Добірка наукової літератури з теми "Lime-pozzolana reaction"

A combined reaction of hydration and carbonation takes place in hydraulic lime and lime-pozzolana mortars. Hydration reactions are the first reaction and carbonation of lime is the complementary reaction in the strength gain. Competition between these two reactions can occur in lime-pozzolana mortars if the pozzolanic material has low reactivity with lime, leading to the consumption of lime by carbonation reaction. The degree and the order of these reactions are strongly influenced by the moisture content. Hydration reactions are enhanced under moist conditions while carbonation is delayed. Curing under dry conditions does not sufficiently increase their strength because the hydration reactions are slowed down or even terminated by the full carbonation of lime in lime-pozzolana mortars. The consequence of this on the mechanical properties of the mortars is remarkable while the same impact is not observed in their porosity. Such mortars require moist conditions to ensure sufficient strength development.

The pozzolanic additions are widely used as concrete component for numerous technical, economic and environmental reasons. Obviously the hydration process in a pozzolana containing system differs from hydration of Ordinary Portland Cement (OPC) what is indicated macroscopically by slower increase of strength and lower hydration heat. This paper aims to study pozzolanic reaction from perspective of chemical kinetics. From this point of view pozzolanic reaction and carbonation are two parallel reactions which are competing for portlandite (Ca (OH)2). The rate of each of these two reactions is characterized by rate constant and order of reaction. The system under study was 1:1 mixture lime – ceramic powder. The course of reaction was primarily studied by thermogravimetry which results were further subjected to kinetic analysis. MAS NMR spectroscopy was used for study of structural changes taking place in material in the course of pozzolanic reaction.

ABSTRACTHydraulic lime binders are considered a technological marvel which revolutionized construction techniques in antiquity. The core material is made of a binder that is a mixture of calcite and hydraulic phases, which are amorphous silicate compounds that nanostructurally polymerize into insoluble phases that harden even underwater, formed during the reaction between lime and reactive silicates such as volcanic ash. This is also what makes hydraulic lime so hard to radiocarbon (14C) date. These insoluble phases contain carbonates that may set centuries following their application, resulting in younger ages, which may contaminate the calcite fraction that is favorable for 14C dating. This calcite fraction forms upon the incorporation of atmospheric carbon dioxide during the setting of the hydrated lime. Therefore, different characterization methods are being constantly developed for identifying and characterizing the components of hydraulic lime-binders. In this work, we present a rapid characterization technique based on Fourier transform infrared spectroscopy (FTIR) that characterizes the atomic disorder and chemical environment of the carbonates and silicates fractions in the binder. The atomic disorder of the calcite crystallites was determined by the ν2 and ν4 vibrational modes, and the silicates were characterized by the main peak asymmetry and full width at half maximum (FWHM). Different hydraulic binders from Caesarea Maritima were examined, including Herodian mortars from the underwater breakwater and on-land plasters and mortars from the portʼs warehouse and vaults. Hydraulic binders, in which the calcite fraction in the binder shows atomic disorder that is comparable to modern plaster binders, was associated with silicates that have asymmetry and FWHM of clays and quartz. These materials are considered to be in good preservation state for 14C dating since their carbonates crystallites are disordered and did not interact with the environment chemically to form stable and ordered crystals. Interestingly, the atomic disorder of binders that underwent chemical alterations and recrystallization processes, are associated with reactive silicates aggregates such as volcanic ash (pozzolana). These results suggest a new way to prescreen materials for radiocarbon dating based on the composition of lime-binders and preservation state of the carbonate fraction and hydraulic products.

Purpose: of this paper is to investigate the durability and the mechanical properties, including compressive and flexural strengths, of the locally compressed earth blocks manufactured from soil in Irbid, Jordan. Moreover, effect of volcanic tuff as new stabilizer material on properties of compressed earth block (CEB). Compressed earth block is a technique that was created to solve environmental and economic problems in construction sector. It is widespread in many countries around the world but hasn't been used in Jordan yet. Design/methodology/approach: 9 mixtures were carried out. One of this mixture is the control mix, beside other mixtures were performed by replacing soil with 40%, 10%, 10%, of sand, volcanic tuff, and lime respectively. In addition, polypropylene fibre was used. After 28 days of curing, the CEB were dried in oven at 105ºC for 24 hours then tested. Findings: Show that absorption and erosion were decreased when the lime used in the soil. On the other hand, the fibres presence significantly improved the durability and mechanical properties in all mixtures. Moreover, the higher compressive strength was obtained in the mixtures which contain lime only while the higher tensile strength was obtained in the mixtures which contain lime with sand replacement. The using of volcanic tuffs produced average compressive strength values. The reason is that in the presence of lime and pozzolana (volcanic tuff) reactions take place at low and slow rate at early ages. Research limitations/implications: volcanic tuff can produce favourable compressive strengths at later ages and this is a point of interest in the future work. Originality/value: Searching for a new material as stabilizer material that improves the properties of the compressed earth block (CEB).

Climate changes are inducing a modification of environmental loads on historical sites, requiring new actions towards their conservation. In the paper, the results of an experimental work on sustainable improvement of a pyroclastic soil belonging to the Orvieto cliff (Central Italy) have been investigated in the perspective of its preservation from degradation. The slightly coherent facies of Orvieto Ignimbrite (pozzolana) was treated with hydrated lime and the subsequent chemo-physical evolution was investigated by means of a multi-scale analysis. The beneficial effects obtained from the improvement in terms of mechanical behaviour were interpreted and correlated to the chemo-physical evolution of the system. Microstructural analyses, X-ray diffractometry, thermo-gravimetric analyses (DTG), SEM observations, mercury intrusion porosimetry performed on raw and treated samples, showed that the pozzolanic reactions develop since the very beginning in the system and that the observed mechanical improvement of the treated soil is mainly due to the formation of calcium silicate hydrates (CSH) and calcium aluminate hydrates (CAH). In the paper, the mechanical improvement is put in evidence by comparing the results of oedometer tests performed on both raw and treated samples.

AbstractThe most obvious characteristics of the Ming Great Wall are external masonry walls made of natural stones, bricks and lime mortars. According to the chemical and mineralogical compositions of the original bedding and pointing mortars, dolomitic lime binder was used dominantly in the construction of the Ming Great Wall in provinces such as those around Beijing and Hebei. Calcium-rich lime and air lime with low natural hydraulically reactive phases, which are hydrated and react slowly with the carbon dioxide in air to form calcium carbonate, were used in some western provinces. Chemical and microscopic investigations show that both dolomitic and calcium-rich lime mortars are almost aggregate-free. Historic dolomitic lime mortars are characterised by high strengths, low porosities and dense micro-scale textures. The most recent conservation principle is to preserve the Ming Great Wall as a ruin. Therefore, the conservation strategy should be redefined in terms of mortars. Since some of the damage to the Great Wall is related to reactions between dolomitic lime mortars and air pollutants, calcium-rich lime binders should be used for conservation and even for restoration of those parts of the Great Wall that were originally built with dolomitic lime. Binders based on natural hydraulic lime and calcium-rich lime gauged with natural pozzolana might be more compatible than other binders” for the structural consolidation of the ruins of the Great Wall.