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In this study, coagulation of kaolinite suspensions at low temperatures is compared with that at an ambient temperature of 22 degrees C, and the process is examined with regard to the coagulation rate (CR) and chemical aspects of coagulation. Experiments using a photometric dispersion analyzer (PDA) show that coagulation of kaolinite suspensions can be taken as a two-phase process. Low temperature greatly reduces the CR of the first phase but not that of the second one. On the other hand, results show that low temperature did not serve to impede the hydrolysis of aluminum [Al(III)] within 1 min of alum addition. The measurements of electrophoretic mobility (EM) indicate that destabilization of kaolinite particles by hydrolyzed Al species was not hindered by low temperature within 1 min of alum addition. Slow coagulation at low temperature is due to the lowered CR but not the altered chemistry aspect of Al(III). Furthermore, the change in settled turbidity after 20-min flocculation as a function of coagulant dosage was more severe in the cold because of the low CR. Elongating floc-growth time, as observed, was able to counterbalance the retarded CR at low temperature and improve turbidity removal efficiency. 相似文献
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U. Gori 《Bulletin of Engineering Geology and the Environment》1994,50(1):37-42
Three clay sediments, concerning Pliocenic clay, Chaotic Complex clay and commercial kaolinic clay, have been studied in order to verify the pH influence on the index properties. The analysed clays have been mineralogically characterized in natural, conditions, and in modified pH conditions. This last procedure, obtained respectively by adding NH4OH or CH3COOH 1 mol., in a pH range between 4.5–11.3 has been carried out. To verify the different experimental conditions the C.E.C. of exchangeable cations as K+, Na+, Ca++ and Mg++, has been measured. The index properties obtained show a different behaviour of the three clays. The kaolin is not much affected only a limited WL% increase is recognizable when the pH decreases. The Chaotic complex clay evidence a considerable rise of the WL with the pH uncrease. In the Pliocenic clay the WL value increased with the pH. The described process can be related to the natural environment, connected also with various pollution phenomena. 相似文献
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《Construction and Building Materials》2010,24(7):1176-1183
The properties of metakaolin-based geopolymer are directly impacted not only by the specific surface and composition of initial metakaolin and the type, composition and relative amount of alkali activator used but they also depend on the conditions during the initial period of geopolymerization reaction. This study aimed to analyze the effect of curing temperature (10, 20, 40, 60 and 80 °C) and time on the compressive and flexural strengths, pore distribution and microstructure of alkali activated metakaolin material. The results have shown that the treatment of fresh mixture at elevated temperatures accelerates the strengths development but the 28 days mechanical properties are deteriorated in comparison with results obtained for mixtures that were treated at an ambient or slightly decreased temperature. The influence of curing temperature on microstructure of geopolymer matrix was verified in terms of pore distribution studied by means of mercury intrusion porosimetry. The study revealed a tendency to increase pore size and cumulative pore volume with rising temperature, which is reflected in mechanical properties. It has been also shown the possibility of monitoring the geopolymerization reaction by means of Infrared Spectroscopy. 相似文献
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Effect of calcination temperature on the pozzolanic activity of sugar cane bagasse ash 总被引:1,自引:0,他引:1
G.C. Cordeiro R.D. Toledo Filho E.M.R. Fairbairn 《Construction and Building Materials》2009,23(10):3301-3303
This work presents the results of the processing of sugar cane bagasse ash (SCBA) under controlled calcination conditions in order to obtain materials with optimum pozzolanic activity. Bagasse samples were burnt in an aired electric oven with a heating rate of 10 °C/min, at 350 °C for 3 h, and at different temperatures ranging from 400 to 800 °C for another 3 h. For all calcination temperatures the pozzolanic activity, structural state of silica and loss on ignition of the ashes were determined. Moreover, the SCBA with greater pozzolanicity was characterized by using chemical analysis, scanning electron microscopy, density, specific surface area and chemical reactivity. 相似文献
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偏高岭土是高岭土在适当温度下煅烧活化形成的硅铝酸盐,以其为原料制备的地聚物具有快硬早强、强度高、和易性好及耐腐蚀等优点。近年来,相关学者针对偏高岭土地聚物力学性能的影响因素开展了大量力学性能试验及基础理论研究工作,为偏高岭土地聚物的推广应用奠定了基础。综述了偏高岭土地聚物的种类、水化机理,总结了激发剂种类、掺量、水玻璃模数、胶凝材料处理方式、液固比、外掺料及养护方式、养护温度等因素对偏高岭土地聚物力学性能的影响,并对偏高岭土地聚物推广应用中面临的问题及未来的研究方向进行了探讨。 相似文献
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Lapyote PRASITTISOPIN Issara SEREEWATTHANAWUT 《Frontiers of Structural and Civil Engineering》2018,12(1):16
Geopolymer, an inorganic aluminosilicate material activated by alkaline medium solution, can perform as an inorganic adhesive. The geopolymer technology has a viability to substitute traditional concrete made of portland cement (PC) because replacing PC with fly ash leads to reduced carbon dioxide emissions from cement productions and reduced materials cost. Although fly ash geopolymer stimulates sustainability, it is slow geopolymerization reaction poses a challenge for construction technology in term of practicality. The development of increasing geopolymerization reaction rate of the geopolymer is needed. ?The purpose of this study is to evaluate seeding nucleation agents (NA) of fly ash geopolymer that can accelerate polymerization reactions such that the geopolymer can be widely used in the construction industry. Results from the present study indicate that the use of NA (i.e., Ca(OH)2) can be potentially used to increase geopolymerization reaction rate and improve performance characteristics of the fly ash geopolymer product. 相似文献
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对地质聚合物技术做了一个简要的介绍,分别从原材料、激发剂、添加剂和养护条件四个方面对近年来国内外学者在粉煤灰基地质聚合物力学性能的影响因素方面所做的工作和研究成果进行了介绍。粉煤灰的物化特性对粉煤灰基地质聚合物的力学性能有决定性的影响;激发剂中的碱形式、碱浓度和硅含量对粉煤灰基地质聚合物的抗压强度影响较大;适当的添加剂能提高粉煤灰地质聚合物的抗压强度;相对较高的养护温度有利于粉煤灰基地质聚合物力学性能的发展。在所有的影响因素中,原材料的成分和性质是最难控制的因素。最后,对研究原材料对地质聚合物力学性能影响的研究给出了建议。 相似文献
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在陕西安塞地区黄土中掺入两种不同纳米黏土材料,设计不同掺量、含水率、养护龄期等多因素影响下的正交试验,并对改良后黄土进行三轴试验,分析凹凸棒土和纳米蒙脱土改善黄土无侧限抗压强度指标以及抗剪强度指标的变化特征,并采用SEM对两种纳米黏土改良黄土进行改善机理微观分析。结果表明:掺量为1%的凹凸棒土、掺量为2%的纳米蒙脱土对黄土抗压强度影响最为显著,在一定含水率下可使素黄土的抗压强度分别提高21%和42.3%; 两种纳米黏土改良黄土应力-应变曲线受试样干密度、围压及掺量的影响,干密度为1.35 g?cm-3、围压为50 kPa的改良黄土有应变软化现象,干密度达到1.65 g?cm-3时,4种不同围压下改良黄土应力-应变曲线均有应变硬化的趋势; 两种纳米黏土对改良黄土的抗剪强度指标影响效果显著,其中1%掺量的凹凸棒土、2%掺量的纳米蒙脱土可以使改良黄土的黏聚力分别提升61.02%和81.70%,内摩擦角分别提升27.86%和21.31%。 相似文献