Performance of Carbon Fibre Reinforced Polymer (CFRP) Strips for Flexural Strengthening of Reinforced Concrete Beams Made of High Strength Fly Ash Concrete

Fibre reinforced polymer (FRP) composites have shown high potential as repair materials
for civil infrastructures. The main attributes of FRP composites are high strength, light
weight, good resistance to chemicals and non-magnetic and non-conductive properties.
Compressive strength is one of the most important design parameters for concrete
structures; it drives the design process and can influence the cost of a project. By the use
of cement replacement materials (CRMs) at the optimum level the cost of concrete can be
substantially reduced and its properties can also be enhanced. Fly ash (FA) is a byproduct
form coal-fired power plants and has extensively been used for producing high
strength, high performance concrete. There is a lack of work in the CFRP external
strengthening of reinforced concrete beams made of blended cement concrete.
In this study, three concrete mixes, with three different cementitious material contents
such as 335, 360 and 380 kg/m 3 that incorporated fly ash content of 0%, 20%, 30% and
40% as the partial replacement of cement. The effects of CFRP system in terms of
optimum length and ductility ratio for flexural strengthening were tested on 150 mm
wide, 200 mm high and 2000 mm long RC beams. Three different lengths of 1333 mm,
1667 mm and 2000 mm of CFRP plate that represented 67%, 83% and 100% respectively
of the total span length were chosen and the control beams were tested without CFRP
strengthening. The behaviours of reinforced concrete beams made of normal and fly ash
concretes strengthened with CFRP plates were compared and examined. It was found that
high strength concrete such as 50 MPa can be produced by mixing as low as 228 kg/m3
OPC content. Concrete compressive strength up to 84 MPa was obtained for the OPC
content of 304 kg/m3 with 20% fly ash content. It was found that by using CFRP system
for external flexural strengthening, an increase in the load-carrying capacity up to 96%
over the control beams was obtained. The length of the CFRP plate that achieved the
optimum load-carrying capacity was 1667 mm which was 83% of the total span length.
This length also provided an adequate ductility index of 3.1 compared to 4.6 for that of
the control beam. The results of ultimate loads and deflections of normal and fly ashbased
RC beams were obtained identical at first crack and at ultimate levels. It has been
proved that the CFRP system could be used as effectively with fly ash based concrete
beams as it has been used with normal concrete beams.