Performance of biocement treatment in improving the interfacial properties of recycled aggregate concrete

Variable quality of recycled aggregates especially attached mortars leading to weak interfaces is a primary drawback of recycled coarse aggregate (RCA). This investigation explores strengthening of such aggregates by biocement treatment and compares it with the conventional cement slurry treatment. The effect of the treatments on the aggregates has been recorded in terms of water absorption and mechanical properties. To study the concrete-aggregate interface, a novel method of fabricating concrete cubes with one aggregate has been devel-oped. Damage evolution at the interfaces has been recorded with advanced monitoring techniques. Micro -structural behaviour and elemental composition in the interface were also recorded. The test results show that the biocement treatment reduces the water absorption of RCA by about 71%. A microstructural study demon-strates that biocement, due to its considerably low viscosity, is able to penetrate the porous interfacial mortar within RCA and densify it. The micromechanical properties using nanoindentation provides more insights in improving of interfacial transition zones. The treatment improves the aggregates to a level that it can be used to replace the natural aggregates without compromising its performance.

Automated summary

The variable quality of recycled coarse aggregate (RCA), especially the attached mortars leading to weak interfaces, is a major drawback. This study investigates the strengthening of RCA using biocement treatment and compares it with conventional cement slurry treatment. The effects of the treatments on water absorption and mechanical properties of the aggregates are recorded. A novel method of fabricating concrete cubes with one aggregate is developed to study the concrete-aggregate interface. Advanced monitoring techniques are used to record damage evolution at the interfaces. Microstructural behavior and elemental composition in the interface are also recorded. The test results show that biocement treatment reduces the water absorption of RCA by about 71%. Microstructural study demonstrates that biocement can penetrate the porous interfacial mortar within RCA and densify it due to its low viscosity. The micromechanical properties using nanoindentation provide more insights into improving interfacial transition zones. The treatment improves the aggregates to a level where they can replace natural aggregates without compromising performance.