Showing papers by "Januarti Jaya Ekaputri published in 2018"

The influence of molarity variations to the mechanical behavior of geopolymer concrete

Abstract: Research on geopolymer concrete has seen a new light in the analyses and experiments for special topics in the field of their mechanical properties. Among the most important are studies of geopolymer concrete subjected to confinement and bond. Regarding the basic material behavior, research of material proportions formulations, mix design formulas and inventions towards the development of a high-performance geopolymer concrete, were conducted. The latest looked into the effects of molar activator concentrations to the 28 days compression strength, and the strength development as a function of concrete age for geopolymer concretes. The specimens were 150 by 300-millimeter cylinders tested in uniaxial compression. The molarity variations were set at 6, 8, and 10 molars. The geopolymer concrete samples were compared to conventional concrete specimens, having the exact same volumetric material proportions. The cement was replaced with fly ash, and the activator with water. The aggregate content was taken as a constant. The concrete strength as a function of molar increase followed a parabolic, convex pattern, suggesting that a maximum value exists. The strength development of all geopolymer concretes had a slower rate when compared to conventional concrete.

Application of GGBFS and Bentonite to Auto-Healing Cracks of Cement Paste

Abstract: Cracks are caused by many factors. Shrinkage and external loading are the most common reason. It becomes a problem when the ingression of aggressive and harmful substance penetrates to the concrete gap. This problem reduces the durability of the structures. It is well known that self – healing of cracks significantly improves the durability of the concrete structure. This paper presents self-healing cracks of cement paste containing bentonite associated with ground granulated blast furnace slag. The self-healing properties were evaluated with four parameters: crack width on the surface, crack depth, tensile strength recovery, and flexural recovery. In combination with microscopic observation, a healing process over time is also performed. The results show that bentonite improves the healing properties, in terms of surface crack width and crack depth. On the other hand, GGBFS could also improve the healing process, in terms of crack depth, direst tensile recovery, and flexural stiffness recovery. Carbonation reaction is believed as the main mechanism, which contributes the self-healing process as well as the continuous hydration progress.

Effects of microbial agents to the properties of fly ash-based paste

Abstract: Specific microbial agents such as bacteria are often used in concrete to improve its performance. Some microbes act as self-healing agents to close cracks in concrete, and to increase concrete strength. This paper presents a study to observe the effects of microbe addition to two types of concrete mixtures the fly ash-based, as geopolymer paste, and portland cement paste containing fly ash. Furthermore, the investigation was conducted to compare the properties of each paste, such as its compressive strengths, specific gravities, porosity, microstructures, and XRay diffracting properties. The results indicate that microbial activities positively affected the properties of both, portland cement paste and geopolymer paste. The result reported here strongly suggests that fly ash can be used to produce a high quality, but environmental friendly construction material when it’s mixed together with useful microbes.

Characterization and compressive strength of fly ash based-geopolymer paste

Abstract: Fly ash is a by-product obtained from coal combustion process. Some of the utilization of fly ash is to produce geopolymer products which have high compressive strength, fire, chemical resistance. This paper proposes fly ash from unit 1-7 Suralaya Power Plant Indonesia. The aims of this study are to obtain characterization of fly ash and mechanical properties of geopolymer paste based on variations of the alkali activator ratio. The method was based on previous research and laboratory investigation. XRF and compressive strength were analysed in this study. Alkali activator was obtained from NaOH and Na2SiO3 mixture. The ratio of Na2SiO3 to NaOH was in the range of 0.5-2.5. Geopolymer paste was casted in acrylic cylinders with a diameter of 2 cm and a height of 4 cm. The curing was conducted at room temperature until the day for the compressive strength test at 28 days. The result showed that the fly ash is classified as F class. Increasing the alkali activator ratio influenced the strength. The best composition of geopolymer paste is made with NaOH 8M, and the mass ratio of Na2SiO3 to NaOH is 2.5. This composition produced compressive strength of 98.6 MPa.

The effect of additional aluminium to the strength of geopolymer paste

Abstract: Alternative cementitious materials have been widely used because of the environmental issue of greenhouse gasses produced by portland cement production. A possible solution is the green concrete made from fly ash based-geopolymer paste. The natural differences of Indonesian coal ash lead to various chemical contents of fly ash. The chemical composition of alkali activated paste is also varied causing differences in the strength of the paste. Silica to alumina ratio is indicated as the greatest influencing factor to geopolymer strength. The bond among silica-alumina preserves a compact microstructure resulting in the strength. This paper proposes a Si-Al ratio between 1.5 and 2.0 by adding a synthetic aluminium substance from some sources. Using a natural aluminium substance from other fly ashes which contain excessive amounts of Al2 O3 was one of that efforts. The result indicated that the addition of a small amount of aluminium powder showed insignificant differences in geopolymer strength. The powder addition of up to 4% of fly ash decreased the strength by up to 60% of the original one. The methods of mixing are indicated as the trigger of lower strength because

Methods to Characterize Fly Ash Quality in the Field

Abstract: Fly ash is applied widely in concrete. Therefore, the quality of fly ash plays a critical role in altering the compressive strength of concrete. As the fact, it is necessary to provide better insight on the characterization of fly ash based on their correlation index against the strength. This is regarded as the prior studies were merely focused on the relationship of fly ash percentage and compressive strength due to high demand and time-consuming. On the other hand, this paper offers more advanced analysis on the utilization of several methods to determine the effect of different fly ashes on the quality of mortar. In this study, 12 types of fly ash and six methods were involved. The differences between the methods consisted of how the samples were prepared and cured. In the mixture, 20% of fly ash and 80% of OPC (Ordinary Portland Cement) were used as a binder. The specimens were cured in two different methods (normal curing and steam curing). After 28-day of curing, specimens were tested under compression load to obtain the strength. The test results indicated that the method, where the fly ash was sieved in the preparation phase and was cured at a high temperature increased gradually, was found to be the fastest to analyze.