An Accelerated Test Method to Evaluate Cementitious Mixtures Subjected to Chemical Sulfate Attack

Abstract

Abstract External sulfate attack continues to be a major threat to the long-term durability of concrete structures. Soil or water containing sufficient levels of sulfates can penetrate and chemically react with the hydrated cement compounds, leading to volumetric expansion, and in severe cases, softening of the hardened cementitious paste. While ASTM C1012, Standard Test Method for Length Change of Hydraulic-Cement Mortars Exposed to a Sulfate Solution, is the most widely accepted performance test method used to access the sulfate resistance of cementitious binders, the test requires at least six months and often up to twelve months to perform. This article presents a new accelerated method that places mortar bar specimens under high-vacuum while immersed in sulfate solution to accelerate the penetration and diffusion of sulfates in the specimens and therefore, the degradation and measured linear expansion of the specimens. Expansion, mass change, and visual degradation were assessed over time on mortar specimens immersed in a 5 % and 0.89 % sodium sulfate solution (Na2SO4) and subjected to the vacuum saturation procedure. Expansion results are compared with companion mortar bars that followed the ASTM C1012 method without vacuum saturation. When compared with the current ASTM method, the new test method showed a significant acceleration in the rate of expansion with severe visual deterioration observed two to three times quicker. Visual degradation and measured expansion occurred more rapidly for specimens subjected to the accelerated method and immersed in 5 % Na2SO4; however, mixtures subjected to the accelerated method and immersed in 0.89 % Na2SO4 still showed much faster expansion than companion specimens tested according to ASTM C1012 in 5 % Na2SO4.