Engineering properties of POFA-GGBS-based fiber reinforced structural lightweight geopolymer concrete / Azizul Islam


The use of ordinary Portland cement (OPC) in concrete construction is under critical review due to the release of high amount of carbon dioxide (CO2) gas in to the atmosphere. Geopolymer concrete (GC) is a novel green material that uses waste materials as the binder instead of OPC. This research focuses on utilizing locally available waste materials – palm oil fuel ash (POFA), ground granulated blast furnace slag (GGBS) and fly ash (FA) – as the binder, manufactured sand (MS) and quarry dust (QD) as replacement materials for the fine aggregate, and oil palm shell (OPS) as the coarse aggregate, which were activated by alkaline liquids to produce sustainable concrete, hereafter called OPSGC (oil palm shell geopolymer concrete). This investigation reports the development of mix design, effect of steel fibre to the impact resistance of POFA-GGBS-based lightweight geopolymer concrete. The engineering properties of OPSGC – compressive, flexural and splitting tensile strength, modulus of elasticity and Poisson’s ratio – were investigated; in addition, the quantity of OPS in impact resistance of steel fibre reinforced geopolymer concrete were studied and reported. Initially, three binders – POFA, GGBS and FA were used to develop an appropriate geopolymer mortar mix. Eleven mixes were prepared with varying binder contents. The other constituent materials such as fine aggregate and water were kept constant. After obtaining the appropriate mix proportion of mortar, nine concrete mixes were prepared for structural grade geopolymer concrete using OPS, crushed granite, MS, QD and conventional sand (NS). The impact behaviour of GC was investigated based on fourteen concrete mixes prepared with and without fibre using different OPS contents. The other constituent materials – fine aggregate (MS), activator and water were kept constant. All the specimens of geopolymer mortar were cured in oven for 24 h at 65 oC and thereafter kept in room temperature (about 26–29 oC) before testing for the compressive strength. However, for the structural grade concrete two curing conditions, oven-dry and ambient curing were observed. Since the ambient curing produced better results than oven cured specimens, the specimens of impact resistance test were cured using ambient condition. The highest compressive strength of about 66 MPa was achieved for the mortar containing 30% of POFA and 70% of GGBS with a total binder content of 460 kg/m3. For structural grade concrete with 40% of POFA and 60% of GGBS, the highest compressive strength of about 33 MPa and 42 MPa for OPSGC and NWGC (normal weight geopolymer concrete), respectively; the binder contents in these mixes were 425 kg/m3 and 220 kg/m3 respectively. The tensile strength of OPSGC was found satisfactorily as the splitting tensile strength of 2.74 MPa fulfilled the minimum requirement of 2 MPa. Its flexural strength of 3.19 MPa was comparable to that of NWGC. In addition, the Young’s modulus of elasticity of 11.12 GPa was obtained for OPSGC. Finally, after adding steel fibre the impact behaviour also investigated. Result shows that the highest compressive strength of about 28 MPa was achieved for the OPSGC containing 50% of POFA and 50% of GGBS with a total binder content of 454 kg/m3 with the lowest OPS content of 181 kg/m3. In contrast, about 40 MPa was achieved for NWGC with a total binder content of 308 kg/m3. The impact energy of 5,945 J for OPSGC specimens with 0.5% steel fibres was found. The tensile strength of OPSGC increases significantly after adding 0.5% of steel fibre as well. The highest splitting tensile strength of 2.72 MPa and flexural strength of 4.11 MPa was found, which was 19% and 39% higher than its control mix. The research shows that POFA could be used as an ideal binder in the development of geopolymer concrete (GC) with GGBS. The development of structural grade OPSGC and its comparable mechanical properties as that of NWGC shows that the former could be used for structural purpose. In addition, the fibre enhanced the impact resistance and other mechanical properties of the OPSGC

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