The Effects of Aggressive Environments on the Properties of Fly Ash based Geopolymers

This paper analyzes the effects of two different aggressive environments, concentrated ammonium nitrate solution (480 g/dm(3)) and sodium sulphate solution (50 g/dm(3)), on the structure and mechanical strength of fly ash based geopolymers. Geopolymer samples were subjected to the aggressive solutions over a period of 365 days. It was found that exposure to the NH4NO3 and Na2SO4 solutions caused small decrease in geopolymer strength (10-20 %). The most valuable insight into the structural changes caused by testing of the geopolymer samples in the aggressive solutions was provided by means of Si-29 MAS NMR. It was found that the immersion of geopolymer samples in the NH4NO3 solution caused breaking of Si-O-Al bonds in the aluminosilicate geopolymer gel structure. On the other hand, treatment of the geopolymer samples with the Na2SO4 solution resulted in breaking of Si-O-Si bonds in geopolymer gel structure and leaching of Si. It was concluded that the major changes in the geopolymer structure were associated with the changes in the pH values of aggressive solutions during the testing

Research of possibilities for use domestic kaolin clays for production of metakaolin

U oblasti građevinarstva, u svetu se intenzivno istražuju mogućnosti primene novih materijala kojima se može supstituisati deo klinkera u Portland cementu ili deo cementa u betonskim mešavinama. Novi materijali treba da zadovolje zahteve u pogledu održivog razvoja, a njihova primena ne sme negativno da utiče na karakteristike materijala. U ovom radu se govoriti o jednom takvom materijalu metakolinu (MK). Osnovna i najčešće korišćena sirovina za proizvodnju MK je kaolinska glina iz koje se MK proizvodi kalcinacijom ili 'termičkom aktivacijom'. Od karakteristika polazne gline zavise mogućnosti njene primene za dobijanje MK. U radu su dati rezultati ispitivanja hemijskog i mineraloškog sastava, kao i termičkih karakteristika uzoraka gline uzetih iz fabrika Kaolin a.d, Valjevo i Keramika, Mladenovac.Environmental concerns coming from the high energy consumption and CO2 emission associated with cement production have brought about pressures to reduce cement consumption through the use of new materials which can be applied for substitution of a part of clinker in Portland cement or a part of cement in concrete. One of the materials that satisfy requirements of sustainable development and, when added in appropriate shares, improves the properties of cement, mortars and concrete, is metakaolin (MK), a processed pozzolana. The main and widely used raw material for production of metakaolin is kaolin clay. MK is produced by calcination or 'thermal activation' of kaolin clay. The possibilities for metakaolin production are strongly related to the characteristics of the used kaolin clay. The samples of domestic kaolin clay used in this study were provided by factories Kaolin, Valjevo, and Keramika, Mladenovac. Chemical composition, mineralogical composition and thermal properties of these samples were determined. Thermal analysis (simultaneous recording of TG, DTG and DTA signals) was carried out at the temperature range from 20 to 1200 °C. For both clays the results show that the loss of mass occurred in two stages. The dehydroxillation of kaolinite and formation of metakaolin occurred in the second stage. Minerals quartz and kaolinite are dominant in the clay Kaolin, Valjevo. Dehydroxillation of kaolinite and formation of metakaolin took place in the temperature range 350-800 °C. This clay does not have clearly distinct exothermic and endothermic peaks. Clay from Keramika, Mladenovac, has a higher content of the kaolinite mineral, i.e. 81.51%. The dehydroxillation of kaolinite and formation of metakaolin occurred in the temperature range 400-700 °C. This clay has two distinct endothermic peaks at 60 and 490 °C. All these results show that both clays can be used for production of metakaolin

