Size Effect On Compressive Behaviors Of Cubes And Cylinders Made Of DCBs&FC And Seismic Behaviors Of Double Thin Skin Hybrid Walls Filled With DCBs&FC

Recycled aggregate concrete (RAC) is an effective approach in recycling demolishedconcrete, but the production process is complicated and requires lots of energy. In addition,the production of RAC also consumes a large amount of cement and water. For this purpose, anew idea is proposed by our research group, which use large scale demolished concrete (i.e.blocks or segments) instead of aggregate. Some preliminary study about the performance ofcubes made of demolished concrete blocks (DCBs) and fresh concrete (FC) and structuralmembers filled with DCBs and FC have been conducted by our research group. Based onabove existing research results, the size effect on compressive behaviors of cubes andcylinders made of DCBs and FC and seismic behaviors of double thin skin hybrid walls filledwith DCBs and FC were researched in this paper.The main achievements include that:Fifty-one cubic specimens and thirty-six cylindrical specimens made of DCBs and FCwere tested under compressive load. The influences of both the specimen dimensions and thecharacteristic size of DCBs on the combined compressive strength, the modulus of elasticityand the strain at peak stress have been experimentally investigated. This research results showthat in the case that the characteristic ratio keeps constant, the combined compressive strengthof the specimens made of DCBs and FC decreases significantly with an increasing of thespecimen dimensions; and the effect of specimen size on the combined strength accords withboth the size effect law and the modified size effect law for conventional concrete; in the casethat the specimen dimensions keep constant, the combined compressive strength of thespecimens made of DCBs and FC decreases gradually with an increasing of the characteristicratio; a formula is established to describe the relationship between the characteristic ratio andthe combined compressive strength, and it agrees well with the test data. A model is proposedto predict the combined compressive strength of specimens made of DCBs and FC withvarious dimensions and different characteristic ratios, and it is in good agreement with the testresults. The specimen dimensions and the characteristic size of DCBs have no clear effects onthe modulus of elasticity and strain at peak stress.Based on digital image correlation (DIC) technology, the failure process of recycled hybrid concrete made of DCBs and FC under compressive load was researched. Test resultsshow that cracks do not assemble at the interfaces between the new concrete and DCBs.Quasi-static tests of seven double thin skin hybrid walls filled with DCBs and FC wereconducted, and influences of some parameters (i.e., replacement ratio of DCBs, thickness ofsteel plate, axial load ratio, rib plate spacing, height-width ratio) on seismic behaviors of thespecimens were investigated. Based on the concept of combined strength of new and oldconcretes, lateral load bearing capacities of the specimens were calculated approximately, andcompared with those of reinforced concrete walls with similar total steel weight. Test resultsshow that the influences of the replacement ratio of DCBs within a range of0~33%on thespecimens’ initial lateral stiffness, lateral load bearing capacity, destructive drift ratio, energydissipation capacity, and shape of hysteretic curve are limited; the axial load ratio of a doublethin skin hybrid wall filled with DCBs and FC should be less than0.35; even the ratio of wallthickness to thickness of steel plate is120, the hysteretic behavior and deformation capacityof a double thin skin hybrid walls filled with DCBs and FC are still well, and its destructivedrift ratio can meet the requirement of Chinese seismic design code; the energy dissipationcapacity of a double thin skin hybrid wall filled with DCBs and FC is similar to or little largerthan that of a reinforced concrete wall; in the case that the sectional area and total steel weightare unchanged, the lateral load bearing capacity of a double thin skin hybrid wall filled withDCBs and FC is similar to that of a reinforced concrete wall.Based on the general finite software of ABAQUS, finite element models about doublethin skin hybrid walls filled with DCBs and FC were created. The horizontal force-horizontaldisplacement curves were numerically simulated considering the influence of size effect ofcombined compressive strengtht.