Test Study On Casting Technology And Uniaxial Compressive Behaviors Of Compound Concrete Made Of Demolished Concrete Lumps And Fresh Concrete

It is indicated that structural members cast with demolished concrete lumps(DCLs)and fresh concrete(FC)are effective approaches of recycling demolished concrete.Some preliminary mechanical behaviors and seismic properties and fire resistance performance of specimens made of DCLs and FC have been conducted by our research group.To better ensure the quality of the construction of compound concrete made of DCLs and FC,to improve the construction efficiency,three parts of research work are involved in this dissertation:1.Casting process tests of vertical structural members made of DCLs and conventional FC or self-compacting FC were conducted,and the influences of some parameters(i.e.,characteristic size of DCLs,type of FC)on the single-maximum-allowable stacking height of DCLs have been revealed.It is found that:(1)The change between 400 mm and 1000 mm of the single stacking height of DCLs has little effect on the nominal replacement ratio of DCLs;(2)When the characteristic size and single stacking height of DCLs are between 150 mm~200 mm and 400 mm~700 mm,the nominal replacement ratio of DCLs is about 1.6%~6.2% higher than the actual replacement ratio of DCLs;(3)The actual replacement ratio of DCLs increases with the increasing of the single stacking height of DCLs,but the type of fresh concrete has limited effect on the actual replacement ratio of DCLs;(4)When the conventional concrete(or self-compacting concrete)with the maximum aggregate size of 25 mm(or 16 mm)is employed as the fresh concrete,the specimens have the single-maximum-allowable stacking height of DCLs no more than 600 mm(or 700 mm).2.Tested under uniaxially compressive loadings of compound concrete made of normalstrength DCLs and high-strength self-compacting concrete were conducted,and influences of the specimen's shape(cubes and prisms)and replacement ratio of DCLs(0,20%,30%,and 40%)on the specimen's compressive behaviors have been investigated.It is found that:(1)the interfaces between DCLs and self-compacting concrete(SCC)are not obviously weak zones in the compound concrete;(2)both the combined compressive strength and the elastic modulus reduce with the increasing of the replacement ratio,and the adverse effect of the replacement ratio on the combined compressive strength is more significant than that on the elastic modulus;(3)with the increasing of the load ratio lower than 0.8,the growing rate of the Poisson's ratio of the compound concrete is similar to that of SCC;but with the increasing of the load ratio larger than 0.8~0.9,the growing rate of the Poisson's ratio of the compound concrete is much faster than that of SCC.3.Tests on the relationships between uniaxial compressive mechanical behaviors and ultrasonic pulse velocity(UPV)were conducted.The influences of the frequency of transducers and the curing age on UPV,the relationships between the compound compressive strength and the UPV,and the relationships between the elastic modulus and the UPV were investigated preliminarily.It is found that:(1)the specimen's UPV measured using the 40 kHz transducers is always slightly higher than that measured using the 30 kHz transducers,and the ratio of the former to the latter is about 1.03~1.10;(2)the UPV of the specimen increases with the increasing of the curing age,and the increase rate of this velocity during the first seven curing days is more notable than that in the following seven curing days;(3)It is better to use the quadratic function to fit the quantitative relationships between the combined compressive strength(or the elastic modulus)and the ultrasonic pulse velocity of compound concrete made of DCLs and FC.