Papers by Keyword: Curing Temperature

Abstract: The depletion of petrochemical resources and greater worldwide environmental consciousness has led to a growing interest in polymers made from renewable resources during the last two decades. Hence, this work has attempted to reduce the dependence on petroleum-based epoxy by partially replacing it with epoxidized castor oil (ECO). The ECO was blended with epoxy at 10, 20, and 30% and cured with amine hardener. The effect of bio-resin on tensile, flexural, impact strength and dynamic mechanical properties were investigated. Further, the result of post-curing temperature on static and dynamic properties was examined. It was found that the addition of ECO up to 30% increased the impact strength. The 20% ECO sample showed balanced stiffness to toughness property and could be considered for semi-structural composite applications. The post-curing of samples at 150 °C showed better mechanical and dynamic properties except for impact strength.

Abstract: Nowadays geopolymer is promising and relevant material that can be effectively used in wide range of application areas. It is possible because of there are a lot of potential sources of raw materials for geopolymer synthesis. Raw components are the one of the key parameters that effect on geopolymer performance. On the other hands, the technological stages of geopolymer synthesis is no less important factor. The purpose of this study was to determine effect of technological parameters of geopolymer synthesis such as component composition of solid state phase, alkaline activator preparation and its introduction onto geopolymer paste as well as curing temperature on performance characteristics of geopolymer. Fly-ash based geopolymer samples were prepared with adding of different mineral components: Portland cement (PC), kaolin, metakaolin; different curing temperature conditions: ambient temperature and temperature treatment at 70 °C in oven during 24 hours; different methods of preparation and application of alkaline activator: using of fresh alkaline solution and using alkaline solution after 24 hours of cooling. The results show that efficiency of curing temperature conditions strongly depend on component composition of geopolymer paste. Samples, containing PC and metakaolin demonstrate better characteristics after curing under ambient temperature. Samples, containing kaolin and reference composition (fly ash only) the temperature treatment in oven is the best curing method (increasing in compressive strength up to 13 times). Using alkaline solution of NaOH after 24 hours of cooling gives a good effect on geopolymerization process and provides increasing in compressive strength value from 13 to 84 % for all experimental geopolymer pastes. However, average density for all compositions is varied slightly.

Abstract: The long-term mechanical stability of the gasket material is critical to sealing and electrochemical performance of the polymer electrolyte membrane (PEM) fuel cells. In this paper, the silicone rubber material, which is being considered as gasket material for PEM fuel cells, was fabricated at different curing temperatures and different curing pressures. Effects of the curing temperatures and curing pressures on the mechanical properties of the silicone rubber material were investigated. The tensile test results show that tensile strength of the specimen cured at the curing temperature of 160 was larger than that for the specimens cured at the curing temperature of 150 or 170 under the same curing pressure. The test results of the compression stress-strain, compression set and compression stress relaxation show that the curing temperature and curing pressure affected significantly the compression elastic modulus, compression set rate and compression stress relaxation behavior. It is found that the silicone rubber material cured at the curing temperature of 160 under the curing pressure of 10MPa had good compression mechanical properties compared to the materials cured at the other curing temperatures and curing pressure in this work.

Abstract: In this study, geopolymer samples were prepared by mixing metakaolin (MA) with activator solution made of potassium alkali silicate solution, potassium hydroxide flakes, and additional water. The aim of the experiment is to evaluate the mechanical strength of hardened samples based on four test variables including the SiO₂/K₂O molar ratios, K₂O concentration, H₂O/MA water coefficient, and curing temperature. The results reveal that K₂O concentration and H₂O/MA water coefficient impact strongly on the compressive strength, whereas varying of SiO₂/K₂O molar ratios in the range from 1.0 – 1.4 does not significantly change the compressive strength of geopolymer samples. On the other hand, high-temperature curing leads to higher mechanical strength of the samples in the early-age compared to curing at room temperature, due to the faster establishment of hard structure in the early-age of geo-polymerization process. However, curing at a temperature range of 80°C – 100°C contributes the non-linear strength development of the samples over the time.

