Time filter

Source Type

Albitar M.,University of AdelaideSouth Australia | Mohamed Ali M.S.,University of AdelaideSouth Australia | Visintin P.,University of AdelaideSouth Australia
Construction and Building Materials | Year: 2017

Geopolymer concretes have emerged as novel engineering materials with the potential to significantly reduce the environmental footprint of concrete manufacture and utilise high volume of industrial waste materials. Although significant experimental research has focused on the development of geopolymer mix design, there is far less information available regarding the performance of geopolymer concretes at a member level. This has implications in transferring geopolymer concretes from a laboratory material to a material in which can be specified in practice. This paper addresses the application of geopolymer concrete at a member level through an experimental investigation on the behaviour of fly ash/granulated lead smelter slag (GLSS)-based geopolymer concrete columns and beams tested under concentric and eccentric loading. Slenderness effect of the geopolymer concrete columns is investigated and axial load-moment interaction envelopes are generated experimentally. The analytical interaction diagrams are compared to those calculated using classical methods for normal reinforced concrete beams and columns. The results of the comparison show that the analytical interaction diagrams overestimated the test results due to variation in material properties. Nevertheless, the results reveal that fly ash/GLSS-based geopolymer concrete exhibits similar structural behaviour to ordinary Portland cement (OPC) concrete. The results also highlight potential issues with the scaling of ambient-cured geopolymer concrete to the structural level. © 2017 Elsevier Ltd

Farokhi H.,McGill University | Ghayesh M.H.,University of AdelaideSouth Australia | Gholipour A.,University of AdelaideSouth Australia
International Journal of Engineering Science | Year: 2017

The nonlinear size-dependent dynamics of a functionally graded micro-cantilever is investigated when subject to a base excitation resulting in large-amplitude oscillations. A geometric nonlinearities due to large changes in the curvature is taken into account. Employing the Mori–Tanaka homogenisation technique (for the material properties), the modified couple stress theory (MCST) is used to formulate the potential and kinetic energies of the system in terms of the transverse and axial motions. A dynamic energy balance is performed between the energy terms, yielding the continuous models for the axial and transverse displacements. The inextensibility condition results in the size-dependent model of the functionally graded micro-cantilever involving inertial and stiffness nonlinear terms. The resultant model is discretised based on a weighted-residual technique yielding a high-dimensional truncated model (required for accurate simulations). A parameter-continuation scheme together with a time integration method is introduced to the truncated model so as to determine the resonances with stable and unstable solution branches with special consideration to the effect of different system parameters, such as material gradient index and the length-scale effect on the nonlinear dynamics of the functionally graded micro-cantilever. © 2017 Elsevier Ltd

Ghayesh M.H.,University of AdelaideSouth Australia | Farokhi H.,McGill University | Gholipour A.,University of AdelaideSouth Australia
International Journal of Mechanical Sciences | Year: 2017

The vibration behaviour of a geometrically imperfect three-layered shear-deformable microbeam is analysed via model development and numerical simulations. Taking into account all the translational and rotational motions, considering continuous variations through the thickness for the displacement field, employing the modified couple stress theory for including small-size effects, and using constitutive relations for both stress and the deviatoric part of the couple stress tensors, the size-dependent elastic energy stored in the three-layered shear-deformable microbeam is obtained. The kinetic energy, work of an internal damping mechanism, and the work due to an external harmonic excitation force of the three-layered microsystem are also obtained and dynamically balanced by the size-dependent elastic energy by means of Hamilton's principle. The continuous expressions obtained for the axial, transverse, and rotational motions of the three-layered microsystem are truncated to high-dimensional reduced-order models with the help of a weighted-residual method. Numerical simulations are conducted by means of the backward differentiation formula (BDF) in conjunction with a continuation method. The nonlinear vibration behaviour of the microsystem is then analysed by plotting the coupled frequency-responses. The effect of the length-scale parameters as well as the material fraction and thickness of each layer on the vibration behaviour of the microsystem is highlighted. © 2017 Elsevier Ltd

Bunder J.E.,University of AdelaideSouth Australia | Roberts A.J.,University of AdelaideSouth Australia | Kevrekidis I.G.,Princeton University
Journal of Computational Physics | Year: 2017

Computational simulation of microscale detailed systems is frequently only feasible over spatial domains much smaller than the macroscale of interest. The ‘equation-free’ methodology couples many small patches of microscale computations across space to empower efficient computational simulation over macroscale domains of interest. Motivated by molecular or agent simulations, we analyse the performance of various coupling schemes for patches when the microscale is inherently ‘rough’. As a canonical problem in this universality class, we systematically analyse the case of heterogeneous diffusion on a lattice. Computer algebra explores how the dynamics of coupled patches predict the large scale emergent macroscale dynamics of the computational scheme. We determine good design for the coupling of patches by comparing the macroscale predictions from patch dynamics with the emergent macroscale on the entire domain, thus minimising the computational error of the multiscale modelling. The minimal error on the macroscale is obtained when the coupling utilises averaging regions which are between a third and a half of the patch. Moreover, when the symmetry of the inter-patch coupling matches that of the underlying microscale structure, patch dynamics predicts the desired macroscale dynamics to any specified order of error. The results confirm that the patch scheme is useful for macroscale computational simulation of a range of systems with microscale heterogeneity. © 2017 Elsevier Inc.

