Study On Physical And Mechanical Properties Of Recycled Concrete Brick Prepared By Village Construction Waste

With the vigorous development of China urban construction, accelerating the urbanization process and increasing the amount of project construction, the amount of construction waste generated is increasing day after day. The random construction waste landfill and stacking has not only affected life of people and the environment but also waste of resources, it has become urgent work to focus on and to solve. At present, the researches on making construction waste into resources are mainly concentrated in cities, while the recycling use of construction waste in towns and villages is less. With the construction of new socialist countryside, rural housing construction and reconstruction are expanding rapidly which are producing a large amount of construction waste, taking a lot of rural farmland and causing serious environmental pollution. How to effectively deal with countryside construction waste has been the problem that can not be avoided. The village construction waste is different from the urban construction waste, because the scale ranges widely and they are hard to screen, and its main component are clay bricks, which have rough surfaces, more edges and corners, low intensity and high water absorption. Compared with the waste concrete in city, their recycling are more difficult. Meanwhile, the current existing town wall materials such as concrete hollow bricks have low strength, poor bearing capacity, poor anti-seismic ability. With the construction of new countryside, energy saving, safe, economic and environmental friendly buildings are promoted in residential areas of towns and villages, and new wall materials for multi- resident need to be developed urgently.By using crushing and screening abandoned bricks of towns and villages as the recycled aggregate to prepare a new recycled concrete three-hole brick, the above problems can be solved. Physical properties, mechanical properties and frost resistance of recycled concrete three-hole bricks can be improved by using surface-coating of aggregate by admixture during mixing to strengthen recycled brick aggregates and interface structure between recycled brick aggregates and cement. The main researches are concentrating on the surface-coating of aggregate’s influence on physical properties, mechanical properties and frost resistance and the effect of interface strengthening of recycled concrete three-hole brick.Firstly, the techniques of recycled aggregate prepared by village construction, groove design and molding process of recycled concrete three-hole brick were studied in this paper, identifying the process of recycled aggregate prepared by village construction, the style, the main process parameters and process of concrete three-hole brick.Secondly, by changing the replacement rate of clay aggregate, the compressive strength, softening coefficient, water absorption, moisture content of recycled concrete three-hole brick are tested. In order to find a reasonable clay aggregate quantity, the clay brick aggregate replacement rate’s influences on physical and mechanical properties of recycled concrete three-hole brick were studied. The results showed that when recycled brick aggregate quantity is 40%, the overall performance of recycled concrete three-hole brick is optimum and the physical and mechanical properties meet the state standards.Thirdly, recycled concrete three-hole brick were prepared with surface-coating of aggregate by admixture during mixing. By changing the content of fly ash and slag powder, the influence of admixture surface-coating of aggregate on compressive strength, water absorption, moisture content, softening coefficient, frost resistance of three-hole brick were studied. The results show that physical and mechanical properties of concrete three-hole brick are improved by using of surface coating by fly ash and slag around aggregates during mixing. And the properties of recycled concrete three-hole brick have reached the using standard of the wall materials. The effect of complex admixture coating of aggregate is superior to single doped admixture, when the replacement rate of recycled clay brick aggregate is 40%, the content of slag 20% and the content of fly ash is 10%, and the modification effect is optimal. The 28d compressive strength of concrete three-hole brick reaches the maximum (47.2MPa), the water absorption meets the minimum (5.0%), the softening coefficient has the maximum (0.96), and the frost resistance is best, which mass loss is the minimum (0.3%) and the strength loss is the minimum (8%).Finally, by using scanning electron microscopy, modification of the interface intensity of admixture single-doped and dual-doped coating of aggregate were analysed. The results show that compared with the three-hole brick without admixture modified, the interface morphology using fly ash coating of aggregate whose interfacial hydrate is richer, more compact, but the interface remains the phenomenon of crystal orientation arrangement; using slag bricks wrapped three-hole aggregate interface, a large number of cluster-like hydration products attached to the recycled aggregate surface, indicating that the higher activity of slag is the direct cause of bond strength of interface of recycled aggregate and cement greatly increase; with complex admixture coating of aggregate ,dense clusters attached to hydrate the surface of recycled aggregate, indicating that the appropriate ratio of compound mixed can play a complementary "overlay effect" to optimize the performance of concrete three-hole brick.The studies show that with admixture coating of aggregate during mixing, the strength and durability of recycled concrete three-hole have been significantly improved. Rural construction waste can be used to produce high performance recycled concrete three-hole brick after modified by admixture and its performance can meet the standard requirements of bearing wall material. This paper provides a theoretical basis and practical basis for rural construction waste used as recycled coarse aggregate preparation of new wall materials and it has high environmental and economic benefits.