دانلود رایگان مقاله لاتین درجه حرارت در بند ژئوپلیمر قلیایی از سایت الزویر
عنوان فارسی مقاله:
اثر درجه حرارت بالا در بندهای ژئوپلیمر قلیایی فعال شده در مقایسه با پرتلند بندهای مبتنی بر سیمان
عنوان انگلیسی مقاله:
Effect of elevated temperature on alkali-activated geopolymeric binders compared to portland cement-based binders
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
Conventional structural concretes begin losing strength quickly when exposed to temperatures above 300 °C [1]. Typically, a hydrocarbon fire can generate temperatures in excess of 1000 °C with heat fluxes around 150 kW/m2 within minutes of ignition [2,3]. Additionally, a hydrocarbon jet fuel can have the same temperatures, but the heat flux could be doubled [2,3]. At those temperatures, the compressive strength of portland cement concrete can be reduced by as much as 90% [2]. This loss of strength is commonly attributed to the degradation of the calcium silicate hydrate (C-S-H) as it begins to lose structural water along with dehydration of other hydrates (e.g., calcium hydroxide (Ca(OH)2) and ettringite (Ca6Al2(SO4)3(OH)12·26H2O)) and initiation of internal thermal stress gradients. In addition, high-density, high-performance concretes (HPCs) with large amounts of portland cement and low water-to-cementitious materials ratios have issues when exposed to high temperatures. HPCs have a high density with low porosity, and as temperature increases the water vapor is unable to escape, causing pressure to build-up in the pores that results in explosive spalling [4,5]. In cases where HPC is in a confined space, flying debris represents a danger to the personnel responding to fires and sudden failures of supporting structural components create a hazard for the entire structure. Development of a cementitious material capable of withstanding elevated temperatures due to extreme environments is required for a variety of civilian and military applications. Currently, an environmentally-friendly construction material capable of retaining mechanical performance at elevated temperatures is being developed that also reduces the amount of carbon dioxide emissions into the atmosphere. Instead of using portland cement as the binding component, industrial byproducts such as fly ash, slag, and/or metakaolin are being incorporated to create a geopolymeric composite material [6–12]. A review of the geopolymer technology prepared by Duxson et al. [13] concluded that a significant amount of research has been performed, however, considerably more research is required to advance the technology to commercial applications. Geopolymer technology has the capacity for widescale applications in the construction industry, as well as in other applications due to similar engineering properties of portland cement and in some cases better thermal properties. Research by Zhao and Sanjayan [14] has shown that geopolymer concretes consisting of non-hydrated aluminosilicate gel binding phases combined with thermally-stable aggregates have survived exposure to fire testing, while similar portland cement concrete structures have failed. Side-by-side experiments of geopolymer and portland cement concretes designed to have comparable compressive strengths revealed that the geopolymer concrete has a higher fire spalling resistance than the portland cement-based concretes. Zhao and Sanjayan [14] attributed this spalling resistance to a highly porous structure thatfacilitates the release of the internal steam pressure build-up after exposure to the elevated temperatures. The research by Zhao and Sanjayan built upon the progress made by Duxson et al. [13] and Kong and Sanjayan [15] that showed that alkaliactivated aluminosilicate gels present in aluminosilicate-based concretes are inherently different from portland cement-based concrete. The use of these type of binders requires a sodium and/or potassiumbased alkali source that reacts with silica- and alumina-rich phases (e.g., clays and glasses), which results in a gel that does not contain the large amounts of chemi- or physi-sorbed water when compared with C-S-H gels produced by portland cement hydration. This open pore structure that distinguishes the aluminosilicate composites reflects the particle sizes of the starting materials [16]. The open pore structure results in a novel inorganic composite material that can withstand temperatures in the range of 600–800 °C with minor loss of strength. Furthermore, Zhao and Sanjayan [14] studied a fly ash based geopolymer and compared the material's response to a portland cement in a simulated gas fire, where the portland cement spalled while the fly ash did not spall.
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کلمات کلیدی:
Geopolymer - Wikipedia https://en.wikipedia.org/wiki/Geopolymer Geopolymers are new materials for fire- and heat-resistant coatings and adhesives, medicinal ... Raw materials used in the synthesis of silicon-based polymers are mainly ..... Indeed, geopolymer cement is sometimes mixed up with alkali-activated .... The comparison proceeds between Portland cement and geopolymer ... [PDF]ALKALI ACTIVATED MATERIAL – GEOPOLYMER 1 ... - Geopolymery www.geopolymery.eu/aitom/upload/documents/publikace/.../2007_praha_skvara.pdf by F Škvára - Cited by 10 - Related articles polymer based on brown coal fly ash. ... materials in comparison with standard Portland cement. Keyword. Geopolymer, alkali activated materials, microstructure, fly ash .... group of inorganic binders with substantial ecological and energetic. Durability of alkali-activated binders: A clear advantage over Portland ... https://repositorium.sdum.uminho.pt/.../Pacheco%20Torgal%20et%20al.%202012.pdf by FP Torgal - 2012 - Cited by 121 - Related articles on the field of alkali-activated binders, state that this new material is likely to have high potential to become .... These authors compared Portland cement concrete and al- .... different results for geopolymers based on fly ash and blast furnace. [PDF]Microstructure and durability of alkali-activated materials as key ... eprints.whiterose.ac.uk/86434/7/Microstructure.pdf by JSJ van Deventer - 2014 - Cited by 11 - Related articles Journal of Sustainable Cement-Based Materials, 4 (2). pp. 116-128. ... AACs (100% slag and 1:1 slag:fly ash) are presented, and compared to Portland cement ... gels) and alkali-activated aluminosilicates (geopolymer gel). Also, blending aluminosilicate- rich materials, such as fly ash, within alkali-activated slag binders has ... [PDF](Micro)-structural comparison between geopolymers, alkali-activated ... https://orbi.ulg.ac.be/bitstream/2268/21028/1/Corrected%20proof.pdf by I Lecomte - 2006 - Cited by 176 - Related articles other two types of Ca-based binders. ... geopolymers, alkali-activated slag cement and ordinary Portland cement .... These spectra are very comparable to those. People also ask What is alkali activation? What is meant by geopolymer concrete? Feedback Searches related to alkali-activated geopolymeric binders compared to portland cement-based what is alkali activation alkali-activated cements and concretes pdf alkali activated cement wiki alkali activators alkali activated slag alkali activated fly ash alkali activated binders alkali activated materials pdf
