Ductility enhancement of geopolymer concrete columns using FRP confinement

Geopolymer concrete is an environmentally friendly, green construction material. However its use is constrained by its increased brittleness and lack of understanding of its behaviour under multi-axial loadings. Similar to Ordinary Portland Cement concrete (OPC), the ductility of geopolymer concrete columns can be increased by lateral confinement and using Fibre Reinforce Polymers is one option in doing that. This research paper aims at investigating the effect of different confinement on the ductility of geopolymer concrete. Three different mixes with varying binder (fly ash and slag) and different curing conditions together with different levels of carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP) confinement were investigated in this research paper. FRP confined normal strength geopolymer concrete shows similar stress-strain behaviour to those for high strength OPC concrete When compared with the same level of confinement, CFRP confined geopolymer concrete marginally outperforms GFRP confined geopolymer concrete in 28 day compressive strength. However ductility levels with GFRP confinement are better than those with CFRP confinement

Analysis of a typical railway turnout sleeper system using grillage beam analogy

A simplified grillage beam analogy was performed to investigate the behaviour of railway turnout sleeper system with a low value of elastic modulus on different support moduli. This study aimed at determining an optimum modulus of elasticity for an emerging technology for railway turnout application - fibre composites sleeper. The finite element simulation suggests that the changes in modulus of elasticity of sleeper, Esleeper and the sleeper support modulus, Us have a significant influence on the behaviour of turnout sleepers. The increase in Us from 10 to 40 MPa resulted in a 15% reduction in the bending moment while the increase in Esleeper from 1 GPa to 10 GPa has resulted in almost 75% increase in the bending moment. The shear forces in turnout sleepers is not sensitive to both the changes of the Esleeper and Us while the sleeper with low Esleeper tend to undergo greater settlement into the ballast. An Esleeper of 4 GPa was found optimal for an alternative fibre composite turnout sleeper provided that the Us is at least 20 MPa from the consideration of sleeper ballast pressure and maximum vertical deflection. It was established that the turnout sleeper has a maximum bending moment of 19 kN-m and a shear force of 158 kN under service conditions

Dynamic behaviour of fibre composite multilayer sandwich plates with delaminations

Composites are continuing to gain prominence for structural as well as non-structural applications all over the world. A structural composite multilayer slab can be manufactured by gluing several of the composite sandwiches together to form a laminated composite slab. Delamination between layers is one of the major failure modes which threaten the reliability of composite structures. Delamination can also cause changes to dynamic behaviour. Dynamic analysis of three dimensional models of structures enables more realistic assessment of their free vibration behaviour. The dynamic behaviour of fibre composite multilayer sandwich plates with different configurations of delamination is presented in this paper. A parametric investigation is carried out to assess the influence of parameters including length, width and location of delamination, size and support conditions of the plates on the free vibration behaviour, using three dimensional modelling with Strand7 finite element software package. Plate elements for skins and brick elements for core of each sandwich layer are used in the model development for plates representing their actual behaviour. It is revealed that the decrease in natural frequency with the increase in the extent of debonding is greatly dependent on the boundary conditions, location of the debond and also on the mode number

Fibre reinforced geopolymer concrete with ambient curing for in-situ applications

Geopolymer concrete is proven to have excellent engineering properties with a reduced carbon footprint. It not only reduces the greenhouse gas emissions (compared to Portland cement based concrete) but also utilises a large amount of industrial waste materials such as fly ash and slag. Due to these positive attributes, it is becoming an increasingly popular construction material. Previous studies on geopolymer concrete report that heat curing plays an important role in gaining higher compressive strength values (as opposed to ambient curing) and hence the application of this material could be limited to precast members. Therefore, this research was aimed at investigating the effect of heat curing by comparing the mechanical properties such as compressive strength and ductility of ambient cured and heat cured geopolymer concrete samples. It is worth noting that there was marginal strength change due to heat curing. In Australia fibre-reinforced geopolymer concrete is being used in precast panels in underground constructions. Commercially available geopolymer cement and synthetic fibres are effectively being used to produce elements that are more durable than what is currently used in industry. As a result, this research investigated the effects of polypropylene fibres in geopolymer concrete using 0.05% and 0.15% fibres (by weight). The addition of polypropylene fibres enhances the compressive strength and the ductility of geopolymer concrete

Geopolymer concrete: the green alternative with suitable structural properties

Concrete is the most widely used building material around the world because of the availability of raw materials, the simplicity in preparation and the moulding into different shapes. One of the main ingredients in a normal concrete mixture is Portland cement. However recent literature reveals that cement industry accounts for approximately 5 % of the current man made carbon dioxide (CO2) emission worldwide. World cement demand and production are ever increasing with the expected growth is from approximately 2836 million tons in 2010 to between 3680 (low estimate) and 4380 million tons (high estimate) by 2050. Knowing that about 1.5 tons of raw materials are needed in the production of every ton of Portland cement concrete and about one ton of CO2 is released in to the environment during the production, developing alternative construction materials is required. This paper will review the utilization of geopolymer concrete as an alternative for Ordinary Portland Cement concrete. The use of new greener material instead of concrete requires two main characteristics: reduced environmental impact which is a main concern in the world and better structural performance. This paper aims at investigating these characteristics using the available literature

