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In recent years, the construction industry has been faced with a decline in the availability of natural sand due to the growth of the industry. On the other hand, the metal casting industries are being forced to find ways to safely dispose of waste foundry sand (FS). With the aim of resolving both of these issues, an investigation was carried out on the reuse of waste FS as an alternative material to natural sand in concrete production, satisfied with relevant international standards. The physical and chemical properties of the FS were addressed. The influence of FS on the behaviour of concrete was evaluated through strength and durability properties. The test results revealed that compared to the concrete mixtures with a substitution rate of 30%, the control mixture had a strength value that was only 6.3% higher, and this enhancement is not particularly high. In a similar manner, the durability properties of the concrete mixtures containing FS up to 30% were relatively close to those of control mixture. From the test results, it is suggested that FS with a substitution rate of up to 30% can be effectively used in concrete production without affecting the strength and durability properties of the concrete.

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The feasibility study on carbon fibre reinforced polymer (CFRP) fabrics in axial strengthening of hollow square sections (HSS) was investigated in this paper. CFRP was used as strips form with other parameters such as the number of layers and spacing of strips. Experimental results revealed that the external bonding of normal modulus CFRP strips significantly enhanced the load carrying capacity and stiffness of the hollow sections and also reduced the axial shortening of columns by providing external confinement against the elastic deformation. The increase in the CFRP strips thickness effectively delayed the local buckling of the above members and led to the inward buckling rather than outward one. Finally, three-dimensional nonlinear finite element modeling of CFRP strengthened hollow square sectionswas created by using ANSYS 12.0 to validate the results and the numerical results such as failure modes and load deformation behaviour fairly agreed with the experimental results.

In the present era, the use of CFST members has become quite popular in the construction industry and at the same time, aging of metallic structures and member deterioration have also been often reported. Therefore, actions such as implementation of new materials and strengthening techniques have become essential to combat this problem. It has already been proved that FRP composites significantly improved the strength of reinforced concrete structures. The application of these materials is implemented in the high-performance steel structures. With this aim, an experimental study has been carried out to investigate the suitability of unidirectional CFRP fabrics in strengthening CFST members under axial compression. The size and height of the specimens used in this study are 91.5 Â 91.5 Â 3.6 mm and 600 mm, respectively. Out of 21 columns, 18 columns were externally bonded by CFRP strips having a constant width of 50 mm with spacing values of 20 mm and 30 mm and the remaining three columns were unbonded. The effect of CFRP layers on the load-carrying capacity of CFST columns was investigated. The strengthened columns exhibited FRP rupture failure due to outward buckling of steel tube. Experimental results also revealed that external bonding of CFRP strips considerably provides the confining pressure to the CFST column and as a result, CFRP-confined columns sustained higher ultimate load and larger axial deformation compared to control column. An analytical model was also proposed herein for predicting the axial load capacity of CFRP-confined CFST columns. The average percentage of difference between the analytical and the experimental loads was found as AE4%.

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