Investigation On Recycled Cementitious Materials Preparing With Recycled Concrete Powder

Recycling of concrete aggregate in general process would produce a lot of micro powder (about 5% of the matrix concrete). The micro powder will degrade the performance of the recycled aggregate, and need to be separated.However, the activity of the original recycled concrete powder is low, so it need to be improved so the recycled concrete powder can be effectively applied in cementitous material.Therefore, this article has carried out the research of improving the activity of recycled concrete powder and application of recycled concrete powder.The experimental research show that the best method of improving the activity of recycled concrete powder is:grinding of recycled fine concrete aggregate then sieving by 0.15 mm sieve, grinding 60 min using ball mill, calcing 2 h in the muffle furnace at 750?.In order to improve the activity index of admixture, this paper selects more active admixture to mix with the recycled concrete powder. This article adopts the ground clay brick powder, recycled glass powder, nano-SiO2 and attapulgite clay mixing with recycled concrete powder to prepare of compound admixtures. Studies show that the activity index of ground clay brick powder and recycled concrete powder is close, and the activity index of composite admixture containing ground clay brick powder and recycled concrete powder in different ratio differs little, so the performance of composite admixture containing ground clay brick powder and recycled concrete powder is poor. The best proportion of recycled glass powder to recycled concrete powder is 7:3, and the activity index reachs 89%. The optimal mixture ratio of Nano silica with recycled concrete powder is 8:22, and the activity index is 82%. The optimum compound ratio of attapulgite clay with recycled concrete powder is 1:5, the activity index is 85%. According to the activity and cost analysis we can see the rank as recycled glass powder> attapulgite clay> nano-SiO2> ground clay brick powder. The microscopic results show that the composite admixture has pozolanic ash reactivity in the hydration process, at the same time, the fine particles of the compound admixture play a role in pore filling.So the composite admixture mixing glass powder, nano-SiO2 and attapulgite clay with recycled concrete powder can be used in ready-mixed mortar.This paper will mix recycled concrete powder with supersulfated cement or fly ash-slag polymer to prepare green cement. Experimentals show that the supersulfated cement of SK4 has best comprehensive performance. There is an increase of 2.6 MPa in compressive strength of 28days when Adding 10% of the recycled concrete powder to SK4. As the recycled concrete powder content increases (>10%), the compressive strength 28 days decreases gradually. When the addition of recycled concrete powder is 0%-20%, the green cement meets the standard of 52.5R Portland cement; as it increases to 20%-40%, the green cement meets the standard of 42.5R Portland cement; when the mixing amount increases to 40%-50% the green cement meets the standard of 32.5R Portland cement. The mechanical strength and microstructural results show that when the dosage of recycled concrete powder is not higher than 10%, most of the recycled concrete powder can react with the hydration products of supersulfated cement; when the dosage of recycled concrete powder is higher than 10%, most of the recycled concrete powder act as inert filler in the paste.Experimentals show that the optimal proportion of fly ash and slag based polymer is S50 (50% fly ash +50% slag), as the replacement ratio of the recycled concrete powder replacement ratio increases, the compressive strength of 28 days decreases gradually. When the dosage of the recycled concrete powder is 0-20%, the performance of composite polymer meets the standard of 52.5R ordinary Portland cement; When the replacement of recycled concrete powder increases to 20%?30%, the properties of composite polymer meet the standard of 42.5 ordinary Portland cement; When the addition of recycled concrete powder goes to 30%?50%, the properties of the composite polymer meet with a magnitude of 32.5 ordinary Portland cement.The test result show the ranking of the mechanical properties of the premixed mortar preparing with RC, GRCS, NSRCS, ARCS and RCSG is RCSG> GRCS> ARCS> NSRCS> RC. The ranking of the utilization rate of RC in the composite admixture and RCSG is RCSG> ARCS> NSRCS>RC> GRCS. According to the calculation results, the ranking of maximum utilization of waste of the several kinds of admixture and green cement is RCSG> ARCS> NSRCS> RC.From the cost analysis and the application in ready-mixed mortar, we can see that the cost of ARCS and GRCS is low and the activity is high, so they can be used in the preparation of mortar products in great quantities; the high cost of NSRCS make it unable being used in the actual project; The cost of RCSG is a little high, but the performance of it in the ready-mixed mortar is excellent, so RCSG can also be used in the preparation of mortar products in moderation.