Albitar M.,University of AdelaideSouth Australia | Mohamed Ali M.S.,University of Adelaide | Visintin P.,University of Adelaide | Drechsler M.,University of Adelaide
Construction and Building Materials | Year: 2017

Durability of concrete strongly influences the service life of structural members. Durable concrete protects embedded reinforcing steel from corrosion and reduces the potential for concrete spalling under chemical attack. This paper evaluates the performance of geopolymer concretes manufactured using either class-F fly ash or blended fly ash and granulated lead smelter slag (GLSS). The performance of ordinary Portland cement (OPC) concrete is also investigated as a reference for evaluating the durability characteristics of geopolymer concretes. All concrete specimens were continuously immersed up to nine months in four different chemical solutions: 5% sodium chloride, 5% sodium sulphate, 5% sodium sulphate + 5% magnesium sulphate, and 3% sulphuric acid. Throughout the exposure period, the change in mass, compressive strength, splitting tensile strength, flexural strength, water absorption, sorptivity and porosity were evaluated. The influence of wetting–drying and heating–cooling cycles on the mass loss and compressive strength was also investigated. The results revealed that the OPC concrete has lower water absorption and sorptivity than the geopolymer concrete. Furthermore, it is shown that sodium sulphate has the greatest impact on geopolymer concretes, while OPC concrete is more susceptible to sulphuric acid attack. The results showed that, in general, the durability performance of geopolymer concrete is superior to that of OPC concrete within the range of the considered exposure. © 2017

Zheng B.,University of AdelaideSouth Australia | Marschner P.,University of AdelaideSouth Australia
Geoderma | Year: 2017

In previous studies we showed the existence of a legacy effect, that is, the C/N ratio of the previously added residue influences soil respiration and nutrient availability after the second residue addition. We hypothesised that the legacy effect is due to microbes decomposing both the remaining previously added residue and the second residue. Thus, the extent of the legacy effect would depend on the amount of previously added residue left in the soil when the second residue is added. In the present study low C/N (L, young faba bean shoots, C/N 19) or high C/N residue (H mature wheat straw, C/N 73) was added at 2.5, 5 or 10 g kg− 1 on day 0, the control was left unamended. The second residue which had the same or a different C/N ratio than the first, was added on day 14 at 10 g kg− 1. Thus, there were 14 treatments, unamended soil in the first period, then H or L residue (Control-H, Control-L). In the other treatments, 2.5, 5 or 10 g kg− 1 of either H or L were followed by 10 g kg− 1 H or L residue, giving the treatments HH, HL, LL and LH. Soil respiration was measured continuously, available N and P and microbial biomass C, N and P (MBC, MBN, MBP) were measured on days 0, 14 (before second residue addition) and 28 (end of experiment). At the end of the first period, cumulative respiration, available N, P and MBC, MBN and MBP were higher with L compared to H. In both H and L, compared to the lowest addition rate, cumulative respiration was about two and four fold higher with 5 and 10 g kg− 1. Microbial biomass C, N and P on day 14 increased with addition rate with a greater increase with L compared to H. Available N on day 14 increased with addition rate in L, but decreased with H. There was a clear legacy effect after the second residue addition because for example, MBC on day 28 was similar in HL and LH whereas available N was lower in HL and Control-L than LL. The extent of the legacy effect was influenced by the initial addition rate. For example, available N on day 28 in HL decreased with rate of H in the first period, but increased with rate of L. It was about 40% higher in LH10 than in LH2.5. It can be concluded that the legacy effect depends on the amount of previously added residue left in the soil when the second residue is added. © 2016 Elsevier B.V.

