干湿循环下改性混凝土硫酸盐腐蚀的断裂性能试验研究

分别掺入粉煤灰、矿渣粉、硅灰和聚酯纤维对普通混凝土进行改性,通过切口梁三点弯曲断裂试验研究干湿循环方式下受5%Na2SO4溶液腐蚀混凝土的抗裂阻裂性能。计算分析了腐蚀后改性混凝土的荷载-裂缝口张开位移P-CMOD曲线特性、断裂韧度与断裂能,给出抗腐蚀增韧系数的定义,并研究了硫酸盐腐蚀环境下改性混凝土相对于普通混凝土的增韧效果,探讨了不同腐蚀时期改性混凝土的劣化机理。结果表明:腐蚀后改性混凝土的P-CMOD曲线经历了损伤初弯段、比例弹性段、稳定扩展段和软化段4个阶段;随干湿循环次数的增加,改性混凝土的抗腐蚀增韧系数总体呈先增大后减小趋势;掺加25%粉煤灰可显著增强腐蚀早期混凝土的断裂韧度,掺入聚酯纤维、矿渣有利于混凝土腐蚀后期失稳韧度的提升和断裂能的增加,而掺入硅灰对腐蚀混凝土的增韧效果不明显。

Experiment study on fracture properties of modified concrete attacked by sulfate corrosion under dry-wet circulation

The ordinary concrete was modified by adding fly ash,slag powder,silica fume and polyester fiber, respectively. Corroded by 5% Na₂SO₄ solution coupling with dry-wet circulation, the concrete beams with notch were performed by means of the three-point bending fracture test to study the cracking resistance behavior of sulfate corrosion concrete. The variation tendencies of P-CMOD (load-crack mouth opening displacement) curves, fracture toughness and fracture energy of modified concrete were analyzed. The anti-corrosion toughening coefficient was defined to research the toughening effects of modified concrete contrast to the ordinary concrete under the condition of sulfate attack. The deterioration mechanism of modified concrete was probed at different corrosion periods. The results indicate that the P-CMOD curves of modified concrete undergo four stages including damage initial flexure section, elastic proportional section, stable extension stage and softening phase after sulfate corrosion. The anti-corrosion toughening coefficients of modified concrete increase firstly and decrease later varied with the dry-wet circulations. The addition of 25% fly ash improves the fracture toughness of concrete in the early corrosion stage significantly, while polyester fiber and slag have the better effects on enhancing the unstable toughness in the late corrosion period as well as increasing fracture energy. Incorporation of silica fume takes little effects on improving the comprehensive fracture properties.