Abstract. There are more than four decades since the last 1970s where geopolymers concrete was first introduced and developed to use as a replacement to conventional concrete material which uses cement as a binder. And since the last two decades, geopolymers which utilized fly ash as aluminosilicate source material, i.e. fly ash based geopolymers, have been investigated. Many researchers present how to produce the best fly ash based geopolymer with a various source of constituent material as well as mixing formula to achieve exceptional concrete performance. Although there is a similar trend towards factors affecting the result of fly ash based geopolymer synthesis, there is still remain a wide range in mixture proportion. The considerable variation in fly ash characteristics as source material in the synthesis can very likely be one of the causes of this problem. This paper attempts to identify the effect of source material variation of geopolymer concrete, particularly which use fly ash as source material and focuses on the variation of its characteristics and the effects to properties of concrete. From the reviews it concluded that different sources (and even the same source, but different batch) of fly ash materials will give some different characteristics of the fly ash, where it would affect the synthesis process of the fly ash based geopolymer concretes.

This study aims to determine whether the surface durability of high volume fly ash (HVFA) concrete can be improved by applying alkali solution on its hardened surface. Concentrations of alkali solution and methods of application were studied on several w/cm ratios and replacement percentage of fly ash in concrete mixture proportion to investigate the durability performance. Durability tests conducted were accelerated sulfuric acid attack and ion chloride penetration to investigate the improved durability of HVFA concrete. From the results, it was shown that applying alkali solution on the surface of HVFA concrete can increase its durability performance. The different w/cm ratio and the percentage of fly ash used affect the increase in durability performance. The optimum alkali solution concentration and method of application need further research to determine their effectivity.

Fly ash, a waste material derived from the coal burning in power plants, could be utilized in concrete mixtures as a filler or as a cement replacement material, either partially or fully. Some papers also report that high-calcium fly ash can be utilized as a cementitious material through the hydration process. However, there are just a few papers that studied the behavior of concrete that utilizes high-calcium fly ash as the sole binder material without any chemical activators. Furthermore, there are no reports about whether the effect of the different water-to-cementitious ratios of this concrete is the same as the ordinary Portland cement concrete. This paper presents an initial development on the use of fly ash as a sole binder material, i.e., 100% fly ash concrete without any chemical solution as an activator. This research utilizes the high calcium content in the fly ash to produce concrete with a commonly used method (just add the water without any alkali activator) and investigates how the water-to-cementitious ratio can influence the compressive strength of the paste and the concrete as well. The calcium content in the fly ash used in this study was in the range of 19–22 percent of the total weight of fly ash. Paste compressive strength of 66.78 MPa was obtained at 28 days with a very low water-to-cementitious ratio of 0.110.

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