasing in workability. The admixtures accelerate the hydration process and increase the cumulative heat release, deepening the hydration degree of cement paste. Both the improvement of fluidity and promotion of hydration are the important reasons for the enhancement of mechanical properties. Results of XRD, FT-IR and TGA indicate that the CH contents increase evidently with the content of admixtures, which further proves that the deepening of hydration process. This study could provide an experimental reference, which is of great significance to the valuable application of admixtures in cement based materials. (C) 2020 Elsevier Ltd. All rights reserved.