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1 – 10 of over 119000Ali Mohamed Ali Aboshia, Riza Atiq Rahmat, Muhammad Fauzi Mohd Zain and Amiruddin Ismail
The purpose of this paper is to develop an alternative new ternary geopolymer mortar (MKSP) to resolve a traditional mortar problem which exhibits several disadvantages, including…
Abstract
Purpose
The purpose of this paper is to develop an alternative new ternary geopolymer mortar (MKSP) to resolve a traditional mortar problem which exhibits several disadvantages, including poor strengths and surface microcracks and the CO2 air pollution.
Design/methodology/approach
The MKSP ternary binder was produced using metakaolin (MK), slag (S), and palm oil fuel ash (POFA) activated with an alkaline mixture of sodium silicate (Na2SiO3) and 10 M NaOH in a mass ratio of 2.5. Seven different mix proportions of MK, slag, and POFA were used to fabricate MKSP mortars. The water-to-binder ratio was varied between 0.4 and 0.5. The mortars were heat cured for 2 h at 80°C and then aged in air. Flexural stress and strain, mortars flow and compressive strength were tested. Furthermore, the mortars were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) analyses.
Findings
The results showed that the sample MKSP6, which contained 40 percent MK, 40 percent slag, and 20 percent POFA, exhibited high compressive strength (52 MPa) without any cracks and flexural strength (6.9 MPa) at 28 days after being cured for 2 h at 80°C; however, the MKSP7 mortar with optimal strength of 55 MPa showed some surface cracks . Further, the results of the XRD, SEM, and FTIR analyses indicated that the MKSP mortars primarily consisted of a crystalline (Si+Al) phase (70 percent) and a smaller amorphous (Si+Ca) phase (30 percent).
Research limitations/implications
The MKSP ternary geopolymer mix has three limitations as an importance of heat curing for development early strength, POFA content less than 20 percent to gain high normal strength and delaying the sitting time by controlling the slag content or the alkali activator type.
Practical implications
The use of geopolymer materials binder in a real building is limited and it still under research, Thus, the first model of real applied geopolymer cement in 2008 was the E-Crete model that formed by Zeobond company Australia to take the technology of geopolymer concrete to reality. Zeobond Pty Ltd was founded by Professor Jannie S.J. van (van Deventer et al., 2013), it was used to product precast concrete for the building structure. The second model was PYRAMENT model in 2002 by American cement manufacturer Lone Star Industries which was produced from the development carried out on inorganic alumino-silicate polymers called geopolymer (Palomo et al., 1999). In 2013 the third model was Queensland’s University GCI building with three suspended floors made from structural geopolymer concrete containing slag/fly ash-based geopolymer (Pathak, 2016). In Australia, 2014, the newly completed Brisbane West Wellcamp airport becomes the greenest airport in the world. Cement-free geopolymer concrete was used to save more than 6,600 tons of carbon emissions in the construction of the airport. Therefore, the next century will see cement companies developing alternative binders that are more environmentally friendly from a sustainable development point of view.
Originality/value
Production of new geopolymer binder of mortar as alternative to traditional cement binder with high early and normal strength from low cost waste materials, less potential of cracking, less energy consumption need and low carbon dioxide emission.
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This paper aims to answer two questions. First, are there any differences in the fire performance of columns made of normal and of high-strength concrete? Second, under which…
Abstract
Purpose
This paper aims to answer two questions. First, are there any differences in the fire performance of columns made of normal and of high-strength concrete? Second, under which circumstances does the fire design govern the cross-sectional dimensions of concrete columns? Is it feasible to replace columns out of normal strength concrete by more slender high-strength concrete columns?
Design/methodology/approach
The author conducted numerical studies using the finite element code “Infocad” of the German company “Infograph”. The studies included the effect of different parameters on the fire performance of columns out of normal and high-strength concrete, i.e. the load ratio and eccentricity, boundary conditions and times of fire exposure.
Findings
Results from the numerical investigations showed that high-strength concrete columns suffer much more from heating than normal strength concrete columns. This is the outcome of the unfavourable mechanical properties of high-strength concrete at elevated temperatures. Although the relative fire performance of columns out of high-strength concrete is worse than that of columns out of normal strength concrete, initial load reserves are beneficial to achieve even high fire ratings.
