Multi-response optimization of hybrid fibre engineered cementitious composite using Grey-Taguchi method and utility concept

This paper presents an experimental investigation conducted to assess the suitability of Taguchi-Grey relational analysis (GRA) and Taguchi method with utility concept (UC) for mix design optimization of a hybrid fibre engineered cementitious composite (ECC). Slag, fly ash and dolomite are utilized as binder materials and the quantity of various constituents of ECC is optimized to achieve improved compressive and tensile performance. In addition, two weighting techniques based on equal weight and maximum deviation are employed in the analysis and their effects on improving the efficiency of the optimization approach is also assessed. The design of experiments is first carried out using a standard Taguchi orthogonal array consisting of five factors viz. total cement replacement level, dolomite to binder ratio, slag to fly ash ratio, fibre proportions, and water binder ratio, at four levels. Thereafter, GRA and UC are applied to evaluate the composite indices and compute the optimal proportions targeting five response parameters namely compressive strength, peak compressive strain, elastic modulus, tensile strength, and ultimate tensile strain. Results indicate that both GRA and UC can be effectively integrated with Taguchi method for obtaining an optimal mix design of the ECC. Moreover, the use of weighting technique based on the maximum deviation method is found to be more appropriate as it can distinguish between relative effectiveness of different response parameters. The best performing mix had total cement replacement of 60%, 15% dolomite content by binder, slag to FA ratio of 1:0.2, 2.25% total fibre content, water-binder ratio of 0.20 and exhibited desired compressive and tensile properties for structural applications

Mechanical properties of high-strength steel–polyvinyl alcohol hybrid fibre engineered cementitious composites

With the advancement of material technology, the use of high-strength and high-performance materials in the construction industry is gaining popularity. Steel–polyvinyl alcohol (steel–PVA) hybrid fibre engineered cementitious composites (ECC) is one of such high-performance class of construction materials whose mechanical properties are not well studied in the literature especially in high-strength matrix. Therefore, in this paper, the mechanical properties of four different grades of high-strength steel–PVA ECC are experimentally investigated. ECC with nominal compressive strengths from 60 to 100 MPa are developed. Their mechanical properties including compressive and tensile stress–strain behaviour, elastic modulus and toughness are studied with particular focus on high-strength matrix. Test results show that the developed steel–PVA ECC could achieve good tensile (~0.8%) and compressive (~0.5%) ductility for general structural applications. Simple empirical relationships to predict the elastic modulus and tensile strength of the developed steel–PVA ECC as a function of their compressive strength are suggested. Moreover, an analytical model to generate a complete compressive stress–strain curve of the high-strength steel–PVA ECC is proposed and verified against the experimental results. The proposed stress–strain model would present a useful reference for non-linear analysis of structural elements utilising steel–PVA ECC

Geochemistry of the Panzhihua Mafic Layered Intrusion (SW China): Petrogenetic Implications for its Giant V-Ti-Magnetite Deposit

published_or_final_versio

On the tortuosity factor of solid phase in solid oxide fuel cell electrodes

2014-2015 > Academic research: refereed > Publication in refereed journalAccepted ManuscriptPublishe

Strength enhancement of high strength steel beams by engineered cementitious composites encasement

This study proposes a method of using Polyvinyl Alcohol Engineered Cementitious Composites (PVA-ECC) encasement to provide continuous restraints along the compression flange of High Strength Steel (HSS) section so that it will reach its sectional plastic moment resistance under bending without lateral restraint. In order to demonstrate the effectiveness of the proposed method, experimental and numerical investigations were carried out to study the flexural strength of the ECC encased HSS beams (ECC-HSS beams). Six simply supported beams fabricated with identical HSS sections but with different encasement configurations were tested until failure. Flexural resistance and failure modes of the ECC-HSS beams were compared with similar bare HSS and normal concrete (NC) encased HSS beams (NC-HSS beams). It was found that when compared with the bare HSS and NC-HSS beams, a significant enhancement in flexural resistance was achieved for the ECC-HSS beams. More importantly, this study confirmed that the compressive ECC layers was crushed after the compression flanges were yielded and therefore successfully prevented the onset of lateral torsional buckling. Besides the flexural responses, the interfacial slip behaviours along the compression flange of the HSS section were also studied. Finally, a finite element (FE) model was developed and validated against the experimental results

Engineered cementitious composites (ECC) encased concrete-steel composite stub columns under concentric compression

