Y. Zarina

The Relationship of NaOH Molarity, Na2SiO3/NaOH Ratio, Fly Ash/Alkaline Activator Ratio, and Curing Temperature to the Strength of Fly Ash-Based Geopolymer

Geopolymer, produced by the reaction of fly ash with an alkaline activator (mixture of Na2SiO3 and NaOH solutions), is an alternative to the use of ordinary Portland cement (OPC) in the construction industry. However, there are salient parameters that affecting the compressive strength of geopolymer. In this research, the effects of various NaOH molarities, Na2SiO3/NaOH ratios, fly ash/alkaline activator, and curing temperature to the strength of geopolymer paste fly ash were studied. Tests were carried out on 50 x 50 x 50 mm cube geopolymer specimens. Compression tests were conducted on the seventh day of testing for all samples. The test results revealed that a 12 M NaOH solution produced the highest compressive strength for the geopolymer. The combination mass ratios of fly ash/alkaline activator and Na2SiO3/NaOH of 2.0 and 2.5, respectively, produced the highest compressive strength after seven days. Geopolymer samples cured at 60 °C produced compressive strength as high as 70 MPa.

Correlation between Na2SiO3/NaOH Ratio and Fly Ash/Alkaline Activator Ratio to the Strength of Geopolymer

Geopolymer requires an alkaline activator to induce it pozzolanic property and to accelerate the geopolymerisation process. The geopolymerisation process occurs due to the mixing of fly ash, sodium silicate and sodium hydroxide as the alkaline activator, which produces aluminosilicate gel that acts as a binder. As such, the ratios of fly ash to alkaline activator and Na2SiO3/NaOH play an important role in obtaining desirable compressive strength; the concentration of NaOH used in this study was 12 M. Different ratios of fly ash to alkaline activator (0.5, 1.0, 1.5, 2.0, 2.5 and 3.0) and Na2SiO3/NaOH (0.5, 1.0, 1.5, 2.0, 2.5 and 3.0) were investigated in order to determine the maximum compressive strength. The alkaline activator was mixed with fly ash with different ratio as mentioned above and the samples were cured at 70°C for 24 hours and tested on the seventh day. The maximum compressive strength was obtained when the ratios of fly ash to alkaline activator and Na2SiO3/NaOH were 2.0 and 2.5 with compressive strength 73.86 MPa.

Feasibility of Producing Wood Fibre-Reinforced Geopolymer Composites (WFRGC)

Wood fibres have long been known as a fibre reinforcement for concrete. Due to its availability and low production cost, this natural fibre has been used in less developed country where conventional construction materials were very expensive. In Japan, the production of these types of composites such as high performance fibre-reinforced cement-based composite (HPFRCB), ultra high performance (UHPFRCB) and strain-hardening (SHCC) fibre-reinforced cement-based composite has been developed rapidly in last decades. Geopolymer, future composite and cement produced by the alkali-activation reaction is well known as a potential replacement to Ordinary Portland Cement. This study aims at studying the possibility to produce wood fibre-reinforced geopolymer composite (WFRGC). The various percentage of fibre have been made from 10% to 50% and cured at 60C, tested for compressive strength for 7th and 14th day and the microstructure examined using SEM. The density and water absorption test have been performed. The results showed are encouraging and indicate the feasibility of producing a wood fibre-reinforced geopolymer composite (WFRGC).

Reviews on the Properties of Aggregates made with or without Geopolymerisation Method

Aggregates are popular for use in concrete and lightweight concrete applications. Recent research shows that the by-product materials such as fly ash can be used as raw material in producing aggregates and lightweight aggregates. The usage of this material can improve the quality of the aggregates produced compared to conventional in term of structurally strong, physically stable, durable, and environmentally inert. This paper summarized the process and mechanical testing on the fly ash aggregates and lightweight aggregates to be used in concrete.

Microstructure Study on Optimization of High Strength Fly Ash Based Geopolymer

The compressive strength and microstructural characteristics of fly ash based geopolymer with alkaline activator solution were investigated. The sodium hydroxide and sodium silicate were mixed together to form an alkaline activator. Three parameters including NaOH molarity, mix design (fly ash/alkaline activator ratio and Na2SiO3/NaOH ratio), and curing temperature were examined. The maximum strength of 71 MPa was obtained when the NaOH solution of 12M, fly ash/alkaline activator of 2.0, Na2SiO3/NaOH of 2.5 and curing temperature of 60°C were used at 7th days of testing. The results of SEM indicated that for geopolymer with highest strength, the structure was dense matrix and contains less unreacted fly ash with alkaline activator

Reviews on the Geopolymer Materials for Coating Application

The application of geopolymer has been expand in many areas where before this it only used for the production of cement and concrete. One of the new applications of geopolymer is for coating. Metakaolin, fly ash and granulated blast furnace slag has been used as source for the production of geopolymer coating. The result for the geopolymer coating showed that it can prevent corrosion in seawater structure, high bonding strength between existing structures (OPC concrete), lower water permeability and also stable during high temperature exposure.

