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

Immobilization of cesium with alkali-activated blast furnace slag

Alkali-activated binders (AABs), as a promising alternative to Portland cement, are now being used on a commercial scale in various applications around the world, including hazardous and radioactive waste immobilization. In this paper, the leaching resistance, strength, and nanostructural alteration of alkali-activated blast furnace slag (AABFS) doped with 2% and 5% cesium were investigated. The addition of cesium caused a significant increase in the compressive strength of AABFS, followed by mild strength reduction after leaching. AABFS can be considered a potentially efficient matrix for cesium immobilization, since the mean leachability index in both cases (2% and 5% of Cs added) was above the threshold value of 6. Both doping with Cs and leaching caused the transformation of the AABFS nanostructure. The majority of the aluminum that was released from the C-A-S-H gel due to leaching remained within the AABFS matrix, initiating gel reconstruction: the C-A-S-H gel was converted to C-S-H gel, and an additional N-(C)-A-S-H gel was also formed. Cesium was preferentially associated with the N-(C)-A-S-H gel rather than with the C-A-S-H gel. The results of this research seem to be in good agreement with the Cross-linked Substituted Tobermorite Model (CSTM)

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

The Quantitative Analysis of the Vascularization Following Two Basic Auditory Canal Skin Incisions

Three groups of nine patients each were analyzed. The first two groups consisted of those that underwent tympanoplastic due to chronic inflammation of middle ear. Two different standard auditory canal skin incisions were applied, i.e. tympanomeatal flap (TMF) or vascular strip (VS). The third control group consisted of non-operated patients. All the operated patients were subjected to a quantitative analysis of the auditory canal revascularization by means of the Weibel stereological test method, i.e. the B 100 double network system. The density of capillaries, arterioles, venulolymphatic spaces and a total volume density of all vascular elements of the auditory canal skin were measured. The obtained results of vascularization were compared with those of the target control group. It was found out that there were no significant differences in vascularization of auditory canal skin between TMF and VS patients from one side and the control group on the other side

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

Effect of synthesis parameters on the performance of alkali-activated non-conformant EN 450 pulverised fuel ash

The fly ash reported in this paper is coarser than conventional pulverised fuel ash (PFA), with loss on ignition (LOI) exceeding 10.8%. Consequently, it is precluded from being used as a supplementary cementitious material (SCM) according to EN 450 and disposed in landfills. Alkali-activation of such PFAs is considered here. Three concentrations of sodium hydroxide (NaOH) were separately blended with water glass at different ratios to modify the silica modulus. Heat of reaction, setting time, compressive strength and drying shrinkage were investigated as a function of activator composition. Specimens were either cured at room temperature or hydro-thermally treated at 75 °C for five hours. The results show that by optimizing the activator composition, a binder with a 28 day compressive strength of 25 MPa can be synthesised from such PFAs even at room temperature. Among the activator parameters, the alkali content was observed to be most influential