Fibre-reinforced roller-compacted concrete transport pavements

Concrete pavements are generally more expensive to construct than asphalt pavements, and are thus mostly used in heavily trafficked sections and to reduce maintenance. The research work presented in this paper, however, indicated that the use of rapid construction techniques (such as roller compaction) and materials with lower embodied energy (such as low-energy cements, recycled aggregates and recycled steel fibres) can lead to concrete pavements that are more economical and environmentally friendly than asphalt pavements (40% less energy consumption during the life cycle of the pavement). The first part of this paper presents an overview of this research, which was undertaken as part of the EU FP6 STREP project ‘EcoLanes’ and investigated the development of long-lasting rigid pavements made with steel-fibre-reinforced roller-compacted concrete. The second part of the paper outlines the work undertaken for the development and optimisation of several trial concrete mixes. It is shown that the flexural behaviour of roller-compacted concrete, under static loads, can be enhanced by the addition of fibres. Furthermore, the results of this study demonstrated the potential of recycling concrete pavements, at the end of their life, for the construction of new pavements

REUSED TYRE POLYMER FIBRE FOR FIRE-SPALLING MITIGATION

Polypropylene fibres (PPF) are used in concrete principally to reduce plastic shrinkage cracking, but also to prevent explosive spalling of concrete exposed to fire. In the EU alone, an estimated 75,000 tonnes of virgin PPF are used each year. At the same time an estimated 63,000 tonnes of polymer fibres are recovered from end-of-life tyres, which are agglomerated and too contaminated with rubber to find any alternative use; currently these are mainly disposed of by incineration. The authors have initiated a study on the feasibility of reusing tyre polymer fibres in fresh concrete to mitigate fire-induced spalling. If successful, this will permit replacement of the virgin PPF currently used with a reused product of equal or superior performance. A preliminary experimental investigation is presented in this paper. High-strength concrete cubes/slabs have been tested under thermo-mechanical loading. This study has shown promising results; the specimens with the tyre polymer fibres have shown lower vulnerability to spalling than those of plain concrete

FirmSolo: Enabling dynamic analysis of binary Linux-based IoT kernel modules

CNS-2127232 - National Science FoundationAccepted manuscrip

Fire Protection of Concrete Tunnel Linings with Waste Tyre Fibres

The damages caused by fire-induced explosive spalling of concrete in tunnels can be tremendous; it could result in enormous economic cost and potential loss of human life. For this reason, the structural fire protection of concrete tunnel linings plays an important role in the tunnel design. Polypropylene fibres have been used in concrete to prevent explosive spalling of concrete exposed to fire. On the other hands, thousands of tonnes of polymer fibres are generated worldwide as a by-product of the recycling of end-of-life tyres. Storage of these fibres is a problem, since it is flammable, of low density (and so very large in volume) and can be carried away by wind and pollutes the surrounding environment. They are also too agglomerated or contaminated with rubber to find any alternative use, and are generally disposed of by incineration. The polymer fibre recycled from tyres has equal high quality and durability as manufactured fibres. Finding ways of introducing these fibres in concrete can potentially reduce the use of virgin fibres and delivery a more environmental-friendly spalling-mitigation solution. This paper shows the preliminary outcomes of this research, which indicates the potential of using these recycled fibres to prevent fire spalling instead of manufactured polypropylene

Post-cracking tensile behaviour of steel-fibre-reinforced roller-compacted-concrete for FE modelling and design purposes

Fracture of steel-fibre-reinforced-concrete occurs mostly in the form of a smeared crack band undergoing progressive microcracking. For FE modelling and design purposes, this crack band could be characterised by a stress-strain (σ-ε) relationship. For industrially-produced steel fibres, existing methodologies such as RILEM TC 162-TDF (2003) propose empirical equations to predict a trilinear σ-ε relationship directly from bending test results. This paper evaluates the accuracy of these methodologies and their applicability for rollercompacted-concrete and concrete incorporating steel fibres recycled from post-consumer tyres. It is shown that the energy absorption capacity is generally overestimated by these methodologies, sometimes up to 60%, for both conventional and roller-compacted concrete. Tensile behaviour of fibre-reinforced-concrete is estimated in this paper by inverse analysis of bending test results, examining a variety of concrete mixes and steel fibres. A multilinear relationship is proposed which largely eliminates the overestimation problem and can lead to safer designs

Effect of impaction on third molar development and age estimation-A study in a Lebanese population.

