Alkali-Activated Cements and Concretes

Shi, Caijun; Roy, Della M.; Schroeyers, Wouter

doi:10.4324/9780203390672

Cited by 660 publications

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Section: Introductionmentioning

confidence: 99%

“…There are several industrial sectors which produce significant amounts of residues such as fly ash (FA), bottom ash, red mud, steel slag, nonferrous slag, etc. which can be used for that purpose (Shi et al, 2006).Millions of tons of FA, a by-product of coal combustion, are being generated annually worldwide (Malhotra, 2002; Coal Ash Facts). Although it has been used as a partial cement replacement for decades, there is an increased pressure to use a higher content of FA in concrete as a result of three main aspects e the economy, environmental and technical benefits.…”

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confidence: 99%

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Radiological and material characterization of high volume fly ash concrete

Ignjatović

Sas

Dragaš

et al. 2017

Journal of Environmental Radioactivity

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The main goal of research presented in this paper was the material and radiological characterization of high volume fly ash concrete (HVFAC) in terms of determination of natural radionuclide content and radon emanation and exhalation coefficients. All concrete samples were made with a fly ash content between 50% and 70% of the total amount of cementitious materials from one coal burning power plant in Serbia. Physical (fresh and hardened concrete density) and mechanical properties (compressive strength, splitting tensile strength and modulus of elasticity) of concrete were tested. The radionuclide content ( 226 Ra, 232 Th and 40 K) and radon massic exhalation of HVFAC samples were determined using gamma spectrometry.Determination of massic exhalation rates of HVFAC and its components using radon accumulation chamber techniques combined with a radon monitor was performed. The results show a beneficial effect of pozzolanic activity since the increase in fly ash content resulted in an increase in compressive strength of HVFAC by approximately 20% for the same mass of cement used in the mixtures. On the basis of the obtained radionuclide content of concrete components the I-indexes of different HVFAC samples were calculated and compared with measured values (0.27 -0.32), which were significantly below the recommended 1.0 index value. The prediction was relatively close to the measured values as the ratio between the calculated and measured I-index ranged between 0.89 and 1.14. Collected results of mechanical and radiological properties and performed calculations clearly prove that all 10 designed concretes with a certain type of fly ash are suitable for structural and non-structural applications both from a material and radiological point of view. KeywordsFly ash, Concrete, NORM, I-index, Radon exhalation 1. Introduction BackgroundThe building industry has one of the largest environmental impacts among all human activities:an annual consumption of 10 -11 billion tons of aggregate (Meyer, 2002) and 4.18 billion tons of cement (USGS, 2015). Apart from extremely high resource and energy consumption, cement production is a significant source of CO2 emissions, accounting for approximately 4.4% of global CO2 emissions from industry in 2007(Boden et al., 2010.There are many ideas that have been proposed to make concrete "greener" and more sustainable but they are all based on two principles: reuse and reduce. Concepts based on the "reduce" principle are oriented towards decreasing cement production based on natural materials and result in a reduction in CO2 emissions. With respect to the requirements for concrete as the world's most used man-made material, a lower production of Ordinary Portland cement must be compensated with alternative sources of binders in concrete production. There are several industrial sectors which produce significant amounts of residues such as fly ash (FA), bottom ash, red mud, steel slag, nonferrous slag, etc. which can be used for that purpose (Shi et al., 2006).Millions of tons of FA,...

