Feasibility Study of Applying Recycled Aggregate from Building Debris in Concrete

Coarse and fine aggregate constitutes an average of approximately 55% to 80% of the total volume of concrete materials.Concrete remains the most commonly-used building material worldwide.As a result,the massive use of aggregate will have a direct impact on the earth′s natural resources if an appropriate replacement material is not found,violating the spirit of sustainable development.This study makes a preliminary examination of using coarse and fine aggregate produced from discarded construction materials in concrete.Results indicate that the compressive strength of densified mixture concrete at 28 days can reach 56.88 MPa(recycled materials used as coarse aggregate,and natural sand used as fine aggregate)and 53.33 MPa(recycled materials used as both coarse and fine aggregate).While this type of material is not yet fully understood,further research into this area should enable feasible applications in concrete.However,unsuitable mixtures have serious impact on the durability and overall economy of concrete.Pending further research on suitable mixture designs,a complete application of recycled aggregate in concrete can be expected.

Role of Co Content on Densification and Microstructure of WC–Co Cemented Carbides Prepared by Selective Laser Melting

WC–Co cemented carbides, well-known as the conventional tooling materials, have not been successfully produced by one step additive manufacturing processes such as selective laser melting(SLM) yet. The microstructure evolution as well as WC grain growth behavior has rarely been investigated in detail during SLM process. In this study, the WC–Co cemented carbides with different Co contents(12–32 wt%) were prepared by optimized SLM processes for comparative investigation of densification behavior, microstructure characterization and mechanical property. The increase in Co content in feedstock carbide granules can improve the densification behavior during SLM process. The SLM processed WC-12 Co shows larger average WC grain size and higher percentage of coarser WC grains as compared with both WC-20 Co and WC-32 Co. The microstructure characterization, combined with finite element simulation, shows the WC grain growth mechanisms include agglomeration and dissolution-deposition of WC during SLM process and agglomeration of WC is an important mechanism especially for WC–Co cemented carbides with Co content as low as 12 wt%. The comparison between horizontal(perpendicular to the SLM laser beam) and vertical(parallel to the SLM laser beam) cross sections of carbides shows that SLM process introduces a certain degree of microstructure and mechanical behavior anisotropy for WC-12 Co, WC-20 Co, and WC-32 Co.