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

从微观角度研究了含膨胀剂的化学预应力钢筋混凝土（CPRC）的抗裂机理：(1)CPRC单轴循环加载试验中，卸荷刚度逐渐降低，直至开裂时残余应变显著增加；CPRC在峰值范围高于普通RC后，具有更高的变形能力和拉加筋效果。(2)对CPRC进行了一系列不同试件尺寸的抗弯试验。截面越小，曲率越大，CPRC的变形能力和开裂荷载越高。横向配筋不仅可以提高极限荷载，还可以提高抗剪刚度，而且在大截面下，横向配筋的作用更为显著，因为在这种情况下，素混凝土区域变大。(3)在膨胀剂含量不变的情况下，对不同配筋率的CPRC进行了抗弯试验，结果表明，化学预应力和化学预应变均能提高CPRC的抗裂能力。然后，对CPRC在长期干燥条件下的抗裂性能进行了测试，发现CPRC在干燥1个月后的抗裂性能与普通RC相比有所下降，但在干燥3个月后又有所恢复。(4)对大体积混凝土内嵌变形钢筋进行了一系列拉拔试验，校核了其粘结特性。与侧约束程度无关，膨胀混凝土与变形钢筋之间的粘结性与普通钢筋基本相同。此外，当钢筋直径大于粗集料的最大粒径时，在很小的应力水平下，钢筋的深层区域出现了非常奇怪的应变分布。由于上述CPRC行为的复杂调控机制，目前还无法建立裂缝宽度和CPRC本构规律的公式

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