The Characteristics Of Mechanical Properties Of Recycled Aggregate Concrete And Influencing Factors

In this thesis, an experimental investigation was conducted to study the influence of attached mortar,damage in stones and soaking treatment with various cement paste (portland cement paste,sulfoaluminate cement paste and aluminate cement paste) to recycled aggregates on the properties of recycled aggregates and mechanical properties of recycled aggregate concrete.Water absorption test and crushed value test were conducted on three kinds of recycled aggregates (recycled aggregate mRA obtained by the process of crashing original concrete,recycled aggregate H-mRA that attached mortar was removed by the process of heating to 620℃and recycled aggregate I-mRA) and two kinds of natural aggregates (natural aggregate NA and natural aggregate H-NA by the process of heating to 620℃). Mechanical properties tests (compressive strength, tensile splitting strength and fracture energy) were conducted on five kinds of concretes (water-binder ratios were 0.250 and 0.586) made with various aggregates above. Influence of damage in stones due to crashing processing,damage in stones due to heating,attached mortar and soaking treatment with cement paste on the water absorption ratio and crushed value of recycled aggregate and mechanical properties of recycled aggregate concrete were obtained from analysis of the results of tests above.The results of the water absorption test and the crushing index test indicate that attached mortar and damage in stones due to crashing process both have a certain negative effect on the properties of recycled aggregate. For the Low-strength recycled aggregate 586RA, attached mortar is the primary parameter inducing the increase of water absorption and crushed value of recycled aggregate, and damage in stones due to crashing processing has a slight negative effect on the water absorption and crushed value of recycled aggregate. For the high-strength recycled aggregate 250RA, attached mortar combined with damage in stones due to crashing processing has a certain negative effect on the water absorption and crushed value of recycled aggregate. Damage in stones due to heating has a certain negative effect on the crushed value of recycled aggregate; however, it has a slight negative effect on the water absorption.The results of the mechanical property test of concrete indicate that damage in stones due to crashing processing and attached mortar both have a certain negative effect on the strength and fracture energy of recycled aggregate concrete. At a high water/binder ratio, attached mortar is the primary parameter inducing the decrease of compressive strength and tensile splitting strength of recycled aggregate concrete, and damage in stones due to crashing processing has a slight negative effect on the compressive strength and tensile splitting strength of recycled aggregate concrete. Damage in stones due to crashing processing and damage in stones due to crashing processing both have certain negative effect on the fracture energy of recycled aggregate concrete. Furthermore, the influence of the latter is more significant. At a low water/binder ratio, influence of attached mortar,damage in stones due to crashing processing on the compressive strength and tensile splitting strength of recycled aggregate concrete is particularly complex. Damage in stones due to crashing processing is the primary parameter inducing the decrease of the fracture energy of recycled aggregate concrete, and attached mortar has a slight negative effect on the fracture energy of recycled aggregate concrete. Damage in stones due to heating has a certain negative effect on the strength and fracture energy of recycled aggregate concrete.The results of the soaking treatment with various cement paste indicate that the soaking treatment with cement paste to recycled aggregates has an almost no significant strengthening effect on recycled aggregate. Water absorption of recycled aggregate increases at a certain degree except the water absorption of recycled aggregate soaking treated with portland cement paste is almost invariant after recycled aggregates were soaking treated with cement paste. After recycled aggregates were soaking treated with cement paste, crushed value of recycled aggregate 250RA increases at a certain degree, and crushed value of recycled aggregate 586RA decreases at a certain degree. Soaking treatment with various cement paste to recycled aggregate has a certain contribution on improving fracture energy of recycled aggregate concrete, but it has an obvious contribution on improving the compressive strength and tensile splitting strength of recycled aggregate concrete, whose reason is that the soaking treatment with cement paste improves the crack growth resistance of recycled aggregate by filling up the pores and the cracks in the recycled aggregate, however, does not strengthen recycled aggregate.