界面含水率对现浇混凝土黏结性能的影响及机理

Effect and mechanism of interfacial moisture content on bonding properties of cast-in-situ concrete

将自密实混凝土(SCC)与普通混凝土(OC)组合应用于连续梁桥0号块,可以解决底腹板混凝土振捣困难问题,还可以节约施工成本。为探究SCC与OC分层浇筑时2种混凝土界面的黏结力学性能及耐久服役性能,厘清SCC与OC组合应用于连续梁桥0号块的可行性。确定了力学性能与收缩性能相近的SCC的配合比,在此基础上,研究了界面含水率对SCC-OC分层浇筑试件的界面劈裂拉伸强度、直接剪切强度及氯离子渗透性的影响,模拟了冷热循环、干湿循环和冻融循环3种服役环境对界面黏结力学性能的影响。结合MIP及SEM多手段分析SCC-OC黏结界面处的孔隙结构特征及界面微观形貌,揭示了界面含水率对SCC-OC组合构件黏结力学及耐久性能的影响机理。结果表明:SCC与OC分层浇筑时需要确保界面含水率不能过低,界面含水率的降低会引起SCC-OC组合试件的孔隙率提高、微裂缝增大,导致黏结力学性能与抗氯离子渗透能力的降低。且界面含水率越低,SCC-OC组合试件在不同的环境下服役后产生的损伤越大。不同的服役环境对SCC-OC黏结界面的损伤程度不同,冻融循环对SCC-OC试样的黏结最不利,冷热循环引起的损伤最小。SCC中掺加减缩剂可以减少SCC内部水分的蒸发,对SCC-OC的黏结耐久性能具有一定的益处。

The use of self-compacting concrete(SCC)and ordinary concrete(OC)in the 0#block of a continuous girder bridge solves the problem of difficult concrete vibrating in the bottom web slab while also lowering construction costs.To investigate the bonding mechanical properties and durable service performance of the two concrete interfaces when SCC and OC are cast in layers,and to clarify the feasibility of applying the combination of SCC and OC in the 0#block of the continuous girder bridge.The fit mixing ratio of SCC with similar mechanical and shrinkage properties was determined firstly.Then the effects of interfacial moisture content on the split tensile strength,direct shear strength and chloride ion permeability of the SCC-OC layered specimens were investigated.Meanwhile,the effects of three service environments(hot and cold cycles,wet and dry cycles and freeze-thaw cycles)on the interfacial bonding properties were studied.The MIP and SEM discussions were performed to investigated the pore structure characteristics and interface micromorphology at the SCC-OC interface,while influence of interfacial water content on the bonding performance of the SCC-OC combination specimens were revealed.The results show that the interfacial water content should not be too low when SCC and OC are cast in layers.The decrease of interfacial water content will cause the increase of porosity and microcracks in SCC-OC composite specimens,which will lead to the decrease of bonding mechanical properties and resistance to chloride ion penetration.And the lower the interfacial water content,the more damage SCC-OC composite specimens maintain after service in various environments.Different service environments cause varying degrees of damage to the SCC-OC bonding interface,with freeze-thaw cycles being the most damaging to SCC-OC specimen bonding and cold and heat cycles causing the least.The addition of shrinkage reducers to SCC can reduce water evaporation inside SCC,which benefits the bonding durability of SCC-OC.