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 The effet of natural pozzolan on accelerated delayed ettringite formation : Michanical microstructural investigations
Tác giả hoặc Nhóm tác giả: Nguyen V-H., Leklou N., Mounanga P., Bonnet S
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Nơi đăng: Proceedings International Conference on Advances in Cement and Concrete Technology in Africa, South Africa.
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; Số: 1;Từ->đến trang: 673-680;Năm: 2013
Lĩnh vực: Kỹ thuật; Loại: Bài báo khoa học; Thể loại: Quốc tế
TÓM TẮT
Delayed ettringite formation (DEF) is a type of internal sulfate attack caused by heat-induced decomposition of ettringite formed during the initial hydration of cement at elevated temperature (above about 70°C) and its re-crystallization in the hardened matrix. Previous studies showed that supplementary cementitious materials (scm) such as metakaolin, fly ash, slag and silica fume were efficient in controlling the expansive behavior of heat-cured mortars. However, research works on the influence of scm on DEF in mortars remain rare. In this study, the effect of natural Algerian pozzolan on the expansion of cement mortars caused by internal sulfate attack was investigated. For this purpose, natural pozzolan was incorporated in mortars in partial replacement of cement, with three different dosages (10, 20 and 30%) and finenesses (fine, medium, coarse). The mortars were then heat-cured at early-age and tests of length changes, mass variation, porosity, compressive strength and dynamic elastic modulus were carried on these mortars over a period of 300 days. The results obtained were analyzed and highlighted the effects of natural pozzolan on DEF and the correlation existing between the expansion of the heat-cured mortars and the evolution of their mechanical properties.

Keywords: delayed ettringite formation, expansion, mortars, pozzolan, heat curing
ABSTRACT
Delayed ettringite formation (DEF) is a type of internal sulfate attack caused by heat-induced decomposition of ettringite formed during the initial hydration of cement at elevated temperature (above about 70°C) and its re-crystallization in the hardened matrix. Previous studies showed that supplementary cementitious materials (scm) such as metakaolin, fly ash, slag and silica fume were efficient in controlling the expansive behavior of heat-cured mortars. However, research works on the influence of scm on DEF in mortars remain rare. In this study, the effect of natural Algerian pozzolan on the expansion of cement mortars caused by internal sulfate attack was investigated. For this purpose, natural pozzolan was incorporated in mortars in partial replacement of cement, with three different dosages (10, 20 and 30%) and finenesses (fine, medium, coarse). The mortars were then heat-cured at early-age and tests of length changes, mass variation, porosity, compressive strength and dynamic elastic modulus were carried on these mortars over a period of 300 days. The results obtained were analyzed and highlighted the effects of natural pozzolan on DEF and the correlation existing between the expansion of the heat-cured mortars and the evolution of their mechanical properties.

Keywords: delayed ettringite formation, expansion, mortars, pozzolan, heat curing
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