硫酸盐侵蚀下硬化水泥浆体微结构演变及膨胀过程的数值模拟

根据硫酸盐侵蚀机理,利用改进的CEMHYD3D水化模型和随机概率方法,建立了硫酸盐侵蚀下硬化水泥浆体的微结构演变模型。在微观层次上,模拟了浆体孔溶液中硫酸根离子的自由扩散、随机碰撞和转化反应,分析了膨胀性侵蚀产物生长导致的微结构损伤和体积膨胀,计算了侵蚀过程中石膏和钙矾石的生成量及浆体的膨胀应变,并与已有试验结果对比分析验证了模型的合理性。在此基础上,数值模拟了硫酸盐侵蚀下不同水灰比水泥浆体的微结构演变及膨胀过程。结果表明:同一硫酸盐浓度下,硬化水泥浆体中氢氧化钙和含铝物相与孔隙的接触面积越小,浆体的膨胀应变越低;水灰比为0.25、0.30和0.35的硬化水泥浆体的孔隙填充程度分别达到9.09%、9.27%和9.41%时,浆体膨胀应变开始快速增大;硫酸盐侵蚀溶液浓度增大,浆体体积快速膨胀的时间提前。

Numerical Simulation on Microstructure Evolution and Expansion Process of Hardened Cement Paste under Sulfate Attack

Based on the mechanism of sulfate attack, a microstructure evolution model of hardened cement paste under sulfate attack was established by using the improved CEMHYD3D hydration model and random probability method. At the microscopic level, the free diffusion, random collision and transformation reaction of sulfate ions in the pore solution of hardened cement paste were simulated, and the microstructure damage and volume expansion induced by the growth of expansive erosion products were analyzed. Meanwhile, the content of gypsum and ettringite and the expansion strain of paste in the process of sulfate attack were calculated, and the model was verified by comparing with the experimental results in present literature. On the basis of the model, the microstructure evolution and expansion process of hardened cement pastes with different water-cement ratios under sulfate attack were numerically simulated. The results show that under the same sulfate concentration, the smaller the decrease in the contact area of calcium hydroxide and phase containing aluminum with pores is,the lower the expansion strain of hardened cement paste is. For hardened cement pastes with water-cement ratios of 0.25, 0.30 and 0.35, their expansion strain begins to increase rapidly when the pore filling degree reaches 9.09%, 9.27% and 9.41%, respectively. As the sulfate concentration increases, the time for rapid expansion of hardened cement paste is advanced.