Research On The Application Of Recycled Aggregates From Waste Brick In Concrete

Recycled concrete is new kind of green materials, and it is an effective way to solve the problem of construction waste recycling. Currently, the durability of concrete is becoming attracting more and more attention, and both of the contents and depth of the research are also expanding. Because of the addition of recycled aggregate, research on the durability issues of recycled concrete becomes more complicated, and related mechanism analysis is also difficult. This paper mainly presented the durability of recycled concrete with aggregates from waste bricks.In the experiment, replacement rate of recycled brick aggregate is 30%, and the dosage of fly ash and superplasticizer are 10% and 1.5% respectively. Concrete samples were prepared based on the mix proportion of C40 concrete. Due to the water absorption of recycled brick aggregates, the amount of water increased. The additional amount of water in this experiment is 10%. First of all, compressive strength, flexural strength and dynamic elastic modulus of recycled concrete were measured. Then, the durability and pore structure of concrete with recycled aggregates from waste bricks were investigated. The conclusions are given as follows :Compare with natural aggregate concrete which have same level concrete mix, there is some difference between recycled concrete and normal concrete. The compressive strength and flexural strength decreased by 13.47% and 4.38% respectively. The miss of flexural strength was greater. The dynamic modulus change was also obvious, whose declining proportion reached 11.18%. Although both compressive and flexural strength of recycled concrete decreased, but the strength value also meet the requirement of C40, and average reached 53.78 MPa.The durability of concrete with recycled aggregates from waste bricks were also studied. For shrinkage performance, the shrinkage strain of recycled concrete after 3 day age reached 690×10-6, which was increased by 46.8% compared with normal concrete; The average penetration height of recycled concrete water seepage was 15 mm, which was 25% higher than that of ordinary concrete; In the case of dry conditions, air permeability of recycled concrete reached 0.058×10-12m2, while under wet conditions it reached 0.032×10-12m2, which was increased by more than 50% than that of ordinary concrete; Resistance to chloride ion penetration was also measured, and chloride ion diffusion coefficient was 9.37×10-12m2/s,which was also 86.1% higher than that of ordinary concrete.For sulfate attack after 20 cycles of wet and dry, there was no mass loss for the recycled concrete, and the relative dynamic modulus of elasticity is maintained at 98% or more. The resistance of carbonation of brick aggregate recycled concrete was good, and the carbonation depth after 28 d was 0 mm. Recycled concrete also showed frost resistance, after 250 freeze-thaw cycles, mass loss rate of recycled concrete was only 0.8%, and relative dynamic modulus remained above 71.1%. The specimen was not damaged.Pore structure of recycled concrete after hardening was also analyzed. The result indicated that, the average chord inside the recycled concrete was 0.065 mm, and bubble spacing factor was 0.093 mm, which was 0.025 mm and 0.005 mm higher than that of normal concrete. So, the frost resistance and the carbonation resistance of recycled concrete was excellent due to the low bubble spacing factor.Durability of recycled concrete is still in its infancy, there are a lot of problems to be solved. Durability issues of recycled concrete like how to link the laboratory test results and the actual environment durability damage and how to combine the macroscopic properties and microstructure of recycled concrete still need further study. Durability standards for recycled concrete is not perfect, and need to improve the standards and guidelines to regulate the design of durability and maintenance in the use process and assessment of building life.