Sulphate attack of Mortar and concrete : Ettringite formation

Authors: Gunther Mosselmans, Bram Dooms, Valérie Pollet and Christian Pierre

International Congress on Durability of Concrete ; paper accepted ; Trondheim, Norway ; 18-21 June 2012

The Organization for Economic Co-Operation and the Development (OECD) has shown that sulphatic attack is the second cause of bridge failure after rebar’s corrosion. The aim of this Research is to better understand these sulphate degradation mechanisms.

In the first part of this work, the sulphate resistance (ettringite formation) of some Belgian cement’s are tested according to the CUR - Aanbeveling 48 (monitoring the longitudinal deformation of the mortar specimens immerged in highly concentrated sulphate solutions) at room temperature. Different cement types were considered: Portland cement as well as Portland-composite, blast furnace and composite cements. In parallel with the expansion tests, the Young modulus and the sound speed through the specimens were also monitored as a function of the immersion time. Different solutions (concentration and sulphate salts type) were considered. Results up to 4 years of these accelerated tests are presented.

In a second part of this study, we present the expansion measurements results on concrete at room temperature. A microscopic study was achieved on the specimens after the tests.

At lower temperatures, the formation of thaumasite is enhanced in presence of carbonates. Therefore, in the third part of the study, to stimulate the sulphate attack by thaumasite development, a part of the cement was substituted by limestone filler and the immersion tests were carried-out on mortars at low temperature (5-10-15°C). Destructive tests (tensile and compressive strength, sulphate concentration profiles in the specimens, microscopic study,…) as well as non-destructive tests (longitudinal deformation, sound speed through the specimen, Young modulus) were performed.