再生细骨料含水状态对砂浆性能的影响

Effect of Moisture State of Recycled Fine Aggregate on Properties of Mortar

采用再生细骨料取代质量分数30%河砂制备砂浆,通过预湿处理将再生细骨料含水率处理为其饱和面干吸水率的0%、30%、70%、100%,分别控制拌合用水量或总用水量一致,研究再生细骨料含水状态对砂浆性能及微观结构的影响规律。结果表明,拌合用水量一致时,砂浆流动度随再生细骨料含水率增大而增大,骨料含水状态对养护后期(28 d)力学性能的影响较小;总用水量一致时,砂浆流动度随再生细骨料含水率增大而减小,再生细骨料干燥状态下砂浆28 d力学性能较骨料含水状态下更好。两种用水量控制方案下,采用干燥再生细骨料配制的砂浆抗氯离子侵蚀性能均表现最优,且可达到与普通砂浆相当或更优的水平。微观结果表明,骨料的含水状态对微观结构影响显著,骨料预湿处理会对使新界面过渡区孔隙率增大、平均显微硬度下降,进而对宏观力学及耐久性能产生不利影响。在工程应用中保证流动度的前提下,应尽可能采用含水率低的再生细骨料配制砂浆。

The recycled fine aggregate(RFA)was used to replace 30%(mass fraction)of the river sand to prepare mortar.The water content of RFA was set to be 0%,30%,70%and 100%of the value measured under the saturated-surface-dried state,by pre-treating RFA in water.The influence of the moisture states of RFA on the properties and microstructure of mortar was experimentally investigated,by taking two types of water control methods,i.e.,to keep a consistent supply of mixing water and total water,respectively.Test results show that at the given mixing water supply,the fluidity of recycled mortar increase as the water content of RFA increase,and the influence of the moisture states of aggregate on the 28 d mechanical properties is insignificant.In contrast,given a consistent total water supply.The fluidity of recycled mortar decrease as the water content of RFA increase,the mortar group prepared with the oven-dried RFA present the best 28 d mechanical properties among all the mortar groups.Besides,it is found that the resistance to chloride ion ingress of recycled mortars prepared with the oven-dried RFA is the greatest among all the mortar groups,and comparable or even higher than natural mortar counterpart,regardless of the water control methods.Test results on the micro scale show that the moisture states of RFA can influence the microstructure of mortar significantly.The pre-wetting treatment of RFA led to enlarge porosity and diminished average microhardness of the new interfacial transition zones,which thereby has a negative effect on the mechanical properties and durability of mortar on the macro scale.It is suggested that the RFA at a low water content should be used to prepare the cement mortar for practical use,given that the fluidity of mortar could be ensured.