A case study on performance enhancement and reliability assessment of lime re-stabilized waste lime soil

Abstract

The disposal strategy of waste lime soil (WLS), as a primary material excavated from the existing road subgrade renovation, has become increasingly critical with the growing emphasis on environmental sustainability and green construction practices. The recycling of lime re-stabilized waste lime soil (LRWLS) can not only solve the challenges of its disposal and the shortage of road subgrade fillers in current and future road renovation and expansion projects, but also can reduce the consumption of lime and avoid the disposal process by transportation transfer, thereby decreasing carbon emissions. Taking the renovation and expansion project of National Highway 312 in Jurong, Zhenjiang, China, as the research background, this study evaluates the engineering performances of WLS first, including their grading characteristics, basic physical properties, and residual active calcium oxide content, and then investigates the performance evolution and application effect of LRWLS. Their compaction characteristics, mechanical properties such as unconfined compressive strength (UCS), tensile strength (TS), shear strength (SS), and California bearing ratio (CBR) with various lime dosages are explored through a series of indoor experiments. Their enhancement mechanism is revealed by observing the changes in pore structure and chemical products at different curing times by Scanning Electron Microscopy (SEM) and conducting theoretical analysis based on the principle of lime stabilization. Finally, the application reliability of LRWLS in the engineering road subgrade is examined comprehensively by subsequent field investigations, including compaction degree, deflection value, and long-term reliability. The results indicate that the demolished WLS contains some large-sized uncrushed calcium nodules that can worsen the particle size distribution of LRWLS should be removed before recycling. The grading of WLS after removing these nodules is favorable, with a residual active calcium oxide content ranging from 0.8 % to 1.5 %. As the lime dosage increases, the maximum dry density of LRWLS decreases linearly, while the optimum moisture content increases. The UCS and TS of LRWLS show a trend of initially increasing rapidly and then gradually decreasing as the lime dosage rises. The UCS and TS of LRWLS with a lime dosage of 2 % increase to approximately three times that of WLS. An increase in lime dosage significantly enhances the internal friction angle of LRWLS, but has a limited effect on cohesion. Similarly, the expansion rate of LRWLS decreases remarkably with the lime dosage, while their water absorption increases slightly at a high lime dosage. Their CBR value increases significantly, but their growth rate gradually slows with the increase in lime dosage. The microstructure and chemical products present indicate that LRWLS has become noticeably clustered at an early curing time and formed a compacted structure with filling of carbonate gels over the curing time. The formation of a dense network structure in the later curing time contributes to the performance enhancement of LRWLS. Field-compacted LRWLS with a newly-added lime dosage of 2 % exhibits that it has been able to meet the design performance requirement of engineering road subgrade no matter of compaction degree and deflection value, even though the UCS growth rate of field core samples is slower than that of laboratory-cured samples, and their softening coefficient after soaking is relatively higher. LRWLS subjected to wet-dry cycles and freeze–thaw cycles can be characterized by two exponential damage models, although it is more likely to lose bearing capacity in wet-dry cycles than in freeze–thaw cycles. The findings of this study can provide important guidance and practical reference for the disposal and recycling of WLS in road renovation and expansion projects.