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No full textLa rivista pubblica articoli scientifici, originali, che riguardano la caratterizzazione di sostanze e/o materiali pericolosi e lo sviluppo di strategie/tecnologie per minimizzare il rischio di contaminazione dell'ambiente, derivante dal loro impiego e/o smaltimento
Reconsideration of ASTM C1260 test results in the light of a recent kinetic model
No full textA recent kinetic model based on nucleation and growth kinetics was used to elucidate the influence of the type (fineness, total alkali content) of Portland cement on the diagnosis of the ASTM C1260 test method with regard to the alkali-silica reactivity (ASR) of five natural siliceous sands of known petrographic characteristics and field performance. Some attempts were also made to apply the kinetic model for interpreting the ASTM C1260 test results obtained when an appositely modified version of this test method was used to assess the capability, of lithium nitrate additions in suppressing or mitigating deleterious ASR with a given aggregate. It was found that the kinetic model is capable of discriminating the alkali-reactivity of the sands investigated, through the use of a plot of the two kinetic parameters, M and In k, derived from the model and assuming In k as a reactivity criterion. Differently from what was observed using a percentage expansion criterion for defining potentially reactive aggregates, the use of In k as a reactivity, criterion yields an ASR diagnosis for every, sand that is independent of the type of Portland cement used in the ASTM C1260 test. A modified version of the ASTM C1260 test procedure can be successfully used to assess the capability, of lithium nitrate additions in suppressing deleterious ASR. Application of the kinetic model provides a suitable means of determining effective lithium dosages for deleterious ASR suppression in ASTM C1260 tests
Disposal of MSWI fly ash through a combined washing-immobilisation process
No full textThe objective of this work was to investigate the feasibility of a combined washing-immobilisation process as a means of optimising the disposal of fly ash resulting from municipal solid waste incineration (MSWI) in cementitious matrices. Two different types of Italian MSWI fly ash and an ordinary Portland cement (ASTM Type I) were used. Washing pre-treatment of fly ash with water always produces a wastewater that can be successfully treated by reducing the pH to values of 6.5-7.5. This treatment is capable of removing the detected contaminants (Al, Cd, Pb, Zn) through two different mechanisms: precipitation of aluminium hydroxide and adsorption of cadmium, lead and zinc ions onto floc particles of Al(OH)(3). Setting and leaching tests on cementitious mixes prove that the hazardous sludge produced from wastewater treatment can be completely mixed with washed fly ash and this mixture can be incorporated into cementitious matrices to a great extent (75 wt.% of total solid) without the risks of an unacceptable delay of cement setting and an excessive heavy metals leachability from solidified products. The better performance of the combined washing-immobilisation process as compared to the immobilisation process of unwashed fly ash may be ascribed primarily to the ability of the washing step in promoting the formation of hydrate phases that incorporate and/or convert heavy metal compounds into less reactive forms and, secondarily, to its ability of removing significant amounts of alkali chlorides and sulphates from fly ash. As a result, MSWI fly ash is transformed into a material that adversely affects cement hydration to a much lower extent than unwashed fly ash. (C) 2003 Elsevier Science B.V. All right
Effects of a washing pre-treatment of municipal solid waste incineration fly ash on the hydration behaviour and properties of ash-Portland cement mixtures
No full textThe effects of a washing pre-treatment Of municipal solid waste incineration (MSWI) fly ash with deionised water on both the physico-chemical characteristics of this material and the hydration behaviour and physical properties of ash-Portland cement mixtures rich in MSWI fly ash (55 wt% of total solids) were investigated in view of a possible reuse of such solidified products as concrete aggregates in the building industry. A four-stage washing pre-treatment was found to be able to convert the raw MSWI fly ash into a material with improved chemical characteristics for its incorporation into cementitious matrices (reduced concentrations of alkali chlorides and sulphates, transformation of metallic species in less reactive forms). As a result, the cementitious mixtures incorporating washed fly ash in place of raw fly ash were found to exhibit better performance characteristics in terms of setting, dimensional stability, compressive strength and environmental quality
Sintering of MSW fly ash for reuse as a concrete aggregate
No full textThe sintering process of municipal solid waste (MSW) fly ash was investigated in order to manufacture sintered products for reuse as concrete aggregates. Four types of fly ash resulting from different Italian MSW incineration plants were tested in this study. A modification of the chemical composition of MSW fly ash - through a preliminary four-stage washing treatment of this material with water - was attempted to improve the chemical and mechanical characteristics of sintered products. The sintering treatment of untreated or washed fly ash was performed on cylindrical compact specimens (15 mm in diameter and 20 mm in height) at different com act pressures, sintering temperatures and times. The sintering process of untreated MSW fly ashes proved to be ineffective for manufacturing sintered products for reuse as a construction material, because of the adverse chemical characteristics of these fly ashes in terms of sulfate, chloride, and vitrifying oxide contents. A preliminary washing treatment of MSW fly ash with water greatly improved the chemical and mechanical characteristics of sintered products and, for all the types of fly ash tested, the sintered products satisfied the Italian requirements for normal weight aggregates for use in concretes having a specified strength not greater than 12 and 15 N/mm(2), when measured on cylindrical and cubic specimens, respectively. A compact pressure of 28 N/mm(2), a sintering temperature of 1140 degreesC, and a sintering time of 60 min were the best operating conditions for manufacturing sintered products of washed MSW fly ash. (C) 2001 Elsevier Science B.V. All rights reserved
Metodi di prova non distruttivi per la valutazione della reattività alcali-silice di conglomerati cementizi
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Rimozione del rame (II) da soluzioni acquose: II. Adsorbimento su carboni attivi e materiali argillosi
No full textRimozione di tensioattivi cationici mediante carbone attivo in polvere: effetti del pH e della temperatura.
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