Evaluation of Mechanical Properties and Thermal Stability of Hybrid Fiber Reinforced Polymer (FRP) Laminates

Abstract

In most cases, the RC structure is durable, strong and performs well throughout its service life. However, in some cases, it does not perform adequately due to various reasons like excess loading to any structural member, inadequate design due to revision of IS codes, natural calamities, fire damage, corrosion effect, etc. These reasons lead concrete structures to damage or deterioration and the structure may fail to serve its purpose. The decision to repair an existing structure depends not only on the field inspection of damaged structures but also on cost/benefit analysis of the different alternatives of strengthening. Strengthening of structures is more economical than demolition and rebuilding.

SSWM has good ductile behavior and economical than CFRP and GFRP, whereas CFRP and GFRP has good tensile strength and modulus of elasticity, but the strength of these FRP is not fully utilized due to debonding problem and brittle tensile behavior, so the combination of CFRP or GFRP with SSWM is a better alternative for wrapping material of strengthening of RC members. An experimental investigation is carried out in this study for the evaluation of mechanical properties and thermal stability of hybrid fiber reinforced polymer (FRP) laminates. Total 5 different types of configurations of FRP are considered for present study. SSWM two layers (SS), GFRP one layer + SSWM one layer (GS), CFRP one layer + SSWM one layer (CS), GFRP two layers (2G), CFRP two layers (2C). The main objectives of the present major project are to evaluate the mechanical properties and thermal stability of these FRP configuration by testing. Tensile strength of FRP, Bond behavior of FRP with concrete specimen, Confinement test of cylinders, Thermal stability of FRP adhesive material and Thermal effect on confinement test of cylinders are evaluated for different FRP configuration.

A tensile test of FRP is conducted on 13 numbers of 500×100 mm coupon specimens for these five types of patterns as per codal provision of ASTM D3039 /D3039M-00. In that double layer CFRP takes maximum load whereas double layer SSWM had more displacement with compare to other patterns. With compare to SS, increase in tensile strength is 216.5 % for CC. Other configuration GS, CS and GG has increment in strength is 32.5 %, 109.1 % and 84.91 % respectively. With compare to SS, % decrement in displacement is 49 %, 29 %, 16 % and 14 % for GS, CS, GG and CC respectively. For checking bond behavior of FRP and concrete, 10 numbers of dumbbell shaped specimens have been prepared and FRPs wrapped by Sikadur 330 and Sikadur 30 LP. The proportion of part A and part B for Sikadur 330 is 4:1 and for Sikadur 30 LP is 3:1. Specimens are tested in UTM with special testing assembly and observed that with compare to Sikadur 330, Sikadur 30 LP has less debonding problem. The strength of specimen wrapped with Sikadur 30 LP is more than SIkadur 330 for same type of wrapping patterns. For the specimens wrapped by Sikadur 330, GG has maximum bond strength and for specimen wrapeed by Sikadur 30 LP CC has maximum bond strength. For both specimen wrapped by Sikadur 330 and Sikadur 30 LP, GG has maximum displacement with compare to other specimens. From the confinement test of 14 cylinders of dia. 150 mm and height 300 mm, it is observed that with compare to control specimen percentage increment in compressive strength of double layer CFRP (CC) is 80 % and double layer GFRP (GG) is 57 %. In hybrid patterns CFRP + SSWM (CS) has 52 % increment and GFRP + SSWM (GS) has 45 % increment in compressive strength. In the thermal stability test 54 numbers of strips of FRPs and epoxy had applied specific temperature range of 100 °C, 200 °C, 300 °C, 400 °C, 500 °C. Temperature is applied for 2 hrs with the help of muffle furnace and after curing of 24 hrs at room temperature tensile test has been performed. It is observed that after exposure to 200 °C the fibers of CFRP and GFRP are disintegrating from laminate, so after that temperature making of coupon specimen was not possible. After 500 °C temperature fibers are started burning. In tensile test CFRP has maximum strength and SSWM has maximum displacement. SSWM takes maximum load at 400 °C, GFRP at 100 °C and CFRP at 200 °C. For all 3 FRPs, there was minor change in displacement for all temperatures. Sikadur 330 and Sikadur 30 LP are turned into blackish colour after 300 °C temperature and after 500 °C temperature, Sikadur 330 became powder. Compressive strength of 24 numbers of cylinders dia. 100 mm and height 200 mm was reduced drastically after 300 °C temperature for all three types of FRP configuration. Increment in compressive strength for ambient temperature specimens is 43 % for CS and 54.3 % for CC, with compare to control specimen. From all these experiments double layer CFRP and GFRP has good strength results. On the other hand, cost of CFRP is 4 times and GFRP is 2 times higher than SSWM. So, the hybrid combination of SSWM with CFRP or GFRP is good alternative for strengthening.