Physical and microstructural properties of recycled concrete aggregates treated by tetraethyl orthosilicate

Property improvement is the key process for realizing the high value-added utilization of recycled concrete aggregates (RCAs). This paper aims to improve the quality of RCAs by employing the chemical agent tetraethyl orthosilicate (TEOS) to harden and fill the porous structure of adhered mortars. For this purpose, a series of experiments were conducted to examine the influence of reaction conditions, including concentrations, tem-peratures, and soaking times of the TEOS treatment, on the physical and microstructural properties of RCAs. Results indicate that the treatment generally increases apparent relative density and decreases water absorption, crushing value, and the amount of the adhered mortar. The physical properties of RCAs treated by 1:1:40 concentration solution at the temperature 40 C with 6 h soaking time were found to attain significant improvement. For example, more than 3.71% increase of apparent relative density and 31.02%, 20.49%, and 13.25% lowering of water absorption, crushing value, and the amount of the adhered mortar, respectively were evidenced. Obvious reduction of the size and number of adhered mortar pores was observed through mercury intrusion porosimetry (MIP) post treatment. Accordingly, tiny particles at the pores and micro cracks in the SEM images of RCAs were observed. Furthermore, reduced Ca/Si ratio was also discovered from the X-ray fluores-cence spectrometry analysis of the treated RCAs, implying that the adhered mortars pores were filled with the hydrolysate of TEOS. These findings contribute to the development of a more efficient chemical solution for improving the properties of RCAs.

Automated summary

This study aims to improve the quality of recycled concrete aggregates (RCAs) by using the chemical agent tetraethyl orthosilicate (TEOS). The results show that the treatment with TEOS can significantly enhance the physical properties of RCAs, including apparent relative density increase and reduction in water absorption, crushing value, and amount of adhered mortar. The treatment also leads to a decrease in the size and number of adhered mortar pores and improvement in the microstructure of RCAs.