Carbonation and leaching of portland cement with various blending materials

Abstract

Degradation of Portland cement concrete, as well as the related protection and ensuring of Portland cement concrete structures against aggressive impacts by chemical agents, regardless whether this concerns liquid, gas or even solid phase under certain conditions, represents a complex problem of utmost importance for the economy in general, and especially for building construction and the construction industry. CaO leaching from Portland cement concrete in soft waters is one of the usual ways of Portland cement concrete degradation. Durability of steel in reinforced concrete is dependent mainly on the concrete protection layer. Usually, this layer has to be at least 4 cm. Also, pH value of this layer has to be higher than 7.5 to ensure alkaline media. But, CO 2 and moisture (acid rains recently) from the air makes this layer permeable to chlorine ions, such enabling steel corrosion. This effect is called concrete carbonation and is dependent of various factors, but mainly on the cement composition, w/c ratio and the concrete density. This paper presents results of CaO leaching content from Portland cements with various blending materials such as natural pozzolana and quartz river sand together with other characteristics of mentioned materials. Presented paper study also the changes produced by the carbonation when Portland cement, Portland fly ash cement and Portland blast furnace slag cement with various w/c ratios are exposed to the action of the atmosphere. The resistance to carbonation is significantly reduced when replacement of Portland cement by fly ash is higher than 15% and with higher w/c ratios.