Development of repair materials based on calcium sulfo-aluminate cement

摘要

Sulfoaluminate cements contain the phases belite (C_2S), yeelimite, or tetracalcium trialuminate sulfate (C_4A_3S), and gypsum (CSH_2) as their main constituents. When CSA cement hydrates, ettringite (C_6AS_3H_(32)) is formed and generates high early strength in cementitious systems. This property has been exploited to develop four materials for repair of infrastructures: concrete with high early strength (40 MPa after 6 hours of age) and workability maintained for 60 minutes, self-levelling topping mortar, glass-fibre reinforced composites (GRC), and rapid hardening mortar at low temperature (5°C). The topping mortar was designed to fulfil the following requirements: 1. self-levelling, 2. time of workability: 30 minutes, 3. final setting within 75 minutes, 4. no curling and limited shrinkage, 5. thickness: 2 to 30 mm, 6. 24-hr strength: > 35 MPa (measured on 40 X 40 X 160 mm prisms). Calcium sulfo-aluminate cement (CSA) does not yield any calcium hydroxide and its alkalinity is lower than that of normal Portland cement (NPC). The behavior of GRC composites prepared with CSA was compared to that of composites prepared with NPC. The results obtained showed a superior behaviour of GRC composites based on CSA: the ductile behaviour obtained when curing the composites in air at 20°C was maintained either after immersion in hot water (60°C) or after 25 wetting-drying cycles.