Polymer cement mortar strengthened RC beams with/without silica fume as repair material

Abstract

Polymer cement mortar (PCM) overlaying methods leads to brittle interfacial debonding before its classical failure causing a sudden decrease of the load-carrying capacity. For a reliable design procedure for the practitioner, a need exits to prevent the interfacial debonding. The proposed modified 5 % silica fume (M) PCM overlay is intended to delay debonding because it increased the concrete-PCM bond (confirmed in our previous study). Fourteen RC beams (size-150x150x1440 mm, a/d – 3.5) using C40 concrete (mix proportion – 1:2.1:2.6) were prepared and strengthened with rebar (2D6 and 2D10), CFRP grid with changing stiffness (low, medium and high), and CFRP strand sheet (50 mm and 150 mm width) as strengthening reinforcement that embedded with normal (N) PCM and MPCM overlay of thickness 20 mm to investigate the effectiveness of silica fume. Four-point bending test were made at room temperature to evaluate the flexural performance. Compared to NPCM, MPCM with all cases of strengthening reinforcement enhanced the crack numbers, ductile behavior, peak load (12–25 %) and debonding load (3–33 %), proving MPCM as ideal cementitious matrix for strengthening. The flexural strengthening configuration using MPCM and reinforcement amount (area x tensile strength) ratio of 0.5 between strengthening and main bar proved to be more efficient as this configuration delayed the debonding failure, shifted fracture to classical mode and confirmed uniform shear stress transfer at the overlay-concrete interface. Conclusively, MPCM overlay nearly achieved a full-strength composite action which is effective to prevent the debonding that benefits practitioners.