Originality/value
Many researchers addressed in experimental and numerical studies the fire performance of columns out of normal and high-strength concrete. A special emphasis was often laid on the spalling of fire-exposed high-strength concrete. However, there are no systematic investigations when the fire design governs the cross-sectional dimensions of high-strength concrete columns. Based on a previous comparison of the relative fire performance of columns out of normal and high-strength concrete, this paper, hence, addresses the question whether there is a reasonable lower limit for the use of these columns. This is an important aspect for designers since there is a tendency to replace columns out of normal strength concrete by columns out of high-strength concrete. Higher concrete strengths allow for smaller cross sections of the columns, and designers may, hence, increase the usable space of buildings.
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R.V. Balendran, T.M. Rana, T. Maqsood and W.C. Tang
The inclusion of pozzolans like pulverised fuel ash (PFA), silica fume (SF) and metakaolin (MK) enhances the properties of concrete both in fresh and hardened states. In the case…
Abstract
The inclusion of pozzolans like pulverised fuel ash (PFA), silica fume (SF) and metakaolin (MK) enhances the properties of concrete both in fresh and hardened states. In the case of high performance concrete (HPC), their role in enhancing the workability, strength and durability is extremely significant. However HPC has been observed to be more vulnerable than normal strength concrete when exposed to elevated temperatures. This paper presents an overview and discusses the strength and durability performance of high‐performance pozzolanic concretes incorporating PFA, SF, and MK subjected to elevated temperatures. Various researchers have demonstrated that addition of silica fume causes HPC to perform poorly when subjected to elevated temperatures. Higher loss of strength and spalling risks are also associated with it. Addition of PFA and MK has been found to improve the fire performance of HPC both in terms of residual strength and durability.
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Sharon Conley and Sherry A. Woosley
Educational researchers have long been concerned with role stress among teachers. In education, research on the consequences of such role stress for teachers has largely concerned…
Abstract
Educational researchers have long been concerned with role stress among teachers. In education, research on the consequences of such role stress for teachers has largely concerned outcomes valued by individuals such as job satisfaction and reduced stress. Less research has focused on examining the effects of role stress on outcomes valued by the organization, such as employee commitment and employee retention. In examining the role stress‐outcome relationship, research suggests the importance of taking into consideration the work orientations of individuals as possible moderators of the role stress‐outcome relationship. Using a sample of elementary and secondary teachers, this study empirically examined, first whether three role stresses – role ambiguity, role conflict, and role overload – are related to two individually and two organizationally valued states and second, whether teachers’ higher‐order need strength moderates these role stress‐outcome relationships. The study found that role stresses relate to individually‐ and organizationally‐valued outcomes among both elementary and secondary teachers.
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Kei Kimura, Takeshi Onogi and Fuminobu Ozaki
This work examines the effects of strain rate on the effective yield strength of high-strength steel at elevated temperatures, through tensile coupon tests at various strain…
Abstract
Purpose
This work examines the effects of strain rate on the effective yield strength of high-strength steel at elevated temperatures, through tensile coupon tests at various strain rates, to propose appropriate reduction factors considering the strain rate effect.
Design/methodology/approach
The stress–strain relationships of 385 N/mm2, 440 N/mm2 and 630 N/mm2-class steel plates at elevated temperatures are examined at three strain rate values (0.3%/min, 3.0%/min and 7.5%/min), and the reduction factors for the effective yield strength at elevated temperatures are evaluated from the results. A differential evolution-based optimization is used to produce the reduction-factor curves.
Findings
The strain rate effect enhances with an increase in the standard design value of the yield point. The effective yield strength and standard design value of the yield point exhibit high linearity between 600 and 700 °C. In addition to effectively evaluating the test results, the proposed reduction-factor curves can also help determine the ultimate strength of a steel member at collapse.
Originality/value
The novelty of this study is the quantitative evaluation of the relationship between the standard design value of yield point at ambient temperature and the strain-rate effect at elevated temperatures. It has been observed that the effect of the strain rate at elevated temperatures increases with the increase in the standard design value of the yield point for various steel strength grades.
