Sustainability assessment of steel fibre reinforced concrete pavements

The current scenario of depleting resources has lead to a major thrust in developing and applying highly sustainable solutions to construction industry. Therefore, it has become essential to devise designs based on materials that cost the least for the transportation network and at the same time have a minimum environmental impact. Though there are a few modern material solutions that may meet these criteria, like the use of steel fibre reinforced concrete (SFRC) for pavement constructions, a proper evaluation of the performance and impact of utilization of such materials is lacking. Life Cycle Assessment (LCA) and Life Cycle Cost Analysis (LCCA) offer the means to evaluate the sustainability, and have been used in this paper to provide frameworks analysing Asphalt, Jointed Plain concrete (JPC) and Steel Fibre Reinforced Concrete pavements. In this work, asphalt, JPC and SFRC pavement sections have been designed as per the respective IRC guidelines so as to get equivalent designs for the given traffic loading, environmental and material conditions. Subsequently, LCCA is done as per the procedure provided in the Federal Highway Administration’s Interim Technical bulletin and LCA is done by using the process approach for each of the pavements. The assessment indicates where sustainable practices can be directed to so as to minimize environmental impacts in the initial stage of the pavement life cycle. The paper also discusses the limitations and difficulties of carrying out life cycle assessment and life cycle cost analysis for highways in India

Improving interface bonding of double-skinned CFST columns

It has been demonstrated that high-strength concrete (HSC) is able to improve the strength-to-weight ratio of reinforced concrete columns and maximise the usable areas of tall buildings. However, closely spaced transverse reinforcement needs to be installed to provide stronger confinement for averting brittle failure of HSC. To resolve the problem, double-skinned concrete-filled-steel-tubular (CFST) columns have been advocated, which eliminates the steel congestion problem for better concrete placing and reduces the concrete arching action thus providing a more uniform confining pressure. Despite these advantages, a major shortcoming of double-skinned CFST columns is that imperfect interface bonding occurs in the elastic stage that reduces elastic strength and stiffness. Thus, the authors proposed to adopt external confinement to restrict the lateral dilation of the outer tube of double-skinned CFST columns. To verify the effectiveness of the proposed external rings, a total of 20 double-skinned normal- and high-strength CFST columns were tested. From the test results, it was observed that the stiffness, axial load-carrying capacity and ductility of ringconfined double-skinned CFST columns were significantly higher than the unconfined columns

Estudio del comportamiento a cortante de vigas de hormigón reforzado con fibras

This study presents a series of tests for characterizing the structural behaviour of fibre reinforced concrete beams subjected to shear loading. The experimental program involves three types of fibres; two steel fibres and a polypropylene fibre. As a reference, plain concrete and conventionally reinforced concrete specimens have also been tested. The ultimate shear capacity of the beams is calculated and these values compared with those predicted by existing formulations. The study confirms that the toughness and shear crack resistance of the material is greatly enhanced by the fibres. However, the incorporation of 1% of fibres yielded lower shear strength than conventionally reinforced beams with the same amount of steel in the form of transversal stirrups. Existing design methods seem sufficiently robust to estimate the maximum shear load, even when using material properties (toughness, tensile strength) extrapolated from code formulae.Este trabajo presenta una serie de ensayos para caracterizar el comportamiento estructural de vigas realizadas con hormigón reforzado con fibras sometidas a cortante. El programa de ensayos incluía tres tipos de fibras, dos de acero y una de polipropileno. Asimismo, se realizó una serie de ensayos con una viga confeccionada con hormigón armado convencional. La resistencia a cortante de las vigas es comparada con los valores que la formulación existente predice. El estudio confirma que la tenacidad y la resistencia a cortante son incrementadas tras la adición de fibras al hormigón. Sin embargo, la incorporación de un 1% en volumen de fibras conduce a valores de resistencia última a cortante inferiores a los obtenidos con vigas de hormigón convencional con la misma cantidad de acero dispuesta en forma de cercos de cortante. Los actuales métodos de cálculo parecen lo suficientemente precisos para evaluar la carga de cortante último, incluso cuando los parámetros mecánicos utilizados en las fórmulas (tenacidad, resistencia a tracción) son deducidos a partir de la formulación propuesta en la normativa

Fracture properties of GGBFS-blended fly ash geopolymer concrete cured in ambient temperature

Fracture characteristics are important part of concrete design against brittle failure. Recently, fly ash geopolymer binder is gaining significant interest as a greener alternative to traditional ordinary Portland cement (OPC). Hence it is important to understand the failure behaviour of fly ash based geopolymers for safe design of structures built with such materials. This paper presents the fracture properties of ambient-cured geopolymer concrete (GPC). Notched beam specimens of GPC mixtures based mainly on fly ash and a small percentage of ground granulated blast furnace slag were subjected to three-point bending test to evaluate fracture behaviour. The effect of mixture proportions on the fracture properties were compared with control as well as OPC concrete. The results show that fracture properties are influenced by the mixture compositions. Presence of additional water affected fracture properties adversely. Fracture energy is generally governed by tensile strength which correlates with compressive strength. Critical stress intensity factor varies with the variation of flexural strength. Geopolymer concrete specimens showed similar load–deflection behaviour as OPC concrete specimens. The ambient cured GPC showed relatively more ductility than the previously reported heat cured GPC, which is comparable to the OPC specimens. Fly ash based GPC achieved relatively higher fracture energy and similar values of KIC as compared to those of OPC concrete of similar compressive strength. Thus, fly ash based GPC designed for curing in ambient condition can achieve fracture properties comparable to those of normal OPC concrete

Steel fibre reinforced concrete for elements failing in bending and in shear

Discrete steel fibres can increase significantly the bending and the shear resistance of concrete structural elements when Steel Fibre Reinforced Concrete (SFRC) is designed in such a way that fibre reinforcing mechanisms are optimized. To assess the fibre reinforcement effectiveness in shallow structural elements failing in bending and in shear, experimental and numerical research were performed. Uniaxial compression and bending tests were executed to derive the constitutive laws of the developed SFRC. Using a cross-section layered model and the material constitutive laws, the deformational behaviour of structural elements failing in bending was predicted from the moment-curvature relationship of the representative cross sections. To evaluate the influence of the percentage of fibres on the shear resistance of shallow structures, three point bending tests with shallow beams were performed. The applicability of the formulation proposed by RILEM TC 162-TDF for the prediction of the shear resistance of SFRC elements was evaluated. Inverse analysis was adopted to determine indirectly the values of the fracture mode I parameters of the developed SFRC. With these values, and using a softening diagram for modelling the crack shear softening behaviour, the response of the SFRC beams failing in shear was predicted.Fundação para a Ciência e a Tecnologia (FCT

Characterizing bridged cracks in fibrous high-strength concrete

An inverse problem based on a bridged-crack model is formulated to characterize the toughening mechanisms in fibrous high-strength concretes. Experimental data of short three-point bend specimens are used in the analysis