Trade-Off Between Water-Absorption Reduction and Strength-Gap Recovery at Three KH560 Treatment-Solution Concentrations for Airport-Pavement Recycled-Aggregate Concrete

This study investigated whether the nominal 3-glycidoxypropyltrimethoxysilane (KH560) treatment-solution concentration associated with the lowest recycled coarse aggregate (RCA) water absorption also yielded the greatest recovery of concrete strength. RCA obtained from a decommissioned airport pavement was treated using solutions with nominal KH560 concentrations of 8%, 10%, and 12% and used as 100% of the coarse aggregate. All mixtures had the same target grading and nominal effective water-to-cement ratio of 0.360. Relative to untreated RCA, the 10% group (SS10) showed 18.7% lower water absorption and a 22.7% lower crushing index. Its 28-day compressive, flexural, and splitting tensile strength means were 13.8%, 31.3%, and 26.4% higher than the corresponding untreated recycled-aggregate concrete means. The SS10 flexural-strength mean reached 94.7% of the natural-aggregate concrete mean. The 12% group (SS12) showed the lowest water absorption at 64.3% below that of untreated RCA, but lower strength means than SS10. Thus, the concentration favored by water absorption differed from that favored by the three measured strength properties. The results provide a preliminary laboratory basis for selecting KH560 treatment levels for further evaluation of the investigated airport-pavement RCA.