硫酸复盐改善混凝土早期抗拉强度的机理分析

Mechanism Analysis of a Sulfate Complex Salt Improving Early Tensile Strength of Concrete

摘要:

采用混凝土轴向拉伸试验，研究了实验室自制硫酸复盐（SN）对混凝土早期抗拉强度的影响.借助X射线衍射仪（XRD）、热重-微商热重（TG-DTG）分析和扫描电镜（SEM），对硬化浆体的物相组成和微观形貌进行表征，并结合胶凝体系的水化放热情况，对SN的作用机理进行了探索.结果表明：掺加SN能够显著提高混凝土的早期抗拉强度，当SN掺量为2.0%时，混凝土1、3、5 d龄期时的抗拉强度分别提高18.7%、23.6%和16.2%，且对混疑土后期抗拉强度几乎无不利影响； SN可以加快胶凝体系早期水化反应进程，促进钙矾石（AFt）、氢氧化钙（CH）和水化硅酸钙（C-S-H）等水化产物生成，且体系中的C-S-H填充于针状AFt形成的交叉搭接结构内部空间，有利于拉应力在硬化浆体内均匀分布，从而有效提高混凝土的早期抗拉强度.

Abstract:

The effect of a sulfate complex salt （SN） was studied by axial tensile test of concrete in the present investigation. The phase composition and morphological structure of hardened paste were characterized by X-ray diffraction （XRD）， thermogravimetric-derivative thermogravimetric （TG-DTG） analysis and scanning electron microscope （SEM）. Combined with the hydration heat release of cementitious system， the working mechanism of SN was discussed. The results show that the early tensile strength of concrete can be significantly improved by using SN. Specifically， compared to the control， the tensile strength at the age of 1， 3 ， 5 d is increased by 18.7%， 23.6% and 16.2%， respectively， while 2.0% SN is dosed into concrete， no obvious adverse effect occurs on the tensile strength at later ages. The incorporation of SN can speed up the early hydration process of cementitious system and promote the formation of hydration products such as ettringite （AFt）， calcium hydroxide （CH） and calcium silicate hydrate （C-S-H） in the cementitious system. Further， the C-S-H is filled in the micro lap-structure formed by needle-shaped AFt， which is beneficial to the uniform distribution of tensile strength and effectively improve the early tensile strength of concrete.