1,721,047 research outputs found
Geopolymeric and cementitious mortars for buildings: Comparison at the same strength class
No full textLa tesi ha riguardato lo studio di malte geopolimeriche e cementizie a parità di classe di resistenza meccanica (R1, R2, R3 e R4 secondo la UNI EN 1504-3:2006) per applicazioni edili.
Nella prima parte sono state testate malte cementizie contenenti fibre o tessuti come rinforzo di pannelli murari assemblati con malta di allettamento in calce aerea o cementizia. I rinforzi migliori sono risultate le malte di classe R2 contenenti fibre in polipropilene, poiché hanno impedito il collasso sotto compressione assiale e incrementato del 47% la resistenza diagonale dei pannelli murari assemblati con malta cementizia.
Nella seconda parte, malte cementizie e geopolimeriche appartenenti alle classi R1, R2, R3 e R4 sono state confrontate in termini di densità, lavorabilità, modulo elastico dinamico, tensione di aderenza, porosità, permeabilità al vapore acqueo, assorbimento d’acqua per capillarità, ritiro igrometrico libero e contrastato, resistenza ai solfati e comportamento a corrosione di eventuali barre immerse in acciaio nero e zincato indotta da cloruri o carbonatazione. Nei geopolimeri il ritiro libero è maggiore rispetto alle malte cementizie, ma quello contrastato è minore per via del basso modulo elastico. Le dimensioni dei pori influenzano la permeabilità al vapore, maggiore nei geopolimeri, e l’assorbimento d’acqua, minore nei geopolimeri con cenere volante. L’alta alcalinità dei geopolimeri ritarda il raggiungimento dello stato passivo delle armature, soprattutto se zincate, ma dopo un mese di stagionatura si ottengono velocità di corrosione simili a quelle riscontrate nelle malte cementizie. Durante l’esposizione ai cloruri e dopo carbonatazione, i geopolimeri in cenere volante proteggono maggiormente le armature in acciaio nero; mentre le malte cementizie proteggono maggiormente gli acciai zincati.
Infine, è stata studiata la possibilità di ottenere geopolimeri “one-part” aggiungendo solo acqua agli ingredienti solidi per renderne più facile l’utilizzo pratico
One part geopolymers activated with potassium-rich biomass ashes
No full textGeopolymers are obtained by the chemical reaction between an aluminosilicate powder and an alkaline solution. Even if geopolymers do not contain Portland cement, they are similar to cementitious materials. Recently, many authors have tried to prepare geopolymers without alkaline activators, since they are user-hostile. These new materials are called one-part geopolymers and appear as a cementitious powder that can polymerize with water.
The aim of this work is to investigate the possibility of using a potassium-rich biomass ash for the activation of one-part geopolymers
Waste materials in the production of traditional building ceramics: effect of GRP dust waste addition on properties of fired bricks
No full textThe total amount of end-of-life and production waste generated by glass thermo-set composites market in Europe reaches 304,000 tonnes (2015) triggering interest in optimizing Glass Reinforced Plastic (GRP) waste recovery. Now, landfill as non hazardous waste remains the most popular solution to manage GRP waste for the difficulty of separating the different parts, its intrinsic thermo-set composite nature and the insufficient knowledge on recycling options. Recently, GRP dust (GRPd) waste in cementitious matrix has been investigated to improve performances. Effects of GRPd waste addition in the production of bricks can also be considered. The polymeric part in GRPd will burn during cooking: additional porosity can be left in the matrix improving final lightness; the glass fibers in GRPd waste can reinforce the ceramic matrix decreasing fragility and increasing the bricks bending strength
Cementitious and geo-polymeric mortars compared with the same mechanical strength class
No full textIn the perspective of using environmentally friendly materials for the rehabilitation and restoration of ancient buildings, the behaviour of geo-polymeric mortars was studied. The research was developed into two main aspects: substitution of Portland cement with an alternative binder and recycling of industrial by-products. The experimentation was carried out comparing the performances of cementitious and geo-polymeric mortars with the same mechanical strength class (R1≥ 10 MPa, R2 ≥ 15 MPa, R3 ≥ 25 MPa, R4 ≥ 45 MPa), according to the European Standard. In particular, four geo-polymeric mixtures were prepared with a sodium silicate/sodium hydroxide proportion of 1:1 with different concentration of NaOH and a sand/fly ash proportion of 2.7:1. Four cementitious mortars were prepared with water/cement equal to 0.5, 0.65, 0.9 and 1.1 by weight, respectively. Different properties both in fresh and hardened state were evaluated and compared. The adherence with brick was reduced when geo-polymeric mortars were used. However, best results were obtained by geo-polymeric mortars with respect to cement ones for vapour permeability, capillarity water absorption, elastic modulus and resistance to salt crystallization
Cement mortars and geopolymers with the same strength class
No full textRecycling of industrial waste materials to manufacture environmentally friendly mortars and concretes is gaining
more and more interest, in particular for sustainability, rehabilitation and renovation purposes. In the present study
geopolymers, which had been made using fly ash as a precursor and were subsequently subjected to curing at room
temperature, were investigated. Geopolymeric and cementitious mortars with the same mechanical strength class
were compared in both the fresh and hardened states. Despite the higher free shrinkage and lower adhesive
strength on brick substrate, geopolymeric mortars behaved better than cement types in terms of lower dynamic
modulus of elasticity, higher water vapour permeability, lower capillary water absorption and higher resistance to
salt crystallisation
Metakaolin and fly ash alkali-activated mortars compared with cementitious mortars at the same strength class
No full textAlkali activated and cementitious mortars belonging to R1 ≥ 10 MPa, R2 ≥ 15 MPa and R3 ≥ 25 MPa strength classes are tested and compared in terms of workability, dynamic modulus of elasticity, porosimetry and water vapour permeability. Capillary water absorption, drying shrinkage, resistance to sulphate attack and corrosion behaviour of embedded bare and galvanized reinforcements have also been investigated.
