Study On Hydration Performance Of Waste Clay Brick Powder-Metakaolin-cement Cementitious Material

Waste clay bricks account for about 50%of the total construction solid waste in China.The traditional disposal methods not only encroach on public resources but also cause secondary pollution to the environment.It is of great significance to seek the way of resource utilization of waste clay bricks.Cement brings convenience to human life but consumes a lot of natural resources and increases greenhouse gas emissions.Therefore,in this paper,metakaolin and clay brick powder prepared by crushing and ball grinding of waste clay bricks were used to jointly replace part of cement and serve as supplementary cementitious materials to prepare waste clay brick powder-metakaolin-cement mortar and clean slurry,so as to reduce the amount of cement and strengthen the resource utilization of waste clay bricks.The heat of hydration,mechanical strength of mortar,hydration products,microstructure,dry-shrinkage performance and resistance to chloride ion penetration of composite cementitious material system were studied.The main results are as follows:(1)The cumulative hydration heat release of the composite cementitious material system decreased with the increase of the content of brick powder.The addition of metakaolin can make up for the cumulative heat release loss of the system,and also make the emergence time of the peak value of hydration heat release advance.The mass loss of Ca(OH)2 increased first and then decreased when the brick powder was added alone.The mass loss of Ca(OH)2 decreased continuously from the early hydration stage when the metakaolin was added,which reflected the difference in the time of volcanic ash reaction between the brick powder and metakaolin.The single addition of brick powder has a negative effect on the pore structure of mortar.The addition of metakaolin can effectively reduce the porosity and enhance the micro-mechanical properties of mortar.(2)The compressive strength of mortar decreases with the increase of the content of brick powder.The compressive strength of mortar increased by 31%in the first and middle period when the monotone was added.The maximum increase of compressive strength reached 38%and the effective substitution rate of clay brick powder was increased by double mixing.The dry shrinkage value of mortar can be reduced by the addition of brick powder alone.The dry shrinkage value of mortar in the early hydration stage increases after the addition of metakaolin,but soon decreases to the level below the control group and the single brick powder group.Both clay brick powder and metakaolin have positive effects on chloride ion permeability resistance of mortar,and metakaolin has more obvious effect.(3)The energy consumption and carbon dioxide emission of composite cementitious material mortar per unit volume were 36.3%and 31.3%,respectively.The energy consumption and carbon dioxide emission of composite cementitious mortar per unit strength growth were 39.3%and 34.5%respectively.The research results of this paper show that the double mixing of clay brick powder and metakaolin can effectively improve the properties of cement-based composite cementing materials and have a positive effect on environmental protection under the premise of reducing the amount of cement,which provides a theoretical basis and experimental data for the application of this method in engineering practice.Figure[27]table[7]reference[78]...