A.O. Sojobi, R. Taiwo, B.A. Salami
City University of Hong Kong,
Hong Kong
Keywords: circular economy, high performance mortar, manufactured sand, waste glass sand, infrastructure durability and resilience, fly ash, waste glass powder decarbonization
Summary:
Circular economy (CE) is a promising concept for achieving sustainable urban and industrial development, green economic growth and sustainable development goals (SDG) 9 and 12. Infrastructure durability is a major concern of governments globally due to costly maintenance and replacement of infrastructure associated with the use of river sand and ordinary portland cement (OPC). This study explores complete replacement of river sand with waste glass sand and manufactured sand and partial replacement of OPC with waste glass powder and fly ash. Partially crushed post-consumer beverage waste glass bottles were washed and oven-dried at 105oC. Waste glass sand which passed through 4.75 mm sieve but retained on 2.36 mm sieve were collected as waste glass sand while the retained coarse waste glass portion were further crushed by ball-mill rotary drum to obtain waste glass powder (WGP). To ameliorate alkali-silica-reaction (ASR)-induced shrinkage, waste glass sand was treated by soaking in GGBS (ground granulated blast furnace slag), fly ash and metakaolin before oven-dried at 105oC. High performance mortars were prepared at binder aggregate ratio of 1: 3 using L9 Taguchi orthogonal experiments while combined mixture design of experiment in conjunction with response surface methodology was used to investigate effects of binary replacement of ordinary Portland cement (OPC) with waste glass power and fly ash as well as binary replacement of river sand with treated waste glass fine aggregates and manufactured sand to produce high-performance mortar suitable for aggressive sulfate-rich environments. The recommended optimum mixture was 15% waste glass powder + 25% fly ash as partial OPC replacement combined with 25% GGBS-treated waste glass sand and 75% manufactured sand as 100% complete replacement of river sand. Manufactured sand has consistent, higher quality and less pollutants due to its controlled production environment compared to river sand resulting in enhanced infrastructure durability. On the other hand, waste glass powder enhances infrastructure durability through reduction of total sorptivity, water absorption, apparent porosity and mass loss deterioration to acid attack and other aggressive agents while fly ash and GGBS reduces alkali silica reaction (ASR)-induced shrinkage cracking. Furthermore, waste glass sand enhances infrastructure durability and resilience by enhancing mechanical properties, improving resistance against chemical attack due to its chemically inert nature and improve resilience against effects of temperature fluctuations. In addition, combined replacement of river sand by waste glass sand and manufactured sand reduces river sand dredging, coastal erosion, improve mechanical properties due to improved bonding and microstructure densification and ensures fast setting time important for fast and durable construction of roads, underground and offshore infrastructures as well as prefabricated concrete structures. Scientometric analysis revealed limited collaborations to drive circular economy of fly ash, waste glass and slag. Therefore, this study called for collaborations between academia, industry, government and countries to drive circular economy and decarbonize cement and steel industries.