The High Value-added Reutilization Of Calcium-rich Powders Of Building Solid Waste

This paper studies the efficient and environmentally friendly method of recycling and utilization of powder construction waste through the waste putty,waste gypsum board and fine aggregate as the raw material,these were belong to the typical calcium-rich powder type construction waste materials.Through the reaction with phosphate solution??NH₄?₂HPO₄,?DAP??,the calcium elements of waste putty,waste gypsum board and fine aggregate can be converted into hydroxyapatite,which can realize high added value of calcium rich and solid waste.This study was carried out on the waste putty-hydroxyapatite to reinforce sand and the waste gypsum board/fine aggregate–hydroxyapatite to adjust the humidity.The following conclusions have been made:?1?The HAP,generated by the reaction of putty powder and DAP,is a network structure of nano-space,which can effectively improve the bond of sand particles and fill the gap of sand particles and form a more dense microstructure.At the age of 28d,the higher the DAP concentration,the more HAP produced,the better the crystallinity.Under the condition of the DAP mass concentration was 15%,the XRD characteristic peak of HAP as the hump,diffuse,peak width is about 3 degrees,poorly crystalline in SEM,microstructure is not dense,and under the condition of the mass concentration was 40%,the XRD characteristic peak of HAP are sharp,peak width to one degree,better crystalline in SEM,relatively dense microstructure.The formation of HAP was beneficial to the improvement of the compressive strength,at the age of 28d,relative to the compressive strength of contrast group without DAP,the compressive strength of the block of DAP mass concentration was 15%,30%and 40%increased by 36%,184%and 36%respectively.?2?The HAP,generated by gypsum board,fine aggregate and DAP,is a network structure of nano-space,which can effectively improve the strength of the composite powder.And because HAP has an excellent adsorption,the composite powder can absorb the moisture in the air effectively and retain it for a long time,which has a good humidifying performance.DAP concentration is higher,the soak time is longer,environment humidity is higher,the performance of water absorption and release performance of composite powders is greater,the XRD characteristic peak of HAP is more sharp,better crystalline in SEM,the microstructure is more dense.Under the condition that the environment humidity was 97%,the composite powder is soaked in a DAP solution with a mass concentration of 30%for 14d,its water absorption is the best,close to 9.3%,and the release water is also the best,close to 2%.