预水化对水泥性能及水泥-聚羧酸系减水剂相互作用的影响（英文）

Effect of Prehydration on Properties of Cement and Interaction Between Prehydrated Cement and Polycarboxylate Superplasticizer

将新鲜的硅酸盐水泥暴露于（20±2）℃,相对湿度为85%~90%的环境中,研究了硅酸盐水泥因暴露于湿空气中产生预水化而对水泥标准稠度用水量、水泥水化行为、水泥胶砂强度以及水泥与聚羧酸系减水剂（PCE）间相互作用的影响。结果表明：随着暴露时间的增长,水泥预水化速率不断降低,标准稠度用水量则先轻微减小后显著增加,预水化4 d的水泥具有最小的标准稠度用水量;预水化作用总体上降低了水泥水化温峰值及水泥水化放热速率,但对于预水化作用不超过10 d的水泥。在其水化200~500 min期间,预水化水泥的水化放热速率随预水化时间的延长而增大,对于预水化10 d的水泥,其水化放热速率甚至一度高于新鲜水泥,这可能会导致预水化水泥的异常凝结。此外,预水化作用不利于胶砂强度的发展,且对抗折强度的不利影响尤为显著。预水化作用还会影响PCE的分散效果,随着预水化时间的延长,PCE的分散性及其分散保持性先增大后减小,对预水化4 d的水泥分散效果最佳,其初始流动度达到新鲜水泥的136%,且120 min后的浆体流动度仍高达235 mm。PCE对预水化20 d和30 d的水泥无分散效果。

Fresh Portland cement was exposed to the specific conditions of （20±2） ℃ and 85%-90% relative humidity. Effect of prehydration on the water requirement of normal consistency of cement, the cement hydration behavior and the development of mortar strength at different exposure time was investigated. The interaction between prehydrated cement and polycarboxylate superplasticizer （PCE） was also assessed. The results show that the prehydration rate decreases with increasing the exposure time. However, the water requirement of normal consistency decreases firstly and then increases rapidly as the growth of exposure time due to prehydration. Meanwhile, prehydrated cement for 4 d exposure has the smallest water requirement of normal consistency. The prehydrated cements exhibit a lower value of highest hydration temperature and a lower exothermic rate than fresh cement. The exothermic rate of cement increases with increasing the exposure time when the exposure time is less than 10 d. The cement for 10 d exposure even has a greater exothermic rate rather than fresh cement sample. This phenomenon can lead to an abnormal setting behavior of prehydrated cement. In addition, prehydration can affect the strength development especially the flexural strength development of mortar. Prehydration also influences the effectiveness of PCE, the dispersion ability and dispersion retention ability of PCE increases firstly and then decreases as the increasing of exposure time. PCE in the paste of prehydrated cement exposed for 4 d exhibit the best dispersion and dispersion retention ability. Its initial fluidity is 136% of that for fresh cement paste, and its fluidity still remains at 235 mm after 120 min. However, PCE lost its dispersion ability to cement exposed for 20 d and 30 d.