Flexural behavior of plain concrete beams strengthened with ultra high toughness cementitious composites layer

Ultra high toughness cementitious composites (UHTCC), which has metal-like deformation and crack width restricting ability, is expected to be utilized as retrofit materials. For this application, much attention needs to be paid to the working performance of structure members composed of UHTCC and existing concrete. This paper presents an investigation on the flexural behavior of plain concrete beams strengthened with UHTCC layer in tension face. The effect of UHTCC layer thicknesses on first crack load, ultimate flexural load, crack width, and load-deflection relationship is examined. The experimental results indicate that the use of UHTCC layer significantly increases the first crack load and ultimate flexural load. The first crack load and ultimate flexural load of composites beams increased with the increase of the UHTCC layer thickness. Considerable reduction in crack width was observed for composite specimens, as UHTCC layer restricted the cracks in upper concrete and dispersed them into multiple fine cracks effectively. Moreover, in comparison to plain concrete beam, composite beams could sustain the loading at a larger deflection without failure. Based on the plane section assumption, etc., a calculation method to predict the flexural capacity of composite beam was proposed. Good agreement between predictions and experiments had been obtained.