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Geopolymer concrete block made with waste coal fly ash.

Geopolymer concrete block made with waste coal fly ash.


Project Type:
urban planning design strategy, architecture

Project Mission/Goal:
increase awareness of the environment and/or address climate change

Project Description:
The coal combustion process produces one of the largest unregulated solid wastes in the United States. Although in recent years a growing percentage of the airborne particulates (‘fly ash’) found uses as a filler in the cement industry, recent changes in EPA regulations aimed at reducing greenhouse gasses (GHG) emissions has resulted in most of the 70 million tons of fly ash produced annually in the US becoming unusable for current construction processes due to high levels of unburned carbon, ammonia and/or other impurities. Furthermore, the significant costs associated with transporting and land filling solids derived from coal combustion could be further increased due to liabilities associated with the eventual leaching of harmful levels of aluminum, chloride, iron, manganese and toxic levels of arsenic, nickel, lead, copper and zinc into subterranean water tables. Thus, the development of innovative technologies for converting tens of million tons of combustion bi-products annually into useful products is an urgent need.

What is Geopolymer:
-A hardened cementitious paste made from fly ash without Portland cement. It has greater compressive and tensile strengths, high strength gain rate, lower porosity and permeability, and greatly enhanced resistance to chemical attack compared with ordinary Portland cement (OPC) concrete. It combines waste products into a useful product, conserving landfill space and promoting sustainability, and compared with Portland cement, it features a 90% or greater reduction in carbon dioxide emission.
-A solution of sodium hydroxide and potassium hydroxide (waste products from the chemical and petrochemical industries) must be prepared separately, then added to the liquid commercial sodium silicate; this solution may then be added to the powdered fly ash (waste product from coal and bio fuel combustion) in the same way as water is added for Portland cement.

Source: Open Architecture Network

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The consumption of Ordinary Portland Cement (OPC) caused pollution to the environment due to the emission of CO2. As such, alternative material had been introduced to replace OPC in the concrete. Fly ash is a by-product from the coal industry, which is widely available in the world. Moreover, the use of fly ash is more environmental friendly and save cost compared to OPC. Fly ash is rich in silicate and alumina, hence it reacts with alkaline solution to produce aluminosilicate gel that binds the aggregate to produce a good concrete. The compressive strength increases with the increasing of fly ash fineness and thus the reduction in porosity can be obtained. Fly ash based geopolymer also provided better resistance against aggressive environment and elevated temperature compared to normal concrete. As a conclusion, the properties of fly ash-based geopolymer are enhanced with few factors that influence its performance.

Source: Academic Journals.org

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Abstract
The present study describes the details of the compressive strength and microstructure of geopolymer binder prepared with class C fly ash and alkali activators at room temperature. The parameters studied were sodium silicate to sodium hydroxide mole ratio and fly ash content. The fly ash contents were 65 and 70 percents by weight, and the mole ratios of sodium silicate to sodium hydroxide were 0.20, 0.30, 040 and 0.50. The results indicated that decreasing the sodium silicate to sodium hydroxide mole ratio and increasing the fly ash content significantly increased the compressive strength of the fly ash based geopolymer. Fly ash based geopolymer had an amorphous to semi-crystalline structure determined by scanning electron microscope (SEM)/energy dispersive X-ray (EDX) and powder X-ray diffraction (XRD). Furthermore, the results presented that class C fly ash can be successfully used as geopolymer binder for concrete products.

Source: Green Binder Technology Development Using Fly Ash Based Geopolymer

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Abstract
So called geopolymers or geopolymeric binders and ce­ments are made by means of an alkaline activation of materials reac­tive in this respect. Such material has to consist of a certain amount of silicate and aluminate phases which can be dissolved by the alka­line medium. In the consequence stable polymeric networks of alumosilicates will be formed. Metakaolins and alumo-siliceous fly ashes, in particular, have by now achieved noteworthy significance. The search for alternative low cost or high available materials may lead among other things to “normal clays”. This material is widely available all over the world and may show certain reactivity after a thermal activation process. This investigation focuses the influence of the clay composition on the geopolymer performance. Clays with different kind and amount of the clay mineral (illite, montmorillonite, and kaolinite) as well as side minerals (calcite and dolomite) were investigated.

Source: Clay Polymers.com

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Abstract
Geopolymers are relatively new types of inorganic binders for production of building materials, which can partly substitute Portland cement used generally for these purposes. Application of geopolymer binders is also favorable from ecological point of view, because of considerably lower amount of carbon dioxide formed during production of geopolymer binders, in comparison with Port­land cement, which enhances total amount of greenhouse gases in the atmosphere. One of main restrictive factors for spreading geo­polymers is the cost of raw materials, including metakaolin, hy­droxides and silicates of alkali metals. Possible way how to reduce the price of geopolymer binder is a utilization of secondary and waste raw materials, e.g. fly ash, slag or low-quality natural alumi­nosilicates. In the case of these raw materials, however, keeping chemical and mineralogical contents uniform is rather problematic. Within the scope of project FI-IM/079 “Application of residual and waste aluminosilicates for production of building materials on basis of inorganic polymers” utilization of aluminosilicate fly dusts from ro­tary kiln as a component for production of two-component geopoly­mer binder on their basis and sodium alkali activator was examined and verified in laboratory and pilot scale. This article is focused on introducing two-component geopolymer binders produced under the commercial name Baucis in České lupkové závody, Inc., on the methods of testing and the results of their mechanical properties, product manufacture qualities, temperature and chemical resistance and total costs of production. Applications of geopolymer binders are being developed in cooperation with Kerasil Comp., which manu­factures objects of art and architectural details on the base of artifi­cial stone, utilizing miscellaneous natural and artificial fillers, with various final product appearance and utility qualities.

Source: Clay Polymers.com

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Abstract
Geopolymers are a new promising binder manufactured by activation of a solid aluminosilicate source material with a highly alkaline activating solution and aided by heat. Fly ash, considered to be a waste material is rich in silica and alumina and hence can be used as a source material for manufacture of Geopolymers. These binders have been reported to achieve high early strength and better durability as compared to Ordinary Portland cement based counterparts.

An experimental study was conducted to assess the acid resistance of fly ash based Geopolymer mortar specimens having percentage Na2O ranging from 5% to 8% of fly ash. The program consisted immersion of specimens in solutions of 10% Sulfuric acid and 10% Nitric acid up to a period of 24 weeks and evaluation of its resistance in terms of surface corrosion, residual alkalinity, changes in weight and compressive strength at regular intervals. Geopolymer mortar samples did not show any noticeable change in colour and remained structurally intact though the exposed surface turned slightly softer. Through Optical microscope, corroded surface could be seen which increased with duration of exposure. Samples almost lost its alkalinity after exposure in the acid solution within 12 weeks and showed very low weight loss in the range from 0.81% to 1.64% in Sulfuric acid and from 0.21% to 1.42% in Nitric acid. Compressive strength loss at the end of test varied from 44% to 71% and 40% to 70% in Sulfuric acid and Nitric acid respectively. Results obtained in the present study indicate that Geopolymers are highly resistant to both Sulfuric and Nitric acid.

Source: Academy Publisher.com

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