Strengthening of lightweight reinforced concrete slabs using different techniques

Abstract

The present study examines the potential of using four different techniques in repairing and strengthening of preloaded, cracked, lightweight, reinforced concrete one-way solid slabs. Nineteen lightweight reinforced concrete (LWRC) slabs specimens were casted with one-third scale dimensions from prototype structure in buildings. The slabs dimensions were 1.2 m in length and cross section of (70 6 500) mm in depth and width. The slabs were reinforced with 3f10 for the main reinforcement and tested under a four-point loading system. The tested slabs were divided into two groups according to preloading level to study the effect of cracking level. Two preloadings were selected, i.e. 60% and 80% from the ultimate load. The strengthening techniques used were ferrocement layer, steel plate, carbon fibre reinforced polymers (CFRP) sheets and CFRP strips. The slabs were loaded up to failure and the structural response of each slab specimen was predicted in terms of the onset of cracking, deflection, collapse load and failure mode. The efficiency of different repair and strengthening techniques and their effects on the structural behaviour of cracked concrete slab had been analysed. It was observed that the type of strengthening technique used affect the load carrying capacity, deflection, stiffness and toughness of the slab. All repair techniques were found to be able to restore and enhance the structural capacity of cracked concrete slabs. The enhancement ratio is found to be affected by the preloading or the cracking level.

Anchorage Effect on Flexural Fiber Reinforced Polymer (FRP) Laminate Strengthening of Lightweight Concrete Beams

“…It is apparent that U-wrap anchorage was effective in confining concrete at the CFRP termination points and helped in delaying cracking and thereby increasing ductility. This finding agrees with previously conducted research on both lightweight and normal weight concrete where U-wraps were used as an anchorage for the flexural CFRP layer (Shannag et al, 2012, Elsafty et. al., 2013.…”

“…The strengthened beams with no anchorage, mechanical anchorage, and U-wrap anchorage failed at loads of 51.4 kN, 54.1 kN and 60.1 kN, respectively. Table 5 presents the stiffness of each beam, defined herein as the slope of the linear elastic portion of the load-deflection curve (Shannag et al, 2012).All the strengthened beams experienced an increase in stiffness compared to the control beams. B3-N, B-4N 13.3 24.9 B5-M, B6-M 15.9 49.9 B7-U, B8-U 10.8 1.3…”

“…The enhanced crack patterns may increase the resistance to chloride ion and moisture intrusion, and resulting steel rebar corrosion, adding to the long-term durability. Previous similar study on CFRP strengthened lightweight concrete beams showed closely spaced and small cracks (Shannag et al, 2012), and no similar comparison to NW concrete was located during the background review.…”

“…FRP laminates significantly reduced steel corrosion in LW concrete, thereby increasing the long-term durability. Shannag et al (2012) strengthened 40 LW concrete beams using carbon FRP (CFRP). The study considered different CFRP configurations, such as jacketing from the bottom and both sides, whole bottom width strips and half-bottom width strips.…”

“…A majority of previously conducted research on CFRP strengthened beam also showed intermediate flexural crack-induced interfacial debonding of CFRP as a prevalent failure mode for both NW and LW concrete (Reed et al, 2005, Teng et. al., 2003, Shannag et al, 2012.…”