100 research outputs found
The influence of chemical activators on the hydration behavior and technical properties of calcium sulfoaluminate cements blended with ground granulated blast furnace slags
No full textThe manufacture of Ordinary Portland cement (OPC) generates around 8% of the global CO2 emissions related to human activities. The last 20 years have seen considerable efforts in the research and development of methods to lower the carbon footprint associated with cement pro-duction. Specific focus has been on limiting the use of OPC and employing alternative binders, such as calcium sulfoaluminate (CSA) cements, namely special hydraulic binders obtained from non-Portland clinkers. CSA cements could be considered a valuable OPC alternative thanks to their dis-tinctive composition and technical performance and the reduced environmental impact of their manufacturing process. To additionally reduce CO2 emissions, CSA cements can also be blended with supplementary cementitious materials. This paper investigates the influence of two separately added chemical activators (NaOH or Na2CO3) on the technical properties and hydration behavior of four CSA blended cements obtained by adding to a plain CSA cement two different ground granulated blast furnace slags. Differential thermal-thermogravimetric, X-ray diffraction and mercury intrusion porosimetry analyses were done, along with shrinkage/expansion and compressive strength measurements
Fabrication and Properties of Blended Calcium Sulfoaluminate Cements Based on Thermally Treated Reservoir Sediments
No full textIn 2021, approximately 4.1 billion tonnes of cement were globally produced and the annual
CO2 emissions from cement plants reached almost 2.8 billion metric tonnes. In recent years, many
efforts have been made to manufacture low-CO2 cements. In this regard, great consideration has been
given towards calcium sulfoaluminate (CSA) binders for both their technical features and sustainable
properties, principally connected to their industrial process. The use of blended cements composed
by CSA binders and supplementary cementitious materials (SCMS) can be an effective way to (a)
reduce the CO2 footprint and (b) produce greener binders. This scientific work studied the utilization
of different amounts (15–35 wt%) of calcined reservoir sediments (RS) as SCMS in blended CSA
binders, where the binders were cured for up to 56 days and characterised by various analytical
techniques. It was found that thermally treated RS were particularly noteworthy as their utilization
allowed for a dilution of the CSA clinker, thus implying a decrease in CO2 emissions and a reduction
in costs related to their production. However, compared to a plain CSA cement, the blended systems
showed rather similar volume stability levels, whilst their compressive strength and porosity values
were, respectively, lower and higher at all the investigated aging periods
Nuovi materiali da costruzione a base di polimeri inorganici
No full textIn questo lavoro sono stati preparati e caratterizzati nuovi materiali a base di polimeri inorganici ottenuti per azione fra caolinite calcinata e silicati alcalini. IL preventivo stadio di calcinazione è stato ottimizzato e la successiva reazione di policondensazione è stata condotta a 25, 40, 60 e 85°C. I prodotti ottenuti nelle varie condizioni sono stati caratterizzati sia dal punto di vista chimico che da quello fisico-meccanico. I risultati sono ampiamente positivi in vista dello sviluppo di leganti e manufatti prefabbricati innovativi nel settore dei materiali da costruzione
Calcium sulfoaluminate and alkali-activated fly ash cements as alternative to Portland cement: study on chemical, physical-mechanical, and durability properties of mortars with the same strength class
No full textThere is an increasing interest towards the development of alternative binders for the manufacture of sustainable mortars and concretes. Ordinary Portland cement (OPC) is the most commonly used material in construction, even if its production process is highly polluting. Both calcium sulfoaluminate (CSA) and alkali-activated cements (AAC) are potential alternative binders to be used in both structural (R3 class, with Rc " 25 MPa) and non-structural applications (R1 and R2 classes, with Rc " 10 MPa and Rc " 15 MPa, respectively) according to UNI EN 1504-3. This paper reports the hydration mechanisms and the evolution of porosity of OPC-, CSA- and AAC-based binders. The properties of fresh and hardened mortars, belonging to the above-mentioned mechanical strength classes, were evaluated and compared with particular emphasis on durability properties in terms of capillary water absorption, drying shrinkage, and resistance to sulfate attack. The results show that CSA-based mortars exhibit the lowest drying shrinkage due to their highest elasticity modulus. AAC mortars are characterized by the highest water vapor permeability and the lowest capillary water absorption for the highest presence of large pores
(>3000 nm)
Utilizzation of chromium exchanged zeolite tuff in the manufacture of blended cements
No full textOn the ground of precedent studies, chromium exchanged zeolite tuff was used as active addition in the manufacture of blenden cements. Their mechanical and chemical properties were investigated and were found to be very good, even better than those of Portland-zeolite tuff cement, taken as reference.
