Shrinkage Behaviour of Steel-Fibre-Reinforced-Concrete Pavements

The use of steel fibres extracted from waste tyres as reinforcement for concrete pavements has been developed at the University of Sheffield. The EU funded EcoLanes Project (Economical and sustainable pavement infrastructure for surface transport) undertook extensive research and developed solutions for Steel-Fibre-Reinforced-Concrete (SFRC) pavements with a particular focus on using recycled steel fibres and roller compacted concrete. The current research project ran alongside the EcoLanes project and aimed at contributing towards the development of design guidelines for pavements reinforced with recycled steel fibres. It was achieved through a study on the restrained shrinkage behaviour of Recycled-Steel-Fibre-Reinforced-Roller-Compacted-Concrete (R-SFR-RCC) pavements, and its consequent effect on the load bearing capacity and fatigue performance of pavements. The work in this thesis is mainly based on numerical investigations, but experiments were carried out to obtain the material properties (moisture transport, free shrinkage and mechanical). These basic physical properties were extracted from test results, using inverse analysis. The extent of distress induced by drying shrinkage was evaluated using moisture transport analysis coupled with stress analysis. The effect of shrinkage distress on the load bearing capacity of the pavement was investigated in a comparative way with and without shrinkage. Fatigue test results were also used to study the long-term load-bearing capacity. It was found that the rate of drying and consequent moisture diffusivity in SFRC is higher than for plain concrete and in RCC it is higher than for CC. Moisture diffusivity varies in the range of 0-5 mm2/day for moisture contents lower than 87-92% and then sharply increases to 30 mm2/day for saturated concrete. Free shrinkage is lower for SFRC compared with plain concrete, at early ages. RCC free shrinkage develops at a more uniform rate compared to CC. For the studied SFR-RCC pavement, surface micro-cracks are formed predominantly due to curling (with opening density of 0.69 mm/m) potentially forming micro-cracks (0.014 mm-0.056 mm width) spaced at 20 mm-60 mm. Cracking at the top surface initiates from the beginning of drying, and stabilises after 180 days. Shrinkage cracking penetrates down to around a quarter of the slab thickness, and the tensile strength at the top surface reduces 50% of the maximum strength; whereas based on the Concrete Society TR34, the strength reduces by 30% at the surface and drops linearly to zero at half depth. The current study found that the stress induced by curling is dominant, compared to that induced by external restraints. Shrinkage induced cracks was found to reduce the ultimate load bearing capacity and the fatigue capacity of the pavement by up to 50%

Moisture transport and drying shrinkage properties of steel-fibre-reinforced-concrete.

Drying shrinkage has a serious impact on the structural and durability performance of concrete pavements. Shrinkage strain development and distress can only be fully understood by knowing the moisture transport and free shrinkage properties of concrete. This paper uses experiments and FE inverse analysis to determine these properties for conventional concrete (CC) and RCC reinforced with recycled-steel-fibres from tyres. Moisture diffusivity versus moisture content and a relationship between free shrinkage and moisture loss are derived. These values can be used to predict shrinkage strains and stresses in road pavements and other ground restrained slabs

Steel-fibre-reinforcement and increasing the load-bearing capacity of concrete pavements.

Elastic theories form the basic concept used in most of the existing design codes for industrial or transportation plain and conventionally reinforced concrete ground slabs. The post-cracking load bearing capacity of slabs-on-ground is not taken into account in most of these codes. Therefore, these codes (e.g. PCA, ACI) cannot be used directly for steel fibre reinforced concrete (SFRC). Guidelines for SFRC (e.g. Concrete Society) use the ultimate limit state concept for fibre reinforced ground floors, but only partially, since cracking is only allowed to occur on the bottom surface of the slab. The highly repetitive nature of the loads which may cause considerable degradation in the mechanical properties of the pavement and foundation also is not considered in this method. The aim of this paper is to evaluate the load-bearing capacity of SFRC pavements through numerical simulations, and to assess the accuracy of the analytical methods used in different design codes

Rubberised concrete confined with thin-walled steel profiles : a ductile composite for building structures

Funding Information: This research was supported by the Royal Academy of Engineering Frontiers of Development Seed Funding scheme on Low-carbon seismic-resistant buildings (FoD2021\4\26).Peer reviewedPublisher PD

Rubberised concrete confined with thin-walled steel profiles: a ductile composite for building structures.

Tyre components are high-quality materials, which can be utilised and disposed into construction projects. Despite its high ductility and impact resistance, rubberised concrete (RuC) with high rubber content has a strength much lower than that of conventional concrete. Previous research shows that confinement by a jacket material can significantly improve the strength of RuC. This paper presents how infilling RuC to cold-formed steel (CFS) sections improves strength of RuC and local-buckling-resistance of CFS thin-walled sections, resulting in composite elements where the advantage of each material cancels out the disadvantage of another. In this research, composite RuC-CFS elements are developed and tested with the purpose of using them for structural frames with high energy dissipation capacity under extreme loading conditions, while providing resource-efficiency by using lightweight CFS and recycled RuC materials. To enable infilling of long steel hollow sections for beams and columns, the experimental RuC mixes are designed for self-compaction (SCC). The results reveal that 35% rubber content (by volume) and 3mm thickness of the CFS profile (S275 grade) gives the best performance of the composite by adding 19% to the capacity of the individual constitute materials

The effect of strong ambient winds on the efficiency of solar updraft power towers: a numerical case study for Orkney.

