Experimental Study On Short-Term Stiffness And Crack Of Beams Formed By Recycled Coarse Aggregate

With advantages such as saving resources, protecting the environment and reducing costs, recycled concrete is becoming a new type of green materials in the recent sustainable development. However, there are few theoretical formulas directly applied to design for the suitability of recycled concrete, in this paper the stiffness and crack of it were studied deeply. By earring out the bending tests on16recycled concrete beams and1ordinary concrete beam, the corresponding results were obtained as following:1、There was cetain difference between related mechanics performance of recycled concrete and common concrete’s, considering the influence of replacement ratio, the corresponding formulas were set up respectively about recycled concrete elastic modulus and tensile strength with compressive strength according to the test results analysis.2、It can be observed the internal crack process from loading the square plate test made by recycled concrete which was parallel to ordinary concrete specimens. In the loading process, recycled concrete plate could be divided into three phases as relatively stable period of original crack, damage stability period and unstable development period according to the crack development law. But the initial cracks appeared earlier than ordinary concrete, and the internal crack width was20%-50%larger.3、The higher the replacement ratio was, the bigger midspan deflection of recycled concrete beam would be under the same load. For the load-deflection curve, it’s similar to ordinary’s, firstly rose along the straight line, then turned a point after cracking in concrete, about80%of limit load or passing yield phase of reinforcement a period of time the deflection changed enormously and beam appeared obvious bending.4、With analysing the experiment results, the coefficient value of internal force arm, elastic-plastic resistance moment coefficient formula were matched, also short-term stiffness formula of recycled concrete beam under bending was rectificated on the basis of corresponding specification formula.5、Recycled concrete beams’short-term stiffness decreased with increasing the replacement ratio, it was about11%lower carried by calculated value than by specification. Compared to actual data and referred to experimental data made by other domestic researchers, it was verified to be applicative for the short-term stiffness formula of bending beam.6、The crack propagation of recycled concrete beam was alike to ordinary’s, but firstly cracking appeared earlier, also earlier coming with the increase of the ratio of longitudinal reinforcement; the main fracture interval had a larger trend while replacement ratio rose, then the NO. of corrsponding crack reduced more and width became bigger, suggesting that recycled concrete crack calculation is different with rodinary concrete.7、The formulas of average crack spacing and the maximal crack width were analyzed by data of recycled concrete, showing good anastomosis compared actual value with calculated value of each beam, and domestic related research materials.