Effect of Warm Mix Asphalt Additives and Marginal Aggregates on Mechanical Properties of Semiflexible Asphalt Mixtures

Abstract

Semi-Flexible Asphalt (SFA) mixture is a wearing course in which Open-Graded Asphalt (OGA) mixes having air voids of 20-35% are grouted with cement mortar. In the present work, an effort was made to assess the effect of the Sand-Cement (S/C) ratio in determining the optimal grout proportions. Taguchi technique combined with Grey Relational Analysis (GRA) was used to obtain the optimal grout proportion. The optimum grout was obtained for an S/C ratio of 0.6, a water-to-cement (W/C) ratio of 0.40, and a polycarboxylic ether-based superplasticizer (SP) content of 0.75% by weight of cement. The SP content was identified as the most influencing factor, along with the S/C ratio. To investigate the effect of aggregate gradation and bitumen type on the mechanical properties of SFA mixtures, a new aggregate gradation with neat and modified bitumen was used to prepare OGA mixtures and later grouted with optimal grout proportion. The Marshall Stability, compressive strength, Indirect Tensile Strength, Cantabro loss, fatigue resistance, moisture and Oil spillage resistance tests were conducted. The results showed that the SFA mixtures prepared with Polymer- Modified Bitumen (PMB) and the new aggregate gradation have better mechanical properties, implying the significance of bitumen type and aggregate gradation. Due to the enormous generation of construction and demolition waste, processing and utilising recycled aggregates in pavement layers, particularly in asphalt layers, is deemed necessary to reduce the disposal problem and depletion of natural resources. Evaluating the performance of asphalt mixtures with recycled aggregates is complex due to the heterogeneity of materials. Therefore, the potential of utilizing the recycled aggregates in semi-flexible asphalt mixtures was explored along with the ferrochrome slag (FCS) aggregate. Though the FCS aggregates exhibited good mechanical and engineering properties, studies on the utilization of ferrochrome slag aggregate are limited. Therefore, in the next phase of this research, the Natural Coarse Aggregates (NCA) in OGA were replaced by Recycled Concrete Aggregates (RCA) (50% and 100%) and Ferrochrome Slag aggregate (FCS) (100%), and the effect on the mechanical properties of SFA mixtures were evaluated. The RCA was obtained by crushing the laboratory-prepared concrete specimens and passing them through the jaw crusher, followed by the ball-milling. SFA with 100% FCS exhibited higher stability, compressive strength, moisture resistance, fatigue life and rutting resistance due to strong aggregate having good impact value. At the same time, SFA with marginal aggregates (RCA and FCS) met the requirements of IRC SP 125. With the objective to reduce working temperatures of OGA mixtures, three Warm Mix Asphalt (WMA) additives, Sasobit (3%), Rediset (0.8%) and Zycotherm (0.1%), were added to PMB 40. The SFA mixtures prepared using WMA-modified binders were evaluated, and concluded that the SFA with Sasobit exhibited better mechanical properties than other mixtures, while the SFA with Rediset exhibited lower mechanical properties; however, all the SFA mixtures satisfied the specifications of IRC SP 125 2019. In the present study, a new approach, based on percentage coating, was adopted to determine working temperatures. The WMA additives reduced mixing and compaction temperatures by 30 oC and 28 - 33 oC. In the final phase, Semi-Flexible Asphalt (SFA) mixtures were prepared using marginal aggregates (50% RCA, 100% RCA, and 100% FCS) combined with WMAmodified binders. The incorporation of WMA additives allowed for a reduction in mixing and compaction temperatures by 25–35°C and 28–33°C, respectively. However, the mixtures 50RCA-R, 100RCA-S, 100RCA-R, and 100RCA-Z showed higher Cantabro weight loss, indicating lower durability, and were therefore excluded from further evaluation. The 100FCS-S mixture exhibited the highest fatigue life across all stress levels. The rut depth and DS results for SFA mixtures with FCS displayed similar values, emphasizing the significant influence of the aggregate quality or type. Only the mixtures 50RCA-S, 50%RCA-Z, 100FCS-S, 100FCS-R, and 100FCS-Z met the IRC requirements. Among these mixtures, SFA mixtures prepared with Sasobit additive and FCS aggregate performed better than other additives and marginal aggregates.