负压成型水泥基材料孔结构特征

Characterization of pore structure of cement-based materials produced in negative pressure

摘要:

为了研究低气压环境对水泥基材料引气性能的影响,采用负压模拟试验的方法,在不同的气压下测试引气剂溶液的发泡性能和气泡稳定性、引气水泥净浆的孔结构以及引气水泥砂浆的气孔结构。水泥净浆与水泥砂浆的试验样品均在设计气压下搅拌成型直至终凝硬化。试验结果表明:FC-1和FC-2两种新型引气剂溶液的泡沫相较三萜皂苷类引气剂（SJ-2）溶液的泡沫具有更强的低气压环境适应性,但该溶液试验的规律不完全适用于水泥基材料；低气压成型会增加硬化水泥净浆的孔隙率及半径为100~1 000 nm孔的体积,但在采用优质引气剂的前提下低气压基本不会对水泥砂浆的含气量和气孔结构产生劣化作用。SJ-2、FC-1和FC-2 三种引气剂均能满足高原低气压环境下抗冻混凝土的引气要求,其中FC-1与FC-2在气孔结构优化与含气量控制方面更具优势。

Abstract:

In order to investigate the effect of low air pressure on the air entrainment of cement-based materials, simulation study of negative pressure was conducted. The foaming performance and bubble stability of air-entraining agent (AEA) solution, pore structure of air-entrained cement paste, and air-void structure of air-entrained cement mortar were tested in different air pressures. The cement paste and cement mortar specimens were stirred and formed in designed air pressures until hardening. Results show that the foams formed by two new types of AEAs (FC-1 and FC-2) were more stable than those formed by triterpenoid saponin type AEA (SJ-2) in corresponding aqueous solutions in negative pressure. However, this finding could not be extended broader to cover cement-based materials. The total porosity and the volume of pores with radii of 100-1 000 nm in hardened cement paste were found higher in negative pressure, while there was little adverse effect of low air pressure on either air content or air-void structure of hardened cement mortar when a suitable AEA was applied. SJ-2, FC-1, and FC-2 AEAs could satisfy the requirements of air entrainment for frost resistant concrete in high-altitude regions with low air pressure, among which FC-1 and FC-2 presented comparative advantages in air-void structure optimization and air content control.