Bond stress between reinforcement bars and fly ash-based geopolymer concrete

Geopolymer concrete is an innovative construction material that utilises industrial by-product materials, such as fly ash and slags to form a cement replacement for concrete manufacture. In order to simulate the behaviour of all types of reinforced concrete at all load levels, an understanding of the bond between the reinforcement and the concrete is required. This study involves 102 pullout test specimens with bar diameters of 12 to 16mm, concrete cover-to-diameter (Cc/db) ratios of 2, 3, 5.8 and 7.8, compressive strength of 33, 38 and 43MPa and a reinforcement corrosion level ranging from 0 to 85% in mass loss. The results show that the bond between the reinforcement and the geopolymer concrete is stronger than the bond that exists between the reinforcement and ordinary Portland cement (OPC)-based concrete. Hence, existing models for OPC can be used as a lower-bounds estimate for analysis and design. Alternatively, new predictive models for the local bond properties and the bond strength variation with corrosion are presented for geopolymer concrete. The results also show that the influence of the Cc/db ratio on the bond strength reduces as the Cc/db ratio increases, while the influence of the compressive strength on the bond strength remains virtual. This is because increasing the compressive strength leads to an increase in the bond strength.Mohammad Albitar, Mohamed Ali, Phillip Visintin, Olivier Lavigne and Erwin Gambo

Structural behaviour of ultra-high performance fibre reinforced concrete columns subjected to eccentric loading

An experimental investigation conducted on ultra-high performance fibre reinforced concrete (UHPFRC) columns is presented in this paper. The columns consisted of longitudinal and transverse reinforcement, tested under concentric and eccentric compressive loads with varying load eccentricities. The UHPFRC manufactured with locally available raw materials attained compressive strengths of 140 to 160MPa. The experimental data of axial load with lateral and axial deformations, mode of failure was obtained for each test. The cover spalling was not observed for all the columns. The interaction diagram of axial load-bending moment is established for compression members and is in good agreement with the test results.Manpreet Singh, M.S. Mohamed Ali, A.H. Sheik

Analytical models for structural behaviour of fibre reinforced concrete beams with steel or FRP bars

Fibre reinforced concrete (FRC) offers an improved resistance to cracking and crack propagation, which leads to increased strength and toughness in flexure. As there is a lack of understanding of structural behaviour of FRC,this paper reports a study on the influence of fibres on the behaviour of flexural members, and it focuses on a partial-interaction structural mechanics model for the deflection calculation of concrete beams reinforced with steel or FRP bars and fibres. For this, a model is developed to incorporate fibres into both tension and compression regions in generating moment-rotation response and also on crack formation and the tension-stiffening mehanism. For calibrating these models an experimental study on the bond-slip relationship between FRP bars and fibre concrete was required for the tension stiffening analysis; and an experimental study on the slip-crack width relationship between fibres and concrete required for the moment-rotation model. The moment-rotation and tension stiffening models were then used to obtain the load deflection (P-Δ) response through integration of discrete rotations at the determined crack locations throughout the member. The theoretical load-deflection responses are compared to the experimental results, showing very good correlation for the ultimate flexural capacity and the ductility of PVA fibre reinforced concrete members.M.S. Mohamed Ali, A.H. Sheikh, D.J. Oehlers and P. Visinti