This study investigates the influence of aggregate gradation, water-to-cement ratio (W/C), pressing pressure, and curing time on the density and compressive strength of dry-pressed concrete bricks. The experimental program incorporated two aggregate gradations (fine and coarse), three W/C ratios (0.35, 0.40, 0.45), and three pressing pressures (15, 25, and 35 MPa), with testing conducted at 7 and 28-day. A total of 108 samples were prepared and analyzed following ASTM standards. Response Surface Methodology (RSM) was applied to establish predictive models and identify significant factor interactions. Results demonstrated that both density and compressive strength increased with pressing pressure up to 35 MPa, attributed to improved particle packing and reduced void content. Fine aggregate mixtures achieved slightly higher strength and density compared to coarse aggregate ones, due to their enhanced packing efficiency and lower porosity. At 7-day, strength improved significantly with pressure, reaching up to 20.4 MPa for fine aggregates (W/C = 0.45, 35 MPa). After 28-day, all mixtures exceeded the ASTM C90 minimum requirement for load-bearing masonry (13.8 MPa), with the highest strength (27.9 MPa) recorded for coarse aggregate mixes at W/C = 0.35 and 35 MPa. Statistical analysis confirmed that the developed RSM models exhibited excellent predictive accuracy, with R2 > 0.80, low lack-of-fit, and high adequate precision (> 8). Quadratic models effectively described the interaction effects between pressing load and W/C ratio on density and compressive strength, except for the 28-day strength of fine aggregates, which followed a linear trend. Three-dimensional response surfaces highlighted the combined influence of pressing load and W/C ratio, revealing optimal conditions for maximizing both density and strength. The findings emphasize the interdependence of mixed design parameters and forming energy in optimizing the mechanical performance of pressed bricks.
Babalghaith et al. (Wed,) studied this question.