Comparison of the microstructure and compressive strength of type 1 Portland cement paste between accelerated curing methods by microwave energy and autoclaving, and a saturated-lime deionized water curing method

The microstructure and compressive strength of a 0.38 water-to-cement mass ratio (w/c) cement paste when subjected to accelerated-curing by microwave energy and autoclave curing were compared with a normal curing method by soaking in saturated-lime deionized water at 25°C. The morphology, atom ratio of Si/Ca versus Al/Ca, phase composition by XRD, and compressive strength were measured in this study. The results indicate the presence of needle-like ettringite (Aft) in pastes that had been cured using the autoclave method. However, the saturated-lime deionized water cured paste showed lath-like or plate-like shapes and did not appear to produce ettringite (Aft). In addition, the microwave-cured paste indicated some evidence of ettringite. The range of Si/Ca and Al/Ca ratios of the autoclave-cured paste were 0.039- 0.052, and 0.207 - 0.234, respectively, while in the microwave-cured paste the ratio shifted to 0.079- 0.091. The compressive strength of the autoclavecured cement paste showed an increase in strength at an early age, while the strength decreased after 7 days of hydration.