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Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

Radiological and material characterization of high volume fly ash concrete

Ignjatović

Sas

Dragaš

et al. 2017

Journal of Environmental Radioactivity

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Section: Introductionmentioning

confidence: 99%

“…It is also known 7,8 that alkali hydroxide (ROH), non-silicic salts of weak acids (R 2 CO 3 , R 2 S, RF), or silicic salts of R 2 O·(n)SiO 2 type can be used as effective activators, where R indicates an alkali metal ion such as Na, K or Li. Various important parameters affecting the activation mechanism of AA mortar are well evaluated as summarized in different review papers [2][3][8][9][10] . Although, numerous investigations 8,10 are published on the optimum mix design of mortar or concrete activated by alkaline solutions, very few test data 11 on concrete activated by powder type activators are available.…”

Section: Introductionmentioning

confidence: 99%

“…Various important parameters affecting the activation mechanism of AA mortar are well evaluated as summarized in different review papers [2][3][8][9][10] . Although, numerous investigations 8,10 are published on the optimum mix design of mortar or concrete activated by alkaline solutions, very few test data 11 on concrete activated by powder type activators are available. However, mortar and concrete in construction industry are generally manufactured from powder-type binders.…”

Section: Introductionmentioning

confidence: 99%

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Flow and Compressive Strength of Alkali-Activated Mortars

2009

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Test results of thirty six ground granulated blast-furnace slag (GGBS)-based mortars and eighteen fly ash (FA)-based mortars activated by sodium silicate and/or sodium hydroxide powders are presented. The main variables investigated were the mixing ratio of sodium oxide (Na 2 O) of the activators to source materials, water-to-binder ratio, and fine aggregate-to-binder ratio. Test results showed that GGBS based alkali-activated (AA) mortars exhibited much higher compressive strength but slightly less flow than FA based AA mortars for the same mixing condition.Feed-forward neural networks and simplified equations developed from nonlinear multiple regression analysis were proposed to evaluate the initial flow and 28-day compressive strength of AA mortars. The training and testing of neural networks, and calibration of the simplified equations were achieved using a comprehensive database of 82 test results of mortars activated by sodium silicate and sodium hydroxide powders. Compressive strength development of GGBS-based alkaliactivated mortars was also estimated using the formula specified in ACI 209 calibrated against the collected database. Predictions obtained from the trained neural network or developed simplified equations were in good agreement with test results, though early strength of GGBS-based alkaliactivated mortars was slightly overestimated by the proposed simplified equations.

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Inorganic Polymers (Geopolymers)

MacKenzie

2017

Encyclopedia of Polymer Science and Technology

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Geopolymers are ceramic-like inorganic polymers produced at low temperature, generally below 100 °C. They consist of chains or networks of mineral molecules linked with covalent bonds. The raw materials are mainly minerals of geological origin, hence the name "geopolymer". They comprise several molecular units for example: silico-oxide (Na,K)-(-Si-O-Si-O-) for (Na,K)-poly(silicate) or (Na,K)-poly(siloxonate), silico-aluminate (Na,K)-(-Si-O-Al-O) for (Na,K)poly(sialate), ferro-silico-aluminate (Na,K)-(-Fe-O-Si-O-Al-O-) or (Na,K)-poly(ferro-sialate), alumino-phosphate (-Al-O-P-O-) for poly(alumino-phosphate), formed in a geopolymerization process. We focus here on the reactivity of calcined kaolinite, an aluminosilicate oxide Si 2 O 5 Al 2 O 2 , metakaolin, which led to the discovery of geopolymers 40 years ago. A distinction is made between two synthesis routes: alkaline medium (Na+, K+, Li+, Ca++, Cs+ and the like) and acidic milieu (phosphoric acid, organic carboxylic acids). The alkaline route is the most important, so far. NMR spectroscopy provides data on the molecular structure and polymeric character. The geopolymerization mechanism starts with polycondensation of oligomers into small ribbon-like molecules. This intermediary stage involves several Si-OH groups together with H 2 O molecules. It is referred to as NASH or KASH by some cement scientists and generalized to the final geopolymer structure. The poly(sialate) final structure consists of well-polymerized individual elementary nanoparticles of 5 to 40 nm in size.

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Alkali-Activated Cements and Concretes

Cited by 660 publications

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Radiological and material characterization of high volume fly ash concrete

Radiological and material characterization of high volume fly ash concrete

Flow and Compressive Strength of Alkali-Activated Mortars

Inorganic Polymers (Geopolymers)

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