EP-4299546-B1 - METHOD FOR MANUFACTURING COAL ASH-BASED GEOPOLYMER FOAM CONTAINING SILICA FUME

Inventors

• LEE, KEEYUN
• KIM, HYO
• HEO, Jihoi

Dates

Publication Date

20260506

Application Date

20210325

Claims (5)

1. A method for manufacturing geopolymer foam with coal ash, the method comprising the steps of: (1) mixing water glass (Na 2 SiO 3 ) and sodium hydroxide (NaOH) to prepare an alkali activator; (2) adding silica fume as a foaming agent to the alkali activator and stirring the same; (3) pulverizing coal bottom ash; (4) mixing the coal bottom ash with coal fly ash to prepare coal ash, wherein the coal fly ash is contained in an amount of 10 to 50 % by weight based on the total weight of the coal bottom ash and the coal fly ash; (5) adding the mixture of silica fume and the alkali activator to the coal ash and then further adding the alkali activator to adjust a ratio of alkali activator/solid material, followed by mixing the same, wherein the ratio of alkali activator/solid material ranges from 0.38 to 0.50; (6) loading and sealing the mixture in a mold to prepare a specimen; (7) curing the specimen in an oven, and (8) exposing to a temperature of as high as 200°C to 600°C for 2 hours the specimen that has completely undergone the curing.
2. The method of claim 1, wherein the alkali activator contains the water glass (Na 2 SiO 3 ) and the sodium hydroxide (NaOH) at a mass ratio of 5 : 1.
3. The method of claim 1, wherein the silica fume is contained in an amount of 15 % by weight.
4. The method of claim 1, wherein the step of pulverizing coal bottom ash is carried out by crushing once with a jaw crusher and then milling four times with a hammer mill, without a sieving process.
5. A geopolymer foam utilizing coal ash, manufactured according to the method of any one of claims 1 to 4.

Description

Technical Field The present disclosure relates to a method for manufacturing a coal-based geopolymer foam including silica fume. Background Art Cement is a generic term for an inorganic binder that reacts with other materials like water to set itself or coagulate them together. Generally, cement refers to ordinary Portland cement (OPC) because OPC accounts for 95% or more of the total cases of use. Portland cement is suitable for mass production due to its abundant raw materials and uncomplicated production method, but the production process suffers from the disadvantage of being very energy intensive and emitting a large amount of carbon dioxide. According to the Davidovits' report, as much as approximately one ton of carbon dioxide is emitted for the production of one ton of cement. Various efforts have been made in the cement industry to reduce carbon dioxide emissions by, for example, using biofuels, introducing new clinker types that consume less energy, and developing environmentally friendly concrete compositions, but due to the increase in cement demand in rapidly developing countries such as China and India, global carbon dioxide emissions increased from 5% in 2000 to 8% in 2014. Geopolymers are attracting attention as an environmentally friendly alternative to OPC. A geopolymer is an inorganic polymer binder synthesized from the alkaline activation of reactive alumino-silicate materials rich in silica (SiO2) and alumina (Al2O3) resulting in three-dimensional polymeric network. Geopolymer has advantages in terms of waste treatment because it can use industrial waste, such as coal materials generated from coal-fired power plants, mineral tailing from the mining industry, and red mud generated during aluminum refining processes, as raw materials. Coal ash is divided into coal fly ash (CFA) and coal bottom ash (CBA). Being spherical in particle shape with a low particle size, fly ash exhibits high geopolymer reactivity. Thus, many studies have been conducted on the use of fly ash, and most of the amount produced is actually being used. In contrast, although being similar in composition to fly ash, bottom ash is difficult to use as a raw material for geopolymers because of its irregular, angular, and large particle size. There have not been many studies for the use of bottom ash, and most of the generated amount thereof is landfilled. In fact, according to the current status of coal ash generation by Korea South-East Power Co., among coal ash generated in 2018, fly ash was recycled in an amount of 79.07% and landfilled in an amount of 17.55% while 76.59% of bottom ash was landfilled. Coal ash landfill is causing various difficulties such as landfill cost and lack of landfill sites as well as soil and water pollution. Therefore, it is necessary to study the use of coal ash, especially bottom ash. Meanwhile, the insulation performance of modern buildings is emerging as an important design standard. Currently, organic insulation materials, which are widely used for buildings, are vulnerable to high temperatures and causes human damage by emitting toxic gas in the event of a fire. Accordingly, an inorganic insulating material with excellent thermal insulation performance and strong resistance to high temperature is attracting attention. Currently utilized in the industry and academy fields is a method for synthesizing concrete and geopolymer foam, in which the reaction of chemical additives is used to generate gas. In the study of J. L. Bell and W. M. Kriven, a geopolymer in a foam structure was formed using hydrogen peroxide and aluminum powder. In addition, Aguilar et al. conducted research on the synthesis of geopolymer foam using various additives including silica fume. In such previous studies, metakaolin and fly ash were mainly used as materials, but the present disclosure is intended to utilize bottom ash as a material for manufacture of geopolymer foam by the form synthesis method. The minimum use of aluminum powder is desired in terms of the environment because its production process is energy intensive. The surfactant is an organic material which may generate toxic materials upon high temperature decomposition. Silica fume is collected as a by-product of the silicon or silicon alloy production during which the reaction of silicon as an impurity is known to produce hydrogen gas. Through such reactions, a more stable geopolymer foam structure can be formed. Accordingly, only silica fume is added as a foaming agent to synthesize geopolymer form, without the use of aluminum powder and a surfactant. Korean Patent No. 10-1901684 discloses a method for preparing geopolymer with high compressive strength by using coal bottom ash. Korean Patent No. 10-2013-0057024 A pertains to a geopolymer binder using a waste disc and a fireproofing mortar composition using same, disclosing a fireproofing mortar composition comprising waste coal bottom ash as a raw material However, the coal-based geopolymer foam includ