nan Antoni

Factors Affecting the Setting Time of Fly Ash-Based Geopolymer

Fly ash is a waste from coal burning, that are generated with fluctuation both in its physical and chemical characteristics. This characteristics of fly ash when used in the making of geopolymer concrete will greatly affect the final products obtained. The pH value measured in fly ash, according previous research, can influence the setting time of geopolymer and fly ash with high pH values can cause flash-setting in the concrete. Understanding more clearly about the factors that affect the setting time of fly ash based geopolymer is important for further progress and development of the material. It was found that factors that influence the setting time of geopolymer was not only from the physical and chemical properties of the fly ash itself. Other factors such as composition and mix design, manufacturing process and environmental conditions can also affect its setting time. The experimental results showed that fly ash particle size, CaO and MgO content, in addition to ratio of sodium silicate and sodium hydroxide in the alkali solution, molarity of NaOH, initial temperature of the mixture, curing temperature, and mix volume could potentially influence the setting time of the geopolymer mixture.

Effects of Calcination Temperature of LUSI Mud on the Compressive Strength of Geopolymer Mortar

The abundant availability of LUSI (a short form of LUmpur SIdoarjo or Sidoarjo mud) mud of a mud volcano located in Sidoarjo, East Java, Indonesia, attracts interest of researchers to seek the possibility of utilizing it; among them is as construction material. This study focuses on the effect of calcinations temperatures of LUSI mud on the compressive strength of geopolymer mortar. Three different calcinations temperatures were investigated, i.e. 700, 800 and 900°C for five hours duration. Characterization of the mud, both the original and the calcined ones, was performed by using X-ray Diffraction (XRD) and X-ray Fluoresence (XRF) analyses. The calcined LUSI mud was then employed as precursor for making geopolymer mortar, and tested for its 7-day compressive strength. It is found that calcinations at 800°C is the optimum calcinations temperature producing the highest compressive strength.

Improving Surface Durability of High Volume Fly Ash Concrete with Application of Alkali Solution

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.

The Use of Borax in Deterring Flash Setting of High Calcium Fly Ash Based Geopolymer

Geopolymer that was made with high CaO content fly ash was found to have higher compressive strength than the low CaO fly ash, using the same mixture composition. This effect could be due to the physico-chemical properties of the fly ash, in respect to its particle size or the chemical composition. Although it was not widely published, the occurrence of flash setting of geopolymer was known to occur when using high CaO content fly ash as the precursor. Geopolymer paste may solidify within minutes after the addition of alkali activators, making it very difficult to cast in big volume. This paper investigate the effect of borax addition to the high calcium fly ash-based geopolymer mixture to reduce the occurrence of flash setting. It was found that the setting time can be extended significantly, with the addition of 5% borax, by mass, of fly ash. The addition of borax also have positive effect on increasing the compressive strength of geopolymer.

Effect of Particle Size on Properties of Sidoarjo Mud-Based Geopolymer

The eruption of Sidoarjo mud volcano that has been taken place since 2006 had caused significant damage to the local social environment, and until now there is no immediate solution that can be offered. Utilization of the Sidoarjo mud as construction material recently has gained some advancement by calcination of the mud, that make the previously inert material to become more reactive and to be more viable for its use as cement replacement or geopolymer precursor. This paper reports an on-going study to utilize the Sidoarjo mud as precursor of geopolymer by investigating the influence of particle size on the reactivity of the calcined Sidoarjo mud. Furthermore, durability properties of Sidoarjo mud-based geopolymer was also studied. The results show that making finer the mud particles by milling in longer period, using a rod-mill drum for 8 hours, can increase the reactivity of the mud. Compressive strength of geopolymer mortar can increase up to 155% when compared to the ones based on milling time of only 2 hours. Durability properties of sulphate acid resistance and chloride penetration are comparable to fly ash-based geopolymer, while the shrinkage measurement showing higher value.

