Papers by Keyword: Setting Time

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.

Abstract: Production of Ordinary Portland Cement (OPC) requires huge quantity of natural resources and energy and it releases large amount of carbon - di - oxide to the environment. Therefore, enormous studies have been carried out throughout the world to establish geopolymer as an alternative binder material for the replacement of OPC to protect the environment. This study intends to explore the effects of alkaline solution on the properties of geopolymer produced with ground granulated blast furnace slag. Properties such as Standard consistency, setting time of slag based geopolymer paste has been determined using Vicat’s apparatus (according to the guidelines given by Indian Standards for OPC). In order to determine the effects of alkaline solution on the properties of geopolymers, the concentration of sodium hydroxide solution has been varied from 6M to 16M and the ratio of sodium silicate solution to sodium hydroxide solution is also varied from 1.0 to 2.0. Results indicate higher standard consistency and significant less setting time for slag based geopolymer paste than that of OPC paste. Compressive strength of the geopolymer paste and mortar cube samples, cured in ambient conditions till the day of testing, is increasing with the increase of the concentration of sodium hydroxide solution. Highest compressive strength is obtained for the samples prepared with alkaline solution having the ratio of sodium silicate solution to sodium hydroxide solution as 1.5. But when the concentration of sodium hydroxide solution is beyond 14M, decreasing trend in compressive strength is observed.

Abstract: The effects of triethanolamine on the compressive strength and setting time of fly ash cementitious materials, slag cementitious materials, and limestone cementitious materials were investigated. The results show that the dosage of 0.04% of triethanolamine can significantly improve the 3d, 7d and 28d compressive strength of fly ash cementitious materials. It possesses less impact on the setting time. The dosage of 0.04% of triethanolamine can significantly improve the 3d and 7d compressive strength of slag cementitious materials while the effect of late strength is not obvious. It extends the initial setting time and the final setting time is not changed, which has retarding effect. The results of hydration heat and XRD show that triethanolamine extends the induction period of cement hydration, and gypsum is exhausted in advance during the hydration process. Triethanolamine promotes the transformation of AFt to AFm and there is no effect on the type of hydration products.

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.

Abstract: Industrial waste products can be considered as renewable resources. Steel industry wastes have a severe impact on the environment whereas this industry involves a myriad of operations which create vast volumes of air emissions, liquid effluents, and solid wastes. This study presents the feasibility of using Electric Arc Furnace Dust (EAFD) as a cement replacement material (CRM) in comparison with silica fume (SF) and fly ash (FA). The EAFD is a complex byproduct material of steel produced by electrical - arc furnace and consisting mostly of metal oxides. The results showed that the workability of the EAFD mixes is comparable to the control mix even when the percentage of the EAFD was increased. On the other hand, as the replacement percentage was increased, the use of FA, SF resulted in higher, lower workability, respectively. Furthermore, the EAFD significantly affected the setting time, where 3% of the EAFD replacement resulted in prolonging setting time reached more than 24 hours, while the use of SF and FA has insignificantly affected the setting time. The 3% of EAFD is found to be the optimum replacement in terms of compressive strength and it has a similar effect to a replacement level of 5% of SF and 15% of FA.

Abstract: In this study, different types of plasticizers were used to investigate their effects on the fresh and hardened properties of high calcium fly ash geopolymers (HCFA). Modified polycarboxylate polymers (G3) and lignin-based polymers (G1) were used as plasticizing admixtures and the results were compared to the effect of tap water addition. The results showed that all the admixtures used are effective in increasing the workability of the HCFA geopolymers mixtures and the workability increased by 25-48% compared to the control mixtures. However, the use of G3 has adversely affected the strength by a reduction of 20%. While the use of G1 reduced the final setting time by 7% which is critical in the case of HCFA geopolymers where the final setting time occurs within 70 minutes. Water can be considered as the best admixture in terms of cost, setting time, and effect on compressive strength and it can be used where medium workability enhancement is required.

Abstract: Geopolymer system is new binding materials in concrete industry that is produced by the alkaline solution and materials rich in aluminosilicate such as fly ash. The effect of the alkaline solution to fly ash ratios of 0.3, 0.4 and 0.5 on mortar geopolymer properties was an issue in this study. The results showed that the higher alkaline solution to fly ash ratio improves the workability and brings a longer setting time, whereas the lower alkaline solution to fly ash ratio gains the significant compressive strength. It was a similar pattern with conventional mortar used ordinary Portland cement, which the compressive strength at 7 days was 85%-90% for 28 days compressive strength, whereas conventional mortar is only 65%-75%. This was due to the higher reactivity in geopolymer system that was faster than the pozzolanic reaction.

Abstract: Because the setting time of magnesium phosphate cement (MPC) was too quick, its further application was restricted. Influence factors about magnesium phosphate cement setting time are summarized and the influence laws are studied in the paper. The results show that with the increase of phosphorus to magnesium ratio (P/Mg) or boron to magnesium ratio (B/Mg), the setting time is both obviously prolonged. The effect of water to binder ratio (W/C) on the setting time of MPC has an optimal point. As the specific surface area increases gradually, the setting time of MPC is greatly shortened. Although fly ash has effect on setting time of MPC, the effect is very small. At the same time, the setting time is closely related with environmental temperature, the pH value of the system and mixing volume.

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.

Abstract: The article deals with heat liberation of barium cements, which influences the crack formation in mass concrete structures. The results of heat release and physical testing of barium cements with a different content of BaO are presented in this paper. The strength of cement and its setting time will decrease significantly, if the content of BaO in clinker is high (about 47%). This cement is characterized by a low water requirement and heat liberation. Properties of cement with a low content of barium oxide (5.5%) are close to the properties of the standard Portland cement. In this case heat liberation is low in the initial period of hardening, but at the later stage it exceeds the exotherm of a reference sample. A small amount of BaO in cement clinker reduces the exothermic effect and increases the thermal crack resistance of concrete.