Evaluation of physiochemical properties and microstructure of cement paste blended with saponified cooking oil and cetrimonium chloride

Sustainable development relies on recycling environmental resources, which includes the recycling of liquid and solid wastes by using them as obtained or after treatment. One such environmentally burdensome material is the used cooking oil, which this study examines after its treatment through saponification and blending with CTAC as a cationic surfactant. The study evaluated five cement paste mixes with different concentrations, ranging from 0% to 5% of saponified cooking oil (SCO). The results pointed out that SCO enhanced the workability and air content (0-30%) but therefore reduced density (2.0-1.39 g/cm³), thermal conductivity (0.72-0.25 W/m•K), and compressive strength (72.7-32.22 N/mm²) as a result of increasing porosity. On the other hand, water absorption decreased by 69% at 1%. SCO outperforms traditional foam cement due to SCO's hydrophobicity. Microstructural analysis (SEM) shows a homogeneous distribution of air voids in the cement paste matrix (~63.1 µm). The cement pastes with SCO dosages (1-5%) were blended with 1% cetrimonium chloride cationic surfactant (CTAC). The results show an increase in the air content (up to 49.5%) and therefore a reduction in density down to 1.010 g/cm³, thermal conductivity (0.20 W/m•K), and compressive strength (15.4 N/mm²) as a result of increasing porosity. On the other hand, water absorption increased about eight times compared to the reference sample at (5% SCO + 1% CTAC) due to high porosity. In conclusion, the utilization of SCO admixture resulted in a significant alteration in the performance of cement pastes. The addition of SCO has a positive effect on cement paste's permeability-related properties by reducing the water absorption into the hardened cement pastes, improving thermal insulation, and making them especially suitable for lightweight construction materials where moisture control is critical. Still, their mechanical characteristics are slightly decreased but within acceptable limits in these cases. These findings highlight the unique behavior of saponified cooking sunflower oil used in cement matrices. When 1% CTAC is blended into the SCO cement mix, the thermal insulation is improved due to the increase in the air content, but this addition reversely affects both compressive strength and water absorption, and remains in the acceptable range for a non-constructive building material.