添加掺合料后再生混凝土的改性试验研究

Experimental study on the modification of recycled concrete with admixtures

针对再生混凝土与普通混凝土的性能差异,在再生混凝土中添加合适比率的粉煤灰、矿粉、硅粉掺合料,分别研究其工作性能和力学性能的改变状况。通过改变掺合料对水泥的取代率、水灰比两个参数,共设计21组试验方案,制作63块试块。通过对再生混凝土拌置过程的观测和试块标准养护28 d后的抗压试验得出以下结论:添加粉煤灰,可以明显提高新拌再生混凝土的流动性和保水性;添加矿粉可以提高再生混凝土的流动性,且流动性随着水灰比的增大而减小,相同水灰比下,矿粉取代率较高的再生混凝土的流动性较强,水灰比较大时,添加矿粉后再生混凝土的强度值明显升高,且替代量越多,强度增大越多;硅粉的添加可以提高再生混凝土的黏聚性和保水性,当水灰比较大时,添加硅粉后再生混凝土的强度值明显升高;无掺合料的再生混凝土试块和掺有3种掺合料的再生混凝土试块的抗压破坏形态与普通混凝土的抗压破坏形态均属于黏结面破坏形式。

In terms of different performances between recycled concrete and normal concrete,the working performance and the mechanical properties of recycled concrete were studied by adding a suitable ratio of admixture such as fly ash,slag and silica fume in the experiment. By changing substitution rate of admixture to cement and water cement ratio,21 groups of design scheme were proposed and 63 test specimens were produced. Through the observation during the mixing process and the compression test of specimen which were subjected to 28 days of curing,several conclusions were summarized as follows. First,fly ash,as a mixture,is able to improve significantly the mobility and water retention characteristics of the new mix of recycled concrete. Second,the addition of mineral powder can improve the mobility of recycled concrete,and it decreases as the water cement ratio increases; under the same water cement ratio,the mobility of the specimen with higher rate of substitution of mineral powder is stronger. With higher water cement ratio,the strength of the recycled concrete with the addition of mineral powder is greater. The more substitution rate of admixture is,the greater strength it shows. Third,silica fume can improve the cohesiveness and water retention characteristics of recycled concrete. With higher water cement ratio,the strength value of recycled concrete with silica fume increases. Fourth,both the failure mechanism of the recycled concrete specimens with the aforementioned three admixtures and the specimens without admixture show adhesive interface failure,which adheres to the failure mechanism of ordinary concrete.