Papers by Keyword: Setting Time

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Authors: J.L. O’Beirne, R.M. Shelton, P.J. Lumley, M.P. Hofmann
Abstract: Mineral trioxide aggregate (MTA) is a Portland cement (PC) based material used for sealing root canals however it has a long setting time which is undesirable for dental applications. This study investigated the effect of three different calcium sulphate additions for accelerating the initial setting of a PC based dental material, whilst attempting to maintain its high compressive strength and low relative porosity. Anhydrous calcium sulphate (CaS), Plaster of Paris, calcium sulphate hemihydrate (PoP) and Gypsum, calcium sulphate dihydrate (Gyp) were each added to PC at 5wt%, 10wt% and 20wt%. Initial setting times, compressive strengths and relative porosity were measured using the Gilmore Needles Test, a universal testing machine and a helium pycnometer respectively. Scanning electron microscopy (SEM) was used to observe any microstructural changes in cements. PoP and CaS had the most profound influence on the setting of PC. 20wt% CaS had the greatest effect on the setting time of PC (10min) although decreased the compressive strength by up to 40%, which may have arisen from the formation of microcracks, observed by SEM analysis. Additions of 10wt% PoP and CaS may have the potential to reduce the long setting time of PC based dental materials.
Authors: Qun Pan, Shuang Zhao, Han Ying Zheng, Bin Zhu
Abstract: This study reports a new type compound admixture YP developed for slag cement activated by water glass. The effect of the compound admixture on properties of slag pastes, including mini slump, setting time and heat of hydration was examined. It is found that the slump of slag paste was increased from 60 mm to 120 mm by using the admixture. Furthermore, the initial and final setting times of paste with the admixture were 96 min and 132 min, while it only took 18 min and 23 min to achieve initial setting and final setting for the paste without using the admixture. In addition, the results also indicate that the initial peak was delayed for nearly 7 hours and the heat flow of hydration was reduced from 5864 μw/g to 461μw/g, when the admixture was added. It can be concluded that the new admixture is capable of imparting a significant improvement of workability of alkali-activated slag cement with a suitable setting behavior.
Authors: Jaroslav Pokorný, Milena Pavlíková, Eva Navrátilová, Pavla Rovnaníková, Zbyšek Pavlík, Robert Černý
Abstract: The effect of a-SiO2 of various origin on the properties of cement paste with incorporated different silica containing materials is experimentally studied in the paper. For the applied a-SiO2 materials, basic physical and chemical properties are accessed, together with their chemical composition. Amount of amorphous phase of SiO2 in particular siliceous materials is determined using XRD analysis. Matrix density, bulk density, total open porosity, compressive and bending strength are measured for all developed pastes with incorporated a-SiO2 containing materials, together with initial and final setting time of fresh mixtures. The obtained data give evidence on a high and fast reaction activity of tested siliceous materials which results in a significant improvement of porosity and mechanical strength of a-SiO2 modified cement pastes.
Authors: Dong Mei Zhang, Ming Shi Lu, Feng Xing Liu
Abstract: Effects of steel slag powder on properties of cement and concrete are investigated. Results show that with the increase of steel slag power, water requirement of normal consistency is decreased, and the setting times are prolonged. The early mortar strength is lower, but late strength rate of increase is great. Steel slag powder is compatible with blast furnace slag. Moreover,concrete,which has harmonious development strength and excellent workability can be obtained by mineral additives two-element compounding.
Authors: Daniela Jörn, Renate Gildenhaar, Georg Berger, Michael Stiller, Christine Knabe
Abstract: The setting behaviour, the compressive strength and the porosity of four calcium alkali orthophosphate cements were examined under laboratory conditions (dry) and under conditions similar to those during clinical application (37°C, contact with body fluid). The results showed an increase of the setting times when specimens were covered with simulated body fluid. Especially, the final setting time (FHZ) was significantly higher for three of the four cements. Furthermore, when specimens were stored in SBF for 16h, an extensive decrease of the compressive strength was noted. The porosity was more than twice as high after 16h in SBF and this may be the cause for the great decrease of the compressive strength.
