VERIFICATION OF COMBINATION USE OF EXPANSIVE AGENT AND LIGHTWEIGHT AGGREGATE ON FATIGUE RESISTANCE OF RC SLAB AND THERMAL STRESS RESTRANT AND ITS UTILIZATION

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It was reported that simultaneous use between expansive agent and artificial lightweight aggregate in cement concrete could restrain thermal stress induced under elevated temperature, and it could also prolong fatigue life of RC slab. In this study measurements of thermal expansion coefficient of specimens and microscopic visual observation around lightweight aggregate were conducted to understand its complicated mechanism. By the experimental investigations two tendencies were suggested as important factors. One is time dependent change of thermal expansion coefficient of this concrete. It is higher than normal concrete at the early age but it becomes small in the longer time. The other is that thermal expansion coefficient of lightweight aggregate is almost half of normal aggregate. Precipitation of additional hydration product at the gap space created around lightweight aggregate due to expansive action was not observed though it was suggested as a possible cause of that mechanism.