International Concrete Abstracts Portal

This paper reports the recent findings of an experimental investigation on the influence of steel fibres in RC blocks under quasi static direct tensile loading. Structural blocks were designed with rebar reinforcement ratios of 0.40, 0.63 and 1.00%. A structural direct tensile testing system was developed at the COPPE laboratories resulting in a state-of-the-art in house apparatus. The RC blocks were reinforced with 1.25% volume fraction of steel fibres and without any type of fibre reinforcement and then tested until a strain level of approximately 0.0015mm/mm. The results show that the steel fibres improved the stress transfer efficiency between the rebars and the concrete matrix. By partially replacing the rebars by steel fibres the ductility of the concrete block was augmented and the post-crack stiffness increased. These results and possible mechanisms are discussed on the basis of the observed crack patterns, deformation measured on the steel rebars, computed deformation of the concrete matrix and on the overall mechanical behaviour of the composite concrete block.

Fibre-reinforced self-compacting concrete uses the flowability of fresh concrete to improve fibre orientation, thereby enhancing toughness and energy absorption capacity. In the past few years there has been a boost in the development of concretes with macro-synthetic fibres added. In this paper, the mechanical properties of self-compacting concrete with low, medium and high fibre contents of macro polyolefin fibres are studied. Their fracture behaviour is compared with plain self-compacting concrete. It is possible to fit this behaviour within the existing standards requirements. Dispersion obtained for mean fracture values among the different amounts was analysed using a fracture surface analysis and the amount and distribution of fibres.

Plastic shrinkage cracking due to a high rate of evaporation detrimentally affects durability and serviceability of concrete structures. The effect of different types of fibres to control these cracks, including steel, glass, polypropylene, and polyolefin fibres on the moisture loss and evaporation rates is investigated by performing ASTM C1579 tests. Using a dual stage methodology of constant drying rate period (stage I) and falling drying rate period (stage II), results are analysed. Moisture diffusivities are computed which in turn can be used for modelling the drying shrinkage and cracking under different environmental conditions. The formation of microcracks is documented using digital photography and processed by image analysis. The results show that moisture diffusivities at stage I drying are similar to each other between FRC and control samples. These magnitudes are approximately 50 times higher than diffusivities at stage II drying. The main difference is observed in stage II drying where the diffusivities in FRC are lower compared to plain concrete. Image analysis results indicate significant effects of fibres on controlling plastic shrinkage cracks.

A new type of green ultra-high-performance glass concrete (UHPGC) was developed at the Université de Sherbrooke using waste glass having varying particle-size distributions (PSD). UHPGC provides several technological, economical, and environmental advantages. It reduces the production cost of ultra-high performance concrete (UHPC) and carbon footprint of traditional UHPC structures. This paper presents the rheological and mechanical properties of selected UHPGCs. The rheology of the UHPGCs was improved by using non-absorptive glass particles. UHPGC greatly improves the concrete microstructure, resulting in higher mechanical and durability properties, which are comparable to those of the conventional UHPC. These strength and rigidity gains were due to the fact that the glass particles acted as inclusions with very high strength and elastic modulus. A special mix design of UHPGC was developed for innovative pedestrian bridges at the Sherbrooke University campus. Concrete performances of this UHPGC are also presented in this paper.

The aim of this paper is to examine the feasibility of using recycled tires steel fibres (RTSF) in recycled aggregate concrete (RAC) for structural applications. The utilization of recycled materials in concrete can potentially conserve the environment by eliminating unnecessary consumption of limited landfill areas and reduce energy consumption. The use of recycled aggregate (RA) from construction and demolition waste and the use of RTSF derived from post consumed tires are good examples. However, the variability in the characteristics of RA and RAC are the main engineering concerns which hinder the use of RAC in structural application. This paper examines the effect of the addition of RTSF and RA on the behaviour of concrete. The results show that RTSF significantly improve the mechanical properties of RAC. The flexural performance of RAC with 2% (by mass) RTSF is better than normal concrete without fibres and equivalent to normal concrete with 2% fibres.