碳化对污水环境下混凝土性能的影响

Effect of Carbonation on Concrete Performance in Sewage Environment

对比研究了未碳化及加速碳化60 d的混凝土试件在强化污水环境下的外观、质量、强度、表面pH值以及微观形貌、矿物组成等变化规律。结果表明：虽然碳化试件的抗压强度显著高于未碳化试件,但其在污水中劣化更为迅速,约为未碳化试件的2倍,腐蚀90 d后强度降低44%,质量损失高达10%,表面pH值也下降至4.21,不过其表面生物膜附着量明显多于未碳化试件。从污水不断降低的pH值和微观试验结果均可判断污水对混凝土的腐蚀主要为微生物代谢产生的酸性物质所致,腐蚀后的水泥石结构变得疏松多孔,Ca（OH）2晶体含量明显减少,特别是碳化后试件在腐蚀1个月后其含量仅为0.20%,当腐蚀3个月后,2组试样中均已看不到明显的水化产物衍射峰。综合分析可知,虽然碳化生成的CaCO3可使混凝土变得更加密实,但碳化收缩产生的微裂纹、碳化导致的弱碱性表面均加速了污水对混凝土的生物酸腐蚀。

The appearance, mass, strength, surface p H value, morphology and mineral compositions of non-carbonated and 60-day carbonated concretes in intensified sewage were investigated. The results show that although the compressive strength of carbonated concrete is significantly greater than that of non-carbonated concrete, it has a faster deterioration rate, which is approximately two times greater than that of non-carbonated concrete. After 90-day sewage corrosion, the strength of carbonated concrete is reduced by 44%, and the mass loss is 10%, as well as the surface p H value decreases to 4.21, however, the mass of biofilm attached is obviously more than that of non-carbonated concrete. The results of the decreased p H value of sewage and the microscopic test show that the corrosion of sewage on concrete is mainly caused by some acidic substances produced by microbial metabolism. The structure of cement paste becomes loose and porous, and the content of Ca（OH）2 decreases greatly, especially for the carbonated specimen, of which is only 0.20% after 1-month corrosion. Furthermore, after 3-month corrosion, no apparent diffraction peaks of hydration products appear in both specimens. The comprehensive analysis indicates that despite Ca CO3 can make the concrete denser, either the microcracks produced by carbonation shrinkage or the weak alkali surface caused by carbonation could accelerate the biologic acid corrosion of concrete.