Preparation and characteristics of aggregates by recycling municipal solid waste incineration fly-ash and other industrial waste through single-and double-step pelletization process

Recently across the globe, the use of recycled materials in the construction and building sector has drawn attention to bring sustainability. For this purpose, eco-friendly lightweight artificial aggregates are suitable alternative for natural aggregates. The municipal solid waste incineration fly-ash (MSWI-FA) (75%, 65%, 55%) along with marble sludge (MS) (15%, 25%, 35%) and ordinary Portland cement (OPC) (10%) as binder were used to prepare various mixtures lightweight artificial aggregates (LWA) through cold bonding pelletization (CBP) process. Before pelletization, the MSWI-FA were pre-treated via two-step washing with water, which significantly reduces the chloride and sulfates content. To enhance the performance of aggregates, they were surface treated with ground 50% granulated blast furnace slag (GGBFS), 20% silica fume (SF) and 30 OPC via CBP and these aggregates were named as double bonded. The double-bonded aggregates (DBAs) have shown improved performance as compared to the single-bonded aggregates (SBAs). The water absorption for SBAs is in the range of 12.87% - 14.21% and in case of the DBAs 16.62% - 17.12% was observed. Overall, the apparent density of aggregates was found to be in the range of 2.04 to 1.71 g/cm³, and mechanical strength was observed in the range of 2.1 to 1.05 MPa. The compressive strength of aggregates decreases as the content of MS increases from 15% to 35% and MSWI-FA decreases from 75% to 55% which is due to reduction in pozzolanic activity. The bigger MS particle size makes it less reactive and remains unreactive in aggregate’s matrix. The XRD analysis showed the formation of hydration products but have poor crystalline or amorphous because their peaks were overlapped by others, like calcite overlapped C-S-H while FTIR and TGA confirm their presences. The SEM analysis showed unreacted MSWI-FA and MS in SBAs samples along with the C-S-H gels in the form of continuous cluster with irregular shapes. The leaching analysis shows that the hazardous content was successfully solidified/stabilized in the aggregates matrix and surface treatment further reduces its leaching as it provides physical barrier.