早强型聚羧酸系减水剂对基准水泥早期水化的影响研究

探究早强型聚羧酸系减水剂(ES-PCE)对水泥水化的作用机制,有助于ES-PCE的研发设计与推广应用。本文通过对水泥水化进程、溶解速率、水化产物生长、凝结时间与抗压强度进行表征,分析了ES-PCE与普通聚羧酸系减水剂(PCE)对基准水泥早期水化的影响机理。结果表明:PCE与ES-PCE均会降低水泥悬浮液的溶解速率;PCE的掺入延缓了水泥水化的诱导期与加速期,降低了水化放热量;而ES-PCE仅略微延迟了水泥水化的诱导期,但缩短了加速期,水化放热量基本不变。与基准水泥相比,ES-PCE分别提早了水泥初凝时间10 min和终凝时间85 min。ES-PCE的掺入提高了水泥早期和后期强度,掺0.2%(质量分数)ES-PCE的水泥7 d抗压强度较基准组提高了14%,而同掺量的PCE强度提高仅为前者的一半。PCE与ES-PCE的掺入释放了水泥颗粒团状絮凝结构中的水分,有利于水泥水化,但二者对水化的影响截然相反;PCE分子结构中大量的羧基络合了溶液中的Ca²⁺,抑制了水泥颗粒表面晶核的形成,起到了一定的缓凝作用;然而,ES-PCE分子结构中羧基含量较低,Ca²⁺的络合作用较弱,缓凝效果并不明显,在体系中有效水分增多的情况下,反而促进水泥的水化,起到了早强效果。水灰比为0.4的水泥砂浆中,ES-PCE的掺量适宜控制在0.3%以下,在保证减水率的同时,对水泥早期和后期强度均起到一定的增强作用。

Effect of Early-Strength Polycarboxylate Superplasticizer on Early Hydration of Reference Cement

Investigating the mechanism of early-strength polycarboxylate superplasticizer (ES-PCE) on cement hydration is helpful to the development, design and application of ES-PCE. In this paper, the influence mechanisms of ES-PCE and regular polycarboxylate superplasticizer (PCE) on early hydration of reference cement were analyzed by characterizing the hydration process, dissolution rate, hydration product growth, setting time and compressive strength of cement. The results show that both PCE and ES-PCE reduce the dissolution rate of cement suspension. The addition of PCE delays the induction and acceleration of cement hydration and reduces the heat release of hydration. ES-PCE only slightly delays the induction period of cement hydration, but shortens the acceleration period and hydration heat release is basically unchanged. Compared with reference cement, ES-PCE advances the initial setting time of cement by 10 min and the final setting time by 85 min. The incorporation of ES-PCE improves the early and late strength of cement. The 7 d compressive strength of cement with 0.2% ES-PCE (mass fraction) increases by 14% in comparison with reference group, while the strength of cement with PCE increases by only half of the former. The addition of PCE and ES-PCE releases the water in the granular flocculation structure of cement, which is beneficial to cement hydration, but their effects on hydration are opposite. A large number of carboxyl groups in the molecular structure of PCE complexes Ca²⁺ in the solution, inhibits the formation of crystal nuclei on the surface of cement particles, and plays a certain role of retarding coagulation. However, the carboxyl content of ES-PCE molecular structure is low, the complex effect of Ca²⁺ is weak, and the retarding effect is not obvious. When the effective water content in the system increases, the hydration of cement is promoted, which has the effect of early strength. In cement mortar with water cement ratio of 0.4, the mixing amount of ES-PCE is suitable to be controlled below 0.3%, which not only ensures the water reduction rate, but also enhances the early and late strength of cement.