Study on the modification mechanism of recycled brick-concrete aggregate concrete based on water glass solution immersion method

Recycling construction waste into concrete through the process of crushing and screening is a vital method of resource conservation. Recycled aggregates often contain imperfections such as micro-cracks, necessitating modification to produce high-performance concrete. Water glass, an economical modifier, addresses this need. However, recycled aggregates often contain concrete and brick aggregates and are difficult to completely separate. At present, there are few studies on the modification of recycled brick aggregates, and there is a lack of comprehensive and systematic research from the aggregate modification mechanism to the macroscopic working performance and mechanical properties of recycled concrete. Based on the above problems, the modification effect and modification mechanism of water glass solution on recycled brick aggregate and recycled concrete aggregate were studied by basic physical properties, SEM, and XRD tests. The relationship between macroscopic mechanical properties and the microstructure of modified recycled brick-concrete aggregate concrete was studied by compressive, flexural, and splitting tensile tests, XRD, NMR, and SEM. The results showed: (1) The best modification scheme for recycled brick aggregate and recycled concrete aggregate is the concentration of water glass solution at 4 % with a soaking time of 5 h; (2) the mechanical properties of recycled brickconcrete aggregate concrete are the best when the brick-concrete ratio is 5:5, and the compressive strength, flexural strength, and splitting tensile strength are increased by 10.84 %, 11.61 %, and 15.08 %, respectively; and (3) the water glass solution improved the pore structure and interfacial transition zone of recycled aggregate. The proportion of harmless pores and less harmful pores increased by 5.66 % and 13.3 %, respectively, and the proportion of harmful pores and more harmful pores decreased by 6.25 % and 12.7 %, respectively. The research results can promote the resource utilization of construction waste.