Azmi Rahmat

The Relationship between Water Absorption and Porosity for Geopolymer Paste

This paper presents an experimental study of the relationship between water absorption and porosity for geopolymer paste. In order to reduce the carbon dioxide (CO2) emissions to the environment, alternatively fly ash was used as binders in making concrete paste. Fly ash is a waste materials produced by combustion of coal at power plant. Geopolymer paste prepared from class F fly ash was obtained from coal power plant and mixed with an alkaline activator. The combination of sodium silicate (Na2SiO3) solution and sodium hydroxide (NaOH) solution were used as alkaline activator. The alkaline activator was prepared 24 hrs prior to use with the ratio of the mixture of Na2SiO3/NaOH is 2.5. Mixed fly ash and alkaline activator placed in moulds and compacted. The samples were kept at ambient temperature in the moulds until it hardened. All the samples were removed from the moulds after 24 hrs. Then, the samples were cured at 60 °C in the oven for 24 hrs. All twelve samples were prepared for water absorption and porosity measurement. The samples were examined after 7, 14, 28 and 90 days in terms of water absorption test and porosity test. It was observed that after day 90 the sample had the lowest water absorption of 3.81% and porosity 3.77%. The sample had the highest water absorption and porosity of 4.65% and 11.95% respectively at day 7. The pore size decreases and the structures became denser. The morphological structure of geopolymer paste pores can be observed by Scanning Electron Microscope (SEM). The porosity and permeability also decreased hence the durability potentially improved. Keywords: Water absorption, porosity, geopolymer, fly ash

The Influence of Nickel and Tin Additives on the Microstructural and Mechanical Properties of Al-Zn-Mg-Cu Alloys

The effects of nickel and nickel combined tin additions on mechanical properties and microstructural evolutions of aluminum-zinc-magnesium-copper alloys were investigated. Aluminum alloys containing Ni and Sn additives were homogenized at different temperatures conditions and then aged at 120°C for 24 h (T6) and retrogressed at 180°C for 30 min and then reaged at 120°C for 24 h (RRA). Comparison of the ultimate tensile strength (UTS) of as-quenched Al-Zn-Mg-Cu-Ni and Al-Zn-Mg-Cu-Ni-Sn alloys with that of similar alloys which underwent aging treatment at T6 temper showed that gains in tensile strengths by 385 MPa and 370 MPa were attained, respectively. These improvements are attributed to the precipitation hardening effects of the alloying element within the base alloy and the formation of nickel/tin-rich dispersoid compounds. These intermetallic compounds retard the grain growth, lead to grain refinement, and result in further strengthening effects. The outcomes of the retrogression and reaging processes which were carried on aluminum alloys indicate that the mechanical strength and Vickers hardness have been enhanced much better than under the aging at T6 temper.

The Role of Direct Chilling, Retrogression and Reaging Treatment on Mechanical Properties of High Strength Aluminum Alloy

The effect of retrogression and reaging heat treatment on microstructure evolution andmechanical properties of 7075 Al alloy in direct chilling casting process was investigated. The subsequent heat treatment process comprised pre-aging at 120°C for 24 h, retrogression at 180°C for 30 min, and then reaging at 120°C for 24 h. By this three-step process, the mechanical properties of the chilled casted samples were substantially improved. The samples retain their high strength at T6 level. They gave yield strength up to 290 MPa, ultimate tensile strength of 386 MPa and elongation of 5.9%. The average value of multiple Vickers hardness tests results were in the range of 210 Hv. The direct chilling process followed by retrogression and reaging heat treatment yielded casts of fine and uniform microstructure as opposed to the microstructure of samples casted by the conventional process.

Evolution of the Retrogression and Reaging Treatment on Microstructure and Properties of Aluminum Alloy (Al-Zn-Mg-Cu)

In this study the evolution of the retrogression and reaging (RRA) heat treatment process on microstructure and mechanical properties of AA 7075 Al-alloys which produced by semi-direct chill (DC) casting process were investigated. Al-Zn-Mg-Cu alloys were homogenized at different heat treatment conditions, aged at 120°C for 24 h (T6), and retrogressed at 180°C for 30 min then re-aged at 120°C for 24 h (RRA). The results showed that this three-step process of the heat treatments, the mechanical properties of alloys was substantially improved. The highest ultimate tensile strength and Vickers hardness attained for the retrogression and re-aging about 530 MPa and 223 HV respectively. The precipitation strengthening is responsible about improve the strength under impact the retrogression and re-aging process.

A study on hardness behavior of geopolymer paste in different condition

This study has been conducted to understand the hardness behavior of geopolymer paste in different conditions; with and without being immersed in water. Geopolymer paste has been used nowadays as an alternative way to reduce global warming pollution by carbon dioxide (CO2) released to the air caused from the production of Ordinary Portland Cement (OPC). Geopolymer has many advantages such as high compressive strength, lower water absorption and lower porosity. Geopolymer paste in this study was made from a mixture of fly ash and alkaline activators. The alkaline activators that have been used were sodium hydroxide (NaOH) solution and sodium silicate (Na2SiO3) solution. Then the mixture was allowed to harden for 24hrs at ambient temperature and then placed in the oven for 24hrs with 60°C for the curing process. The hardness testing was conducted after a few months when the samples already achieved the optimum design. The samples were divided to two conditions; without immersion which was placed at ambient ...