Compressive Strength of Geopolymer Based on the Fly Ash Variation

. This study was conducted to determine the factors that may affect the compressive strength of fly ash-based geopolyme, manufactured using fly ash obtained from different power plants. Fly ash obtained from different sources may have very different characteristics that affect the properties of geopolymer product. The source of variations in the geopolymer properties from the view point of the source materials can be classified into internal and external factors. Internal factors include the physical and chemical properties of the fly ash, while external factors associated with mixture proportion of geopolymer and the manufacturing process. From the experimental results, it was found that the size of the fly ash granules, the CaO and MgO content, and the carbon content in fly ash are the internal factors that may affect the compressive strength of geopolymer. On the other hand, the ratio of sodium silicate to sodium hydroxide in the alkaline solution and the molarity of the sodium hydroxide solution are the external factors influencing the compressive strength of geopolymer.

Rapid Indicators in Detecting Variation of Fly Ash for Making HVFA Concrete

The use of fly ash as an alternative material for cement substitute in concrete mix already a common practice nowadays. However, as a waste material, fly ash varies in quality and condition, as shown by variation of its fineness, specific gravity, Loss on Ignition (LOI) and also on its chemical composition. By measuring the acidity (pH) of the fly ash in water solution, percentage of mass retained on 45 μm sieve, and superplasticizer demand of the fly ash, we can develop a quick estimation of the quality of fly ash. This study aims to investigate a quick method to estimate the quality of fly ash by measuring the physical and chemical pointers, as indicator for its properties and the effect on the setting time and compressive strength of mortar. Fly ash content was varied from 0-70% of the total mass of cementitious materials to make HVFA mortar. Fly ashes were obtained from four power plants in Indonesia. Tests conducted were material characterization, setting time, temperature rise, and compressive strength of mortar at different ages. Different fly ash quality can be shown by the fast pointers; namely pH, superplasticizer demand and % retained on 45 μm sieve. Setting time and strength development were affected by the different properties of fly ash.

A review on the effect of fly ash characteristics and their variations on the synthesis of fly ash based geopolymer

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.

Effect of adding acid solution on setting time and compressive strength of high calcium fly ash based geopolymer

Fly ash with high calcium oxide content when used as the base material in geopolymer concrete could cause flash setting or rapid hardening. However, it might increase the compressive strength of geopolymer concrete. This rapid hardening could cause problems if the geopolymer concrete is used on a large scale casting that requires a long setting time. CaO content can be indicated by pH values of the fly ash, while higher pH is correlated with the rapid setting time of fly ash-based geopolymer. This study investigates the addition of acid solution to reduce the initial pH of the fly ash and to prolong the setting time of the mixture. The acids used in this study are hydrochloric acid (HCl), sulfuric acid (H2 SO4), nitric acid (HNO3) and acetic acid (CH3 COOH). It was found that the addition of acid solution in fly ash was able to decrease the initial pH of fly ash, however, the initial setting time of geopolymer was not reduced. It was even faster than that of the control mixture. The acid type causes vario...

A Preliminary Study on Cracking Tendency of Cement Paste Incorporating High Calcium Fly Ash

Fly ash is a waste material from burning coal that can be used to reduce the amount of cement in making concrete and to improve the characteristics of concrete. Besides being able to improve the flowability of fresh concrete, fly ash can also serve to reduce cracking of concrete. But in certain cases, cement paste incorporating fly ash type C (high calcium fly ash) experiences cracks, right after being released from formwork. The purpose of this study were to investigate the causes of cracking of cement paste incorporating fly ash type C, the influence of fly ash variations, and the countermeasures. The evaluation conducted for this experiment were based on visual inspection and compressive strength test of cement paste at 28 days. Test specimens were made in the form of cement paste with fly ash content of 50%, by mass. Fly ash used was of type C taken from three different batches from one source; with fly ash type F from three different sources used for control specimens. Superplasticizer, silica fume, and calcium carbonate were used as additives to evaluate their effect in mitigating cracks. The results show that the use of fly ash type C may cause cracks on the surface of hardened paste. Fly ash content, especially CaO and MgO, are the key factors affecting the cracks tendency on the surface of cement paste, due to expansion. Superplasticizer and silica fume can be used to mitigate cracks of cement paste.