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Yulin Li, Jiabao Wang, Hang Zhang and Ruilin Pei
The purpose of the paper is to make a high speed motor based on the characteristics of high strength silicon steel. With the higher requirements for torque density and power…
Abstract
Purpose
The purpose of the paper is to make a high speed motor based on the characteristics of high strength silicon steel. With the higher requirements for torque density and power density of the driving system of electric vehicles (EV), conventional magnetic materials have been difficult to meet the demands in the future. In this paper, a new type of high-strength non-grain-oriented (NGO)material is tested.
Design/methodology/approach
Through analyzing the characteristic of high strength silicon steel, it is applied to the rotor part of a high-speed motor. A topological optimization is applied to achieve higher power density and higher efficiency of the motor.
Findings
The feasibility of the scheme was analyzed by the finite element method, and a prototype was also fabricated to verify the analysis.
Originality/value
In this paper, the characteristics of new soft magnetic materials as a breakthrough to manufacture a new generation of high-performance electrical machine (EM) are discussed. Consequently, the presented work greatly facilitates further explorations and guides the innovative application of soft magnetic materials and the iterative optimization of motor structure.
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Muhd Afiq Hizami Abdullah, Mohd Zulham Affandi Mohd Zahid, Afizah Ayob and Khairunnisa Muhamad
The purpose of this study is to investigate the effect on flexural strength of fire-damaged concrete repaired with high-strength mortar (HSM).
Abstract
Purpose
The purpose of this study is to investigate the effect on flexural strength of fire-damaged concrete repaired with high-strength mortar (HSM).
Design/methodology/approach
Reinforced concrete beams with dimension of 100 mm × 100 mm × 500 mm were used in this study. Beams were then heated to 400°C and overlaid with either HSM or high-strength fiber reinforced mortar (HSFM) to measure the effectiveness of repair material. Repaired beams of different material were then tested for flexural strength. Another group of beams was also repaired and tested by the same procedure but was heated at higher temperature of 600°C.
Findings
Repair of 400°C fire-damaged samples using HSM regained 72 per cent of its original flexural strength, 100.8 per cent of its original toughness and 56.9 per cent of its original elastic stiffness. Repair of 400°C fire-damaged samples using HSFM regained 113.5 per cent of its original flexural strength, 113 per cent of its original toughness and 85.1 per cent of its original elastic stiffness. Repair of 600°C fire-damaged samples using HSM regained 18.7 per cent of its original flexural strength, 25.9 per cent of its original peak load capacity, 26.1 per cent of its original toughness and 22 per cent of its original elastic stiffness. Repair of 600°C fire-damaged samples using HSFM regained 68.4 per cent of its original flexural strength, 96.5 per cent of its original peak load capacity, 71.2 per cent of its original toughness and 52.2 per cent of its original elastic stiffness.
Research limitations/implications
This research is limited to the size of the furnace. The beam specimen is limited to 500 mm of length and overall dimensions. This dimension is not practical in actual structure, hence it may cause exaggeration of deteriorating effect of heating on reinforced concrete beam.
Practical implications
This study may promote more investigation of using HSM as repair material for fire-damaged concrete. This will lead to real-world application and practical solution for fire-damaged structure.
Social implications
The aim of this research in using HSM mostly due to the material’s high workability which will ease its application and promote quality in repair of damaged structure.
Originality/value
There is a dearth of research on using HSM as repair material for fire-damaged concrete. Some research has been carried out using mortar but at lower strength compared to this research.
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Daniel Paul Thanaraj, Anand N. and Prince Arulraj
The purpose of this study is to investigate the effect of standard fire on the strength and microstructure properties of concrete with different strength grades.
Abstract
Purpose
The purpose of this study is to investigate the effect of standard fire on the strength and microstructure properties of concrete with different strength grades.
Design/methodology/approach
Different strength grades of concrete used for the investigation are M20, M30, M40 and M50. An electrical bogie hearth furnace was developed to simulate the International Standards Organization 834 standard fire curve.Concrete samples were subjected to high temperatures of 925, 1,029, 1,090 and 1,133°C for the duration of 1, 2, 3 and 4 h, respectively, as per standard fire curve. Compressive strength, tensile strength, thermal crack pattern and spalling of heated concrete specimens were evaluated by experimental investigation. Scanning electron microscopy and thermo-gravimetric analysis were performed to investigate the microstructure properties of heated concrete specimens.
