Optimizing the potential use of waste palm oil clinker powder in cementitious grouts for semiflexible pavements using response surface methodology.

Cement is one of the major industrial sources of global CO₂ emissions, which highlights the need for sustainable alternatives in pavement construction. In this context, the present study examines the partial substitution of cement with waste palm oil clinker powder (POCP) to develop cementitious grouts for semi-flexible pavements (SFP). In this study, POCP was used at different proportions (0–30%) across water–cement ratios (W/C) ranging from 0.40 to 0.55, in the presence of a superplasticizer to improve grout flowability. The performance of the grout was assessed by measuring flowability and compressive strength at 1, 7, and 28 days. The experiments were designed using Response Surface Methodology (RSM), which was used to analyze statistical correlations and determine the optimal POCP content and W/C. The optimized grout mixture with 20% POCP was subsequently used to produce SFP specimens (PSFP), which were assessed for marshall stability, moisture susceptibility, indirect tensile stiffness modulus, cantabro loss, and resistance to fuel spillage, and then compared with control SFP (CSFP) and conventional hot mix asphalt (HMA). Microstructural analysis using Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS) indicated that the addition of POCP increased the porosity relative to the control sample. The marshall stability for both CSFP and PSFP was more than twice that of conventional HMA with a moisture-induced loss of about 9%, compared to about 16% in HMA. However, the rigid nature of SFP and the interface between the grout and bitumen-coated aggregates, which creates a weak zone, led to greater mass loss under impact loading than in HMA, highlighting the need for higher viscoelasticity in SFP samples.