BACKGROUND The effect of impaction on third molar development is disputable as the scientific literature is not uniform. In parallel, population-specific studies have been encouraged in dental age estimation. This study aimed to investigate the effect of impaction on third molar formation in a sample of Lebanese individuals. MATERIALS AND METHODS The sample consisted of 518 panoramic radiographs of females (n=229) and males (n=289) between 15 and 23.9 years. Mandibular third molars were classified based on their position as non-impacted and impacted (with horizontal, vertical, mesioangular, and distoangular impaction). Dental development was classified according to Demirjian's 8-level staging system. RESULTS Most teeth presented mesioangular impaction (#38=29.7%, #48=33%). Developing third molars were predominantly distributed between stages D and G. The mean age of most developmental stages was higher among impacted teeth, meaning that third molar mineralization could be slower in the presence of impaction. In general, the delayed dental development did not have statistically significant effects (P12 months-suggesting a potential clinical significance (despite the lack of a statistical one). Furthermore, differences changed based on sex and side (#38/#48). CONCLUSION Therefore, dental age estimation from third molars in the selected Lebanese population should preferably be performed in non-impacted third molars whenever available

Mechanical properties of SFRC using blended manufactured and recycled tyre steel fibres

This paper investigates the mechanical properties of 10 steel fibre reinforced concrete (SFRC) mixes at fibre dosages of 30, 35 and 45 kg/m3. Manufactured Steel Fibres (MSF) are used on their own, or blended with sorted steel fibres recycled from end-of-life tyres (RTSF). To characterise the flexural behaviour of the mixes, two flexural test methods, BS EN 14651:2005 3-point notched prism tests and ASTM C1550-05 centrally loaded round panel tests are employed. A strong correlation is found in the flexural behaviour of the SFRC prism and round panel specimens, with corresponding conversion equations proposed. The mechanical properties of hybrid mixes using RTSF vary depending on dosages, but are comparable with those of MSF-only mixes at the same fibre dosage. A positive synergetic effect is derived from hybrid mixes containing 10 kg/m3 of RTSF

Effects of recycled steel and polymer fibres on explosive fire spalling of concrete

Modern high-performance concrete, increasingly used in tunnels and other important infrastructure, is susceptible to explosive fire-induced spalling. To prevent fire spalling, modern codes recommend the use of small quantities (e.g. 2 kg/m3 as recommended by the Eurocodes) of polypropylene fibres in the concrete mix. This paper presents an experimental study investigating, the effect of cleaned recycled fibres extracted from end-of-life tyres on the explosive fire-induced spalling of concrete. This paper presents 24 spalling tests, indicating that recycled tyre polymer fibres, at dosages equal to or larger than 2 kg/m3, might help prevent fire spalling. Recycled tyre steel fibres also show the potential of preventing fire spalling damage by keeping spalled concrete attached to the heated surface, thus protecting the main steel reinforcement. The use of these fibres might lead to safe and sustainable fire spalling mitigation solutions

Fibrous roller-compacted concrete with recycled materials - Feasibility study

This paper presents fundamental work done to enable fibre reinforcement of roller-compacted concrete (RCC). Procedures for mixing and casting two types of steel fibres in RCC were developed. Fresh properties, uniaxial compressive and bending behaviour were examined in a pilot study dealing with cement content, fibre type and dosage. It was found that different fibre types and dosages require different moisture contents. It is concluded that low cement content (less than 300 kg/m3) steel-fibre-reinforced roller-compacted concrete (SFR-RCC) mixes do not have sufficient paste and are prone to fibre agglomeration, hence SFR-RCC mixes richer in paste and at optimum moisture content are recommended. Mixes with cement content of 300 kg/m3 coped better with fibre reinforcement. Despite causing some loss in compressive strength, fibres help enhance the flexural performance and even SFR-RCC mixes with recycled masonry and concrete aggregates performed equally well as natural aggregate mixes. A fullscale trial has been conducted to confirm the findings. This paper is followed by a companion paper dealing with a comprehensive parametric study leading to the development of σ-ε models for SFR-RCC

Single Dose Novel Salmonella Vaccine Enhances Resistance against Visceralizing L. major and L. donovani Infection in Susceptible BALB/c Mice

Visceral leishmaniasis is a major neglected tropical disease, with an estimated 500,000 new cases and more than 50,000 deaths attributable to this disease every year. Drug therapy is available but costly and resistance against several drug classes has evolved. Despite all efforts, no commercial, let alone affordable, vaccine is available to date. Thus, the development of cost effective, needle-independent vaccines is a high priority. Here, we have continued efforts to develop live vaccine carriers based on recombinant Salmonella. We used an in silico approach to select novel Leishmania parasite antigens from proteomic data sets, with selection criteria based on protein abundance, conservation across Leishmania species and low homology to host species. Five chosen antigens were differentially expressed on the surface or in the cytosol of Salmonella typhimurium SL3261. A two-step procedure was developed to select optimal Salmonella vaccine strains for each antigen, based on bacterial fitness and antigen expression levels. We show that vaccine strains of Salmonella expressing the novel Leishmania antigens LinJ08.1190 and LinJ23.0410 significantly reduced visceralisation of L. major and enhanced systemic resistance against L. donovani in susceptible BALB/c mice. The results show that Salmonella are valid vaccine carriers for inducing resistance against visceral leishmaniasis but that their use may not be suitable for all antigens