Engineering and Environmental Assessment of Foam Glass Lightweight Aggregate for Pavement Application

Foam-Glass Lightweight Aggregate (FG-LWA) is an innovative lightweight material based 95% on waste and recycled glass. Several European countries use this type of material in the pavement structure and mainly as lightweight fill material. The major advantage of the FG-LWA is being more than 10 times lighter than traditional mineral aggregates, which makes it an ideal solution in cases where the dead load of the aggregates is an issue. The objective of this thesis is to evaluate and assess the potential of using FG-LWA, as an alternative to other lightweight fill materials such as Expanded Polystyrene (EPS) Blocks, in flexible pavements structures. \nPhysical and mechanical properties of two commercially provided types of FG-LWA were previously studied at the CPATT laboratories of the University of Waterloo. To this end, particle size distribution, particle density, water absorption, minimum and maximum dry densities, California Bearing Ratio (CBR), Los Angles (LA) abrasion, resilient modulus, Mico-Deval and freez-thaw resistance of the material were evaluated by Schneider (2016). The results from this previously conducted study are summarized in this thesis and are used to determine whether the FG-LWA material is suitable to be employed as an alternative granular material in pavement construction, and whether it conforms to the requirements of the Ontario Provincial Standard Specification (OPSS) 1010 for granular A, M, O, S and B. \nIn this thesis, it was deemed necessary to further investigate the effect of changes in the manufacturing processes on the formulation and microstructure of the FG-LWA with the aim of enhancing its mechanical properties for pavement construction applications. Therefore, the manufacturing processes were modified to adjust the microstructure (e.g. shapes and sizes of the pores) and phase compositions. Furthermore, in order to produce an enhanced FG-LWA, the application of ceramic colors, other glassy raw materials and glass-ceramics with a controlled microstructure was also investigated in this thesis. Examining the microstructure of the products indicated improvements in the physical characteristics of the enhanced FG-LWA as compared to the original product containing waste glass. Incorporation of coloring oxides in the foam formulation was also examined as an innovative method to increase the mechanical strength of a colorful product. In addition, chemical evaluation was conducted based on the results of leachate test. The results were evaluated thoroughly, and further tests were conducted at the Golder & Associates laboratories, accordingly. \nGiven the considerable economic, environmental and societal impacts related to pavement construction and maintenance activities, it is crucial to evaluate the sustainability of the proposed pavement structure with FG-LWA. Several techniques are available to measure sustainability of a pavement structure. In this thesis, the mechanistic pavement design approach, along with a conceptual Life Cycle Assessment (LCA) model are used to evaluate the effectiveness of using FG-LWA as an alternative lightweight fill material as compared to the commonly used Expanded Polystyrene (EPS). For the purpose of mechanistic evaluation of FG-LWA application in the pavement structure, an existing Ministry of Transportation (MTO) project was re-evaluated and the results were used as the baseline of this study. The re-evaluation consisted of two phases of pavement design. Under phase one, the same pavement structure proposed by the MTO was adopted identically, except that the EPS in the original design was replaced with the same thickness of the FG-LWA material. In the second phase, four scenarios with different structural layer types and thicknesses were studied. The objective of the second phase was to find different, but equivalent, pavement structures with the use of FG-LWA, while achieving equal or smaller values than the original MTO design for the critical strains at the bottom of the asphalt layer and on top of the subgrade layer. To this end, KenPave program was used to determine the stresses and strains in the pavement layers using a multilayer elastic approach. \nFinally, LCA approach was used to quantify the relative environmental impacts of using FG-LWA and EPS in the pavement structure. The SimaPro software program was used to analyze the performance of the products with respect to sustainability measures. Two flexible pavement structures, previously designed at the University of Waterloo for a specific set of traffic and climatic conditions (Schneider, 2016), were used in the LCA study. The first pavement structure, considered as the reference scenario, used Expanded Polystyrene (EPS) as lightweight fill material. In the second scenario, the EPS was replaced by FG-LWA, and thicknesses of all other layers (i.e. asphalt concrete and granular layers) were determined using the AASHTO 93 Pavement Design Approach, hence the two pavement structures could be assumed equivalent and structurally comparable. The environmental impact categories considered in the LCA studies included: Ozone depletion potential, global warming potential, acidification potential, eutrophication potential, carcinogens, noncarcinogens, smog potential, respiratory effects, ecotoxicity, and fossil fuel depletion. The impacts are calculated using the characterization factors from the TRACI 2.1 LCA model. Two methods of manufacturing foam glass are evaluated, namely using electricity versus natural gas in Ontario. Based on this comparison, it was determined that it is feasible to transfer the new foam glass technologies to Canada’s road network instead of using other non-environmentally friendly materials. The results indicate that FG-LWA can be used as a light fill material in the flexible pavement structure to achieve better or equivalent structural capacity as compared to the traditional EPS. The environmental impacts assessments also indicate lower emission level and environmental impacts when using FG-LWA instead of EPS for pavement construction.

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