自然浸泡对水泥基材料渗透性能的影响及作用机理

Influence and mechanism of surface permeability of cement based materials under immersion

将混凝土和砂浆样品浸泡在超纯水中,定期检测表层渗透性能、孔结构及微观形貌,研究浸泡环境对水泥基材料渗透性能的影响及作用机理。研究结果表明：随着浸泡龄期的延长,表层渗水系数逐步减少,浸泡150 d后的表层渗水系数仅为浸泡30 d的50%;随着龄期的延长,水泥基材料的孔结构得到优化,相比浸泡30 d的孔结构,浸泡150 d后,孔径小于100 nm的孔体积是浸泡30 d的1.17倍,而孔径为100~200 nm孔体积是浸泡90 d的64%,微观孔结构进一步细化;与标准养护28 d的砂浆基准样相比,超纯水浸泡180 d后,XRD曲线中Ca（OH）_2的峰值强度明显减弱,水化浆体中Ca（OH）_2的质量分数减少;浸泡90 d后水化浆体晶体结构松散,表面凹凸明显,有一些细小的孔洞。

Concrete and mortar specimens were immersed in ultrapure water to study the influence of immersion on the surface permeability of cement based materials by monitoring the evolution of surface permeability, pore structure and paste microstructure following the prolonging of immersion period. The results show that 30 d after reaching the maximum value, the surface permeability of concrete decreases following the further increase of immersion duration. The surface permeability coefficient after a 150-d immersion is only half of that measured after a 30-d immersion. The long-term immersion facilitates the refinement of the pore structure of cement based materials. Compared with the situation of the immersion age of 30 d, the volume of pores with the aperture less than 100 nm is 1.17 times as much as the volume at the immersion age of 150 d, while the volume of pores with the aperture from 100 to 200 nm decreases to 64% of that measured after a 90-d immersion. Compared with the reference mortar with standard curing at 28 d, calcium hydroxide intensity on the XRD pattern of the mortar immersed in ultrapure water for 180 d becomes much weaker, and the mass fraction of calcium hydroxide decreases. In addition, as shown by microscope images, the surface of crystals in immersed mortar becomes loose, rough and shows small defects after a 90-d immersion.