Evaluation of mechanical and fracture behaviour of POFA-FA-Metakaolin based geopolymer fibre reinforced concrete / Iftekhair Ibnul Bashar

The depletion of natural resources, emission of CO2 from the cement industries and the waste products from industrial by-products pose irreparable danger to the ecological balance. There have been many attempts to replace ordinary Portland cement (OPC) and the aggregates through the use of industrial by-products and waste materials in recent years. In Malaysia, the availability of industrial by-products such as palm oil fuel ash (POFA) and fly ash (FA) could be considered as viable binders along with Metakaolin (MK) to develop geopolymer concrete (GC). In addition, other industrial by-products such as manufactured sand (M-sand) and oil palm shell (OPS) could ideally replace the conventional fine and coarse aggregates, respectively. This dissertation reports the development of POFA-FA-MK-based geopolymer concrete (PFMGC) using M-sand and OPS as fine and coarse aggregates, respectively. The mechanical properties of GC varying different proportion of POFA, FA and MK as binder was investigated. An appropriate mixture design for structural grade PFMGC is also proposed. The effect of steel fibres on the development of mechanical properties and fracture behaviour was investigated for two different aspect ratios (AR 80 and 65) and three different percent of volume as 0.25%, 0.50% and 0.75%. The ratios of Msand/ binder, OPS/ binder, water/ binder and alkaline solution/ binder were kept constant as 1.125, 0.375, 0.18 and 0.4, respectively. The specimens were cured in oven of 650C temperature for 48 hours and then kept in room temperature and relative humidity of 280C and 79%, respectively till the age of testing. The mechanical properties and the fracture behaviour of the fibre-reinforced PFMGC were compared with fibred and non-fibred concrete consisting OPS and crushed granite aggregate.The results show that the POFA-MK based geopolymer concrete (PMGC) achieved better strength than that of the PFMGC due to presence of the appropriate ratios of Silica/ Alumina, Sodium oxide (and Potassium oxide)/ Silica and Sodium oxide (and Potassium oxide)/ Alumina as 8.73, 0.11 and 0.93, respectively. The corresponding 28-day compressive strengths of concretes having 90% and 80% of POFA with MK as binder were 23.2 and 23.6 MPa, respectively. The highest values of the splitting tensile strength and flexure strength of 2.14 MPa and 3.41 MPa were obtained for the binder consisting 90% of POFA and 10% of MK. The early strength development at the age of 3-day was found above 80% and this is attributed to geopolymerization process at high temperature. The low values of static modulus of elasticity and the Poisson’s ratio of 6.36 GPa and 0.176, respectively for PMGC (POFA: MK=90:10) is due to the low stiffness of OPS aggregate. The stress-strain relations of PMGC fit well with the expression developed for OPC concrete. The flexural strength, splitting tensile strength and fracture behaviour were significantly affected by the AR and the volume of steel fibres. The addition of steel fibre with AR of 80 produced higher splitting tensile & flexural strengths and total fracture energy, respectively of 5%, 6% and 50-80% compared to results of the corresponding values with steel fibre with AR of 65

Bond strength evaluation of palm oil fuel ash-based geopolymer normal weight and lightweight concretes with steel reinforcement

This article presents a comparison of the bond behaviour between palm oil fuel ash (POFA)-derived geopolymer and conventional cement-based normal weight and lightweight concretes. A total of 16 variables were tested, which includes concrete cover (50 and 100 mm), bar diameter (12 and 16 mm) and types of concrete (POFA-based geopolymer normal/ lightweight concrete and cement-based normal/lightweight concrete). Results showed that the bond strength of cement-based concretes had higher critical bond stress and ultimate bond strength as well as lower slip at the ultimate bond strength compared to the corresponding POFA-based geopolymer concretes. The cement-based and geopolymer lightweight concrete specimens also exhibited greater bond strength than the normal weight concrete specimens. All of the concrete specimens generally exhibited similar bond stress-slip curves. Besides that, bond strength models proposed in the past predicted satisfactory match (difference of up to 35%) to the experimental ultimate bond strength values in the case of cement-based normal weight concrete and geopolymer concrete whereas a difference in the range of 16–138% was found for the case of lightweight concrete