Investigation Of The Bond Between PVA-ECC And Concrete After High Temperatures And The Shear Behaviors Of Brick Masonry Walls Strengthened With PVA-ECC

PVA-ECC(Polyvinyl alcohol Fiber-Engineered Cementitious Composites)is a new type of cementitious composites,experiments have showed that PVA-ECC performs well in toughness,anti-spalling,crack control,anti-permeability and so on,so it has wide application prospects in the maintenance and reinforcement for concrete and masonry structures.However,materials's deterioration is the basic reason for structure's repairment,in which one of the main causes is high temperature.Researchers from home and abroad have studied on the temperature stability of PVA-ECC and the bond behavior between PVA-ECC and concrete,while the latter mainly at room temperature,interfacial bond property between PVA-ECC and concrete after high temperature has not been studied on.In addition,investigations on brick masonry wall strengthed with PVA-ECC are few,there are no other reports except that several reaserchers applied PVA-ECC for the wall plastering.On the basis of the analysis above,Main reasearches of the thesis are as follows:1.The slant shear test and splitting tensile test of 66 specimens including PVA-ECC/existing concrete and new concrete/existing concrete have been implemented,in which high temperature first and bonding later,ie existing concrete as substrate was subjected to high temperature firstly,and then PVA-ECC or new concrete as overlay was bonded with existing one,finally mechanical property was measured correspondingly.The tests aim to investigate on the bonding conditions between PVA-ECC and existing concrete structure,which was subjected to high temperature first and then repaired with PVA-ECC,and have a comparison with traditional repairing method.Results show that when temperature increase to 200°C,the interfacial bond property of PVA-ECC and exiting concrete increase too;the bond property declines when temperature beyond 200°C,while its still perform better than new concrete ones;when it comes to 800°C,the existing concretes are burnt totally and cannot be repaired any more.2.Similarly,slant shear test and splitting tensile test of 66 specimens including PVA-ECC/existing concrete and new concrete/existing concrete have been implemented,in which bonding first and high temperature later,ie existing concrete as substrate was bonded with PVA-ECC or new concrete as overlay firstly,and then subjected to high temperature,finally mechanical property was measured correspondingly.The tests aim to investigate on the bond between PVA-ECC and existing concrete structure under high temperature conditions,and compare the differences with new concrete one.Results show that when temperature range from room one to 600°C,the bond is well between PVA-ECC and existing concrete,while when temperature increase nearly to 600°C,new concrete ones are spalled seriously and separated from existing concrete sunstratecs;when temperature increase to 800°C,PVA-ECC and existing concrete are separated from one another,but not spall out.3.It was found that PVA-ECC with high proportion of superplasticizer(SP)has high liquidity cannot be applied to wall plaster very well,on the other hand,PVA-ECC with low or even no proportion of superplasticizer,can be well adherent to masonry wall.On the basis above,the influence of superplasticizer on mechanical properties of PVA-ECC after high temperatures was studied.Through cube compressive,prism flexural and sheet three-point bending experimental studies,results indicate that:at room temperature,all mechanical properties of PVA-ECC added SP perform better than not added ones;while with the temperature increases,the loss on ignition for PVA-ECCs not added SP change larger than added ones,though the strength loss rates are smaller;the ultimate temeperature for PVA-ECC not added SP is 600~oC,while added one is 800 ~oC.4.On the basis of the third study result above,PVA-ECC added SP was used as masonry mortar and PVA-ECC not added SP was used as plaster mortar;meanwhile,PVA fiber was added to ordinary mortar with 1/1000 fiber volume content,which was used as masonry mortar and plaster mortar too.Through different groups of“masonry mortar+plaster mortar”,seven brick masonry wall specimens were designed for diagonal shear test.The results show:comparied with the group of“ordinary masonry mortar+ordinary plaster motar”,when PVA-ECC added SP is applied to masonary mortar,the specimen's shear capacity increases 36%;when PVA-ECC not add SP is applied to plaster mortar,the specimen's shear capacity and shear modulus both promote significantly;when 1/1000 PVA fiber reinforced mortar is applied to plaster,the shear capacity increases only 12%,while46%when it is used to masonry mortar.