| The consumption of mortar as a building material is very huge every year,and most of the mortars are ordinary mortars,which are prepared by natural sand.The use of recycled mortar can not only reduce the consumption of natural sand and stone,alleviate the environmental pollution caused by the abandonment or stacking of construction waste,but also give full play to the economic and environmental benefits.At the same time,the recycled fine aggregate is usually divided into two types according to the manufacture process,namely the accompanying recycled sand and the whole component recycled sand.The accompanying recycled sand has the characteristics of poor quality and low production cost,while the whole component sand has the characteristics of high quality,high site and mechanical requirements and high cost.However,both the recycled plastering mortar and the recycled masonry mortar prepared by the above two fine aggregates have the defects of poor rheological property,great dispersion of mechanical strength,poor durability in practical application and so on.Although fly ash(FA)and waste brick powder(RBP)with good active-filler and micro-aggregate effect used as mineral admixtures can improve the consistency loss rate of the recycled motors to some extent,and has economic and environmental benefits,they also face the problems of reducing the strength of recycled mortar and none matching optimized mix proportion,thus hindering the further generalization of them.In connection with the above problems that need to be solved urgently in the application of recycled mortar,The accompanying recycled sand or the whole component recycled sand was used as fine aggregate,Which the accompanying recycled sand has the characteristics of poor quality and low preparation cost,While the whole component recycled sand has the characteristics of high quality and high site and mechanical requirements.and FA or RBP with internal curing effect was used as mineral admixtures to replace cement in different proportions to prepare the recycled mortar.The amount of water in the recycled plastering or masonry mortar with different dosage of water reducing agent was determined through control of the initial consistency in 70-80 mm and 90-100 mm,respectively,and the 2 h consistency(Sp2h)loss rate,water retention(CS),apparent density(ρ),28 d compressive strength(f28m,cu),14 d tensile bond strength(f14at)of recycled mortar was comprehensivelyinvestigated;In addition,recycled mortar prepared by full component sand with superior properties was selected for the study of the drying shrinkage ratio(εat)and freeze-thawing property.The samples before and after freezing-thawing testing were characterized by SEM,and the difference and change of the interface between aggregate and cement hydration were analyzed.The optimal mix ratio at different strength grade of recycled mortar was accordingly determined.The results show that:(1)The recycled mortar doping with the accompanying recycled sand,FA and RBP with the binder/sand ratio(B/S)being 1:5,1:6 can well prepared to meet the performance requirements.the fundamental performances of recycled mortar doping FA is superior to those doping RBP,among which the f28 m,cu of recycled mortar can be generally improved by about 2MPa,and the Sp2 h with B/S of 1:5 and 1:6 of recycled mortar can be decreased by about 3% and 2%,respectively.The mechanical properties of the recycled mortar decrease with the increase of FA or RBP dosages(WFA,WRBP).The basic performance of recycled mortar can be better improved with the increase of the water reducing agent dosage.When the water reducing agent dosage exceeds 0.75%,the improvement of basic properties of the regenerated mortar is low,the corresponding Sp2 h is generally reduced by about 1%,and the corresponding f28 m,cu is generally increased by about 0.5MPa.(2)The fundamental performances of recycled mortar prepared with the whole component recycled sand as fine aggregate are superior to those prepared with the accompanying recycled sand,among which the f28 m,cu of recycled mortar can be generally improved by about 2MPa and Sp2 h are generally reduced by about 2%.At the same time,the fundamental performances of recycled mortar doping FA is superior to those doping RBP,and the mechanical properties decrease with the increase of WFA or WRBP.When the water reducing agent dosage exceeds 0.75%,FA or RBP just influence the fundamental performances of recycled mortar less.(3)Through economic analysis on the accompanying recycled sand-based reclaimed mortar with different strength grades shows that,when preparing the reclaimed mortar with M5 grade strength,the maximum economic benefit can be obtained by selecting B/S is 1:7,WRBP is 40% and water reducing dosage is 0.65%.For recycled mortar with M25,M20,M15 and M10 strength grades,can be selected respectively B/S is 1:5,WFA is 40%,and waterreducing dosage is 0.65%,and B/S is 1:6,WFA is 40%,water reducing dosage is 0.75%,and B/S is 1:6,WFA is 40%,water reducing dosage is 0.65%,and B/S is 1:7,WFA is 30%,water reducing dosage is 0.65%,which have the greatest economic benefits.(4)Through economic analysis on the whole component recycled sand-based reclaimed mortar with different strength grades,it can be concluded that when recycled mortar with higher strength grades of M30 and M25 are prepared,the maximum economic benefits can be obtained by selecting mortar with B/S is 1:5,WFA is 20%,water reducing dosage is 0.75%,B/S is 1:5,WRBP is 40% and water reducing dosage is 0.65% respectively.For recycled mortar with M20,M15 and M10 strength grades,B/S is 1:6,WFA is 40%,water reducing agent dosage is 0.75%,B/S is 1:6,WRBP is 20%,water reducing agent dosage is 0.75%,B/S is 1:7,WRBP is 40% and water reducing agent dosage is 0.75%,which have the greatest economic benefits.(5)According to the durability study of mortar prepared by whole component recycled sand,the durability of mortar mixed with FA is better than that mixed with RBP.Which dry shrinkage of 28 d decreased by about 0.02%,and after 25 cycles of freezing-thawing mass loss rate decreased by about 0.12% and strength loss rate decreased by about 0.7%.With the improvement of WFA and WRBP,the durability index of mortar prepared decreases to different degrees and is greatly affected by the water reducing agent dosage,Although the increase dosage of water reducing agent can better improve the durability of mortar to a certain extent,When the water reducing dosage exceeds 0.75%,its improvement on the durability of mortar is small. |
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