Radon exhalation from fly-ash geopolymer mortar

Geopolymers are a type of alkali activated binders, inorganic aluminosilicate polymers with amorphous cross-linked structure. Fly-ash is produced in abundance during coal firing, and poses an environmental and health risk in untreated powder form. Fly-ash geopolymer presents a sustainable alternative to Portland cement, due to lower net greenhouse gas emissions. Presence of naturally occurring radioactive elements in fly-ash is one of the factors taken into account when estimating the safety of fly-ash based building materials. Radon, a radioactive noble gas originating from the decay of radium, can leave the material and contribute to internal dose in closed spaces, so radon exhalation is of special interest. Radon exhalation for a standard sample of fly-ash geopolymer mortar was measured

Supstitucija glinovite mineralne komponente lignitskim elektrofilterskim pepelom pri sintezi portland-cementnog klinkera

Elektrofilterski pepeo iz četiri termoelektrane u Srbiji (TE "Morava" - Svilajnac, TE "Kolubara" - Veliki Crljeni, TE "Kostolac" blok B1 i B2 - Kostolac i TE "Nikola Tesla" blok A i B - Obrenovac) upotrebljen je kao polazna komponenta za sintezu portland-cementnog klinkera. Kao druge dve polazne komponente upotrebljeni su krečnjak i kvarcni pesak iz fabrike cementa "Holcim-Srbija, a.d.". Na bazi hemijskog sastava polaznih komponenti, kao i zadatih cementnih modula, izračunato je njihovo učešće u sirovinskim mešavinama. Pripremljeno je šest različitih sirovinskih mešavina - svaka se sastojala iz krečnjaka, peska i različitog elektrofilterskog pepela. Kao referentni materijal korišćena je sirovinska mešavina iz industrijske proizvodnje fabrike cementa "Holcim-Srbija, a.d.". Pripremljene sirovinske mešavine sinterovane su u laboratorijskoj peći na 1400°C. Sintetizovani klinkeri analizirani su u pogledu hemijskog i mineralnog sastava. Karakteristike sintetizovanih klinkera na bazi elektrofilterskog pepela, upoređene su sa karakteristikama industrijskog portland-cementnog klinkera iz fabrike cementa "Holcim-Srbija, a.d.". Rezultati istraživanja pokazali su da je elektrofiletrski pepeo iz termoelektrana Srbije pogodan za dobijanje portland-cementnog klinkera

Ispitivanje svojstava elektro-filterskog pepela termoelektrana u cilju njegove upotrebe kao sekundarne sirovine za proizvodnju portland-cementnog klinkera

U ovom radu predstavljeni su rezultati ispitivanja svojstava elektrofilterskog pepela iz četiri termoelektrane u Srbiji. Izvršena je fizička, hemijska, mineraloška i termička karakterizacija elektrofilterskog pepela u cilju utvrđivanja mogućnosti njegove upotrebe kao sirovine u industriji građevinskih materijala, pre svega cementne industrije. Među ispitivanim uzorcima elektrofilterskog pepela postoje određene razlike u pogledu fizičkih, hemijskih i mineraloških karakteristika, budući da osobine pepela zavise od vrste uglja, uslova sagorevanja u peći, efikasnosti elektrofiltera i brojnih drugih faktora. Međutim, ispitivani uzorci pepela su u pogledu termičkih karakteristika veoma slični. Zaključeno je da upotreba elektrofilterskog pepela, kao jedne od komponenti sirovinske mešavine za proizvodnju portland-cementnog klinkera, ne samo da omogućava supstituciju prirodnih sirovina, nego bi mogla da ima i pozitivan uticaj na sniženje temperature sinterovanja portland-cementnog klinkera

Mechanical and microstructural properties of alkali-activated fly ash geopolymers

