Preparation And Road Performances Of Cementitious Material Made By Concrete Slurry Waste And One-part Alkali-activated Materials

In order to achieve efficient recycling of concrete slurry waste(Concrete slurry waste,CSW)in road materials,the suitability of CSW as micro-aggregates in P·O 42.5 Portland cement and one-part alkali-activated materials was evaluated based on the physical and chemical nature of CSW.Particularly,the one-part alkali-activated materials were composed of "blast-furnace slag(BFS)-fly ash(FA)" as precursors,and powdered sodium carbonate(Na2CO3)which was furtherly supplemented by powdered sodium metasilicate pentahydrate(Na2SiO3·5H2O)/silica fume(SF)to provide additional silica sources,as the combined powdered activators.Two kinds of composite cementitious materials,CCSW(CSW+cement)and OAM(CSW+alkali-activated materials),were prepared by mixing the same mass and homogenized CSW with cement and one-part alkali-activated materials,respectively,at the same mixing parameters.The macro properties including flowability,setting time,exothermal behavior and mechanical properties,and micro structures referring to the crystal phase composition,characteristics of chemical bands,thermal stability,micro morphologies and elements analysis of productions were studied,and the corresponding pavement concrete materials were prepared to conduct a comparative study about the road performances,and economic and environmental benefits.The main conclusions are as follows:(1)The flow diameter,and the setting time of cement were reduced significantly due to the addition of CSW,while the flowability and setting time of OAM were mainly affected by BFS and activator dosage,and the flowability and setting time of OAM were both benefit by increasing the combined activator dosages;When the substitute rate of SF for Na2SiO3·5H2O exceeded 50%,the flowability and setting time of OAM were both reduced greatly.(2)The addition of CSW into cement greatly facilitated the early heat liberation of CCSW;The compressive and flexural strengths of CCSW at 28d achieved 43.6MPa and 5.9MPa,respectively;Generally,the exothermal curves of OAM was relatively gentle,and a comparative strength could be reached,when the BFS:FA equaled to 1:1 and activator dosage reached 15%-20%;There was insignificant effect on the mechanical properties of OAM with the SF substitute rate less than 25%.(3)The main products in the OAM were C-N-A-S-H,gaylussite,calcite and hydrotalcite phases;The content of chemical bonded water in the CCSW was higher than that in the OAM;The microstructure of OAM was denser than that of the CSW,with the most probable aperture of 10nm.(4)Pavement concrete materials that used OAM as cementitious materials not only obtained a satisfactory workability for slipform construction,higher mechanical properties which met the design standards of concrete pavement for medium traffic flow,and good wear resistance,but also reduced the carbon emission of 258kg and eliminated 239.94kg CSW in per cubic meter production of alkali-activated concrete.