Experimental study on recycled steel fiber concrete
Some basic properties of recycled steel fiber aggregate were tested, such as surface features, water absorption, apparent ensity, crushing index, cube compressive strength and so on. Recycled steel fiber aggregate were used to replace the natural aggregate by 0%, 25%, 50% and 100% proportion to make concrete. Afterward, compressive strength, splitting tensile strength and flexural strength were investigated at ages 3, 7 and 28 days. The results showed that thorn appearance of recycled steel fiber aggregate makes packing density decrease, crushing value and absorption increase. The compressive strength, splitting tensile strength and flexural strength of the recycled concrete depend on the mix proportions. Generally, the strength of recycled concrete can be 15–25% lower than that of concrete made with virgin aggregate.
Properties of Recycled Coarse Aggregate and Its Influence on Recycled Concrete
Some properties of recycled coarse aggregate (RCA) were tested. The basic performance of recycled concrete with or without considering the high water absorption of RCA was studies. The results indicate that properties of RCA are different from that of natural coarse aggtegate (NCA), mainly characterized as low density, high water absorption and crush index as well as low soundness. The slump and compressive strength of concrete with recycled aggregate are lower than that of concrete with natural aggregate when high water absorption of RCA is not considered. However, when high water absorption is considered, the compressive strength decreases further, while the slump can be similar to that of concrete with natural aggregate.
Study on Relationships between Strength Indexes of Recycled Concrete
The influence of different recycled coarse aggregate (RCA) replacement ratios on the strength of recycled concrete was investigated. Based on the data regression, the relationships between the cube compressive strength and other strengths are obtained. It is shown that the compressive strength of recycled concrete is lower than that of normal concrete, while the flexural strength is only marginally less compared to normal concrete and the interrelationship of strength indexes for recycled concrete is different from that of normal concrete. Finally, some basic strength indexes of C20～C40 recycled concrete with 100% RCA are proposed.