Stephanie Barnett

Fast-Track Construction with Slag Cement Concrete: Adiabatic Strength Development and Strength Prediction

The early-age strength development of concrete containing slag cement has been investigated to give guidance for its use in fast-track construction. Measurements of temperature rise under adiabatic conditions have shown that high levels of slag cement-for example, 70% of the total binder-are required to obtain a significant reduction in the peak temperature rise. Despite these temperature rises being lower than those for portland cement mixtures, however, the early-age strength under adiabatic conditions of slag cement concrete can be as high as 250% of the strength of companion cubes cured at 20 °C (68 °F). The maturity and, hence, strength development were calculated from the adiabatic temperature histories based on several maturity functions available in the literature. The predicted strength development with age was compared with the experimental results. Maturity junctions that take into account the lower ultimate strengths obtained at elevated curing temperatures were found to be better at predicting the strength development.

Multiscale Shannon’s Entropy Modeling of Orientation and Distance in Steel Fiber Micro-Tomography Data

This paper is concerned with the modeling and analysis of the orientation and distance between steel fibers in X-ray micro-tomography data. The advantage of combining both orientation and separation in a model is that it helps provide a detailed understanding of how the steel fibers are arranged, which is easy to compare. The developed models are designed to summarize the randomness of the orientation distribution of the steel fibers both locally and across an entire volume based on multiscale entropy. Theoretical modeling, simulation, and application to real imaging data are shown here. The theoretical modeling of multiscale entropy for orientation includes a proof showing the final form of the multiscale taken over a linear range of scales. A series of image processing operations are also included to overcome interslice connectivity issues to help derive the statistical descriptions of the orientation distributions of the steel fibers. The results demonstrate that multiscale entropy provides unique insights into both simulated and real imaging data of steel fiber reinforced concrete.

Modelling behaviour of ultra high performance fibre reinforced concrete

Abstract The cohesive crack model (CCM) is the most commonly accepted discrete crack approach for modelling concrete based materials. It is applied to ultra high performance fibre reinforced concrete (UHPFRC) in this study because it can be easily represented as cohesive interface elements in finite element modelling. Cohesive crack model using a bilinear traction–separation relationship is used to simulate the load–deflection behaviour of UHPFRC test specimens. Cohesive crack model based numerical simulation of three-point bend specimens are implemented using cohesive elements in ABAQUS FE software. Progressive crack propagation and failure mechanism of UHPFRC test specimens are simulated in order to predict their load capacities. Comparison of the simulation to existing experimental test results indicates that CCM with a bilinear traction–separation curve can provide predictions of both the load–deflection curves and peak load of 100 and 150 mm deep UHPFRC test specimens to  = /−6% of the average for 50 and 100 mm wide beams and to  = /+20% for 150 mm wide beams. Model predictions of the peak load for the 50 mm wide and 50 mm deep beams were to  = /−25% of the average.

Effects of steel fibre-aggregate interaction on mechanical behaviour of steel fibre reinforced concrete

ABSTRACT This work investigated the effects of fibre type, dosage and maximum aggregate size on the mechanical behaviour of concrete reinforced with steel fibres. Hooked-end steel fibres with 50 and 60 mm length and aspect ratios (length/diameter) of 45, 65 and 80 were used with maximum sizes of coarse aggregate of 10 and 20 mm. The same mix proportions of concrete were used throughout the investigation. Flexural testing of 600 mm square panels was performed. Subsequently, cores were taken from these panels and X-ray computed tomography was used to analyse the positioning of fibres in hardened concrete. The experimental results show that the performance of steel fibre-reinforced concrete improved drastically when compared to plain concrete without fibres. Longer, thinner fibres and smaller aggregates were noted to give the best results.

Distribution and orientation of steel fibres in steel fibre reinforced concrete

The use of fibres to reinforce brittle materials for better performance has been employed since time immemorial. Therefore, inclusion of steel fibres in concrete has always improved the post-cracking strength and concrete ductility to a large extent while full potential of steel fibre reinforced concrete (SFRC) is still yet to be exploited in practice. This study investigated the effects of fibre type, dosage and maximum aggregate size on distribution and orientation and hence, the flexural performance of steel fibre reinforced concrete. Hooked-end steel fibres with 50 mm and 60 mm length, aspect ratio of 45, 65 and 80, and dosages of 0 kg/m³, 25 kg/m³, 40 kg/m³, 50 kg/m³ and 60 kg/m³ were used with maximum sizes of coarse aggregate of 10mm and 20mm. X-ray Computed Tomography was employed for imaging cores taken from the slab specimens after testing. The experimental results show a remarkable improvements in flexural strength up to 83% observed at larger dosage of steel fibre and when good interaction leading to better distribution and orientation of fibres within concrete matrix is sustained between right fibre geometry and appropriately sized aggregate.

Effects of hook shape and cement replacement materials on pullout behaviour of steel fibres

The purpose of this study is to investigate the effect of hook shape and material of high tensile strength hooked end steel fibres and the impact of cement replacement materials on pullout behaviour of steel fibres from cementitious composites. The cement replacements which have been used in this research included silica fume, pulverised fuel ash, limestone filler and ground granulated blast-furnace slag. In total, more than 800 samples have been manufactured for experimental research on compressive strength and pullout behaviour of hooked end steel fibres from cementitious matrices. The effects of parameters such as water/binder ratio, cement replacement content, age of sample, hooked end shape and tensile strength of fibre on fibre–matrix pullout behaviour were determined. The results of tests and analysis indicate that hook shape, tensile strength of fibre and silica fume affect the maximum pullout force and ground granulated blast-furnace slag can significantly improve the residual pullout energy which would be useful for the optimisation of steel fibre reinforced concrete. The outcome of this research may be useful to widen the potential applications of the material across civil engineering.

Cement and concrete science

The ‘Cement and Conference Science’ conference is an annual conference series that attracts over 100 delegates from around the world with an interest in the development of cement and concrete science. Organised by the Cementitious Materials Group of the Institute of Materials, Minerals and Mining, the conference provides attendees with an opportunity to share the outcome of their research findings and at the same time identify how further progress can be made. A major aim of the conference organising committee has been to encourage participation of student researchers, providing them with the opportunity to present their work and also meet leading researchers and industrialists in the field of cement and concrete research.

Study of fibre orientation and distribution in UHPFRC by electrical resistivity and mechanical tests

ABSTRACT This paper presents experimental tests carried out on steel fibre reinforced concrete samples, including mechanical tests as well as non-destructive technique (electrical resistivity) and non destructive technique on cores (X-ray). Electrical resistivity measurements are done as a blind test, to characterise the electrical anisotropy and deduce the distribution and the orientation of fibres. These results are compared to X-ray imaging to check the quality of the non destructive evaluation. Then, flexural and compressive strength are measured on specimens to assess the influence of fibre distribution on the concrete properties.