Yildirim T.,University of Wollongong | Ghayesh M.H.,University of AdelaideSouth Australia | Li W.,University of Wollongong | Alici G.,University of Wollongong
Energy Conversion and Management | Year: 2016

An energy harvester has been designed, fabricated and tested based on the nonlinear dynamical response of a parametrically excited clamped-clamped beam with a central point-mass; magnets have been used as the central point-mass which pass through a coil when parametrically excited. Experiments have been conducted for the energy harvester when the system is excited (i) harmonically near the primary resonance; (ii) harmonically near the principal parametric resonance; (iii) by means of a non-smooth periodic excitation. An electrodynamic shaker was used to parametrically excite the system and the corresponding displacement of the magnet and output voltages of the coil were measured. It has been shown that the system displays linear behaviour at the primary resonance; however, at the principal parametric resonance, the motion characteristic of the magnet substantially changed displaying a strong softening-type nonlinearity. Theoretical simulations have also been conducted in order to verify the experimental results; the comparison between theory and experiment were within very good agreement of each other. The energy harvester developed in this paper is capable of harvesting energy close to the primary resonance as well as the principal parametric resonance; the frequency-band has been broadened significantly mainly due to the nonlinear effects as well as the parametric excitation. © 2016

Afroughsabet V.,Polytechnic of Milan | Ozbakkaloglu T.,University of AdelaideSouth Australia
Construction and Building Materials | Year: 2015

This study investigates the effect of the addition of steel and polypropylene fibers on the mechanical and some durability properties of high-strength concrete (HSC). Hooked-end steel fibers with a 60-mm length were used at four different fiber volume fractions of 0.25%, 0.50%, 0.75%, and 1.0%. Polypropylene fibers with a 12-mm length were used at the content of 0.15%, 0.30%, and 0.45%. Some mixtures were produced with the combination of steel and polypropylene fibers at a total fiber volume fraction of 1.0% by volume of concrete, in order to study the effect of fiber hybridization. All the fiber-reinforced concretes contained 10% silica fume as a cement replacement. The compressive strength, splitting tensile strength, flexural strength, electrical resistivity, and water absorption of the concrete mixes were examined. Results of the experimental study indicate that addition of silica fume improves both mechanical and durability properties of plain concrete. The results also indicate that incorporation of steel and polypropylene fibers improved the mechanical properties of HSC at each volume fraction considered in this study. Furthermore, it was observed that the addition of 1% steel fiber significantly enhanced the splitting tensile strength and flexural strength of concrete. Among different combinations of steel and polypropylene fibers investigated, the best performance was attained by a mixture that contained 0.85% steel and 0.15% polypropylene fiber. Finally, the results show that introducing fibers to concrete resulted in a decrease in water absorption and, depending on the type of fibers, significant or slight reduction in the electrical resistivity of concrete compared to those of the companion plain concrete. ©2015 Elsevier Ltd. All rights reserved.

Hudson R.J.,University of AdelaideSouth Australia | Falcinella A.,University of AdelaideSouth Australia | Metha G.F.,University of AdelaideSouth Australia
Chemical Physics | Year: 2016

Titanium oxide and gold-titanium oxide clusters of stoichiometry MxOy (Mx = Ti3, Ti4 & AuTi3; y = 0 − (2x + 2)) have been investigated using density functional theory. Geometries of determined global energy minimum structures are reported and other isomers predicted up to 0.5 eV higher in energy. The Ti3On geometries build upon a triangular Ti3 motif, while Ti4On stoichiometries template upon a pseudo-tetrahedral Ti4 structure. Addition of a gold atom to the Ti3On series does not significantly alter the cluster geometry, with the gold atom preferentially binding to titanium atoms over oxygen atoms. Adiabatic ionization energies, electron affinities and HOMO/LUMO energies increase in magnitude with increasing oxygenation. The HOMO-LUMO energy gaps reach the bulk anatase band gap energy at stoichiometry (Au)TimO2m−1, and increase above this upon further oxygen addition. The most stable structural moieties are found to be a cage-like, C3v symmetric Ti4O6/7 geometry and a Ti3O6 structure with an η3-bound oxygen atom. © 2016

Mo K.H.,University of Malaya | Visintin P.,University of AdelaideSouth Australia | Alengaram U.J.,University of Malaya | Jumaat M.Z.,University of Malaya
Engineering Structures | Year: 2016

This paper presents the investigation on the local bond stress-slip behaviour of lightweight oil palm shell concrete (OPSC). The bond properties of the OPSC specimen with varying reinforcing bar diameters (12 and 16 mm), concrete cover sizes (50, 75 and 100 mm) and compressive strengths (25 and 35 MPa) were explored. A concrete cover size to reinforcing bar diameter (C/D) ratio of more than 4.17 resulted in pull-out failure while the ratio of 3.13 caused splitting cracks in the OPSC specimens. The reinforcing bar diameter, concrete cover size and compressive strength affected the normalized bond strength, provided that the splitting failure occurred in the concrete specimens. The proposed bond model for splitting failure incorporating the C/D ratio used in the closed-form solution for prediction of the serviceability crack width was found to give good estimation of the experimental results obtained from the full-scale beam tests. © 2016 Elsevier Ltd

Loading University of AdelaideSouth Australia collaborators
Loading University of AdelaideSouth Australia collaborators