| In recent years,with the continuous advancement of infrastructure construction,the demand for cement has been increasing,which has also caused serious environmental problems.It is an effective method to properly solve the above-mentioned environmental problems by carrying out alkali-acitivated cementitious system to replace the traditional cement cementitious system,and recycling construction waste.Therefore,in this paper,experimental studies on alkali-slag concrete based on ground granulated blast furnace slag(GGBFS),a by-product of the smelting industry,was carried out.At the same time,construction waste was used as a substitute for natural sand to conduct an experimental study on the performance of alkali-acitivated slag concrete(AASC).The main research contents are as follows:(1)Aiming at the problem of excessive shrinkage of AASC,a method of using emulsified edible oil as shrinkage reducing agent was proposed.The type of admixture,dosage,and W/B has been setted as the parameters to evaluate the influence of cooking oil on the properties of AASC.In the macro-level,setting time,autogenous shrinkage,drying shrinkage,carbonation depth and strength properties has been tested to evaluate the influence of emulsified cooking oil on AASC.Test results show the applying of emulsified cooking oil could highly reduce the shrinkage of AASC.The benefits of emulsified waste cooking oil are slightly lower than natural cooking oil,but show great value on the reutilization of domestic waste.The addition of emulsified cooking oil could reduce the surface tension and the porosity of AASC owing to the saponification reaction which is one of the main reasons of the shrinkage reducing effect.(2)Based on the rapid setting of AASC,a slow-setting method of AASC according to the principle of slow release is proposed.Part of the alkali activator has been processed into sustained release pills and capsules to reduce the contact surface of alkali activator and GGBFS to retard the early age hydration.The replacement ratio and the size of capsules and pills are setted as the parameters,the setting time,strength,shrinkage and carbonation has been studied.Test results show the applying of pills and capsules could highly prolong the initial setting of AASC,and also show positive influence on the shrinakge and carbonation of AASC.When the replacement ratio of pills is 20%,the 90 days strength is even higher than the control mixture.The alkali-activated pills show selfhealing ability,the healing ratio of cracks is higher than 40%.Test results also show the size of capsules and pills show very limit influence.When the replacement ratio and size of pills is 20% and 12 mm,the modification performance is best.At the microscopic level,the mechanism of alkali-induced coagulation retardation was analyzed through the processes of dissolution,transmission and precipitation of sustained-release capsules and sustained-release tablets.(3)The GGBFS and recycled aggregate were used to replace cement and natural sand and gravel,respectively,to prepare an environmentally friendly AASC materials.The replacement ratio of recyeld fine and coarse aggregates ratio are setted as the parameter,the strength,shrinkage and carbonation properties have been tested.The binder and aggregate are considered highly reduce the environmental burden.Test results show recycled aggregate may reduce the properties of AASC,but the reduction ratio is considered in the acceptable range.When the replacement ratio of recycled coarse and fine aggregates is 100%,the 28 days compressive strength reduce 13.6% and 21.0%,respectively.Results also show positive influence of recycled fine aggregates on the 1-day strength of AASC.Drying shrinkage and carbonation depth on 28 th day only increase approximately 5% and 10% when 100% recycled fine aggregates used.It is concluded that although the use of recycled aggregates slightly reduces the mechanical properties and durability of alkali-slag concrete,the mechanical properties of alkali-slag recycled concrete are obtained by introducing the research results of edible oil shrinkage reduction technology and alkali activator slow-release technology.And the conclusion that the durability performance will be greatly improved.It is found the attached paste on the surface of recycled fine aggregate may supplement the alkali content in AASC and accelerate the hydration,hence increased the 1-day strength.(4)Based on the emulsified waste edible oil shrinkage reduction technology and tablet-type alkali activator slow-release technology proposed in this paper,it was applied to AASC and the mechanical properties and durability of alkali-slag recycled concrete were compared with the same water-binder ratio.Experimental results show after applying double techniques,the autogenous shrinkage,drying shrinkage and carbonation resistance properties have been significantly improved,and the negative influence on the long age strength is very limited.Except carbonation resistance,recycled aggregate based AASC show better or similar performance with OPC-based concrete.According to this study,the emulsified cooking oil technique and sustained release technique could highly improve the performance of AASC,and helps for the widely application of AASC in our country. |
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