Browsing by Author "Bhayat, Moegamat Tashriq"

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    Strength, durability, thermal performance and sustainability assessment of one-part geopolymer concrete masonry units.
    (Stellenbosch : Stellenbosch University, 2024-12) Bhayat, Moegamat Tashriq; Babafemi, Adewumi John; De Villiers, Wibke; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ANGLISH ABSTRACT: South Africa currently faces a major backlog in the delivery of affordable housing units, which are typically constructed with conventional fired clay-based or cement-based masonry units. Additionally, the production of clay-based and cement-based masonry places a significant impact on the natural environment due to the clay firing and limestone calcination procedures, respectively. The need for alternative masonry units (AMUs) satisfying social, economic and environmental performance is evident. One-part geopolymer cement, produced from the alkali activation of aluminosilicate waste via solid alkali activators, has become an attractive low-carbon cement alternative showcasing superior mechanical, durability and thermal properties. Additionally, the use of alternative concrete aggregates is valuable toward mitigating the intense pressure placed on conventional aggregate resources by the built environment. This study investigated fly ash (FA), ground granulated blast furnace slag (GGBFS) and metakaolin (MK)-based one-part geopolymer concrete-based AMUs synthesised by solid alkali activators comprising sodium hydroxide (NaOH), sodium metasilicate pentahydrate (Na₂SiO₃.5H₂O) and calcium hydroxide (Ca(OH)₂). Additionally, expanded vermiculite (EV) and recycled plastic waste (RESIN8) were substituted as an alternative fine aggregate. The AMUs developed in this study include the FA and GGBFS-based (FABS) and the FA and MK-based (FAMK) units. EV was incorporated at 15% replacement in the development of the EV-based FA and GGBFS (FSEV) unit and the EV-based FA and MK (FMEV) unit. RESIN8 was incorporated at 5% replacement in the development of the RESIN8-based FA and GGBFS (FSR8) unit. All AMUs were subject to ambient curing. The AMUs were tested for their mechanical properties (compressive strength and elastic modulus) and density, durability properties (cold and boiled water absorption, initial rate of absorption, shrinkage and efflorescence extent), thermal properties (thermal conductivity, thermal resistance and thermal transmittance of wall specimens) and sustainability (cost analysis and lifecycle assessment). The average compressive strength of all AMUs satisfies the minimum strength requirement for masonry units. The elastic modulus for all AMUs falls within an acceptable range for masonry materials. The water absorption for all AMUs falls under the absorption limit for concrete-based masonry units. The initial rate of absorption for all AMUs are within an acceptable range for masonry units. All AMUs exhibit higher shrinkage in comparison to conventional concrete. The extent of efflorescence for all AMUs was slight to none. The thermal resistance (R-value) for all AMU wall specimens does not meet the minimum requirement for external walls in South Africa, yet the walls still possess comparable R-values to that of conventional concrete-based masonry units used in South Africa. The cost of the AMUs is roughly two times higher than that of a conventional concrete-based masonry unit, highlighting the economic challenge of adopting one-part geopolymer concrete as an alternative to conventional masonry materials for affordable housing construction. A cradle to gate and cradle to grave life cycle analysis of all AMUs showcased a reduction between 30% to 90% in the carbon footprint when compared to conventional masonry units. Overall, the outcomes of this study showcase the potential of one-part geopolymer cement and alternative aggregates to replace conventional masonry materials.