Efficiency Assessment of CFRP Flexural Strengthening of Low Performance Concrete Elements

About six decades ago, small to medium building structures were constructed in Israel with low-performance concrete (LPC), characterized by low compressive strength (< ~ 10 MPa) and/or by the use of relatively very large aggregates (up to ~300 mm maximum size). These buildings include exterior as well as interior unreinforced walls, which carry gravity loads. Many of these buildings are likely to remain in service. Strengthening of concrete buildings is commonly done by employing CFRP sheets. However, LPC properties do not comply with those required for standard concrete, by provisions for the application of this strengthening method. This paper presents initial results from the first stage of an experimental research aimed at studying the efficiency of flexural strengthening by CFRP sheets of LPC structural members. This stage of the work was planned to examine the feasibility of applying this strengthening method for non-standard, low strength concrete elements, by testing relatively small LPC beam specimens that were prepared at the laboratory (authentic specimens are planned for the next stage). To best represent the authentic structures, the specimens were cast using suitable mixture ingredients and they were un-reinforced. Moreover, to avoid failure under their self-weight, their length had to be limited. Therefore, they were extended at each of their sides in a special setup by two regular RC “prostheses”, thus positioning the short LPC specimen at the middle of a longer, 3-point-bending scheme. These specimens were strengthened by CFRP sheets for both shear (to ensure flexural failure) and for flexural moment. Results include the load-deflection curves, mode of failure, and measured load capacity, where the latter was compared to its calculated value according to common design procedures.