Solar updraft tower (SUT) is a simple power plant in which ventilation of heated air inside a channel drives a turbine. This system is recognised as suitable for areas with abundant solar radiation. As a result, there is no extensive research on the performance of SUTs under mild solar radiation. Studies show that strong ambient crosswinds can affect the performance of a SUT. In this paper, the efficiency of SUTs in areas which benefit from strong winds, despite low solar radiation, is investigated through numerical modelling. Comparison is made between the efficiency of a commercial-scale SUT in Manzanares (Spain) with intensive solar radiation, and one of the same size potentially located in the windy and mild climate of Orkney Islands in Scotland. The results show that ambient crosswinds can increase internal air speed and efficiency of a SUT by more than 15% and 50%, respectively. Consequently, such a SUT in Orkney can offer more than 70% of the efficiency of the one in Manzanares. The results show that, for a given power capacity, a wind turbine enclosed in a SUT can be considered as an alternative to a number of conventional wind turbines installed at height in the open air

Shrinkage behaviour of SFRC industrial ground floors.

Restrained shrinkage is an important issue in design of concrete industrial ground floors, although it is often overlooked. This paper studies shrinkage behaviour of a SFRC floor subjected to static racking load, through FE simulation. The ultimate load bearing capacity and cracking of the floor is assessed. It is shown that shortly-spaced surface micro-cracks are formed due to shrinkage. These cracks are not initially visible, but get longer and wider after loading. As a result, the load-carrying capacity of the floor reduces significantly, and the equivalent crack opening by up to 10 times

Experiments on cyclic behaviour of cold-formed steel-rubberised concrete semi-rigid moment-resisting connections.

This paper presents the results of full-scale physical tests on a recently developed cold-formed steel (CFS) semi-rigid moment-resisting connection infilled with rubberised concrete (RuC) for seismic application. The connection comprises side-plates attached to both sides of built-up tubular CFS beam and column sections through either screwed or welded connections. The tests were performed on both bare steel and CFS-RuC composite connections under cyclic loading for comparison purposes. The predominant modes of failure are beam local buckling and side plate plasticity in the bare steel connections and screw shear failure in the composite connections. The results show that the composite connection typically reaches 45% higher strength and 21% greater energy dissipation capacity than the bare steel connection both having 24 screw arrays. These indicate the beneficial effects of the infill RuC in prevention of the beam local buckling in connections with identical connection configuration. The energy dissipation capacity of the bare steel connection having 36 screw arrays, however, was 70% greater than that of the composite connection with 24 screw arrays. This reflects side plate plasticity being a more effective energy dissipation mechanism than the other identified mechanisms

The effect of shrinkage cracks on the load bearing capacity of steel-fibre-reinforced roller-compacted-concrete pavements.

This paper demonstrates the effect of shrinkage cracks on the static load bearing capacity and on the fatigue performance of RCC pavements reinforced with steel fibres recycled from post-consumer tyres, with the aid of a case study. A numerical method is adopted using material properties (moisture transport, free shrinkage, mechanical and fatigue) derived from experiments. It is shown that surface micro-cracks initially develop predominantly due to differential shrinkage (curling). These micro-cracks penetrate down to approximately a quarter of the slab thickness and it is shown that they reduce the ultimate load bearing and fatigue capacity of the pavement by up to 50%. Even though shrinkage does not initially induce visible cracks, it significantly intensifies the crack opening due to traffic load by up to 500% for a crack width of 0.5 mm. For the case studied herein, to assure the long-term performance of the pavement the allowable stress ratio should be reduced by half, to account for the effect of shrinkage distress. This study is useful because for the first time the mechanical characteristics are coupled with the moisture transport mechanism, as well as the shrinkage and fatigue characteristics. This methodology can be used for other similar materials and geometries and can lead to general conclusions regarding the importance of shrinkage distress on the design of pavements

Composite cold-formed steel rubberised concrete building framed systems.

In this research, with the use of cold-formed steel (CFS) sections in-filled with rubberized concrete (RuC), a new low-carbon construction system is developed and assessed for its structural resilience and environmental impact compared to the current conventional earthquake-proof construction. First, connection level moment-rotation responses of the new form of CFS-RuC framed structure are validated against the results obtained from detailed finite element analyses. Next, nonlinear pushover analyses are undertaken on the CFS-RuC framed system in conjunction with conventional hot-rolled steel and reinforced-concrete (RC) frames for a case study selected in Istanbul. Lastly, economic and environmental impact analyses are conducted on the frame systems. The results show that the new CFS-RuC composite system offers both structural and environmental advantages compared to conventional systems. In terms of seismic performance of multi-storey buildings, it is shown that the ductility capacity of the CFS-RuC system can be improved by increasing the number of stories