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浇筑了普通混凝土和双掺粉煤灰、矿粉两种矿物掺合料的混凝土小梁试件39个,采用螺杆对试件施加混凝土极限抗弯承载力30%和60%的持续荷载,在“氯盐溶液浸泡+CO_2环境干燥”、“去离子水浸泡+CO_2环境干燥”和“氯盐溶液浸泡+大气环境干燥”3种不同干湿循环制度下进行干湿循环试验,分析了荷载、碳化和氯盐作用下混凝土的劣化规律。结果表明:双掺粉煤灰和矿粉的混凝土,因发生“二次水化反应”消耗了大量Ca(OH)_2,其抗碳化性能比普通混凝土差;碳化后混凝土孔隙中多被CaCO_3填充,孔隙率降低,因此碳化速率随碳化龄期的增长减缓;干湿循环作用下,随着循环次数的增加,对流区深度会逐渐趋于稳定,在7~9 mm之间,而碳化作用使混凝土表层氯离子堆积明显;干燥过程中,氯盐存在使混凝土表面孔隙出现结晶,亦会抑制碳化反应的速率;碳化作用对混凝土中氯盐的传输起到双重作用:使混凝土孔隙率降低从而降低氯盐的传输速率,又会使部分结合氯离子释放为自由氯离子,从而提高自由氯离子含量;荷载水平由0.3倍极限荷载增加到0.6倍极限荷载,碳化和氯盐传输深度显著提高,随循环次数增加,荷载作用对碳化和氯盐传输影响愈加明显。
Thirty-nine concrete trabecular specimens of ordinary concrete and double-mixed fly ash and mineral powder were cast. Continuous load of 30% and 60% Wet and dry cycles were carried out under three different drying and wetting cycles: “salt solution immersion + CO_2 environment drying”, “deionized water immersion + CO_2 environment drying” and “” chloride salt solution soaking + atmospheric environment drying “ Test, analysis of the load, carbonation and chloride salt under the law of deterioration of concrete. The results show that the concrete with double fly ash and mineral powder consumes a large amount of Ca (OH) 2 because of ”secondary hydration reaction", its carbonation resistance is worse than ordinary concrete. With the increase of the number of cycles, the depth of convection zone will gradually become stable, ranging from 7 to 9 mm, while the carbonization rate increases with the increase of carbonization age. In the process of drying, the presence of chloride salt crystallizes the pores on the concrete surface and also inhibits the rate of carbonization reaction. Carbonization plays a dual role in the transmission of chloride in concrete: it reduces the porosity of the concrete Thereby reducing the transfer rate of the chloride salt, which in turn causes the release of some of the bound chloride ions as free chlorine ions, thereby increasing the free chlorine ion content. The loading level increases from 0.3 times the ultimate load to 0.6 times the ultimate load, and the carbonation and chloride salt transport depths significantly increase , With the increase of the number of cycles, the effect of load on the carbonation and chloride transport more pronounced.