Study On The Properties Of Desulphurization Gypsum-fly Ash Cementitious System

Desulfurization gypsum and fly ash as waste residues can be widely used in theindustry. Calcinated desulfurization gypsum can be prepared by architectural gypsumso that a new kind of gel system is prepared using the composites of gypsum and flyash. Modified gel system has lightweight of building plaster, rapid hardening, thecharacteristics of stability, volume is due to fly ash in sulfate excitation generated afterhydraulic hydration products, and has the characteristics of water resistance, high latestrength. However, the system of the compound of gelled material is still notresearched. In this paper, the cementitious system was modified through addingdifferent admixtures so that the compound gel system of application performance wasimproved and the cost was reduced. The slurry fluidity, the setting time, strength anddurability of desulfurization gypsum-fly ash gelling system were systemicallyresearched. And influence of the different admixtures (excitation agent, water reducingagent and retarder) and glass fiber on the performance of the desulfurization gypsumand fly ash composite gel system was discussed. The desulfurization gypsum-fly ashcement ternary cementitious system characteristics were also studied through XRD,SEM and hydration heat test. The hydration mechanism of the binary and ternarysystem was discussed.The main research contents and results were as follows:Firstly, performance characteristics and hydration mechanism of thedesulfurization gypsum-fly ash gel system was researched in the paper. The flow of thegel system performance was improved and the setting time was prolonged throughadding fly ash into the desulfurization gypsum system. The heat quantity of the gellingsystem was reduced due to the early stage of the fly ash was less involved in hydration reaction. The addition of fly ash could reduce the strength of the gel system. Differenttypes of excitation agent (lime, alkali and sulfate, the silicate, chlorine salt) on thestrength of the binary system had certain stimulating role. The most effectivecompound excitation agent for lime, calcium chloride and potassium aluminium sulfatewere mixed for binary system. The mixed water reducing agent could improve thestrength of the two kinds of gel system and increase the flow property. Andnaphthalene series water reducing agent for improvement of the strength of the binarysystem effect was better than that of poly carboxylic acid water reducing agent, but theflow of poly carboxylic acid water reducing agent on the system performance wasbetter. The setting times of the two kinds of gel system with citric acid and sodiumtripolyphosphate were slow. The same dosage of citric acid on the setting time ofbinary gelling system effect was better. The more setting time was delayed, the moreloss of strength was high.Flexural strength of binary gelling system was improved through adding glassfiber. For excess dosage of the fiber, the compressive strength was damaged.10mmglass fiber was more suitable for this system than the20mm fiber. The optimalperformance of the gel system with the dosage of1%of the10mm fiber was achieved.Secondly, the performance and hydration mechanism of desulfurizationgypsum-fly ash cement gel system was researched in the paper. In the desulfurizationgypsum-fly ash cement system, the flow performance was improved, the setting timedecreased and the strength of the gel system increased. Different types of excitationagent (lime, alkali and sulfate, the silicate, chlorine salt) on the strength of the ternarysystem had certain stimulating role. The best effect of ternary cementitious systemcompound excitation agent was the mixture of lime, calcium chloride, sodium sulfate.The mixed water reducing agent could improve the strength of the two kinds of gelsystem and increase the flow property. And the effect of naphthalene series waterreducing agent for improvement of the strength of the ternary system was better thanthat of poly carboxylic acid water reducing agent, but the flow of the system using polycarboxylic acid water reducing agent was better. Citric acid and sodiumtripolyphosphate prolonged setting time of the two kinds of gel system. For the samedosage, the effect of citric acid on the setting time of ternary cementitious system was better.Compared with the gypsum gelling system, desulfurization gypsum-flyash-cement system had good waterproof. After25times of freezing and thawing cycle,the quality of ternary system increased with the increase of the desulfurization gypsumcontent.In the concentration of75%CO2, due to the lack of OH-, the carbonation rate wasquick. Gypsum expansion effect compensated the drying shrinkage of ternarycementitious system. Therefore the shrinkage of the ternary system was smaller.The research results showed that industrial solid waste was used by thedesulfurization gypsum-fly ash gelling system and desulfurization gypsum-fly ashcement ternary cementitious system. And the systems had a good application value.