Accelerated Curing Of Cement Based Materials

Portland cements are slow hardening materials and several techniques are used to expedite the attainment of a satisfactory strength, i.e., chemicals, reduction of particle size, heat. Increasing the temperature is by far the most effective. Dielectric heating is a well established technique in materials technology but the cement industry has so far expressed little interest in this technology, probably because the effects on the final properties of mortars and concrete are not well established yet and for the greater complexity of the process compared, for instance, to steam curing. Fear of radiation leakage from high power applicators not correctly designed and operated has placed a further constraint to the acceptance of this technique. Although early results of microwave heating were unsatisfactory, likely because of overheating effects, the availability of temperature controlled microwave applicators now makes it possible to choose temperature profiles that favourably influences the final properties of the materials. Here we report on the effects of microwave treatments on three types of modified portland cements: one contained microsilica and the others granulated slag or flyash from coal burning. In all cases an acrylic superfluidifier was used to keep water content low. The microwave treatment was given at 80°C for 0 to 16 h. The mechanical properties of the microwave treated samples were compared to those of samples treated in water at 80°C for 24 h. Mercury intrusion porosimetry, thermal analysis and SEM examination were also carried out to investigate the microstructural modifications brought about by the microwave treatment.