Strengthening and retrofitting of low strength reinforced concrete slabs with high strength overlay: experimental and numerical investigation

The study examined the effect of high-strength overlay on the flexural strength of low-strength reinforced concrete (RC) slabs weakened by inadequate curing conditions and aimed to validate these findings through numerical simulations. Although the concrete was specified to be 28 MPa, the slabs were cast with 18 MPa concrete. Eight 100 mm thick slabs were tested using the third-point loading test; two failed in the compression zone without any strengthening. The remaining six were reinforced with a 50 mm overlay of 35 MPa compressive strength: two with anchors, two with epoxy, and two with both anchors and epoxy. Additionally, two unstrengthened slabs were retrofitted, one with anchors and the other with epoxy. Results showed that strengthening and retrofitting increased the flexural capacity by 70% and shear capacity by 10%. The failure mechanism shifted from compression in unstrengthened slabs to shear in strengthened and retrofitted slabs. Numerical analysis corroborated the experimental results.