Rohaya Abdul Malek
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Rohaya Abdul Malek
Official Name
Rohaya, Abdul Malek
Alternative Name
Abdul Malek, Rohaya
Abdul Malik, Rohaya
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Scopus Author ID
55992567600

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  • Publication
    The effect of HAP addition on properties F-75 alloy fabricated via P/M 6 for biomaterial applications
    ( 2010)
    Rohaya Abdul Malek
    A Co-Cr-Mo (ASTM F-75) alloy is generally used because of their mechanical properties, good wear and corrosion resistance as well as biocompatibility. In order to obtain chemical similarity and interfacial bond form between implanted biomaterials and living tissue, addition of Hydroxyapatite (HAP) is required. This study has focused on a research on F-75 alloy mixed with HAP fabricated by powder metallurgy (P/M) technique. The effect of HAP addition ranging between 2 and 10 wt.% on biocompatibility, physical and mechanical properties were examined. During compaction, 500MPa of pressure was applied using uniaxial press machine. The samples were sintered into tube furnace at 1100˚C in argon atmosphere. The samples with dimensions of approximately 5mm in thickness and 19mm in diameter were produced. To analyse the result, the reference sample (F-75 alloy without HAP powder) and composites were compared. All the samples were tested to determine shrinkage, grain size, bulk density, apparent porosity, microhardness and corrosion test. For biocompatibility (corrosion test), all samples were immersed into simulated body fluid of 0.9% sodium chloride solution at 37˚C in 6-week duration. Every interval of 48 hours, the weight loss per area was recorded. By increasing amount of HAP, it is noticed that the composites were less shrink and grain size getting larger compared to the reference sample. The largest grain size was obtained for composite consists of 10 wt.% of HAP (32.56μm) meanwhile the smallest grain size was obtained for reference sample (21.43μm). These results are inversely proportional to the decreasing value of bulk density and microhardness. The result of apparent porosity closely to 30% is obtained due to the increasing amount of HAP. Higher result of apparent porosity is required for bone ingrowth purposes. For microstructure analysis, the composites microstructure showed agglomeration of HAP and pores scattered on the composite surface. Meanwhile, biocompatibility test has indicated that the corrosion rate are increasing due to addition of HAP except for composite that consists of 2 wt.% of HAP which has the lowest corrosion rate among others (2.53mpy). The possibilities that contribute to the increasing of corrosion rate as a function of HAP addition are; the formation of general attack and pitting between matrix and electrochemical solution used. Besides, the formation of apatite layer can be clearly seen on the composite surface as predicted. According to the results, composite contains 6 wt.% of HAP shows an interesting result for apparent porosity and corrosion resistance that can be correlated to the requirement of biomaterial applications.
  • Publication
    Efficiency of impressed current cathodic protection in repaired reinforced concrete
    (Trans Tech Publications Ltd., 2020)
    Rohaya Abdul Malek
    ;
    Atsushi Hattori
    ;
    Kawano Hirotaka
    ;
    Nadia Kamaruddin
    Corrosion attack in reinforced concrete and thus contribute to degradation of concrete influenced by aggressive environment, represent a great concern in relation to the durability of reinforced concrete structures. In this respect, an interesting need is required that is patch repair with additional protection known as ICCP method to prolong the serviceability of the concrete structures. However, details inspection is crucial to understand the effect of different repairing materials and chloride content towards application of ICCP. To clarify this issue, non-protected and protected test specimens were prepared, and analyzed up to 175 days of protection. The result reveals that, reference specimen was found as most corroded specimen unable to obtain 100 mV depolarization at 56 days installation compared to repaired ones. However, all specimens show only greater depolarization values beyond 129 days of installation. To clarity further effectiveness of ICCP system to the studied specimens, time-dependence within 24 hours disconnecting CP current has been carried out and depolarization values was recorded every 4 hours interval. In the final analysis, all specimens are satisfying the CP criteria by obtaining depolarization potential ranging 100 to 250 mV at 4 and 24 hours monitoring period.
  • Publication
    Exploring the Properties of Mortar Containing Incineration Fly Ash
    ( 2021-11-26)
    Norlia Mohamad Ibrahim
    ;
    Rohaya Abdul Malek
    ;
    Nur Liza Rahim
    ;
    Mustaqqim Abdul Rahim
    ;
    Roshazita Che Amat
    ;
    Syakirah Afiza Mohammed
    ;
    Badri N.A.
    Fly Ash (FA) is one of the waste materials generated from the combustion of solid waste through incinerator and contains hazardous substances. Further treatment to the ash needs to be done to avoid further environmental destruction. As an alternative solution for this problem, FA is used as a replacement material for cement in the mortar. The main objective of this study is to explore the potential use of FA as partial replacement of cement in mortar. The percentage of FA used to replace the cement in this study is 0%, 5%, 10%, 15% and 20%. Several important tests were conducted to identify main properties of the mortar such as compressive strength, water absorption, density and ultra-pulse velocity. Mortar containing 15% of fly ash has the highest of compression strength which is 35 MPa after 28 days. Besides, the mortar containing 5% of fly ash has the highest result of water absorption test and density test whereas mortar containing 20% of fly ash has the highest value for pulse velocity after 28 days. Thus, mortar containing fly ash has good physical and mechanical properties.
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