Abstract: High amount of calcium oxide (CaO) in source material is known to positively influence the mechanical strength of fly ash based geopolymer. This study was conducted to investigate the suitability of paper mill sludge ash (PMSA) to partially replace fly ash in geopolymer mortar based on its degree of reaction. Fly ash was activated by a combination of sodium silicate solution and 6 M sodium hydroxide solution. The mixtures were designed to replace fly ash content with PMSA at 5%, 10% and 15% (by weight of fly ash). To observe its effect on the mechanical strength, the specimens were cured in three different temperatures, which are 30°C, 60°C and 90°C for 24 hours. After 24 hours, the hardened specimens were demoulded and placed at room temperature until the testing days. Measurement on fresh geopolymer properties was conducted with setting time and flowability tests, while degree of reaction tests was conducted on the hardened specimen. Based on the results, 5% PMSA demonstrated superior degree of reaction than other mixtures, particularly at higher curing temperature.

Abstract: The paper describes alkali-activation of the brick body with potassium water glass having the silicate modulus of 1.0. The 28-days compressive strengths, elasticity modulus, effective fracture toughness, effective toughness, and specific fracture energy of the specimens stored at 20, 40 and 60 °C are evaluated. The storage temperature of specimens and the content of the alkaline solution have a significant influence on all mechanical fracture properties of the studied materials.

Abstract: The present study is to estimate long-term characteristics of low-heat cement-based ternary blended concrete prepared for reducing hydration heat in mass concrete. 15% modified fly ash and 5% limestone powder were added for partial replacement of the low-heat cement. To achieve the designed compressive strength of 42 MPa, water-to-binder ratios were determined to be 27.5, 30 and 32.5% for ambient curing temperatures of 5, 20 and 40°C, respectively. Test results showed that, with the decrease in curing temperature, the drying shrinkage strains tended to decrease, whereas creep strain increased.

Abstract: Melamine-formaldehyde polymer was synthesized into the form of self-supporting films. The structural stability of these films was investigated by means of spectroscopy and thermal analysis. The curing temperature and time has effects on the structural stability of the resulting polymer films. In this work, polymer film cured at 200 °C for 12 hours showed highest structural stability compared to those cured at lower temperature and shorter time duration.

Abstract: With the aim to test the applicability of the commonly used maturity concept introduced by Freiesleben et al [1] to modern concrete and to investigate the impact of the curing history on the compressive strength of laboratory samples cured at elevated temperatures, four concretes with different binder compositions (a pure CEM I 42.5N, CEM I 42.5N with fly ash, CEM I 52.5N with fly ash and a CEM III/B) were cured and tested at temperatures ranging from 5 to 60 °C.To test the maturity concept, the development of the compressive strength of samples cured at temperatures ranging from 5 to 60 °C were tested at maturities ranging from 1 to 28 days.To test the impact of curing history at elevated temperatures on the compressive strength, concrete samples were cured at 60°C using two different temperature scenarios: (1) at a constant temperature of 60 °C and (2) at gradually increasing temperature from the casting temperature to the maximum temperature of 60 °C.It was found that the commonly used maturity concept is still applicable to modern concrete although the activation energy is dependent on the binder composition. Concerning the impact of curing history it was found that at 28 days of maturity, the strength of concrete cured at constant temperature of 60 °C was significantly lower than that of concrete cured at 20 °C. For the concrete exposed to gradually increasing temperature up to 60 °C, only a slight decrease in strength was observed for the pure cement concretes while the strength of the binder systems with fly ash increased.

Abstract: The aggregates factory consumes a big quantity of energy; by consequence, it costs money, in the other hand it produces a lot of waste material or SCM (sustainable concrete material). The main aspects which guide this study is the current tendency to make mortar based on a very abundant material which are crushed limestone aggregates and naturals dunes sand. The results obtained in this study summarize up the importance of SCMs aggregates on behavior of the mortar, this different kind of SCM aggregate offered different behavior at the fresh state of the batch and by consequence its result with different mechanical behavior at the hardened state of mortar. This study focus also on the behavior of the new kind of chemical admixture, which is acrylic superplasticizer. The principal aim of adding rolled or crushed SCM is makes a mortar, which can resist to exhaustive environment (at curing temperature).