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The instability of earth structures resting on granular materials, such as embankments and tailing dams, is caused by the infiltration of water which can lead to their failure. This paper presents the potential use of tyre crumbs for controlling the stability of structures made of sand. Constant shear drained experiments were carried out on mixtures of sand and tyre crumbs to understand the onset of instability. Conventional drained shear tests were carried out on all samples up to a deviator stress of 200 kPa. Tests were then carried out on the sheared samples by reducing the confining pressure until the onset of instability. This was determined by a drop in stress, by second-order work and by the strain ratio approach. The value of mean effective stress at instability was found to decrease with the addition of tyre crumbs to the mix of up to 20% and then increase with further addition of tyre crumbs. The strain ratio approach was found to predict the onset of instability easily and efficiently, similar to the second-order work method.

Cross-sectional analyses of circular and square reinforced concrete (RC) columns strengthened with reactive powder concrete jacketing and fibre-reinforced polymer (FRP) wrapping were undertaken. The stress block method was used to determine theoretical axial load–bending moment (AL–BM) interactions of the columns. These were then compared with experimental results and found to be in very good agreement. A parametric study was also undertaken to investigate the most important factors that influence the AL–BM capacity of circular and square strengthened columns. Finally, a group of theoretical AL–BM interactions for circular and square strengthened columns was produced. These can be used in a wide range of applications for strengthening RC columns with high-performance concrete jackets and FRP wraps.

Geopolymers are recognised for their environmental benefits and excellent chloride and sulfate resistance. However, information on the material characteristics and bond behaviour of geopolymers based on fly ash (FA) and slag is still relatively scarce. This paper presents a comprehensive study on the integration of two modern construction materials – geopolymer concrete (GPC) based on FA and ground granulated blast-furnace slag and glass-fibre-reinforced polymer (GFRP) bars. The aim of the study was to assist concrete structural design by identifying the key preparation parameters such as hardening and bond behaviour. It was found that the hardening of the GPC was much faster than that of ordinary Portland cement (OPC) concrete at an early age and the stress–strain curves, elastic moduli and splitting tensile strengths of the GPC were accurately predicted by existing models developed for OPC concrete. The GFRP bars in the GPC outperformed those in the OPC concrete in terms of normalised bond strength. The GPC reinforced with both GFRP and steel rebars exhibited similar bond–slip curves to the OPC concrete. Overall, the behaviour of the GFRP-reinforced GPC was found to be analogous to that of the OPC concrete while providing adequate compressive, tensile and bond strength for the construction of foundations of low-rise buildings.

This study presents an experimental evaluation of three different methods for determining the tensile strength of steel fibre reinforced concrete (SFRC). The test methods include the splitting test (ST), double punch test (DPT) and direct tensile test (DTT). The compressive strength of the concrete used in this study ranged between 30 and 80 MPa with 0%, 1·5% and 3% steel fibre by volume of the concrete. In total, 81 concrete cylinders were cast and tested for 28-d compressive strength, splitting tensile strength and double punch tensile strength of the concrete. In addition, 27 concrete prism specimens were cast and tested to determine the direct tensile strength of the concrete. The test results show that, compared to the ST, the DPT is more effective in predicting the tensile strength of SFRC, as the tensile strengths obtained from the DPT and the direct tensile test are very close. The DPT is easier to perform and costs less than the ST and the DTT.

This study explores the effect of length to diameter (L/D) ratio on the axial load capacity of small-diameter self-compacting concrete-filled steel tube (SCFT) specimens. The SCFT specimens with L/D ratio of 2 to 14 were tested. Two different cold-formed steel tubes with diameters of 26·9 and 33·7 mm were used in the construction of the SCFT specimens. The behaviour of the SCFT specimens was compared with the unfilled steel tube (UT) specimens. The axial load capacity of SCFT specimens was found to be higher than the axial load capacity of UT specimens. The compressive failure of SCFT and UT specimens with a ratio of 2 and 4 occurred due to local buckling, and with L/D ratio ≥ 6 failure occurred due to global buckling. However, the self-compacting concrete inside the steel tubes improved the ductility and the post-peak axial load–axial deformation response of SCFT specimens compared to the UT specimens.

Significant research efforts have been devoted in recent years to the development of displacement-based seismic assessment and design methodology, recognising the shortcomings of traditional, code-specified force-based procedures. Recent advances in direct displacement-based seismic design of columns rely on the estimates of yield curvature for determining seismic design forces to satisfy the specified seismic performance levels. This paper presents simple expressions for estimating the effective yield curvature for normal- and high-strength circular reinforced concrete columns based on moment–curvature analyses of a large number of column sections. Such expressions can be programmed into spreadsheet format and can be used for the direct displacement-based design of circular reinforced concrete columns. Influences of different parameters on the effective yield curvature have been quantified. Effective yield curvature is presented in terms of the gross diameter of the section and the yield strain of longitudinal reinforcement together with three modification factors that take into account the effects of the strength of concrete, axial load ratio and the amount of longitudinal reinforcement. An example illustrating the preliminary design of bridge columns based on the developed expressions is presented.