Utilization of wollastonite, jarosite, and their blends for the sustainable development of concrete paver block mixes containing reclaimed asphalt pavement aggregates.

While several research studies considered the utilization of reclaimed asphalt pavement (RAP) aggregates for asphalt and concrete pavements, very few attempted its possible utilization for precast concrete applications like concrete paver blocks (CPBs). Moreover, few attempts made in the recent past to improve the strength properties of RAP inclusive concrete mixes by incorporating certain supplementary cementitious materials (SCMs) have reported an insignificant or marginal effect. The present study attempts to comprehensively investigate the utilization potential of some locally and abundantly available materials having suitable physicochemical properties to improve the performance of a zero-slump CPB mix containing 50% RAP aggregates. The studied filler materials, namely, wollastonite (naturally occurring calcium metasilicate mineral) and jarosite (hazardous zinc industry waste), were used to replace 5-15% and 10-20% by volume of Portland cement in the 50% RAP CPB mix. Apart from their individual effects, the efficacy of wollastonite-jarosite blends was also investigated. Considering the lack of indoor storage facilities and economic aspects of CPBs, the influence of water spray curing regime on the performance of the RAP CPB mixes was studied and compared to that of continuous water curing regime. Inclusion of the considered fillers was found to statistically and significantly enhance the flexural strength, tensile splitting strength, and abrasion resistance of the 50% RAP CPB mix; however, the compressive strength (in most cases), permeable voids, water absorption, and water permeability properties showed an insignificant improvement. Results of thermogravimetric analysis confirmed the occurrence of pozzolanic reactivity, and microstructure analysis revealed improvements in packing of concrete matrix and ITZ with filler inclusion qualitatively substantiating the improvements in strength and durability characteristics. The toxicity characteristics of heavy metals that may leach from the hazardous jarosite-based RAP CPB mixes were found to be within permissible limits. Based on the performance requirements specified by IS, IRC, and ASTM standards, all the RAP CPB mixes with filler inclusions fulfilled the acceptance criteria for heavy traffic applications, and water spray curing can enact as an alternate method for curing these mixes. However, to avail maximum performance benefits, it is recommended to use 5% wollastonite, 15% jarosite, and a combination of 10% wollastonite and 10% jarosite as a Portland cement substitute to produce sustainable eco-friendly RAP CPB mixes.

Novel concentration master curve and rheological characterization of recycled asphalt binders.

The recycling of asphalt pavements requires a good understanding of the material's characteristics. However, the rheological behavior of recycled binder is still not well understood. In this study, a novel method is introduced to construct the master curve of the recycled binders. The concentration of reclaimed asphalt pavement (RAP) binder is used to find the shift factors of the master curve. This master curve is called the concentration master curve (CMC). To verify the applicability of the concept, the CMC was plotted for three different RAP sources procured from two states and the capital of India. The percentage of RAP binder content in the recycled binders was varied (0, 15, 25, 40, 65, 80, and 100%) by weight of the total binder. In all three cases, smooth master curves were obtained. To calculate the allowable RAP, an alternative approach based on the damping energy area (DEA) of recycled binders was proposed. It was found that the allowable RAP content based on the DEA criteria was 40-50% less compared to the conventional high PG temperature (PGH) criterion. An attempt is made to understand the rheological interaction between the RAP binder and RA using the recycled binder compatibility index (RBCI). It was observed that the RAP source is the determining factor behind the compatibility and interaction level between the RAP binder and RA in a recycled binder.