Journal Articles

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https://hdl.handle.net/20.500.14170/316

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Browsing Journal Articles by Author "Andrei Victor Sandu"
  • Publication
    Characterisation at the bonding zone between fly ash based Geopolymer Repair Materials (GRM) and Ordinary Portland Cement Concrete (OPCC)
    ( 2020)
    Warid Wazien Ahmad Zailani
    ;
    Mohd. Mustafa Al Bakri Abdullah
    ;
    Mohd Fadzil Arshad
    ;
    Rafiza Abd Razak
    ;
    Muhammad Faheem Mohd. Tahir
    ;
    Remy Rozainy Mohd Arif Zainol
    ;
    Marcin Nabialek
    ;
    Andrei Victor Sandu
    ;
    Jerzy J. Wysłocki
    ;
    Katarzyna Błoch
    In recent years, research and development of geopolymers has gained significant interest in the fields of repairs and restoration. This paper investigates the application of a geopolymer as a repair material by implementation of high-calcium fly ash (FA) as a main precursor, activated by a sodium hydroxide and sodium silicate solution. Three methods of concrete substrate surface preparation were cast and patched: as-cast against ordinary Portland cement concrete (OPCC), with drilled holes, wire-brushed, and left as-cast against the OPCC grade 30. This study indicated that FA-based geopolymer repair materials (GRMs) possessed very high bonding strength at early stages and that the behavior was not affected significantly by high surface treatment roughness. In addition, the investigations using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy have revealed that the geopolymer repair material became chemically bonded to the OPC concrete substrate, due to the formation of a C–A–S–H gel. Fundamentally, the geopolymer network is composed of tetrahedral anions (SiO4)4− and (AlO4)5− sharing the oxygen, which requires positive ions such as Na+, K+, Li+, Ca2+, Na+, Ba2+, NH4+, and H3O+. The availability of calcium hydroxide (Ca(OH)2) at the surface of the OPCC substrate, which was rich in calcium ions (Ca2+), reacted with the geopolymer; this compensated the electron vacancies of the framework cavities at the bonding zone between the GRM and the OPCC substrate.
      8  14
  • Publication
    Performance of Sn-3.0Ag-0.5Cu composite solder with kaolin geopolymer ceramic reinforcement on microstructure and mechanical properties under isothermal ageing
    ( 2021)
    Nur Syahirah Mohamad Zaimi
    ;
    Mohd Arif Anuar Mohd Salleh
    ;
    Andrei Victor Sandu
    ;
    Mohd Mustafa Al Bakri Abdullah
    ;
    Norainiza Saud
    ;
    Shayfull Zamree Abd Rahim
    ;
    Petrica Vizureanu
    ;
    Rita Mohd Said
    ;
    Mohd Izrul Izwan Ramli
    This paper elucidates the effect of isothermal ageing at temperature of 85 °C, 125 °C and 150 °C for 100, 500 and 1000 h on Sn-3.0Ag-0.5Cu (SAC305) lead-free solder with the addition of 1 wt% kaolin geopolymer ceramic (KGC) reinforcement particles. SAC305-KGC composite solders were fabricated through powder metallurgy using a hybrid microwave sintering method and reflowed on copper substrate printed circuit board with an organic solderability preservative surface finish. The results revealed that, the addition of KGC was beneficial in improving the total thickness of interfacial intermetallic compound (IMC) layer. At higher isothermal ageing of 150 °C and 1000 h, the IMC layer in SAC305-KGC composite solder was towards a planar-type morphology. Moreover, the growth of total interfacial IMC layer and Cu3Sn layer during isothermal ageing was found to be controlled by bulk diffusion and grain-boundary process, respectively. The activation energy possessed by SAC305-KGC composite solder for total interfacial IMC layer and Cu3Sn IMC was 74 kJ/mol and 104 kJ/mol, respectively. Based on a lap shear test, the shear strength of SAC305-KGC composite solder exhibited higher shear strength than non-reinforced SAC305 solder. Meanwhile, the solder joints failure mode after shear testing was a combination of brittle and ductile modes at higher ageing temperature and time for SAC305-KGC composite solder.
      10  2
  • Publication
    Strength development and elemental distribution of Dolomite/Fly Ash geopolymer composite under elevated temperature
    ( 2020)
    Emy Aizat Azimi
    ;
    Mohd. Mustafa Al Bakri Abdullah
    ;
    Petrica Vizureanu
    ;
    Mohd Arif Anuar Mohd Salleh
    ;
    Jitrin Chaiprapa
    ;
    Sorachon Yoriya
    ;
    Andrei Victor Sandu
    ;
    Kamarudin Hussin
    ;
    Ikmal Hakem Aziz
    A geopolymer has been reckoned as a rising technology with huge potential for application across the globe. Dolomite refers to a material that can be used raw in producing geopolymers. Nevertheless, dolomite has slow strength development due to its low reactivity as a geopolymer. In this study, dolomite/fly ash (DFA) geopolymer composites were produced with dolomite, fly ash, sodium hydroxide, and liquid sodium silicate. A compression test was carried out on DFA geopolymers to determine the strength of the composite, while a synchrotron Micro-Xray Fluorescence (Micro-XRF) test was performed to assess the elemental distribution in the geopolymer composite. The temperature applied in this study generated promising properties of DFA geopolymers, especially in strength, which displayed increments up to 74.48 MPa as the optimum value. Heat seemed to enhance the strength development of DFA geopolymer composites. The elemental distribution analysis revealed exceptional outcomes for the composites, particularly exposure up to 400 °C, which signified the homogeneity of the DFA composites. Temperatures exceeding 400 °C accelerated the strength development, thus increasing the strength of the DFA composites. This appears to be unique because the strength of ordinary Portland Cement (OPC) and other geopolymers composed of other raw materials is typically either maintained or decreases due to increased heat.
      4  8
  • Publication
    Strength development and elemental distribution of Dolomite/Fly Ash geopolymer composite under elevated temperature
    ( 2020)
    Emy Aizat Azimi
    ;
    Mohd. Mustafa Al Bakri Abdullah
    ;
    Petrica Vizureanu
    ;
    Mohd Arif Anuar Mohd Salleh
    ;
    Andrei Victor Sandu
    ;
    Jitrin Chaiprapa
    ;
    Sorachon Yoriya
    ;
    Kamarudin Hussin
    ;
    Ikmal Hakem Aziz
    A geopolymer has been reckoned as a rising technology with huge potential for application across the globe. Dolomite refers to a material that can be used raw in producing geopolymers. Nevertheless, dolomite has slow strength development due to its low reactivity as a geopolymer. In this study, dolomite/fly ash (DFA) geopolymer composites were produced with dolomite, fly ash, sodium hydroxide, and liquid sodium silicate. A compression test was carried out on DFA geopolymers to determine the strength of the composite, while a synchrotron Micro-Xray Fluorescence (Micro-XRF) test was performed to assess the elemental distribution in the geopolymer composite. The temperature applied in this study generated promising properties of DFA geopolymers, especially in strength, which displayed increments up to 74.48 MPa as the optimum value. Heat seemed to enhance the strength development of DFA geopolymer composites. The elemental distribution analysis revealed exceptional outcomes for the composites, particularly exposure up to 400 °C, which signified the homogeneity of the DFA composites. Temperatures exceeding 400 °C accelerated the strength development, thus increasing the strength of the DFA composites. This appears to be unique because the strength of ordinary Portland Cement (OPC) and other geopolymers composed of other raw materials is typically either maintained or decreases due to increased heat.
      23  7