Browsing by Author "Van Wyk, Abraham Erasmus"

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    The influence of pristine graphene on conventional concrete
    (Stellenbosch : Stellenbosch University, 2024-02) Van Wyk, Abraham Erasmus; Combrinck, Riaan; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: Population growth and rapid urbanisation have brought forth the demand for infrastructure development and the need for durable, low cost and accessible materials. Material compositions such as concrete are commonly used in the built environment. Cement is the primary binding agent in concrete. To produce one metric ton of cement, 0.59 metric ton of CO2 is emitted into the atmosphere (IEA, 2022). The Global Cement & Concrete Association (GCCA) implemented the Net Zero Emissions vision 2050 to reduce the industry’s CO2 emissions. Significantly reducing the amount of cement used in concrete is a viable strategy to lower CO2 emissions during this transitional period towards Net Zero Emissions 2050. This can be achieved by increasing the mechanical and durability properties of concrete whilst reducing the cement content. This research study aims to substantially improve the mechanical and durability properties of conventional concrete by using pristine graphene (PG), which has the potential to ultimately reduce the carbon footprint of cement-based materials (CBMs). PG used in concrete has shown the potential to improve concrete’s mechanical and durability properties significantly, but to unlock the full potential of PG has been one of the greatest challenges. Thus, to unlock the potential of PG and improve the mechanical and durability properties of conventional concrete, different PG application techniques (PGATs) were developed. These PGATs are known as pre-dispersion methods and have two functions namely, 1) reduce the number of layered graphene (exfoliate) and 2) facilitate the distribution of graphene throughout the cementitious matrix. This is done by using three different pre-dispersion methods namely, 1) wet pre-dispersion, 2) dry pre-dispersion and 3) combined (wet and dry) pre-dispersion. All three pre-dispersion methods were used in this study. The PG was obtained from First Graphene Ltd Australia. Two PG forms namely, flake (PUREGRAPH) and agglomerate (PUREGRAPH AQUA) were used in this study. The PG in flake and agglomerate form that was used has a lateral platelet size of 56.9 μm and 52.1 μm, respectively. Additionally, the PGATs aims to resolve some of conventional concrete’s oldest problems. Concrete is described as a heterogeneous material. Therefore, concrete is not uniform in composition due to the difference in stiffness of each traditional constituent (sand, cement and coarse aggregate). The difference in stiffness causes predominantly smaller sized particles to be situated in a region near the surface or aggregates when concrete is formed. This causes porous crystalline structures to form in a region around aggregates which are susceptible to mechanical failure and durability issues. This region is known as the interfacial transition zone (ITZ). Thus, this study strategically positioned PG in the ITZ to improve the bond between the mortar matrix and the surface of coarse aggregate to improve the mechanical and durability properties of conventional concrete. The compressive and in-direct tensile splitting strength of conventional concrete were improved by 18.8% and 7.6%, respectively after 56 days of water curing. Additionally, the amount of crystalline growth on the surface of the coarse aggregate were investigated to determine the bond between the mortar matrix and the surface of the coarse aggregate. The bond strength between the mortar matrix and the surface of the coarse aggregate was quantified by using a direct tensile test referred to as the ITZ strength test. PG improved the bond strength by 22.1% after 28 days of water curing. Furthermore, the oxygen permeability and water absorption were reduced by 42.8% and 17.4%, respectively. Therefore, PG applied to conventional concrete have shown the potential to improve the ITZ which directly influences the mechanical and durability properties. Although significant research still needs to be conducted, this study shows that PG could facilitate greener, stronger and longer lasting concrete as well as provide a partial solution to decrease the global cement consumption which will lower carbon emissions of the cement industry.