Synthesis Of Compound Admixtures And Application In Concrete Modified By Coal Chemical Solid Waste

As for energy resources,China is known to be rich in coal,scarce in oil and gas.Lots of modern coal chemical plants were built to ensure the energy security of China last decades.Nevertheless,vast of solid waste of coal chemicals were produced which is difficult to deal with and causing a serious impact on the environment,especially the ash and slag produced by coal gasification.Gasification ash is a solid waste produced during the coal gasification and mainly composed of inorganics of coal.Its main components are Si O₂,Al₂O₃,Ca O and Fe₂O₃,which are similar to the main components of cement.Therefore,gasification ash could be used as an alternative of cement for producing concrete.It is certain that mixing solid waste of coal chemical would affect the performance of concrete.Admixtures is a kind of materials which could improve and adjust the performance of concrete and it is an indispensable material of producing concrete.Hence,study and develop high performance concrete admixtures to improve the quality of concrete modified by solid waste of coal chemical is significance.Four kinds of admixtures,modified lignin admixtures,naphthalene-based admixtures,melamine admixtures and polycarboxylic acid admixtures were prepared in laboratory.The functional groups and molecular weights were characterized.The performance of each admixture,and compound admixture were studied.It is found that compound admixture could effectively improve the concrete quality and reduce the cost of admixture.Among the four kinds of admixtures,naphthalene-based admixtures and polycarboxylic acid admixtures display best water reducing effects.For the physical compound admixtures,when the mass ratio of sodium lignosulfonate and naphthalene-based admixtures is 3:7,sodium lignosulfonate and polycarboxylic acid superplasticizer is 4:6 presented best water reducing effects.Moreover,the chemical compound admixtures are also better than the single admixtures,and the cost of admixtures production could further be reduced.The physical characteristics of cement,gasification ash,gasification slag and fly ash were analyzed by BET,XRF,FTIR and XPS.The specific surface area of cement is about 0.6m²/g.However,The specific surface area of fly ash and gasification slag are 4 times and 10 times that of cement,respectively.It is found that Si O₂,Fe₂O₃,Ca O and Al₂O₃are the main components of gasification ash and slag;the main components of fly ash are Si O₂and Al₂O₃,followed by Ca O;Ca O and Si O₂are the main components of cements,which account for the 68%of total composition.The XPS demonstrated that of binding energies of the main elements Al,Si,Ca and O in cement,fly ash,gasification ash,gasification slag,concrete and concrete modified solid waste were almost the same.It is indicated that partial replacement of cement by solid waste of coal chemical in concrete is feasible.Based on the interfacial chemistry,the adsorption properties of admixtures on the cement,gasification ash,gasification slag,fly ash and its main components were studied.It is found that the naphthalene-based admixtures and polycarboxylic acid admixtures were easily adsorbed on the cement and solid waste.The Zeta potential of naphthalene-based admixtures and polycarboxylic acid admixtures were highest which indicated that these two admixtures could present high dispersion stability in concrete.