| Along with the fast development of the national economy and the infrastructure ,the processing that abandon the concrete causes the people's concern more and more. But the creation and developments of the recycled concrete technology, found out a new path that can keep on the development for the concrete engineering, have already become a brand-new direction of the engineering material and the structure development, and it is the new hot point that most countries scientist study.Because of the complexity of the recycled concrete material, the fracture mechanism of the recycled concrete want to go deep in to be understood urgently again, as a result the research of the splitting characteristic of the recycled concrete has the important realistic meaning and engineering value. Owing to this, the splitting function to the recycled concrete, will be mainly carried on following on trial research and theories analysis of several:1> By using three-point bend beam specimens with the size of 515mm x 100mm x 100mm , the main influence factors on the fracture toughness of the recycled concrete have been investigated. The test results show : The bonding function of aggregates and cement stones in recycled concrete can be improved by the preprocessing method availably, which make its fracture toughness to raise 20% equally or so; Along with the increase of maximum grain size, its fracture toughness grows, but the elevated range declines gradually, for instance, a fracture toughness of a maximum grain size with 20mm differs 0.0031% only for the 25 mms, which can think that both are equal; Along with the increase of age, its fracture toughness grows, and the elevated range is in accordance with the natural aggregate concrete basically; Its fracture toughness is similar to that of nature aggregate concrete, and both increase together with the declining water cement ratio; Its fracture toughness is smaller than that of nature aggregate concrete, and its fracture toughness is about (75~97)% of that of nature aggregate concrete , but fracture toughness of recycled concrete which was made to use recycled aggregate with the maximum grain size of 20mm which was handled by preprocessing methods with cement paste joined the right amount of fly ash, is equal with natural aggregate concrete for 90 days.2, The main influence factors on the fracture toughness of recycled concrete have been carried on the outstanding analysis ,and the results show that curing age, preprocessing method of coarse aggregate, water cement ratio and maximum grain size of coarse aggregate are one by one in order smaller than etc. According to the analysis result, a calculation formula of many factors in the fracture toughness of recycled concrete has been built up.3, By the stiffness of test machine improved and using the computer system of automatic collecting data, the whole curve of the relation of load and deflection the whole curve of the relation of load and crack mouth opening displacement (CMOD) and the whole curve of the relation of load and crack tip opening displacement(CTOD) have been obtained.4, How fracture energy of recycled concrete can be influenced by the preprocessing method of recycled aggregate, curing age, maximum grain size of coarse aggregate and water cement ratio has been studied. And the different characteristic of the fracture function between recycled concrete and nature aggregate concrete have been investigated. The test results show : Preprocessing method make fracture energy of recycled concrete to raise 10% equally or so; Along with the increase of maximum grain size, its fracture energy grows, but the elevated range declines gradually, for instance, a fracture energy of a maximum grain size with 20mm differs 2.33% only for the 25 mms, which can be thought that both are equal; Along with the increase of age, its fracture energy grows, and the elevated range is in accordancewith the natural aggregate concrete basically, but the elevated range declines gradually; Its fracture energy is similar to that of nature aggregate concrete, and both increase together with the declining water cement ratio; Its fracture energy is slightly smaller about 10% than that of nature aggregate concrete, but fracture energy of recycled concrete which was made to use recycled aggregate with the maximum grain size of 20mm which was handled by preprocessing methods with cement paste joined the right amount of fly ash, is equal with natural aggregate concrete for 90 days.5, The main influence factors on the fracture energy of recycled concrete have been carried on the outstanding analysis ,and the results show that water cement ratio, curing age, maximum grain size of coarse aggregate and preprocessing method of coarse aggregate are one by one in order smaller than etc. According to the analysis result, a nonlinear calculation formula in the fracture energy of recycled concrete has been built up.6> How fracture energy of recycled concrete can be influenced by the preprocessing method of recycled aggregate, curing age, maximum grain size of coarse aggregate and water cement ratio has been studied. And the different characteristic of the fracture function between recycled concrete and nature aggregate concrete have been investigated. The test results show : Except that CMODC of recycled concrete by two preprocessing method of wet, cement paste joined fly ash about 10% and 20% slightly can be improved, CMODC of the rest is smaller about 5% than that of no preprocessing method, but CTODC of the whole is higher about (8-17)% than that of no preprocessing method; Along with the increase of maximum grain size, its CMODC and CTODC grows, but the elevated range declines gradually, for instance, CMODC and CTODC of a maximum grain size with 20mm respectively differs 0.12%, 1.97% only for the 25 mms, which can think that both are equal; Along with the increase of age, its CMODC grows, but its CTODC has no obvious change, and the average of its CTODC is 0.0202mm ; Together with the declining water cement ratio, its CMODC increases and its CTODC declines as a whole,but the trend is smaller and smaller; Its CMODC and CTODZ is respectively higher about 25.23% and 14.42% than that of nature aggregate concrete.7 > The expending process on the crack in the body of recycled concrete has been analyzed, and the uniform theory model on the fracture process zone-of tiny crack in which two different strain softening curve have been used, has been built up. As a result the fracture critical load and equivalent fracture toughness considering subcritical crack growth has been got, which quantitatively prove in theory that the calculation formula of fracture toughness recommended from the hydraulic rules of fracture can be applied for fracture toughness of recycled concrete .8, According to the test result, some applied opinions and suggestions that have been put forward in the application of recycled concrete engineering, can be the reference of the actual engineering.
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