Porous Solid Carbon Dioxide Adsorbent Using Cost Effective Materials: A Review

Greenhouse effects were generated from anthropogenic emissions of carbon dioxide (CO2) into the atmosphere. High concentration of CO2 has recognised as major causes of global warming. In order to keep CO2 at a manageable level, adsorptions of these gases from the flue gases is necessary. Developing a low cost porous solid adsorbent as adsorption media become a great attention due to environmental and economic concerns. This paper has reviewed the cost effective materials with a suitable methods to fabricate the porous solid adsorbent. This paper also has discussed the adsorption mechanisms of CO2 on the selective cost effective materials.

Synthesis of Al–Ni Intermetallic Compounds by Mechanical Alloying

In this study, nanocrystalline Al–Ni intermetallic compounds were synthesized by mechanical alloying (MA) of elemental powders. In all MA runs, the ball-to-powder weight ratio was 10:1, the rotation speed was 350 rpm, and the milling time ranged from 4 h to 12 h. The phase evolution and microstructural changes of the powders during MA were investigated by x-ray diffraction (XRD), scanning electron microscopy, and energy-dispersive x-ray spectroscopy. The crystallite sizes of the milled powders were estimated based on the broadening of the XRD peaks using the Williamson–Hall formula. Results showed that an optimum MA time of 12 h resulted in the formation of an Al–Ni intermetallic phase with a crystallite size of <40 nm.

A Study on Relationship between Porosity and Compressive Strength for Geopolymer Paste

This paper presents a study on the relationship between porosity and compressive strength for geopolymer paste. In this research, geopolymer paste was made from fly ash class F based geopolymer mixed with alkaline activator; sodium hydroxide solution and sodium silicate solution. Twelve mixes were cast in 50mm x 50mm x 50mm moulds and the samples were cured for 24 hrs at 60 °C in the oven. The samples were examined after 7, 14, 28 and 90 days in terms of porosity test, pulse velocity test and compressive strength test. It was concluded that the sample at day 90 had the highest compressive strength of 56.50 N/mm2 had porosity 3.77%. Thus, the sample with lowest porosity had highest pulse velocity 3303 m/s during ultrasonic testing with lowest transmission time 15.17 μs. Keywords: porosity, compression strength, geopolymer, pulse velocity

Electrochemical Measurement of PBS Using Cyclic Voltammetry and AAO Fabricated at Ambient Temperature and Low Potential

Anodic aluminium oxide fabricated at ambient temperature and low potential in phosphoric acid electrolyte was used as the working electrode for the electrochemical measurement of phosphate buffer saline under different pH conditions using the cyclic voltammetry tool. We investigate the reversibility of the electrochemical reaction as a redox reaction from the cyclic graphs that were obtained. We observed that the ratio of the peak current passed at both the reduction and oxidation when measured was very close to unity in all the pH but except one which produced a none reversible reaction with a non cyclic graph. The peak potential for both reduction and oxidation reactions using phosphate buffer saline as the analyte under different pH of 3, 5, 7, and 9 was also obtained.

Effect of Geopolymer Coating on Mild Steel

This paper presents the results of a study on the effect of geopolymer coating on mild steel. Geopolymer is synthesis of a fly ash and alkaline activators which are sodium hydroxide solution (NaOH) and sodium silicate solution (Na2SiO3). Fly ash is one of residue produced during the combustion of coal in coal power plant. In this study, fly ash class F based geopolymer was used as a source material. The alkaline activators then were mixed with fly ash to produce the geopolymer paste which acts as a coating material. The mixture was placed in molds and reinforcement bar were embedded in geopolymer paste. After that, the corrosion behavior of reinforcement bars for all samples were observed by using Open Circuit Potential (OCP) testing. Referring the pourbaix diagram regarding OCP testing, samples are in passivity region. Besides that, mild steel also were coated with geopolymer paste for adhesion test. Elcometer 108 was used for adhesion strength test. Morphology analysis also been used to determine the microstructure of fly ash and geopolymer paste. Phase analysis was used for the analysis phase between fly ash, geopolymer paste and mild steel coated with geopolymer paste. From OCP test, pourbaix diagram shows that samples is placed in the passivity region, iron (III) oxide (Fe2O3) which is in stable phase and iron (II, III) oxide same results as in phase analysis. The minimum potential value for OCP is 0.015 V and the maximum potential value is 0.133 V. For adhesion strength, day 14 got the highest results compared day 7 and day 3 which the results are 2.0 Mpa, 1.9 Mpa and 1.5 Mpa respectively. It is because from day 3 until day 14, the structure of geopolymer paste becomes more compact, denser and better crystallization as shown in morphological analysis.