In alkali activated mortars, drying shrinkage is higher than that of cementitious mortars but restrained shrinkage is lower due to lower modulus of elasticity. Water vapour permeability is more pronounced in alkali activated mortars, and capillary water absorption is lower in those prepared with fly ash. The high alkalinity of alkali activated mortars was seen to delay the onset of the passive state in particular for galvanized reinforcements, but after one month of curing they were found to reach the same corrosion rates of those embedded in cementitious mortars
Influence of binders and aggregates on VOCs adsorption and moisture buffering activity of mortars for indoor applications
No full textThe implementation of energy efficiency measures leads to more tightly sealed buildings. These energysaving
measures directly worsen indoor air quality leading to increased humidity and concentration of
pollutants as Volatile Organic Compounds (VOCs). Our work compares the de-pollution efficiency and
moisture buffering capacity of five mortars for indoor applications. Methyl-ethyl-ketone (MEK) is chosen
as pollutant model. The effect of binders (cement, cement + air-entraining admixture, lime) and aggregates
(sand, zeolite, perlite) on the mechanical properties, water absorption and morphology of mortars
was also evaluated. All mortars adsorb MEK during the first period, but only those manufactured with
lime–zeolite do not saturate after 30 min with a de-pollution efficiency of about 85% after 24 h. The Moisture
Buffering Capacity (MBC) of lime mortars is three times higher with respect to that measured in
cement mortars. The MBC of lime–zeolite mortars is double with respect to that measured in lime–sand mortars
Comparison between cementitious and geopolymeric mortars with the same mechanical strength class
No full textIn the perspective of environmental sustainability for the rehabilitation and restoration of masonry buildings, the properties of geopolymeric mortars were studied and compared with those of traditional cement-based ones with the same mechanical strength class and workability.
To this aim, four different geopolymeric and cement mixtures were manufactured in order to obtain mortars belonging to R1 10MPa, R2 15MPa, R3 25 MPa and R4 45 MPa strength class.
In particular, geopolymeric mixtures were prepared with a sodium silicate/sodium hydroxide equal to 1:1, by using different concentration of the solutions, and sand/fly ash proportion equal to 2.7:1. The respective four cementitious mortar mixtures were prepared with water/cement equal to 0.5, 0.65, 0.9 and 1.1 by weight.
Geopolymer mortars behave better than cement ones in terms of lower elastic modulus, higher water vapour permeability, lower capillary water absorption and higher resistance to salt crystallization
Valorisation of Limestone in Sustainable Cements
No full textThis study investigates the development of two sustainable cements, CEM II/B-LL and CEM VI, in accordance with the UNI EN 197-1 and 197-5 standards. CEM II/B-LL was produced by replacing Portland cement with limestone (LS) at varying dosages (0%, 15%, 25%, and 35% by mass), and CEM VI was made by substituting blast furnace slag with limestone at different levels (0%, 10%, 20%, 30%, and 40% by mass). The results show that both binders are classified as structural cements. LS substitution increases the setting time of CEM II/B-LL but does not significantly affect the setting time of CEM VI. When cured at low temperatures (10 °C), CEM VI mortars retain their mechanical properties even at high LS levels, making them particularly suitable for cold climates. Mortar properties such as total porosity and capillary water absorption increase with LS content, with CEM VI exhibiting lower sensitivity to LS additions. Free shrinkage in CEM II/B-LL mortars decreases with LS content, whereas in CEM VI mortars, it initially increases with up to 20% LS and then decreases at higher LS levels (30–40%). Restrained shrinkage is also lower in CEM VI than in CEM II/B-LL. The Global Warming Potential (GWP) of CEM II/B-LL decreases significantly with increased LS content, whereas in CEM VI, it remains almost constant up to a 40% substitution. However, CEM VI demonstrates a 50% lower environmental impact compared to CEM II/B-LL, underscoring its superior sustainabilit
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