Papers by Keyword: Setting Time

Abstract: The aim of this work was to evaluate the setting time, adhesion, sealing ability, and ion release of a novel endodontic sealer (CEOE) and of the commercial Sealer 26^® cement. The setting time was determined in accordance with ANSI/ADA specifications #57. The adhesion of the materials to the canal walls was evaluated through bond strength using the push-out technique. The sealing ability was assessed by fluid filtration measurements. The released ions of interest to be analyzed are OH^1- and Ca²⁺. The concentration of hydroxyl and calcium ions was evaluated by pH measurements and atomic absorption spectroscopy technique, respectively. The data were analyzed statistically using the analysis of variance and the Tukey’s test. The results obtained showed that the setting time of CEOE cement is 35% shorter than of Sealer 26^® and both cements meet the British Standard BS (1988) recommendation. No significant difference was observed in the bonding strength and permeability values for both cements. Statistically, the CEOE released more hydroxyl ions than Sealer 26^® in the first 72 h, and more calcium ions in the first 48 h.

Abstract: Renovation mortars used to restore damaged stucco elements are materials with special physical properties due to the nature of the work and environment in which they are applied. They must be characterized by low shrinkage, relatively short setting time, appropriate working properties and hydrophobic nature of hardened mortar. This paper analyzes the impact of mortar stucco ingredients on these parameters. The analysis was performed by experimental studies. The effect of the content ratio of aluminate cement to Portland cement on the change in mortar setting time was studied. Suitable workability of fresh mortar is achieved by the use of consistence-modifying additives. To assess this parameter, flow table method was applied in accordance with PN-EN 1015-3: 2000. The additives used were a system of thickeners, which included: cellulose ether in the form of hydroxyethylmethylcellulose and modified starch ether (starch 2-hydroxypropyl ether). Hydrophobic properties were obtained by the addition of triethoxyoctylsilane. The results were presented as graphs and tables. It was found that the ratio of aluminous cement to Portland cement most beneficial in terms of the setting rate of the resulting stucco mortar is 25% (m/m). This amount accelerates the end of setting time to 2 hours, the beginning of the setting time being 20 minutes. Suitable working characteristics were obtained by the addition of 0.080% of hydroxyethylmethylcellulose and 0.025% (m/m in dry mix) of starch 2-hydroxypropyl ether. Best hydrophobic properties of the hardened mortar was obtained by the addition of 0.075% (m/m in dry mix) of triethoxyoctylsilane.

Abstract: In scores of experiments indicates that the super-retarding mortar, keeping plasticity long-term, can make cement setting and hardening at a slower speed through chemical additive. Based on large numbers of orthogonal tests and theoretical analyses, the super-retarding mortar which satisfies the demands of actual engineering was developed successfully in present paper. And it is consist of cement, sand, water and composite retarder blended in an appropriate rate. From 0°C to 40°C, setting time can be adjusted from 1 day to 22 days in the light of to the engineering requirements, and after condensation, it begins to harden gradually and ends with the compression strengthen over 30MPa. Experiments were employed to test the influences of accession amounts of composite retarder dosage on setting time and compression strengthen of super-retarding mortar. Besides, the retarding mechanism was studied, and the super-retarding mortar was applied to experimental models. The results show the super-retarding mortar can be applied to the actual engineering, and it can be treated as the theoretical reference for the actual project application of the new prestressed concrete system.

Abstract: The results of studies of modified hardened cement paste with glyoxal-containing additive are given in this article. The goal was to study the patterns of influence of crystalline glyoxal on compressive strength of hardened cement paste. Introduction of crystalline glyoxal in the amount of 0.01-0.05% by weight of cement in the cement paste enables the increase in the compressive strength of hardened cement paste in 28 days by 7-8%. The studies have established that the introduction of crystalline glyoxal in the amount of 0.1-1% by weight of cement is inefficient; there is a decrease of the strength values in comparison with control samples. The results of microstructure investigation (of control samples and samples of the modified hardened cement paste) have shown that the introduction of crystalline glyoxal in the amount of 0.01-0.05% by weight of cement provides the structure of hardened cement paste that does not contain sedimentative pores and increases the quantity of hydroaluminate.

Abstract: The paper introduces development of new type of high-performance Portland cement based composite applicable for number of practical utilization. The fundaments of performed research was to design mixture with controlled process of hydration, easy production, suitable time of setting, good workability and rapid evolution of mechanical properties as well as satisfactory long-term stability of hardened composite. Selected mixture were evaluated by means of mechanical properties and volume changes determination.

Abstract: 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.

Abstract: This paper describes the result of investigating volcanic ash of Mount Kelud as fly ash substitute material to produce geopolymer concrete. The test was held on geopolymer concrete blended with 0%, 25%, 50% and 100% fly ash replacement with volcanic ash. Natrium Hidroxide (NaOH) with concentration of 12 molar and Natrium Silicate (Na₂SiO₃) were used as alkaline activator. While alkali-activator ratio of 2 was used in this research. The physical properties was tested by porosity and setting time test, while split tensile strength presented to measure brittle caracteristic of geopolymer concrete. The result shown that increasing volcanic ash content in the mixture will increase setting time of geopolymer paste. On the other hand increasing volcanic ash content will reduce split tensile strength and porosity of geopolymer concrete. After all replacing fly ash with volcanic ash was suitable from 25% to 50% due to its optimum physical and mechanical properties.

Abstract: 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.

Abstract: In this study, influences of mixing procedure on the latex adsorption behavior, slurry fluidity and setting time of latex modified cement paste (LMCP) mixed with polycarboxylate (PC) as superplasticizer were analyzed. There were three kinds of mixing procedure: LMCP added latex later than PC (LMCP-L), LMCP added latex before PC (LMCP-B), LMCP added latex and PC simultaneously (LMCP-S). The results show that, the adsorption isotherm of SAE latex by cement grains fits the Langmiur type, and the presence of PC can affect the adsorption behavior. Regardless of the m_latex/m_cement (4% or10%), LMCP-B had the highest amount of adsorbed latex and slurry fluidity while LMCP-L had the lowest. And, the LMCP-B also had the longest initial and final setting times, while the setting times of LMCP-L and LMCP-S were comparable.

Abstract: Pure cement mortar and concrete possess disadvantages such as brittleness, low bonding or adhesion strength, low tensile strength, large drying shrinkage, low chemical resistance. In order to overcome these disadvantages, polymer concrete is used as a construction material in Singapore as the properties of polymer-modified (or polymer cement) mortar and concrete are superior to conventional cement mortar. In Singapore, new products or technologies can be found through distributers, agents, etc. Singapore is able to afford and try high quality products to maintain the quality of a building and structure. The importance of applying polymer to protect, repair, coat and strengthen concrete structures in Singapore have grown in the last two decades. To ensure and maintain the standards of construction and building quality, polymer concrete are used extensively in new developments in Singapore. In this paper, the mechanical properties and its corresponding testing methods for several types of polymer concrete used in Singapore are discussed. These products include mortar used to repair concrete spalling, acrylic polymer cementitious coating, waterproofing membrane, epoxy mortars and grouts, fibre reinforced plastic (FRP) and epoxy resin. In addition, the specifications for the above products used in Singapore’s Housing Development Board (HDB) are discussed in the paper as it’s a requirement for suppliers to test their products in accredited laboratories before it can be used.