Repair Systems for Post-Tensioned Slabs with Composite Material

Abstract

In this research project four post-tensioned slab specimens were tested. Two of the specimens were simply supported, two-way slabs with two-way post-tensioning. One of the specimens was a one-way slab with fixed ends and one-way post-tensioning. The last specimen was a one-way slab with one fixed end and one simply supported end and one way post-tensioning. Part of this research project was focused on the study of cracking, deflection and ultimate strength behavior of un-bonded post-tensioned slab specimens. Loading was stopped prior to collapse and the heavily cracked slabs were saved. The main objective of this investigation was to repair these slabs with CFRP (Carbon Fiber Reinforced Polymer) composite materials and find the flexural capacity, cracking pattern and general behavior. Two simple supported two-way slabs with similar un-bonded post-tensioning arrangement and with different mild steel were tested with uniform load. The approximate dimension of the slab was 9' ½ x 9' ½ x 3 depth. Sixteen ¼ diameter un-bonded post-tensioning strands were placed uniformly in each direction. The post tensioned strands had a parabolic drape and were stressed to appropriately 70% of ultimate strength of the strands. Theoretical estimate was made for cracking at elastic stage and at collapse stage using Yield Line Theory. The cracked slabs were externally repaired and strengthened by using CFRP fabric and adhesives. Two different strengthening schemes were used and compared. The repaired slabs were tested again to collect similar data as it was done for the original slabs. Comparisons were made between the repaired and control specimens and the measured values and estimated values of the tested slabs. The support conditions for the two one-way slabs were varied. Sixteen un-bonded post-tensioning strands and mild steel reinforcement were placed in one direction only. Other details and testing procedure remained similar to that of the two-way slabs.