A process, in which quarry dust, a very cheap by-product of the cutting of zeolite tuff, is intended to remove chromium from wastewaters and to be used as active addition to Portland clinker to prepare blended cements, is proposed
STABILIZZAZIONE DI SEDIMENTI LACUSTRI PER MEZZO DI PROCESSI CEMENTIZI COADIUVATI DA BENTONITE ORGANOFILA
No full textIn questo lavoro i sedimenti provenienti dal Lago d’Averno sono stati sottoposti ad un trattamento di stabilizzazione per mezzo dell’applicazione di un processo a base di cemento pozzolanico. Inoltre, per contrastare gli effetti negativi a cui le sostanze organiche presenti nei sedimenti possono dare luogo nei confronti dell’idratazione del sistema cementizio, è stata impiegata, quale coadiuvante della stabilizzazione, una bentonite resa organo fila. La bentonite modificata è stata ottenuta attraverso un processo di scambio ionico con benzildimetilottadecilammonio cloruro e per essa è stata successivamente verificata la capacità adsorbente nei confronti della frazione organica presente nei sedimenti. Per minimizzare la quantità di acqua richiesta è stato applicato una schema a più stadi. Infine, l’efficacia del trattamento è stata valutata da tre differenti punti di vista: chimico, ambientale e tecnologico. Dal ounto di vista chimico si è potuto osservare che la qualità dei prodotti dell’idratazione non è influenzata dalla presenza della bentonite e dei sedimenti, mentre, dal punto di vista quantitativo si nota un ritardo sul processo di idratazione, sebbene l’effetto positivo della bentonite sia chiaramente evidente. Per quanto riguarda, invece, le validazioni ambientale e tecnologica, è stato mostrato che la presenza della bentonite organo fila migliora sensibilmente le prestazioni dei prodotti finali nei confronti dei sistemi di controllo privi di bentonite. Infatti, per i prodotti stabilizzati le quantità di materiale organico rilasciate sono sensibilmente ridotte e le resistenze meccaniche a compressione sono aumentate. I valori di queste ultime incoraggiano l’impiego dei manufatti nel settore dei materiali da costruzione
Zeolitized tuff in environmental friendly production of cementitious material: Chemical and mechanical characterization
No full textThe feasibility of some widespread zeolite-rich tuffs to act as pozzolanic material for manufacturing blended cements was evaluated by chemical and mechanical characterization. Two different methods were used: (a) Fratini's test, that allowed to evaluate the ability of the pozzolanic material to combine with Ca(OH)2 in a blended cement; (b) Saturated Lime Test, where the pozzolanic behaviour was directly evaluated in a lime saturated solution. Mechanical characterization was carried out by measuring compressive strength of blend mortars, after 28-day curing. The good pozzolanic behaviour proved by all the tuffs, coupled with their low cost, makes very promising the use of zeolitic tuffs for the production of eco-sustainable blended cement
Calcium sulfoaluminate cement and fly ash-based geopolymer as sustainable binders for mortars
No full textThis work investigates the hydration behaviour and the physico-mechanical properties of mortars based on calcium sulfoaluminate (CSA) cements and fly ash-based geopolymers (GEO) as alternatives to ordinary Portland cement. According to the EN 1504-3, mortars were prepared in order to reach three compressive strength classes, namely R1, R2 and R3 (R1 with Rc ≥ 10 MPa, R2 with Rc ≥ 15 MPa and R3 with Rc ≥ 25 MPa). CSA mortars were prepared by using sulfoaluminate cement alone (R3) or in mixture with a limestone filler (R1 and R2); GEO mortars were manufactured by alkali-activation of coal fly ash and calcium aluminate cement with a sodium silicate and potassium hydroxide water solution. The hydration behaviour was evaluated on pastes submitted to differential thermal-thermogravimetric and X-ray diffraction analyses. Mortars was analysed through mercury intrusion porosimetry; their mechanical properties were evaluated in terms of compressive strength and dynamic modulus of elasticity. Furthermore, capillary water absorption and drying shrinkage tests were carried out in order to evaluate their durability. Due to the rapid ettringite formation, CSA-based mixtures reached their maximum compressive strength values faster than the corresponding GEO mortars. Results showed that the lower modulus of elasticity of GEO mortars causes the higher drying shrinkage. Moreover, the lower porosity exhibited by GEO mortars was responsible for the lower water capillary absorption
Potential application of coal–fuel oil ash for the manufacture of building materials
No full textIn this paper coal–fuel oil ash has been characterized in terms of leaching behaviour and reactivity against lime and gypsum in hydratory
systems for the manufacture of building materials. Its behaviour was also compared to that of coal ash. Metal release was measured in a
dynamic leaching test with duration up to 16 days. The results have shown that coal–fuel oil ash behaves very similarly to coal ash. The
reactivity of coal–fuel oil ash against lime and gypsum was measured in mixtures containing only lime and in mixtures containing both lime
and gypsum. These systems were hydrated at 25 and 40 ◦C under 100% R.H. The results have shown that the main hydration products are the
same as those that are usually formed in similar coal ash-based systems. That is, calcium silicate hydrate in coal–fuel oil ash/lime systems
and calcium silicate hydrate plus calcium trisulphoaluminate hydrate in coal–fuel oil ash/lime/gypsum systems. From the quantitative point of
view, hydration runs showed that the amounts of both chemically combined water and reacted lime measured in the case under investigation
are very similar to those found in similar coal ash-based systems. Finally, the measurement of unconfined compressive strength proved that
the systems have potentiality for the manufacture of pre-formed building blocks
Physical-mechanical characterization of blended cements manufactured with zeolite-bearing tuffs
No full textAs an integration of a study aiming to evaluate the feasibility of zeolite-rich sedimentary ricks (i.e., zeolitic tuffs) to act as pozzolanic material for manufacturing blended cements, four of the most widespread zeolite-bearing rocks, namely a chabazite-phillipsite-rich tuff, a clinoptilolite-rich tuff, an erionite-rich tuffand a phillipsite-rich tuff were used to obtain experimental blended cements, by replacing portions as high as 10%, 20% and 40% of the ordinary Portaln cement. Standard mortars, made with the mentioned blends, cured for different times, were subjected to mechanical resistance evaluation. Results were highly encouraging, because the measured compressive strength of the blends, ranging, after 28-day curing, between 35.7 and 60.4 N.mm-2, according to nature of zeolitic tuff and its substitution extent, were all included in the three classes of pozzolanic cements considered by the European Standards specification EN 197/1. This result, coupled with the excellent pozzolanic behavior demonstrated by all tuffs and thei low cost, makes very promising a possible use of zeolitic tuffs for the production of blended cements. This could also represent a valuable strategy for energy efficiency improvement and reduction of carbon dioxide emission in the cement industry
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