This paper presents an experimental investigation on the behaviour of a new form of engineered cementitious composites (ECC) encased concrete-steel composite stub columns. The proposed column section uses ECC encasement as a potential confinement layer to control the premature concrete spalling and explosive brittle failure of concrete encased steel composite columns. In this study, twelve stub columns including two bare steel and ten composite sections are tested under concentric compression. The effects of some key parameters such as material strengths, steel section type and column section configuration on the performance of proposed column sections were investigated in terms of failure behaviour, load deformation response, toughness and ductility. It was found that ECC encasement improved the compressive failure behaviour of encased composite columns and enhanced their ductility and toughness. Strain analysis was performed to trace the strain development and damage patterns of different materials. Finally, a simple equation to estimate ultimate strength of proposed columns was proposed which gave good predictions agreed well with test results

Compressive behaviour of engineered cementitious composites and concrete encased steel composite columns

This paper presents the results of an experimental study on the compressive behaviour of engineered cementitious composites and concrete encased steel (ECC-CES) composite columns. Two configurations of ECC-CES composite columns based on fully and partially concrete encasement were considered. A total of eleven short columns with different ECC and concrete encasing configurations were tested under pure compression. The effects of ECC strength, concrete strength and column configuration on the column compressive behaviour were investigated and reported in terms of failure modes, load-deformation curves, ductility and toughness. In addition, in order to study the confinement effect of different thickness ECC covers on high strength concrete (HSC), three ECC encased HSC short columns without encased steel section were also tested. The experimental results were compared with the ultimate strength predictions from different design codes for the tested columns. It was found that current design guidelines were generally conservative. Therefore, new equations with modified factors to predict the ultimate strength of ECC-CES columns were proposed. Finally, a comparison of performance of ECC-CES with conventional CES columns suggested that the ECC encasement could provide an alternative way to confine concrete core in columns applications

Compressive performance of ECC-concrete encased high strength steel composite columns

The use of high strength steel (HSS) in the construction of concrete encased steel (CES) composite columns is often limited by the strain incompatibility issue between HSS and concrete at peak-load. This study proposes an alternative approach to confine the high strength concrete with Engineered Cementitious Composite (ECC) to improve its compatibility with high strength steel. The main purpose of this study is to experimentally evaluate the axial compressive performance of the proposed composite column cross-section configuration. Behaviours of fifteen short columns including twelve ECC-CES columns are investigated in terms of failure modes, load-deformation curves, ductility and energy absorption capacity. The test parameters included ECC and concrete strengths, ECC cover thickness, steel section shape and column section's aspect ratio. It was found that ECC generally improved the failure behaviour of high strength steel CES columns and increased the deformation and energy absorption capacity. On average ECC-CES columns showed around 12% and 8% higher ductility and toughness than control concrete column, respectively. A detailed 3D nonlinear finite element model was developed and validated against experimental results. Applicability of current design codes to predict the ultimate strength of ECC-CES columns was also evaluated. Finally, a method to calculate the ECC-CES column's capacity considering effective material stresses at peak-load was proposed

Numerical and analytical investigations of flexural behaviours of ECC–LWC encased steel beams

By conducting a series of experimental study, the authors recently demonstrated that engineered cementitious composites (ECC) can be employed to encase the compression flanges of structural steel sections to prevent slender flanges from local buckling and lateral torsional buckling of laterally unconstrainted beams. In this context, this paper presents comprehensive numerical and analytical investigations on the flexural behaviour of ECC-lightweight concrete (LWC) encased steel beams with a wide range of steel section geometry (from compact to slender) and steel grade (from normal strength to high strength). In the numerical study, a validated three–dimensional (3D) nonlinear finite element (FE) model was adopted to carry out a parametric study on the flexural capacity of 234 encased beams with different design parameters such as steel grade, ECC and LWC strengths, compactness of steel section, beam depth to width aspect ratio and flange and web thicknesses etc. Furthermore, an analytical model was developed by using the strain compatibility and force equilibrium conditions to predict the load-deformation curves of the encased beams until the flexural failure of the beams. Finally, in order to reduce efforts needed for day-to-day design, a simplified analytical solution was also proposed, and its accuracy was validated

Extreme rejuvenation and softening in a bulk metallic glass.

Rejuvenation of metallic glasses, bringing them to higher-energy states, is of interest in improving their plasticity. The mechanisms of rejuvenation are poorly understood, and its limits remain unexplored. We use constrained loading in compression to impose substantial plastic flow on a zirconium-based bulk metallic glass. The maximum measured effects are that the hardness of the glass decreases by 36%, and its excess enthalpy (above the relaxed state) increases to 41% of the enthalpy of melting. Comparably high degrees of rejuvenation have been reported only on microscopic scales at the centre of shear bands confined to low volume fractions. This extreme rejuvenation of a bulk glass gives a state equivalent to that obtainable by quenching the liquid at ~1010 K s-1, many orders of magnitude faster than is possible for bulk specimens. The contrast with earlier results showing relaxation in similar tests under tension emphasizes the importance of hydrostatic stress