Findings
Test results indicated reduction in the strength and changes in the microstructure properties of concrete exposed to elevated temperature. The degree of weight and the strength loss were found to be higher for concrete with higher grades. An empirical relation is proposed to determine the residual strength of concrete with different strength grade using regression analysis.
Social implications
Results of this research will be useful for the design engineers to understand the behavior of concrete exposed to elevated temperature as per standard fire.
Originality/value
When concrete is exposed to elevated temperature, its internal microstructure changes, thereby strength and durability of concrete deteriorates. The performance of concrete with different strength grade exposed to standard fire is well understood. This research’s findings will be useful for the designers to understand more about fire resistance of concrete. A simple relationship is proposed to determine the residual strength of concrete exposed to various durations of heating.
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Ashok Kumar Sahani, Amiya K. Samanta and Dilip K. Singharoy
Present study focuses on scope of developing sustainable heat resistant concrete by adding steel fibre (Sf) and polypropylene fibre (PPf) along with partially replacement of…
Abstract
Purpose
Present study focuses on scope of developing sustainable heat resistant concrete by adding steel fibre (Sf) and polypropylene fibre (PPf) along with partially replacement of ordinary portland cement (OPC) and natural fine aggregate with fly ash (FA) and granular blast furnace slag (GBFS). Replacement percentages of FA and GBFS were 40% and 50%, whereas Sf and PPf for fibre-added mixes were 1% by volume of concrete and 0.25% by weight of cement, respectively.
Design/methodology/approach
An experimental work had been carried out to make comparison between control mix (CM), fibre-added sustainable mix (SCMF) and fibre-added control mix (CMF) with reference to weight loss, mechanical strength (compressive, split and flexure) after exposed to room temperature (27°C) to 1000°C at the interval of 200°C for 4 h of heat curing followed by furnace cooling and then natural cooling. Furthermore, microstructural analysis was executed at 27°C, 400°C and 800°C, respectively.
Findings
Colour change and hair line cracks were started to appear at 600°C. Fibre-added control mix and sustainable mix did not exhibit any significant cracks as compared to control mix even at 1000°C. Major losses were occurred at temperature higher than 600°C, loss in compressive strength was about 70% in control mix, while 60% in fibre-added mixes. SCMF exhibited the highest retention of strength with respect to all cases of mechanical strength.
Research limitations/implications
Present study is based on the slow heating condition followed by longer duration of heat curing at target temperature.
Practical implications
Present work can be helpful for the design engineer for assessing the fire deterioration of concrete structure existing near the fire establishment such as furnace and ovens. Building fire (high temperature for short duration) might be the further scope of work.
Originality/value
Concept of incorporating pozzolanic binder and calcareous fine aggregate was adopted to take the advantage pozzolanacity and fire resistivity. To the best of author’s knowledge, there is a scope for fill the research gap in this area.
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Arunangshu Mukhopadhyay, Subrata Ghosh and Somes Bhaumik
This paper seeks to report an experimental investigation on the tearing and tensile strength behaviour of military khaki fabrics from grey to finished process.
Abstract
Purpose
This paper seeks to report an experimental investigation on the tearing and tensile strength behaviour of military khaki fabrics from grey to finished process.
Design/methodology/approach
Uses three different types of military fabric (3 up 1 down twill), differing in type of constituent yarns (ring/rotor) in order to test their tearing and testing strength behaviour.
Findings
Tearing strength of fabric is found to be very much susceptible to change due to the process variation, while fabric tensile strength is relatively less sensitive. Ring spun yarn fabric shows higher tearing strength compared with rotor spun yarn fabric. However, the difference in their tearing strength reduces substantially as the process approaches towards the finished state. On the other hand, rotor spun yarn fabric exhibits higher tensile strength along the warp. Tearing strength along bias direction is in between warp and weft wise tearing strength; whereas tensile strength is lowest while tested along the bias direction. During the grey to finished process, tear strength falls at bleaching and dyeing, and particularly drops in strength is being more at the dyeing stage.
Originality/value
This study has investigated the tearing and tensile strength behaviour of military khaki fabrics from grey to finished state, developing understanding of the impact of different processes on the tearing strength, so that fabric of the required tear strength can be developed with process modification.
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