Influence of supplementary cementitious materials along with construction and demolition waste in pavement cement-treated sub-base applications

The research seeks to experimentally evaluate the utilisation of construction and demolition waste (CDW) in cement-treated sub-base, incorporating a blend of fly ash and lime. This involved mixing CDW-based recycled concrete aggregates (RCA) with natural aggregates in varying proportions (25%, 50%, 75%, and 100%) with a 25% increment. Additionally, 10%, 15%, and 20% of the cement (C) percentage was replaced with a mixture of fly ash and lime (FA + L). Overall, this investigation highlights the potential benefits of utilising CDW and waste fly ash in construction projects. The research involved conducting physical properties tests on natural aggregates and RCA, adhering to IS codes and MoRTH: 5th revision specifications. Strength and durability tests were performed in the laboratory, meeting IS, AASHTO Code and IRC: SP: 89 specifications. The physical and chemical properties of C + FA + L mixes with RCA blends were investigated. Numerous properties like specific gravity, Atterberg's limit, pH, compaction, UCS, and CBR were determined to understand the effect of these blends. By conducting SEM and XRD analysis, we are able to delve into the microstructural properties of the mixture containing RCA, fly ash, and lime. This is especially important as the high specific gravity of RCA results in an improved MDD for the C + FA + L blend. After testing various proportions, it was found that a combination of 50% RCA and 50% NA with 6% fly ash and 6% lime produced the best results. Not only did this mixture increase the UCS value from 0.24 to 1.09 MPa, but it also showed an increase in the modulus of resilience (Mr) value. By introducing fly ash and lime into RCA + NA, significant enhancements in strength properties are achieved, thanks to the formation of CASH gel and CSH, as evidenced by X-ray diffraction analysis. This is further exemplified by the clear reflections of C-S-H gel revealed in the SEM image of the original CDW mix sample.