低温养护下溴化锂对水泥早期水化的影响

Effect of lithium bromide on early hydration process of cement at low temperature

传统早强组分已不能满足绿色、高性能混凝土的要求,加之早强剂在低温(尤其是5℃)下的研究较少,且低温早强性能有限、低温作用机理尚不明确。本文以溴化锂(LiBr)作早强组分,研究5℃下LiBr对砂浆强度、净浆凝结时间以及水泥早期水化特性的影响。结果表明:5℃低温下,LiBr的掺入使净浆初凝、终凝时间略有缩短,可显著加快砂浆试件早期强度的发展,且28 d强度仍有较大幅度提高;掺0.5%LiBr砂浆1 d、3 d、7 d和28 d抗压强度分别提高383%、54%、41%和11%,各龄期强度已接近对比样20℃养护下的强度。LiBr的存在可促进低温下C3S的溶解,使其溶解量有明显增大趋势;增大Ca(OH)2溶解量、使溶液pH值增大,有利于水化产物的沉淀生成。LiBr使低温下水泥水化的诱导期缩短、加速期提前,最大放热速率增大、放热量增大;使水泥水化更早进入了受扩散控制的D阶段;水化12 h时产物中即有大量Ca(OH)2生成,且生成了水化硅酸钙和水化溴氧铝酸钙产物。

The traditional early strength components can not meet the requirements of green and high performance concrete,and the researches of early strength accelerators at low temperature(especially 5℃)were relatively few,and their effects were limited,and the mechanism was also not understood well.In this study,as an early strength component,the effect of LiBr on the compressive strengths and setting times at5°C were investigated,and its effect on the early hydration process of cement was also discussed.The results show that with the addition of LiBr at low temperature of 5℃,both the initial setting and final setting time of cement paste are slightly shortened,which can significantly accelerate the development of the early strength of the mortar speciment,and thestrength is still greatly improved at 28 d.Meanwhile,the compressive strengths of motars mixed with 0.5%LiBr can increased by 383%,54%,41%and 11%at1 d,3 d,7 d and 28 d respectively,each of them is close to the strengths of the contrast sample cured at20℃at the same age.The presence of LiBr can promote the dissolution of C3 S at low temperature,resulting in a significant increase in its dissolved amount.With the increased amount of Ca(OH)2 dissolved and the solution pH value,it is beneficial to the precipitation reaction of hydration products.At low temperature,LiBr can promote hydration reaction of cement at the early stage,and shorten the induction period of cement hydration,advance the acceleration period,and increase the maximum heat release rate and the heat release rate.The presence of LiBr can make the cement hydration entered into the D stage earlier which is controlled by the diffusion factor.A large amount of Ca(OH)2 is formed in the products after only12 hours of hydration,and some calcium silicate hydrate and hydrated calcium bromoaluminate products are also produced.