The present article deals with the analysis of experimental results, in terms of load-carrying capacity and strain, obtained from tests on plain- and reinforced-concrete (RC) cylinders strengthened with external carbon-fiber-reinforced polymer (CFRP). The parameters considered are the number of composite layers and the compressive strength of unconfined concrete. The effective circumferential FRP failure strain and the effect of the effective lateral confining pressure were investigated. In total, 30 cylinders were subjected to axial compression, which included control specimens. All the test specimens were loaded to failure in axial compression and the behavior of the specimens in the axial and transverse directions was investigated. Test results showed that the CFRP wrap increases the strength and ductility of plain- and RC cylinders significantly. A simple model is presented to predict the compressive strength and axial strain of FRP-confined columns.

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This paper presents the results of an experimental study on the behaviour of axially loaded short concrete columns, with different cross sections that have been externally strengthened with carbon fibre-reinforced polymer (CFRP) sheets. Six series, forming the total of 60 specimens, were subjected to axial compression. All the test specimens were loaded to failure in axial compression and investigated in both axial and transverse directions. According to the obtained test results, FRP-confined specimen failure occurs before the FRP reached the ultimate strain capacities. Thus, the failure occurs prematurely and the circumferential failure strain is lower than the ultimate strain obtained from the standard tensile testing of the FRP composite. In existing models for FRP-confined concrete, it is commonly assumed that the FRP ruptures when the hoop stress in the FRP jacket reaches its tensile strength from either flat coupon tests, which is herein referred to as the FRP material tensile strength. This phenomenon considerably affects the accuracy of the existing models for FRP-confined concrete. On the basis of the effective lateral confining pressure of the composite jacket and the effective circumferential FRP failure strain, new equations were proposed to predict the strength of FRP-confined concrete and corresponding strain for each of the cross section geometry used, circular and square. The estimations given by these equations were compared with the experimental ones and general conclusions were drawn.

This paper presents a detailed experimental investigation of the acid resistance of economical self-compacting concrete (SCC) prepared with natural pozzolan, immersed for up to 12 weeks in sulphuric acid (H2SO4) and hydrochloric acid (HCl) solutions. The results are compared with those from a control concrete and other SCCs prepared with fly ash and limestone filler. The different factors considered in this study were the effect of mineral admixture type and the strength classes (30, 50, and 70 MPa) of the concrete specimens. In total, 12 formulations were tested. Mass and compressive strength losses are the main properties investigated. Scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses were used to better understand the kinetics of deterioration of each type of concrete. The results show the positive influence of natural pozzolan on the behaviour of SCC under both sulphuric and hydrochloric acid mediums.