Mechanism elucidation and constitutive laws of expansive concrete for durable and high performance concrete structures

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Crack resistant mechanism of chemical prestressed reinforced concrete (CPRC) with expansive agent was studied in microscopic point of view as followings,(1) In cyclic loading of uni-axial test for CPRC unloading stiffness is gradually decreased and residual strain is remarkably increased up to cracking. Further, CPRC has higher deformability and tension stiffening effect after peak range is higher than normal RC.(2) A series of flexural test of CPRC with various specimen sizes were conducted. The deformability and cracking load of CPRC is higher in smaller cross section in which curvature becomes large. Not only ultimate load but also shear stiffness are enhanced by providing lateral reinforcement The effect of lateral shear reinforcement is more significant in larger cross section since plain concrete zone becomes larger in that situation.(3) Flexural test for CPRC was conducted where reinforcement ratio was varied under constant content of expansive agent It is shown that crack resistance is enhanced in accordance with not only chemical prestress but also chemical prestrain. Then, crack resistance of CPRC under long-term drying was also tested It was found that crack resistance of CPRC subjected to 1 month drying is decreased like normal RC, however it is recovered in 3 months drying.(4) A series of pull-out test of deformed bar embedded in massive concrete was conducted to check bond characteristic. Bond between expansive concrete and deformed bar is almost same as normal RC irrelevant of degree of lateral confinement Further, it was found in case where bar diameter is larger than maximum size of coarse aggregate, that very strange strain distribution appears in deeper zone of re-bar at very small stress level.Due to the above mentioned complicated governing mechanism of CPRC behaviors, formulations for crack width and constitutive laws for CPRC could not be yet established