Characterisation of cement bitumen-treated material using response surface methodology

In recent years, the pavement construction industry has been increasingly investigating the application of cement bitumen treated material (CBTM) as a base course solution. By integrating both cement and bituminous binders, CBTM formulations offer enhanced load-bearing capacity and resistance to permanent deformation while mitigating the susceptibility to shrinkage cracking typically associated with cement-stabilised layers. This study aims to systematically characterise CBTM mixtures for base course applications by evaluating the effects of different cement-to-bitumen (C/B) ratios. This study includes a comprehensive analysis of the curing period, cement, bitumen emulsion contents and their interactive influence on the volumetric and mechanical properties of CBTM mixtures. scanning electron microscopy (SEM) was also employed to investigate the microstructural morphology with varying C/B ratio. The mix design optimisation was accomplished using central composite design (CCD), a method within the framework of response surface methodology (RSM). Results show a positive correlation between the mechanical properties of the mixes with cement and the bitumen content, but cement was observed to have a greater influence than the bitumen emulsion. The optimised mix design was further validated through confirmatory testing, demonstrating the robustness and applicability of the proposed methodology for designing and predicting the performance of CBTM mixtures in pavement base layers.