Comparative Study of Different Strengthening Techniques for RC Beams with and without Fire Damage

Abstract

Concrete is a heterogeneous material with relatively inert aggregate that is held together by hydrated Portland cement paste. When the concrete is exposed to high temperatures, changes in mechanical and physical properties occur. Concrete at elevated temperature is sensitive to the temperature level, heating rate, thermal cycling and temperature duration. Changes in mechanical and physical properties may result in undesirable structural failure. Therefore, the properties of concrete retained after fire are of still importance for determining load carrying capacity and restoration required for fire-damaged concrete structures to maintain them in a serviceable condition. A comprehensive experimental programme with 20 number of RC beams, involving effect of fire and various strengthening techniques implemented are taken in the present study. 3 control RC beams(CC); 3 control fire damage RC beams(CCF); 2 Control(CSMC) and 2 Fire damaged(FSMC) RC beams strengthened with Micro-Concrete; 2 Control(CSSC) and 2 Fire damaged(FSSC) RC beams strengthened with Seismocrete; 2 Control(CSFRP) and 2 Fire damaged(FSFRP) RC beams strengthened with FRP; 2 Fire damaged(FSWM) RC beams Strengthened with SSWM. RC Beams are designed as per IS:456(2000) and SP-16 provisions. Reinforcement of Fe 500 and Concrete of M25 grade with OPC, Coarse Aggregate (both 10 mm and 20mm), Fine Aggregate, Portable water and Superplasticizer are used. Concrete mixture design is finalized based on IS:10262(2009). Compressive strength of concrete cubes are evaluated at 7 and 28 days. The RC beams are given fire exposure of 900oC for 1-hour duration. The effects of fire exposure on the RC beams are observed. During strengthening of RC beams using different technique includes chipping off cover concrete and strengthening of chipped portion using Micro-Concrete, Seismocrete(UHPFRCC) and Polymer Modified Mortar, respectively. The RC beams thus strengthened are cured with water for 28 days. After curing, the RC beams strengthened with Polymer Modified Mortar are wrapped with FRP and SSWM, respectively. All the beams are tested under two-point loading and the behavior of beam is compared based on failure mode, change in load carrying capacity, load v/s deflection at mid-span, load v/s strain at center position of RC beam in top and bottom. Change in appearance, formation of surface cracks, spalling of concrete, etc. is observed for fire damaged beams.