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

从微观角度研究了掺膨胀剂的化学预应力混凝土的抗裂机理：（1）在单轴试验的循环加载过程中，化学预应力混凝土的卸载刚度逐渐减小，残余应变显著增加，直至开裂;此外，CPRC具有更高的变形能力和拉伸硬化效应后的峰值幅度高于普通钢筋混凝土。(2)对不同尺寸的CPRC试件进行了弯曲试验。截面越小，曲率越大，混凝土的变形能力和开裂荷载越大。横向配筋不仅提高了混凝土的极限承载力，而且还提高了混凝土的抗剪刚度。在截面较大的情况下，横向抗剪配筋的作用更为显著，因为此时素混凝土区域变大。(3)在膨胀剂掺量不变的情况下，对CPRC进行了不同配筋率的抗弯试验。试验结果表明，CPRC的抗裂性能不仅与化学预应力有关，而且与化学预应变有关。试验结果表明，CPRC在干燥1个月后，其抗裂性与普通混凝土一样下降，但在干燥3个月后，其抗裂性又恢复到正常混凝土的水平。(4)为了检验大体积混凝土中异形钢筋的粘结性能，进行了一系列的拉拔试验。膨胀混凝土与变形钢筋的粘结性能与普通钢筋基本相同，与侧向约束程度无关。此外，当钢筋直径大于粗骨料的最大尺寸时，在很小的应力水平下，钢筋的深层区域会出现非常奇怪的应变分布。CPRC的裂缝宽度公式和本构关系尚不能建立

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