Effect of Fly Ash on Performance and Design Slab Thickness of Jointed Plain Concrete Pavements

The effect of fly ash (up to 30% replacement level) on the compressive strength and coefficient of thermal expansion (CTE) of concrete mixtures up to 360 and 28 days, respectively, was investigated. The results show that 0% and 30% fly ash mixtures presented 30%–55% and 52%–116% strength gain over 360 days. The fly ash mixtures demonstrated lower CTE than mixtures without fly ash. AASHTOWare Pavement Mechanistic-Empirical Design (PMED) software was utilized to study performance predictions of jointed plain concrete pavements (JPCPs). Level 3 PMED simulations predict that fly ash increases pavement roughness and transverse cracking and reduces joint faulting. However, these simulations use 28-day strength data, which do not account for the long-term performance of fly ash. Increasing the slab thickness of the 30% fly ash JPCP mixtures to 1 in. can present comparable performance indicators to those of 0% fly ash mixtures. Level 2 simulations show a better depiction of pavement performance, as they incorporate a wider picture (up to 90 days) of strength gain than Level 3 simulations. However, the 90-day strength data do not completely portray the long-term strength gain of the fly ash–based concrete mixtures either. This study highlights limitations arising because PMED software limits the incorporation of strength data to 90 days under Level 2 simulations, whereas fly ash–based paving concrete develops significant strength at later ages. Therefore, it is necessary to validate these findings with the field performance of in-service pavements and to incorporate the long-term strength gain of fly ash mixtures in PMED software.