Authors: T. Watanabe, Kimitoshi Ando, T. Ito, Naritaka Kitamura, Kazuhiko Nakata, Shozo Tsuruta, Tatsushi Kawai, Hiroshi Nakamura
Abstract: There is little information concerning the physical properties of various commercialized water-based temporary filling materials. In this study, the setting characteristics of 5 water-based temporary filling cements, i.e., Caviton, HY-seal, Lumicon, Cavit-G, and Cavit-W, were examined. Reinforced plastic pipes were filled with the test materials, and the specimens were then immersed in distilled water at 37°C. Setting time of each specimen was determined by a penetration test using a Vicat penetrometer; and setting layer depth was measured with micrometer calipers. Cavit-W exhibited the fastest setting time, whereas Caviton and HY-seal demonstrated the slowest setting time. These results indicate that the setting properties of these materials used in this study were significantly different for each material, which showed some changes on the surface and the internal part after the start of water absorption.
Authors: Khanthima Hemra, Shuntaro Yamaguchi, Takaomi Kobayashi, Pavadee Aungkavattana, Sirithan Jiemsirilers
Abstract: Class C fly ash is widely used as a geopolymer raw material. It contains high calcium oxide and iron oxide resulting in a fast setting property. The influence of using kaolin and metakaolin replaced class C fly ash in geopolymer processing were investigated in term of compressive strength and setting time. Kaolin and metakaolin which calcined at different temperature of 600°C and 700°C replaced Class C fly ash between 0 to 50 wt. %. The geopolymers were prepared at constant KOH concentration as 6.0 M, K2SiO3/KOH ratio as 1.0, solid/liquid ratio as 1.5 and 7 days of curing. The compressive strength is obviously increased when fly ash was replaced with both kinds of metakaolin, although, it is inclined to decrease when replaced by kaolin. The compressive strength is increased up to 13% and 47% with the replacement by 50 wt. % of metakaolin calcined at 600°C and 700°C, respectively. On the other hand, the replacement by 50 wt. % of kaolin give the initial setting time prolonging from about 6 min to 80 min. However, the initial setting time of metakaolin calcined at 600°C and 700°C replacement is also improved to about 37 min and 20 min, respectively. These results from their difference of amorphous phase and reactivity of the replacement materials. XRD analysis reveals the combination phases of amorphous geopolymer gel that is the broad hump centered at 28 – 30° 2θ, and products from the reaction such as calcium oxide, arcanite, calcium silicate hydrate, quartz and muscovite which the two latter are from unreacted metakaolin. They are confirmed by FT-IT result and microstructure evaluation by SEM. Therefore, the partially replacement of fly ash with kaolin and metakaolin in fly ash-based geopolymer production are affected to the compressive strength and resulted to modify the setting time.
Authors: Zdeňka Bažantová, Karel Kolář, Petr Konvalinka, Jiří Litoš, Miroslav Petrtýl
Abstract: This paper describes the fundamental principles for the development of high performance composites applicable in severe condition. Studied composite is based on the advanced silicate matrix consisted of cement and suitable addition modifying mineral additives. Experimental work was focused on the study of the evolution of mechanical properties and determination of frost resistance of developed composite at early age, what is crucial parameter for quick reconstruction. Obtained results confirmed that the action of frost did not interrupted the process of hydration of developed binding system, because index of frost resistance determined on the base of studied mechanical properties had increasing trend during the freeze/thaw cycling. Present paper declares high potential of silicate binders for difficult application.
Authors: Dong Mei Chen, Ri Hua Zhang, Zhan Guo Zhao
Abstract: At present, cement stabilization and sand are mainly used as Chinese road bases. Portland cement which causes shrinkage crack of road base can’t be suitable for construction requirements. One kind of new type cementitious materials of road base was developed to substitute for Portland cement by the construction requirements that the fly ash is the main raw materials. This product is not only suitable for construction requirements, but also reduces crack of road base for its suitable strength and micro expansive.
Authors: Hai Wang, Qian Jin Mao, Yue Gao, Zi Ming Wang, Su Ping Cui
Abstract: Sodium fluosilicate (Na2SiF6) is prepared from by-product of phosphate fertilizer production. According to a certain percentage of Na2SiF6 mixed in the cement, the influence of different dosages on the setting time of cement under different water-cement ratio was discussed, and the effect of different forms of fluoride compounds on the setting time of cement were compared. The effect and mechanism of sodium fluosilicate on the hydration products of cement were researched by using the X-ray diffraction analysis and micro electron microscope. Experimental results show that the retarding effect of sodium fluosilicate on the coagulation time had a critical effect, and beyond a certain value, it sharply decreased the setting time. The critical dosage increased with the increase of water-cecment ratio. Compared with the retarding effect of Na2SiF6、MgSiF6、NaF and CaF2 on the coagulation time of cement, Na2SiF6 was the best. The incorporation of Na2SiF6 does not change the types of the hydration products, the main function of FN is hydrolyzed with Ca2+ ions to form CaF2 with a very low solubility.
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