非金属专业毕业设计外文文献--水泥与混凝土研究 .doc
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1、 Hydration and properties of novel blended cements based on cement kiln dust and blast furnace slag Maria S. Konsta-Gdoutos,1, Surendra P. Shah Center for ACBM, Department of Civil Engineering, Northwestern University, Evanston IL 60208, USA (03)00061-9,How to Cite or Link Using DOI Permissions & Re
2、printsAbstractThe aim of the present paper is to address the key technical issues pertaining to the utilization of cement kiln dust (CKD) as an activator for ground granulated blast furnace slag (GGBFS) to create nonconventional cementitious binders for concrete. The relatively high alkaline content
3、 of CKD is the predominant factor preventing its recycling in cement manufacture. However, it was observed that depending on the water-soluble alkali and sulfate compounds, CKD could provide the environment necessary to activate latent hydraulic materials such as GGBFS. Binary blends containing slag
4、 and CKDs from different sources were characterized and compared in terms of the rates of heat evolution and strength development, hydration products, and time of initial setting. A study of the effects of the influencing factors in terms of soluble alkali content, particle size, and free lime conte
5、nt was undertaken. The results confirm the dependence of the dissolution rate of slag on the alkalinity of the reacting system, and the importance of the optimum lime content on the rate of strength gain.Keywords X-ray diffraction; Hydration; Compressive strength; Cement kiln dust; GGBFS1. Introduct
6、ionThe environmental concerns related to Portland cement production, emission and disposal of cement kiln dust (CKD), is becoming progressively significant. CKD is a fine-grained, particulate material readily entrained in the combustion gases moving through the kiln. It is composed primarily of vari
7、able mixtures of calcined and uncalcined feed materials, fine cement clinker, fuel combustion by-products, and condensed alkali compounds1. The generation of CKD is responsible for a significant financial loss to the cement industry in terms of the value of raw materials, processing, energy usage, a
8、nd dust collection and disposal. Cement manufacturing plants generate approximately 30 million tons of CKD worldwide per year2. The U.S. cement industry generates about 4.1 million tons of CKD every year, 3.3 million tons of which is landfilled and only 0.75 million tons enter commerce as by-product
9、s3.The relatively high alkaline content of CKD is the predominant factor preventing its recycling in cement manufacturing. All CKDs frequently contain alkalis (Na2O, K2O) and sulfates in much higher percentages than those in Portland cement. CKD often contains a large amount of free lime, thus makin
10、g it a substitute for fertilizers and lime in stabilizing wastewater streams. Furthermore, studies have shown that CKD can be effectively used in soil and sludge stabilization. It has also been successfully used as inorganic filler in bituminous paving and asphaltic roofing4.Because the characterist
11、ics of CKD vary from plant to plant, only a small amount of CKD (15% cement replacement) is used in the cement and concrete industry. However, its high alkali and sulfate content makes it an excellent activator for pozzolanic materials. The dissolution rate of materials with latent pozzolanic proper
12、ties such as blast furnace slag generally depends on the alkali concentration of the reacting system5. Latent hydraulic materials develop pozzolanic activity and act as hydraulic cements once their glass network disintegrates when attacked by OHions. The solubilities of Si, Ca, Al, and Mg are functi
13、ons of the pH. At a pH lower than 11.5, the equilibrium solubility of silica is low and slag does not dissolve. As a result, more Ca+2and Mg+2enter into the solution and an impermeable aluminosilicate coating covers the surfaces of the slag grains, which inhibits further hydration6. A chemical activ
14、ator is required for further hydration of slag. Activators generally include all alkali hydroxides and salts, with the least soluble salts being the most effective7and8. Because all salts are neutral solutions they exhibit only a weak activating effect; however, when they are combined with lime they
15、 undergo an exchange reaction with Ca+2and hydroxide ions. Solutions of sodium or potassium hydroxides are then formed, which attack and disintegrate the aluminosilicate glass. The presence of sulfate ions, supplied either by gypsum or alkali sulfates, accelerates the dissolution of slag by reducing
16、 the concentrations of Ca+2and Al+3in the mix to form ettringite.Limited information on the pertinence of CKD as an activator for pozzolanic materials is available. Sprouse9applied and received a patent for a cement that combined ground blast furnace slag with CKD. Amin et al.10studied the effect of
17、 kiln dust content and the calcination temperature on the hydration of granulated slag. Hydration products such as CSH, C4AH13, C2AHX, Ca(OH)2, hydrogarnet, and calcite were identified using the DTA technique. Their results indicated that the crystallinity and the content of the cementitious phases,
18、 especially -C2S, increased with calcination temperature. They concluded that activation of slags increases with increasing the content and the calcination temperature of the CKD. El-Didamony et al.11evaluated the effect of washed and calcined kiln dust with anhydrite. They found that the activation
19、 of the slag increases with firing temperature of the kiln dust and the amount of added anhydrite. Kiln dust calcined at 1300 C with 15% anhydrite was found to be suitable for the production of supersulfated cement. Recently, the production of active -C2S, C12A7and C2AS cements using different propo
20、rtions of a low-CaO fly ash and a lime-rich CKD as raw materials was proposed12.The objective of the present work is to understand the interaction of CKD with slag in order to explore the feasibility and the approaches to development of a new generation of more durable CKD-activated slag blends. Gro
21、und granulated blast furnace slag (GGBFS) has successfully been used with Portland cement to produce high-performance cement blends that are more economical and environmentally friendly. The use and effectiveness of CKD as an activator for slag depends upon its physical and chemical characteristics,
22、 most importantly, the alkali and free lime content, and the amount of carbonates and sulfates. The effectiveness of the alkali activation of slag will depend on the alkalinity provided by the CKD. It is expected that the high free lime content of the CKD will improve the hydration process by accele
23、rating hydration and forming more crystalline products of hydration. Sulfate ions provided either by alkali salts or anhydrite will expedite the hydration process and accelerate the pozzolanic reaction through the formation of ettringite. The experimental approach in this work includes the character
24、ization of binary blends containing 50% slag and 50% CKD in terms of the rates of heat evolution and strength development, hydration products, and time of initial setting. A study of the effects of the influencing factors of four different CKDs in terms of soluble alkali content, particle size, and
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