Studies On Compressive Behavior Of Recycled Lump/Aggregate Concrete And Mechanical Behavior Of Prefabricated Laminated Slab Made Of Recycled Lump/Aggregate Concrete

To further improve the recycling efficiency of waste concrete,a strategy of recycled lump/aggregate concrete(RLAC),which uses the mixture of recycled lumps(DCLs)and fresh recycled aggregate concrete(RAC)to fabricate the structural members,was proposed by our research group.This thesis conducted the compression tests on RLAC,and the environmental impacts of three different waste concrete recycling strategies were also compared.In addition,an optimized configuration of RLAC prefabricated laminated slab was proposed,and the corresponding experiment research and numerical analysis on such members were carried out.The main work and achievements include that:1.Compression tests on 27 RLAC cylinders have been carried out,and the mercury intrusion porosimetry tests and scanning electron microscope tests were conducted to explain the macroscopic test results.The results showed that:(1)the waste content of RLAC can reach more than twice of that of RAC in engineering practice;even if the DCL and recycled aggregate(RA)replacement ratios reached 35% and 70%,respectively,satisfactory compressive strength of RLAC can be attained;(2)RLAC’s compressive strength decreased with the increasing of DCL replacement ratio when the compressive strength of DCLs was lower than that of RAC;and when the RA replacement ratio was 100%,the reduction was significantly greater than that of 50% and 70%;(3)the porosity and harmful pores of the new mortar in the RAC around the DCLs increased when the replacement ratio of RA was 100%;and(4)when the elastic modulus of RAC was apparently lower than that of DCLs,some microcracks between DCLs and RAC was observed,which led to the deterioration of the compressive property.2.To avoid the deterioration of RLAC’s compressive property in actual engineering,compression tests on 54 RLAC cylinders were conducted,and a corresponding guarantee strategy was proposed.After that,the artificial neural networks for predicting RAC’s compressive strength and elastic modulus were established.The results showed that(1)apparent discrepancies in elastic modulus of RAC might exist even if RAC’s compressive strengths were similar;(2)when the elastic modulus of RAC was significantly lower than that of DCLs,the RLAC’s elastic modulus reducing effect induced by DCLs diminished;(3)when the elastic modulus of RAC was apparently lower than that of DCLs,increasing RAC’s strength can effectively prevent the interface between RAC and DCLs becoming an obvious weak link,preventing the compressive property deterioration of RLAC,and the predicting methods on RLAC’s compressive strength and elastic modulus were proposed;and(4)two BP artificial neural networks were constructed,which showed good predicting accuracy.3.The environmental impacts of RLAC,recycled lump concrete(RLC),and RAC were assessed and compared when fabricating the prefabricated members to show the advantages of RLAC’s environmental benefits.It was found that(1)RLAC exhibited the lowest environmental impacts indicators for almost all the cases,showing the most remarkable environmental benefits;(2)all environmental impact indicators reduced with the increase of DCL replacement ratio,while all environmental impact indicators except for the Global warming potential also decreased with increasing RA replacement ratio,but the decreasing amplitude was lower than that of DCLs;(3)when fabricating the prefabricated members with lower concrete strength,greater environmental benefits could be attained for using whether DCLs or RA;(4)cement production is the most significant contributor to all environmental impact indicators,followed by the material transportation;and(5)RLAC and RLC were more sensitive to the location of the recycling plant than RAC.4.In the case of steel consumption remaining unchanged,an optimization scheme was proposed to convert the truss reinforcement in the conventional structure into the stressed reinforcement to improve the bearing capacity of the RLAC prefabricated laminated slab.The flexural tests on the corresponding prefabricated bottom slabs and laminated slabs,and the shear tests on the laminated surface of slabs,were respectively conducted.The results showed that(1)the uncracked flexural stiffness of the RLAC prefabricated bottom slab without truss reinforcement was comparable to that of the conventional prefabricated bottom slab with truss reinforcement;(2)the bearing capacities of the RLAC prefabricated bottom slab and laminated slab without truss reinforcement both increased significantly by comparing with the conventional prefabricated bottom slab and laminated slab,and the corresponding increasing amplitudes were not less than 50% and 20%,respectively;and(3)the shear behavior of the laminated surface of the RLAC prefabricated laminated slab without truss reinforcement was obviously better than of the conventional prefabricated laminated slab,and the shear capacity of the former was 2.3 times of the latter.5.Numerical analysis was carried out to illustrate the influential mechanism of the protruding DCLs on the uncracked flexural stiffness of the RLAC prefabricated bottom slab.The results showed that(1)basing on the surficial point cloud data obtained by 3D laser scanning technique,the flexural stiffness calculation on 3D slabs could be simplified to those on multiple vertical 2D sections,which significantly reduced the simulating cost and enhanced the feasibility of the parametric analysis of those components with a complex surface;(2)the numerical model established for the RLAC prefabricated bottom slab had good calculation accuracy;the proposed generating method and random placing algorithm with satisfactory modeling efficiency can well achieve the randomness of the size,shape and distribution of DCLs;(3)the uncracked flexural stiffness of the prefabricated bottom slab increased with increasing the replacement ratio and characteristic size of the DCLs,and generally decreased as the shape of DCLs becomes slender,spherical,and oblate;and(4)when DCLs of different shapes were mixed and used,the uncracked flexural stiffness of RLAC prefabricated bottom slab without truss reinforcement can be not less than that of the conventional slab with truss reinforcement,as long as the lower limits of characteristic size and replacement ratio for DCLs were reasonably determined.