Mechanical performance and durability assessment of crushed rock road base stabilised by enzyme-induced carbonate precipitation

The growing demand for sustainable, durable road pavement infrastructure has spurred interest in alternative stabilisation techniques to improve the performance of road materials. This study investigates the application of enzyme-induced carbonate precipitation (EICP) to well-graded crushed rock base (CRB), a commonly used pavement material. Unlike previous EICP studies that focused mainly on idealised granular materials such as poorly graded sands, this study evaluates the performance of EICP in a well-graded aggregate. Mechanical, durability and microstructural characteristics of EICP-treated CRB were investigated using Unconfined Compressive Strength (UCS), Indirect Tensile Strength (ITS), wetting–drying durability tests and Scanning Electron Microscopy (SEM) analysis. The results indicated that the performance of the CRB was greatly improved with increasing cementation level. The compressive strength obtained was 5.12 MPa at a CaCO₃ content of only 15.3%, which was 39 times higher than that of the untreated CRB. The tensile resistance increased 54 times, reaching 1.28 MPa at a CaCO₃ content of 15.3%. Durability assessment confirmed the stability of the cementitious bond, with no significant strength loss after wire-brush abrasion before wetting–drying cycling. SEM observations confirmed progressive densification of carbonate bridges between EICP-treated CRB particles as cementation increased. The achieved strength levels indicate that EICP treatment can transform the CRB from unbound behaviour to bound material behaviour, consistent with pavement material classifications. The results of this study demonstrate that EICP can significantly enhance the strength and durability of CRB, even at comparatively low carbonate contents, highlighting its viability as an alternative to traditional Ordinary Portland cement-treated road base materials.