Study On Property Of Recycled Coarse Aggregate Concrete

With the rapid increment of broken concrete and the obvious conflict between the disposal and environment problems, broken concrete, as a kind of important recyclable resource, can be widely used in the recycled coarse aggregate concrete. Compared with natural crushed stones, recycled coarse aggregates have characteristics such as shape similarities, great void percentage, great hydrophilic, low strength, high crushing index, small apparent density, clear sharp angle and insufficient gradation, etc. These characteristics lead to the great difference in properties between the recycled coarse aggregate concrete and original concrete.In the paper, the author has probed into the basic physics and geometric properties of recycled coarse aggregate, the basic working performance of recycled coarse aggregate concrete, the different mixing ways of fly ash and the influence on recycled coarse aggregate concrete. Also, he has explored mix-proportion formula and elastic modulus of recycled coarse aggregate concrete as well.In the experiment, the author has broken and graded the abandoned concrete, used the grains within 5-20 millimeters as coarse aggregate concrete to replace recycled concrete compounded from crushed stones, then he has contrasted it with common concrete on mobility, wet form view density, the anti-presses strength and elastic modulus, etc. By using 30% act for rate recycled coarse aggregates as original concrete, mixing fly ash with them according to different ways, the author also has made experiments on the collapse, compressive strength and elastic modulus of fly ash recycled coarse aggregate concrete, contrasting fly recycled coarse aggregate concrete with original concrete. Besides, based on the data from the experiment and those from relevant materials, he has obtained mix-proportion formula according to the regression analysis of mix-proportion formula of recycled coarse aggregate concrete. According to the testing data and relevant contrast, he has come to the following conclusion: First, with the dosage increment of recycled coarse aggregate, the apparent density, collapse and elastic modulus of recycled coarse aggregate concrete fall. Second, when the dosage of the recycled coarse aggregate is below 30%, it has no obvious negative effects on the 28-day compressive strength and elastic modulus of recycled coarse aggregate concrete, and it meets the request of D25 frost resistance. Third, after being added high-efficiency water reducer, recycled concrete can also meet the collapse and strength request of corresponding construction, its collapse can come to that of common concrete and nearly that of original concrete, its ratio of elastic modulus to strength is almost unchangeable. Fourth, among the different adding methods of fly ash, 30% adding method has the best efficiency from strength point, and it has the same strength increasing regulation as that of common concrete. Fifth, elastic modulus of recycled coarse aggregate is smaller than that of original concrete, but when added 30% fly ash, it is larger. Finally, mix-proportion formula's regression coefficient of recycled coarse aggregate concrete is different from that of common concrete. Elastic modulus formula of common concrete is not suitable for recycled coarse aggregate concrete.The experimental research has provided practical reference data for the application of recycled coarse aggregate concrete.