Recycled Concrete Crack Resistance

At present, although the recycled use of waste concrete has become the focus of attention, the studies on the cracking resistance of recycled concrete are rare. Therefore, the cracking resistance of recycled concrete is systematically studied in this paper. The main contents and conclusions of the paper are as follows:1. According to the relevant standards, codes, documents and test dates, the performance requirement of the basic nature of recycled coarse aggregate is concluded and summarized.2. The appraisal indexes of cracking resistance of recycled concrete are chosen. The relational degrees between the ratio of tensile strength to compressive strength, the ratio of elastic modulus to compressive strength, toughness factor and fracture energy are 0.75, 0.62, 0.86 respectively, in which toughness factor has the greatest relationship degree with fracture energy. Therefore, toughness factor is selected as evaluation index of cracking performance in this paper.3. The effects of the composition of raw materials on the cracking resistance of recycled concrete were studied. When the water——cement ratio is under 0.35, the cracking resistance of recycled concrete increases with the increasing water——cement ratio; when the water——cement ratio increases from 0.35 to 0.45, the toughness factor of recycled concrete decreases by 20.2%. With the replacement of recycled coarse aggregate increases, the cracking resistance of recycled concrete reduces; when the replacement of recycled coarse aggregate increases from 0 to 100%, the toughness factor of recycled concrete decreases by 27.5%. With the amount of cement materials increase, the cracking resistance of recycled concrete reduces; when the amount of cement materials increase from 300 kg/m~3 to 500 kg/m~3, the toughness factor of recycled concrete decreases by 17.3%. In certain range, with the sand percentage increases, the cracking resistance of recycled concrete reduces; when the sand percentage increases from 32% to 36%, the toughness factor of recycled concrete decreases by 8.2%. The cracking resistance of recycled concrete increases with the age increased, but the velocity of increase is more and more slow.4. The technical channels that improving the cracking resistance of recycled concrete were studied. The use of mineral admixture could improve the early cracking resistance of recycled concrete, and there is a best adulterate amount of long——term cracking resistance. In the view of improving the long——term cracking resistance of recycled concrete, the best amount of single——admixture of fly——ash and slag are 30% and 20% respectively. Adding polypropylene fiber could improve the cracking resistance of recycled concrete.5. The toughness factor of recycled concrete is forecasted by the neural network. The relative error between the forecast value and the measure value is under 10%.