Investigating the performance of floodway in an extreme flood event

Resilience of critical infrastructure such as roads, telecommunications and power is vital in support activities for disaster response and recovery. In the event of natural disasters such as the Queensland floods, resilient roads were critical to survival and safety, as well as to the health and security of the region. Disaster damage to road structures such as bridges, culverts and floodway significantly increases the vulnerability of communities. This research paper investigates the damage caused by the recent floods in Queensland on the floodway. Floodway in Lockyer Valley Regional council (LVRC) area in Queensland has been selected as a case study. LVRC has identified a major need to re-examine the design of flood-ways, which have to be designed to be submerged during a flood and return to complete functionality after the flood water subsides. In 2011 flood, about 58% of the floodway were damaged in LVRC area. Many of the flood-ways were damaged during the period of submergence and are currently the weakest links in Lockyer Valley roads after a flood. There are no standard design guidelines for these structures accepted at national level. In this case study, data such as the dimensions, materials used (concrete, gravel with concrete overlay), culvert details and the type of road where the floodway are situated will be collected. Inspection of damaged floodway revealed that the damage due to the floods was mainly due to the excessive debris load and impact load. This paper aims at developing a strategy for flood-way design considering impact loading and debris loading by using a detailed analysis of flood-ways in this region

Testing and characterization of pultruded glass fiber reinforced polymer (GFRP) beams

Elastic properties of the fiber reinforced polymer (FRP) composite represent a significant effect on the structural behaviour of this material. Therefore, it is important to use an accurate method to determine these properties as the behaviour is often governed by deflection rather than strength. In this study, full size pultruded glass FRP (GFRP) beams were used to determine the elastic properties using static four-point bending with different shear span to depth (a/d) ratios. Two different methods -back calculation and simultaneous - were then employed to evaluate the flexural modulus and shear stiffness and were compared with the results of the test using coupon specimens. The results indicate that the elastic properties determined from full scale test using back calculation method can reliably predict the load - deflection behaviour of the pultruded GFRP beams

The effect of shear span-to-depth ratio on the failure mode and strength of pultruded GFRP beams

The use of structural pultruded fibre reinforced polymers (FRP) sections have gained wide acceptance in civil engineering applications due to their favourable structural characteristics like high strength, light weight and durability in severe environmental conditions. However, due to their relatively low modulus of elasticity and thinned walls, these sections are vulnerable to local buckling which can affect their ultimate strength. This paper investigates experimentally the flexural behaviour of pultruded GFRP beams with shear span-to-depth (a/d) ratios in the range of 1.2 to 6 using full scale pultruded profiles. Failure modes, strength and crack patterns are the main parameters that were examined in this study. The study shows that shear span has a minor effect on the failure modes of the beams while it has a noticeable effect on the ultimate strength. In addition, fibre model analysis was used to validate the experimental results. Comparison between the experimental and the theoretical analysis results shows a good approximation of the moment - deflection behaviour and failure moment of pultruded GFRP beams

Behaviour of hollow pultruded GFRP square beams with different shear span-to-depth ratios

It is important to determine accurately the elastic properties of fibre-reinforced polymer composites material, considering that their member design is often governed by deflection rather than strength. In this study, the elastic properties of the pultruded glass fibre-reinforced polymer square sections were evaluated firstly using full-scale with different shear span to depth (a/d) ratios and tested under static four-point bending. Back calculation and simultaneous methods were then employed to evaluate the flexural modulus and shear stiffness and were compared with the results of the coupon tests. Secondly, the full-scale beams were tested up to failure to determine their capacity and failure mechanisms. Finally, prediction equations describing the behaviour of the pultruded glass fibre-reinforced polymer square beams were proposed and compared with the experimental results. The results indicate that the back calculation method gives more reliable values of elastic properties of glass fibre-reinforced polymer profiles. In addition, the behaviour of the beams is strongly affected by the a/d ratios. The shear was found to have a significant contribution on the behaviour of beams with lower a/d ratios while the flexural stress played a major part for higher a/d ratios. The proposed equation, which accounts for the combined effect of the shear and flexural stresses, reasonably predicted the failure load of pultruded glass fibre-reinforced polymer square beams

Flexural behavior of glued GFRP tubes filled with concrete

The corrosion of steel reinforcement is considered the greatest factor limiting the service life of reinforced concrete structures. Glass fiber reinforced polymers (GFRPs) are known as cost-effective materials offering long-term durability and less maintenance. As a result, these materials show great potential for use in the civil engineering applications. Due to the high cost of the manufacturing die, pultruded GFRP tubes are produced in specific cross-section dimensions only. For high load applications and to comply with the serviceability requirements, a number of these pultruded sections can be assembled together by gluing them appropriately. This study presents an experimental investigation onto the flexural behavior of glued GFRP tube beams with 1, 2, 3 and 4 - cells filled with concrete under four-point loading. The results show that the strength of the 4 cells glued beams increased by 150 % and 88% for hollow and filled beams, respectively, compared with its counterpart single cell beam. The filled beams failed at 42 – 88 % higher load and showed 10 – 22 % higher stiffness compared with their hollow counterparts. The results also show that gluing small section tubes to produce large section beam is a practical solution to enhance the flexural performance of the composite tubes