Effects of polycarboxylate superplasticisers with various functional groups on the pore structure of cement mortar

Abstract

The air-entraining capabilities of polycarboxylate superplasticisers (PCEs) with different functional groups were systematically analysed. Using different molecular PCEs, the evolution process from bubbles in fresh cement mortar to pores in hardened cement mortar was investigated, considering their effects on mortar workability and mechanical performance. The results showed that PCEs with various functional groups have different air-entraining capabilities. PCEs with ester groups decreased the surface tension and significantly promoted the air-entraining capability, resulting in a notable increase of air content in fresh cement mortar. PCEs with sulfonic acid groups increased the surface tension and remarkably decreased the air content in the fresh cement mortar. A higher air-entraining capability benefits the dispersing properties of PCEs and therefore the PCEs with ester groups performed better in dispersibility in comparison with the PCEs with sulfonic acid groups. The stability of bubbles entrained in fresh cement mortar leads to differences in the pore structure of hardened cement mortar. The PCEs with ester groups diminished the size of large bubbles, leading to significantly decreased porosity of the hardened mortar. PCEs with sulfonic acid groups in the backbone barely optimised the pore structure, with a large amount of large pores remaining in the hardened mortar. Decreased porosity and pore size hence led to higher compressive strength of the hardened cement mortar.

Research on the performances of VPEG macromonomer grafted different functional groups to prepare polycarboxylate superplasticizers

“…The test results illustrate that carboxylic acid groups are beneficial in decreasing the surface tension of the solution, while the introduction of amide and sulfonic acid groups increases the surface tension of the solution, with the most significant increase in PCEs with addition of sulfonic acid groups, a result that is consistent with the literature. 35…”

“…From the test results of surface tension and fluidity, it can be found that the smaller the surface tension of the PCE solution, the better the dispersion retention performance, this is due to the PCEs incorporation leads to changes in the air-entraining capacity in the cementwater system, 35,56,57 the low surface tension solution will introduce more bubbles, the bubbles in the inter-particle Combined with the test results of surface tension, heat of hydration of cement, setting time and compressive strength of mortar, it is known that the different molecular structure of PCE, the hydration effect on cement is also different, in which the molecular structure of carboxylate group with high density, the chelating effect with Ca 2+ in cement is stronger, so as to delay the hydration of cement more, 58 and the addition of amide group will accelerate the hydration of cement is due to the amide group of the N atom can provide a lone pair of electrons, which will make the Ca 2+ , AL 3+ , and Mg 2+ ions accelerate the hardening of flocculation and promote the hydration reaction. 59,60 However, Sodium methacrylsulfonate showed the best promotion of hydration and setting, probably due to its low air attraction caused by its low surface tension, and the lesser introduction of air bubbles resulted in a reduced retarding effect on the cement.…”

Bubble Evolution under the Action of Polycarboxylate and Air-Entraining Agent and Its Effects on Concrete Properties—A Review

“…Sulfonic acid group. When a small number of sulfonic acid groups was used to replace the carboxyl groups in the main PCE chain, the fresh mortar with sulfonic acid group-containing PCE had a significantly increased or decreased air void of 5–6%, as shown in Figure 17 below [ 63 ]. As the sulfonic acid group gradually increased, the air-entrainment amount in the cement mortar gradually decreased because more sulfonic acid groups would lead to an increased concentration of PCE adsorbed on the cement particle surface.…”

“…After the grafted ester group enters the side chain, PCE has a lower surface tension, which can significantly improve the air-entraining ability and change large bubbles into small bubbles. PCE with sulfonic acid groups inserted in the main chain cannot optimize the pore structure of concrete, with a large number of macropores still present in the hardened cement mortar [ 63 ]. Therefore, how to use the above experimental methods to optimize the PCE molecular structure is still worthy of further study.…”

The Influence of Water Reducing Agents on Early Hydration Property of Ferrite Aluminate Cement Paste

“…The FAC paste will rapidly lose fluidity or workability due to its excessive hydration rate, and greatly reduce its construction performance. Water reducing agents is a kind of important chemical admixture for Portland cement-based materials [24][25][26][27]. They can increase the workability of fresh concrete without additional water, or reduce the amount of water for a given fluidity [28][29][30][31].…”