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Nazari A.,Swinburne University of Technology | Maghsoudpour A.,WorldTech Scientific Research Center | Sanjayan J.G.,Swinburne University of Technology
Construction and Building Materials

In this work, a method for incorporating fly ash in constructional technology was developed by production of boroaluminosilicate geopolymers. These new class of geopolymers were appropriately synthesized from mixtures of fly ash and anhydrous borax and compressive strengths as high as 64 MPa were achieved by using suitable amount of borax. Different types of microstructures were observed by changing mixture proportion of the specimens. All of specimens revealed a brittle fracture with no crack branching in the mixture. Additionally, less unreacted fly ash particle was observed in the considered pastes indicating a totally different fracture mechanism in boroaluminosilicate geopolymers than aluminosilicate ones. FT-IR analyses of the mixtures revealed an additional B-O bond in comparison with aluminosilicate geopolymers. It was shown that this bond is a key factor to determine compressive strength and specimens with no B-O bond have lower strengths. © 2014 Elsevier Ltd. All rights reserved. Source

Sanjayan J.G.,Swinburne University of Technology | Nazari A.,Swinburne University of Technology | Pouraliakbar H.,WorldTech Scientific Research Center
Materials and Design

In this study, fracture toughness of steel fibre-reinforced aluminosilicate geopolymers is investigated experimentally and is modelled by explicit finite element method. Nine geopolymeric pastes with various alkali activators to fly ash weight ratios, sodium hydroxide (NaOH) to sodium silicate weight ratios, NaOH concentrations and curing temperatures were prepared and their fracture toughness was measured by pre-notched three point bending specimens. All samples were then reinforced by substituting of 2, 3 and 5. vol.% of geopolymeric pastes by steel fibres with diameter and length of 0.5 and 30. mm respectively. The effects of four different parameters on experimental and predicted fracture toughness were probed. Results indicated that NaOH to sodium silicate and alkali activator to fly ash weight ratios do not cause any deviation between experimental and predicted results. On the other hand, NaOH concentration and curing temperature were the most significant parameters that caused deviation of predicted results from experimental ones. Generally, it is possible to use the proposed modelling procedure to predict fracture toughness of steel-fibre reinforced geopolymers with a reasonable approximation. © 2015 Elsevier Ltd. Source

Khalaj G.,Islamic Azad University at Saveh | Pouraliakbar H.,Islamic Azad University at Saveh | Pouraliakbar H.,WorldTech Scientific Research Center
Ceramics International

Five different tool steels (DIN 1.2080, 1.2210, 1.2344, 1.2510 and 1.3343) have been targeted for a duplex surface treatment consisted of nitriding followed by vanadium thermo-reactive diffusion (TRD). TRD process was performed in molten salt bath at 575, 650 and 725 C for 1 to 15 h. A duplex ceramic coating of vanadium carbonitride (VCN) with a thickness up to 10.2 μm was formed on tool steel substrates. Characterization of the ceramic coating by means of scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) indicated that the diffused compact and dense layers mainly consisted of V(C,N) and V2(C,N) phases. Layer thickness of duplex coating has been modeled by gene expression programming (GEP). Recently, application of GEP as a computer-aided technique has got appreciable attraction especially for modeling and to formulate engineering demands. For GEP approaches, chemical composition of steel substrates along with different bath and processing parameters totally composed of 17 different parameters were considered as inputs to establish mathematical correlations. Finally, the training and testing results in models have shown strong potential for predicting the layer thickness of duplex treated ceramic coating on tool steels. © 2013 Elsevier Ltd and Techna Group S.r.l. Source

Nazari A.,Swinburne University of Technology | Maghsoudpour A.,WorldTech Scientific Research Center | Sanjayan J.G.,Swinburne University of Technology
Construction and Building Materials

In the present work, flexural strength of plain and fibre-reinforced boroaluminosilicate geopolymers is studied. Traditional aluminosilicate geopolymers are produced by alkali activation of an aluminosilicate source. Alkali activator is normally made by mixing a high alkali solution (such as sodium hydroxide) and a silica-rich source (such as sodium silicate). Alkali activation of fly ash in this study, to fabricate boroaluminosilicate binders, was performed by mixtures of anhydrous borax and sodium hydroxide. Flexural strength of the specimens in unreinforced and reinforced conditions was measured by three-point bending. Reinforced specimens were prepared by using 2, 3 and 5 wt.% of steel fibres, with length and diameter of 30 and 0.5 mm respectively. The highest flexural strength of unreinforced specimens was 9.5 ± 0.4 MPa, with borax to NaOH solution weight ratio of 0.912 and alkali activator to fly ash weight ratio of 0.9. Reinforcing of this mixture by 5 wt.% of steel fibres resulted in the highest flexural strength, 11.8 ± 0.9 MPa. Maximum and minimum average increase of flexural strength of about 47% and 5% were achieved by adding 5 and 2 wt.% of steel fibres to some mixtures respectively. Results indicated the ability of these new classes of construction materials for using in flexural load-bearing sections in both unreinforced and reinforced situations. © 2014 Elsevier Ltd. All rights reserved. Source

Amirafshar A.,Tarbiat Modares University | Amirafshar A.,University of Applied Science and Technology of Iran | Pouraliakbar H.,University of Applied Science and Technology of Iran | Pouraliakbar H.,WorldTech Scientific Research Center
Measurement: Journal of the International Measurement Confederation

In this research, friction stir processing (FSP) technique is applied for the surface modification of ST14 structural steel. Tungsten carbide tools with cylindrical, conical, square and triangular pin designs are used for surface modification at rotational speed of 400 rpm, normal force of 5 KN and traverse speed of 100 mm min-1. Mechanical and tribological properties of the processed surfaces including microhardness and wear characteristics are studied in detail. Furthermore, microstructural evolutions and worn surfaces are investigated by optical and scanning electron microscopes. Based on the achievements, all designed pins were successfully applicable for low carbon steel to produce defect-free processed material. By the microstructural changes within the stirred zone, the processed specimen is obtained higher mechanical properties. This is due to the formation of fine grains as the consequence of imposing intensive plastic deformation during FSP; however, this issue is highlighted by using square pin design. In this case, minimum grain size of 5 μm and maximum hardness of 320 VHN, as well as, maximum wear resistance are all examined for the specimen modified by square pin. © 2015 Elsevier Ltd. All rights reserved. Source

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