Matrix strength influence on composite fibre reinforced concrete behaviour in flexure and single fibre pull-out

Abstract

Composite glass and carbon fibres were used to investigate fibre reinforced concrete behaviour and single fibre pull-out resistance depending on concrete matrix strength. Composite fibres with smooth surface, uneven and undulated shape were used. Fibre diameters were from 1.52 to 2.18 mm and 50 mm length. Three different concrete matrices were developed with low, average and high compressive strength. Concrete consistency (slump flow), compressive strength development and shrinkage were measured to characterize concrete matrices. Beam samples (100 x 100 x 400 mm) with 1.5 vol. % of fibres were manufactured and tested in four-point bending. Force was measured and deflection in the middle of the span. Bending test results and bending behaviour were analysed as well as the number of fibres in the crack plane. Composite fibre reinforced concrete behaviour in flexure was compared with known straight and undulated steel fibres with the same dosage. Composite fibres show significantly smaller first crack strength compared to steel fibres, but contrary to steel fibres they show stable strain hardening after the first crack in both concrete matrices - with high and average strength. Tested fibre reinforced concretes show strain softening in the low strength concrete matrix. Single fibre pull-out samples were manufactured to investigate the matrix strength influence on pull-out resistance. Fibre peak pull-out force for smooth composite fibres increases significantly, when the concrete matrix strength increases. Pull-out force for rough surface fibres is initially very high in low strength concrete matrices and rises relatively less, when the strength increases compared to smooth fibres.