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Glass-based goods are produced and consumed in relative abundance, making glass a material that is found in most households, thereby leading to its accumulation in alarming quantities throughout the globe and posing an environmental challenge. This being said, glass has been widely acknowledged to possess a variety of desirable physiochemical properties, making it suitable for utilisation as an engineering aggregate. The properties include its non-biodegradable nature, resistance to chemical attack, low water absorption, hydraulic conductivity, temperature-dependent ductility, alterable particle gradation, and its availability in a multitude of forms/chemical compositions. Owing to these properties, glass has been employed in a myriad of civil engineering studies and field trials to assess its efficacy as an engineering aggregate and to provide sustainable management schemes for waste glass. These studies/trials have incorporated glass in many forms, including fine recycled glass (FRG), medium recycled glass (MRG), coarse recycled glass (CRG), glass powder, glass fibres, foamed glass, and glass-based geopolymers. Although the beneficial properties of glass can be exploited in numerous engineering endeavours, this review paper focuses on the possible application of glass to subsurface layers of pavements. In turn, the current study centres on research studies/trials presenting results on the physicochemical, mechanical, and durability aspects of pavement layers (base, subbase, and subgrade) containing pure glass samples or glass as percentage replacements in materials, including but not limited to unbound granular materials (i.e., recycled concrete aggregate (RCA) and crushed rock (CR)) and clay soils. Through the knowledge compiled in this review article, it is reasonable to state that glass shows solid potential as a road pavement material.

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Low plasticity clays are found in abundance worldwide, exerting undue stresses on civil structures, road pavements and railway infrastructure, owing to the periodic settlement caused by their low bearing capacity and slight swelling potential. They are often encountered as natural soil when constructing road subgrade and have the potential to compromise the integrity of the entire pavement system unless improved appropriately. Furthermore, the accumulation of vast quantities of non-biodegradable glass waste is identified as a challenge in many countries. Considering the above, this paper aims to provide a sustainable solution by studying the effect of crushed glass (CG) at varied inclusions of 0, 5, 10, 15 and 20% in a clay subgrade. The testing procedure implemented includes three distinct testing phases, namely, material properties, microstructural properties and mechanical strength tests. The material property tests involved particle size distribution, X-ray fluorescence (XRF) and X-ray diffraction (XRD) testing. Microstructural tests considered include scanning electron microscope (SEM) and micro-CT (CT) testing, which enabled a vital understanding of how the introduction of glass affects the internal structure of the clay matrix, where an increase in the porosity was evident upon adding CG. The mechanical testing phase involved standard compaction, unconfined comprehensive strength (UCS), California bearing ratio (CBR), resilient modulus and swelling–shrinkage tests. It can be concluded that introducing CG improved the clay’s mechanical strength with respect to UCS, CBR and resilient modulus whilst also reducing its swelling potential, where the optimum inclusion of CG at 15% best enhanced the mechanical strength properties of the low plasticity clay.

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