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Geopolymers are novel binding materials produced by the alkaline activation of rich aluminosilicate materials. Geopolymer binders are considered as green building materials that have increasing potential to replace the ordinary Portland cement in the concrete industry. This study investigated the alkali solution effects on the physical and mechanical properties of the high calcium fly ash based geopolymers. The parameters involved in this study were the NaOH solution molarity and the Na 2 SiO 3 /NaOH ratio. Three NaOH concentrations (8, 10, and 12 molars) were investigated. The Na 2 SiO 3 /NaOH ratio was varied between 1 and 2.5. The results showed that the studied parameters significantly affected the properties of the produced geopolymer mortars. The workability and setting time were found to decrease by increasing the NaOH concentration or by increasing the Na 2 SiO 3 /NaOH ratio. The influence of the NaOH concentration was higher on the workability and setting time while the Na 2 SiO 3 /NaOH ratio highly affected the compressive strength. The initial setting time was in the range of 45-105 minutes while the final setting occurred quickly after that within 70-115 minutes. Oven curing method resulted in high strength at early ages where all of the mixes were able to achieve more than 75% of the 28 days strength within the first 3 days. The 28-days compressive strength ranged between 60-85 MPa, which promotes the use of the high calcium fly ash for the production of early high strength geopolymer concrete.

In order to address maintenance need of specific structures, a criticality analysis of the structures is essential. This paper presents an analysis of experts’ judgment using Analytic Hierarchy Process (AHP). Four criteria; people, assets, environment and reputation were considered as criteria. Sample representatives of Ten (10) civil engineering structures from onshore process plant were treated as alternatives. The judgment of the criteria with respect to the main goal was consistent with consistency value of 0.03. Control building (CB) was considered to be the most critical among the selected structure. Although, the technique is based on subjective experts’ judgment, but is considered very important in designing maintenance plan for existing structures where design data is not available.

This research was conducted to compare class C and class F fly ash as cementitious materials. The fly ash was supplied by local power plants in Malaysia. The chemical composition analysis showed that class F fly ash has more Si and Al content compared to class C fly ash which affects the amount of the produced gel during the pozzolanic reactivity or/and geopolymerization. The chemical bonding analysis showed that class F fly ash has more bond structure (C–S–H, C–A–H, –Si–O–Al–, and –Si–O–Si–) than class C fly ash. Finally, the microstructure images indicated the similarity of the fly ash particles shape on both classes. Furthermore, the microstructure images showed a correlation between the chemical composition and the bond structure in terms of the high element content (Si and Al) forming the gel and the bond structure in the cementitious process during pozzolanic reaction or/and geopolymerization.

One of the important criteria of supplementary cementing material (SCM) in concrete is to possess high content of reactive silica that is essential in concrete strength development. Indeed, it is proven that rice husk ash (RHA) contains high amount of amorphous silica that is vital in the reaction of SCM in concrete. However, usage of conventional RHA is unfavourable in current concrete industry. One of the reason that hindered the utilization of conventional RHA nowadays is due to its properties inconsistency namely chemical and mineralogical properties. This phenomenon occurs due to sensitivity of the material towards burning temperature. In this regard, improvement on the RHA properties by introduction of thermochemical pretreatment prior to burning procedure is seen as an excellent way to reach the goal. In this paper, the effect of burning temperature to the characteristics of pretreated rice husk ash were tested. Raw rice husk was pretreated using 0.1N hydrochloric acid (HCl) and heated at 80 o C. After that, the pretreated rice husk was mechanically activated by high energy planetary ball mill for 15 minutes at speed of 300 rpm and ball-to-powder ratio (BPR) of 15:1. The effect of burning temperature to its chemical composition, particle size analysis, and microstructure properties of ultrafine treated rice husk ash (UFTRHA) were determined accordingly. As for amorphous silica content of the optimum sample was recorded as 97.00% incinerated at 700 o C with three hours of pretreatment soaking duration. In terms of particle size analysis, it was also observed that, burning temperature of 700 o C, pretreated at three hours were recorded to produce finest size of UFTRHA where D10, D50 and D90 were obtained as 1.417 μm, 4.493 μm and 14.884 μm respectively.