Influence of Dolomite on the Mechanical Properties of Boiler Ash Geopolymer Paste

The waste material from palm oil industry has been increasing since Malaysia was the world largest exported of palm oil mill. The waste such as palm fibers, nut shells, palm kernel and empty fruit bunches are the solid waste the obtained from palm oil processing for oil extraction. When these wastes were incinerated, the waste from the burning process known as boiler ash was obtained at the lower compartment of the boiler. The production of boiler ash was estimated to be over 4 million tones/ year. This paper investigates the influence of dolomite on the mechanical properties of boiler ash based geopolymer pastes. The boiler ash was calcined at 800oC for 1 hour. After that, the dolomite was replaced in boiler ash at 1, 2, 3, 4 and 5% wt where the geopolymer samples were cured 80 oC. Sodium silicate and sodium hydroxide (NaOH) with concentration 12 Molar has been used as alkaline activator to synthesis the boiler ash to produce geopolymer paste. The ratio of solid/liquid and sodium silicate/NaOH was 1 and 2.5 for all geopolymer paste. The result showed the addition of dolomite has decrease the strength of boiler ash based geopolymer. The geopolymer sample without addition of dolomite showed the maximum compressive strength (19.4 MPa) at 28 days testing. Meanwhile the addition of 4% of dolomite into geopolymer paste has the maximum compressive strength (7.3 MPa) compared to others. Additions of dolomite into boiler ash based geopolymer have reduced the compressive strength at 28 days of testing.

Microstructure Studies on the Effect of the Alkaline Activators of Fly Ash-Based Geopolymer at Elevated Heat Treatment Temperature

Fly ash-based geopolymers are new binding materials produced to replace the ordinary Portland cement (OPC) used in concrete. In this research, the effect of alkaline activators on the compressive strength and the microstructure of low-calcium (Class F) fly ash-based geopolymers were studied. Fly ash and the alkaline activator were mixed with alkaline activator to fly ash ratios of 0.30, 0.35, and 0.40 at a constant ratio of water glass (sodium silicate) to sodium hydroxide (NaOH). The alkaline activator solution was prepared by mixing water glass with a 15 M NaOH solution. The samples were cured at a temperature 70 °C for 24 hr and maintained at room temperature until the testing was conducted. The test results indicated that the compressive strength increased when the ratio of alkaline activator to fly ash was increased at 7 days. The ratio of 0.4 produced the maximum compressive strength, which was 8.61 MPa. This was due to high reaction rate between the fly ash and the alkaline activator solution. Morphology studies, conducted by SEM analysis of the geopolymer samples, indicated that geopolymers synthesized at a ratio of 0.4 also had the most homogeneous and less porous microstructures, which was attributed to the high dissolution of the fly ash particles in the alkaline activator solution. The microstructure appearance of geopolymers treated heat temperature of 400, 600 and 800°C, shows a sintering process takes place for unreacted fly ash microspheres. It was observed as an overall, the visible microcracks formed on the surface of the highest compressive strength geopolymers only, was due to loss of water during heating.

Review of the characterization and processing of palm ash as a geopolymer composite

Malaysia is the worlds largest producer and exporter of palm oil and it produces a million tons of palm oil waste annually. Palm ash is a by-product from the use of palm oil shells and palm oil bunches, which are used to power electricity generation plants. The characterization of palm ash showed that it has high amorphous content with silicon dioxide (SiO2) as the main constituent. Using SEM, it was determined that the microstructure of palm waste is a porous texture that is spongy with irregular and angular particles. Research related to the use of palm ash in the production of geopolymer composites is very limited. The only geopolymer composites that have been studied extensively are mortar and concrete. In the production of geopolymers, the source material must have a high content of silicon dioxide (SiO2) and aluminum oxide (Al2O3). However, palm ash is rich only in SiO2, which results in low-strength geopolymer concrete and mortar. Hence, another raw material that is rich in Al2O3, such as metakaolin or fly ash, is required to successfully produce geopolymer composites. Keywords; Palm ash, Palm oil waste, Geopolymer composite

Study of Concrete Using Modified Polystyrene Coarse Aggregate

Polymer recycling has received a great deal of attention in recent years. At the present time, small percentages of polymer wastes in Malaysia are being recycled. The recycling process has typically consisted of reprocessing the waste material to make other polymeric products or energy recovery from complete combustion. Thus, the development of concrete using non-conventional aggregates, such as polymer waste (especially polystyrene), ceramic waste, or other wastes, has been investigated to determine the comparative properties of the various concretes and the comparative costs. This paper the results of an experimental study in which the coarse aggregates used in conventional concrete were replaced by polystyrene waste aggregate to produce a lightweight material. The proportions of the mixtures were varied to determine the water-cement ratio and the content of polystyrene waste aggregates that provide the best results. The properties of the aggregates were also compared. Strength tests were conducted after the experimental concrete was cured for 28 days, and the experimental results indicated that the strength of the concrete made with polystryene waste aggregate ranged from 14 to 17 MPa. In addition, the density of these concretes ranged between 1467 to 1560 kg/m3, which means that they would be categorized as lightweight concretes. The results also indicated that the workability of the polystyrene waste aggregate concretes was good, and the strength characteristics were comparable to those of conventional concrete.