测试混凝土孔溶液的pH值研究混凝土的碳化性能

设计了单掺30%粉煤灰、单掺30%矿渣微粉、复掺粉煤灰和矿渣微粉总量为30%以及不加矿物掺合料的普通混凝土试件,运用混凝土孔溶液的表观pH值测试法对上述混凝土的碳化性能进行研究,并与酚酞溶液测试结果进行对比.研究表明,pH值测试法是一种能反映混凝土抗碳化能力的可靠测试方法.混凝土抗碳化能力越高,混凝土表层的pH值越大,该值在混凝土内部恒定时的深度越小.结合两种测试方法可将碳化混凝土内部分为完全碳化区、部分碳化区和未碳化区,两种测试方法得出的完全碳化区深度基本相等,部分碳化区深度约为完全碳化区深度的2倍.在钢筋混凝土抗碳化性能设计中,要求部分碳化区深度不允许超过混凝土保护层厚度更为科学.

Experimental investigation of carbonation profiles in concrete using pH value test

Apparent pH test method of the pore solution was presented to investigate carbonation profiles of four kinds of concrete specimens. These concrete specimens were respectively prepared using fly ash of 30%, slag of 30%, both fly ash and slag of 30% in cement replacement ratio, along with 100% portland cement. The test results were also compared with those obtained by using the phenolphthalein test method. It indicates that pH test is a reliable method to reflect carbonation resistance of concrete. The near-surface pH values increased and the depth to relatively constant pH decreased if concrete has better carbonation resistance. According to these two test methods, fully carbonated zone, partially carbonated zone and non-carbonated zone were defined. The depth of fully carbonated zone is approximately equal determined by these two test methods, and the depth of partially carbonated zone is twice of that of fully carbonated zone. It is more scientific for carbonation resistance design of reinforced concrete structure if its cover thicknesses is greater than partially carbonated zone.