This paper investigates the properties of geopolymer obtained by alkali-activation of fly ash (FA), i.e. the influence of characteristics of the representative group of FA (class F) from Serbia, as well as that of the nature and concentration of various activators on mechanical and microstructural properties of geopolymers. Aqueous solutions of Ca(OH)(2), NaOH, NaOH + Na2CO3, KOH and sodium silicate (water glass) of various concentrations were used as alkali activators. It was established that the nature and concentration of the activator was the most dominant parameter in the alkali-activation process. In respect of physical characteristics of FA, the key parameter was fineness. The geopolymer based on FA with the highest content of fine particles ( lt 43 mu m), showed the highest compressive strength in all cases. Regardless of FA characteristics, nature and concentration of the activator, the alkali-activation products were mainly amorphous. The formation of crystalline phases (zeolites) occurred in some cases, depending on the reaction conditions. The highest compressive strength was obtained using sodium silicate. Together with the increase of sodium silicate SiO2/Na2O mass ratio, the atomic Si/Al ratio in the reaction products was also increased. Under the experimental conditions of this investigation, high strength was directly related to the high Si/Al ratio

Development of fly ash-based geopolymer microstructure at room temperature

The development of geopolymers, as an alternative to traditional cement, by alkali activation of fly ash is a research topic in the scientific community. Many authors have agreed that there is a strong link between mechanical properties and microstructure of geopolymers. The aim of this study was to investigate the development of fly ash-based geopolymer microstructure at room temperature and to establish relationship with its mechanical properties. By scanning electron microscopy and microanalysis of geopolymer, a more detailed understanding of the geopolymer microstructure formation and development was achieved. It was established that significant changes of geopolymer microstructure occurred during the first 28 days of reaction at room temperature. After this initial period, less significant changes of fly ash based geopolymer microstructure were observed up to 180 days

Research of possibilities for use domestic kaolin clays for production of metakaolin

Environmental concerns coming from the high energy consumption and CO2 emission associated with cement production have brought about pressures to reduce cement consumption through the use of new materials which can be applied for substitution of a part of clinker in Portland cement or a part of cement in concrete. One of the materials that satisfy requirements of sustainable development and, when added in appropriate shares, improves the properties of cement, mortars and concrete, is metakaolin (MK), a processed pozzolana. The main and widely used raw material for production of metakaolin is kaolin clay. MK is produced by calcination or 'thermal activation' of kaolin clay. The possibilities for metakaolin production are strongly related to the characteristics of the used kaolin clay. The samples of domestic kaolin clay used in this study were provided by factories Kaolin, Valjevo, and Keramika, Mladenovac. Chemical composition, mineralogical composition and thermal properties of these samples were determined. Thermal analysis (simultaneous recording of TG, DTG and DTA signals) was carried out at the temperature range from 20 to 1200 °C. For both clays the results show that the loss of mass occurred in two stages. The dehydroxillation of kaolinite and formation of metakaolin occurred in the second stage. Minerals quartz and kaolinite are dominant in the clay Kaolin, Valjevo. Dehydroxillation of kaolinite and formation of metakaolin took place in the temperature range 350-800 °C. This clay does not have clearly distinct exothermic and endothermic peaks. Clay from Keramika, Mladenovac, has a higher content of the kaolinite mineral, i.e. 81.51%. The dehydroxillation of kaolinite and formation of metakaolin occurred in the temperature range 400-700 °C. This clay has two distinct endothermic peaks at 60 and 490 °C. All these results show that both clays can be used for production of metakaolin

The influence of mechanical activation of fly ash on the toxic metals immobilization by fly ash-based geopolymers

This paper investigates the influence of mechanical activation of fly ash on the toxic metals immobilization by fly ash-based geopolymers. Fly ash was firstly mechanically and then alkali-activated. Mechanical activation of fly ash was conducted in a planetary ball mill. Alkali activation of fly ash was carried out at room temperature by use of sodium silicate solution as an activator. Toxic metals (Pb and Cr) were added in the form of water soluble salts during the synthesis of geopolymers. The immobilization process was assessed via investigation of the mechanical and leaching properties of geopolymers. Structural changes of geopolymers during the toxic metals immobilization were assessed by means of gas adsorption and SEM analyses. Mechanical activation of fly ash led to a significant increase in geopolymer strength and to a reduced leaching of toxic metals from geopolymers