Degradation Kinetics of Portland Cement Pastes, Mortars and Concretes in Acidic Environments

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Title: Degradation Kinetics of Portland Cement Pastes, Mortars and Concretes in Acidic Environments

Author(s): Yves Lefebvre, Carmel Jolicoer, Monique Page and Phil T. Seabrook

Publication: Special Publication

Volume: 170

Issue:

Appears on pages(s): 1487-1510

Keywords: Acids; cement pastes; chlorides; concretes; diffusion; durability; leaching; mortars (material); porosity; sulfates.

Date: 7/1/1997

Abstract:
The degradation of samples of cement pastes, mortars and concretes in acidic solutions (pH 2-4) ha s b een investigated over relatively short periods, e.g. -72 hours at 25°C. The degradation rate of the cementitious material is taken as the rate of alkali leaching at constant pH; the latter is obtained directly from the amount of acid required, as function of time, to maintain the pH at a preset value. The data allow the calculation of apparent rate constants, the magnitude of which is expected to be related to the durability of the materials investigated in acidic environments. Paste degradation rates were obtained at two W/C (0.35 and 0.45); the role of several additives (silica fume, superplasticizers, air entraining agents) and the influence of solution composition (pH, ionic strength, other electrolytes) were investigated. Kinetic data were also obtained for the acid reaction rate of several mortar and concrete samples of varying mixture compositions and in the presence of S0,-2. Under the conditions of this study, the acid degradation rate appears largely controlled by H+ diffusion through the leached zone of the matrix. The diffusional rates values are moderately influenced by changes in mixture compositions, in reasonable agreement with expectations from greatly enhance the acid degradation rate, an effect zone and the related studies. Sulfate ions which can be understood from pH gradients in the leached activity coefficients of the H+ in the presence of sulfates.