Flexural behaviour of high strength steel fibre normal and lightweight concrete beams

Zurgani, Mohamed Abdulhakim (2018) Flexural behaviour of high strength steel fibre normal and lightweight concrete beams. Masters thesis, Memorial University of Newfoundland.

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Abstract

An experimental study was conducted to investigate the flexural behaviour of high strength normal and lightweight reinforced concrete beams with steel fibres. Three different mixtures were developed for each type of concrete with three different steel fibre volume ratios. The target compressive strength was 85 MPa. Material and structural experimental programs were performed. In the material investigation, twenty four prisms with dimensions of 100 mm × 100 mm × 400 mm and one hundred and twenty cylinders with dimensions of 100 mm × 200 mm were cast, cured and tested to determine the mechanical properties for all different mixtures. The investigated mechanical properties included the compressive strength, splitting tensile strength, modulus of rupture and flexural toughness. In the structural investigation, a series of six high strength lightweight aggregate (LWAC) concrete reinforced beams and six high strength normal weight (NWC) reinforced concrete beams were cast and tested. The beams were 200 mm × 400 mm × 3200 mm and were simply supported on a clear span of 2900 mm. The main variables in this study were the concrete type (normal weight concrete and light weight aggregate concrete), steel fibre volume ratio, (0 %, 0.375%, 0.75%), and the longitudinal reinforcement ratio, (0.85%, 1.50%). The structural behaviour of the test beams was examined in terms of load-deflection behaviour, steel reinforcement strain, concrete strain, crack pattern, crack width, crack spacing, mode of failure and ultimate moment capacity. The test results revealed that the addition of steel fibres to high strength lightweight or normal weight concrete improved the mechanical properties. The compressive strength, splitting tensile strength and the modulus of rupture of fibrous LWAC and NWC concrete increased compared to the plain concrete. Adding steel fibre to both high strength normal and lightweight concrete increased both cracked and un-cracked stiffness in addition to increasing the ultimate flexural capacity. The steel fibres also enhanced the cracking behaviour for both NWC and LWAC beams, reduced the crack widths and increased the number of the cracks for both type of concrete. The LWAC beams developed more cracks but less cracks width compared to their identical NWC beams. The ductility indexes of fibrous and non-fibrous NWC beams were higher than the ductility indexes measured for the corresponding LWAC beams. For all fibre reinforced NWC and LWAC beams, CSA A23.3-14, ACI 318-08, EC2-04, and EC2-91 codes overestimated the maximum crack width due to the fact that these models do not consider the presence of steel fibres. The Rilem TC162-TDF was found to accurately predict the maximum crack width of fibrous NWC beams. However, the model was seen to be conservative when predicting the maximum crack width for fibrous LWAC beams.

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