溶液法合成纳米钙矾石的水泥晶种效应研究

Study on Cement Seed Effect of Nano-ettringite Synthesized by Solution Method

为研究钙矾石晶体在水泥水化过程中的晶种效应,以十八水合硫酸铝与四水合硝酸钙为原料,氢氧化钠调节pH,通过溶液法得到钙矾石纳米晶体,利用Zeta电位计、XRD、SEM等技术探究纳米钙矾石的微观结构;将其以不同掺量引入至水泥浆体中,考察钙矾石掺量和水灰比对水泥凝结时间以及早龄期力学强度的影响规律。结果表明:利用溶液法制备出纳米尺度、晶型完整、纯度高的钙矾石产物,在聚羧酸减水剂辅助下可均匀稳定地分散于水中,适合作为晶种用于提升水泥净浆的早期强度,在最佳掺量0.3%条件下,水泥的1、3 d胶砂抗压强度分别提高了15%、8%;纳米钙矾石的晶种效应导致普硅水泥的初凝时间延长而终凝提前,即水泥的初-终凝时间差缩短。

In order to study the seeding effect of ettringite crystals in the hydration of Portland cement,ettringite crystals in nanoscaled diameter were synthesized by a method of solution reaction,of which aluminum sulfate and calcium nitrate were employed as the reactants,and sodium hydroxide was used to adjust the pH value.After the microstruactural characterization by means of Zeta potential,X-ray diffraction(XRD),and scanning electron microscope(SEM),the nanoscaled ettringite seed in designed content were introduced into Portland cement mortar with different water/cement ratio to explore the influence of such ettringite crystal seed to the setting time and mechanical strength of Portland cement.The experimental results showed that the ettringite crystal seed synthesized by the method of solution reaction synthesis method was featured out with nanoscaled diameter,high degree of crystallinity,and high purity,which could make it be evenly dispersed in water with the aids of polycarboxylate water reducer,and thus significantly improve the early strength of cement mortar.By making use of the ettringite crystal seed at an optimized content of 0.3%,the compressive strengths of cement mortar at the age of 1 d and 3 d were improved by 15%and 8%,respectively.In the meanwhile,it was found that the initial setting time was elongated due to the involvement of ettringite crystal seed,while the final setting time was shortened to a certain extent simultaneously,and thus the initial-final setting time difference of cement was shortened.