Effect of Limestone Powder on Acid Attack Characteristics of Cement Pastes
Keywords:cement paste, acid attack, limestone powder, strength, microstructure
AbstractThe acid resistance of cement pastes containing limestone powder with two different water-binder (w/b) ratios exposed to acetic (pH = 4) and sulfuric acid (pH = 2) solutions respectively were investigated in this paper. Limestone powder, fly ash and silica fume were also added to the cement paste mixture at different proportions. Static and flowing aqueous environments were set in this experiment. Strength and microstructure of the pastes after acid attack were investigated by using strength test, X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The experimental results show that the erosion degree depends not only on pH value of the solution and w/b ratio of the pastes, but also on the content of limestone powder. Acetic acid reacts with calcium hydroxide and carbonate thus dissolving the pastes, while sulfuric acid consumed calcium hydroxide, and generated gypsum and ettringite. The consumption of calcium hydroxide in the flowing solution group is higher than that in the static solution because the flowing sulfuric acid solution has negative effect upon the gypsum crystallization. Fly ash and silica fume are beneficial to limestone cement paste because of the less calcium hydroxide formation, which is among the hydrates vulnerable to acid erosion.
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