Investigation into the mechanism and performance characteristics of ECOroads enzyme-modified lateric soils to predict pavement performance

Abstract

Recently, suitable virgin materials possessing the desired engineering properties are depleting and therefore increasing the cost of investments. Soil stabilization techniques using either traditional or non-traditional methods have been adopted to combat this challenge. However, traditional stabilization techniques have some shortcomings and environmental concerns. Innovations in pavement materials and engineering have emerged using non-traditional stabilization techniques to enhance soil engineering properties, address environmental concerns, and promote sustainable development. This study examines the influence of ECOroads enzyme, one of the non-traditional additives on the fundamental mechanism of enzyme-based lateritic soil stabilization, engineering properties, and response modeling of variables. Response Surface Methodology (RSM) which combines both experimental designs and statistical techniques for empirical model building and optimization was adopted. A novel method using STATEASE 360 software and a popular central composite design in RSM was used to build the model to optimize processes and predict performance. Soil samples were prepared using three dosages of ECOroads enzyme R2, R6 & R7 in replicates for tests at each curing time of 0, 7, 14 and 28 days as per the design of the experiment. The test results showed an increase in CBR values from 34% to 101%; UCS from 289kPa to 1349kPa after 28 days of curing. A reduction in Liquid Limits and an increase in Plastic Limits were registered, resulting in a reduction in Plasticity Indices of the soil materials. The developed RSM predictive models of independent variables (enzyme dosage, curing time & compaction levels) and two responses (UCS & CBR) were significant (p ≤ 0.05) and the diagnostic has a strong relationship between the measured and predicted values. The optimal response values of CBR of 76% and UCS of 994kPa were achieved at an enzyme dosage of 0.047mL/kg of soils, cured for 16days when samples were compacted at 98% of the MDD at optimal moisture content with desirability of 0.727. Microstructural tests were conducted on ECOroads enzyme-modified soil samples and results revealed an increase and reduction in some soil minerals highlighting variations in atomic counts and images compared to the control specimens. These results of the microstructural tests for the mechanism might explain the increase in strength, stability, and stiffness registered during macro-structural tests. From the results of this study, ECOroads enzyme can be used to stabilize marginal soil materials to meet requirements of new pavement layers and addresses environmental concerns.