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Journal ArticleDOI

Thermal analysis of hydrated calcium aluminates

01 Sep 1996-Journal of Thermal Analysis and Calorimetry (Kluwer Academic Publishers)-Vol. 47, Iss: 3, pp 765-774
TL;DR: Differential scanning calorimeter has been used to study the dehydration characteristics of hydrated calcium aluminates such as CA, CA2 and C12A7 where C and A stand for CaO and Al2O3 respectively.
Abstract: Differential scanning calorimeter (DSC) has been used to study the dehydration characteristics of hydrated calcium aluminates such as CA, CA2 and C12A7 where C and A stand for CaO and Al2O3 respectively. Dehydration of CAH10 and C2AH8 (whereH=H2O) occur ∼ at 160–180°C and 200–280°C respectively. These two phases are unstable and ultimately get transformed to AH3 and C3AH6. Dehydration of AH3 and C3AH6 occur between 290 and 350°C and overlap at lower scanning rate. The activation energy for dehydration of the stable AH3 and C2AH6 phases has been found to be 107.16 and 35.58 kJ mol−1 respectively. The compressive strength of the hydrated calcium aluminates has been determined. The result shows that in the case of CA, almost 90% of ultimate strength has been attained in 1 day whereas in CA2, ultimate strength has been attained in 14 days and in C12A7 in 1 day. DSC results have been correlated with the rate of strength developments.
Citations
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01 Jan 2009
TL;DR: In this article, a detailed multi-techniques approach was developed to follow the microstructural development during hydration with strong emphasis on phase quantification (using isothermal calorimetry, XRD, TGA, BSE-IA, MIP).
Abstract: Calcium Aluminate Cements (CAC) are renowned in the field of construction for specific applications requiring rapid hardening and chemical resistance. These properties result from rapid exothermic reactions occurring immediately after setting. Due to the much lower use of CACs compared to Portland cements based materials, there is a lack of knowledge on the hydration of this cement and especially on its microstructural development. This study aimed to understand the hydrated phase assemblages in CACs systems and in particularly blended systems using Supplementary Cementitious Materials (SCMs). A detailed multi-techniques approach was developed to follow the microstructural development during hydration with strong emphasis on phase quantification (using isothermal calorimetry, XRD, TGA, BSE-IA, MIP). The cement pastes and mortars were cured in realistic self heating conditions to simulate the thermal effects occurring in practical sections of concrete. The effects of SCMs (nucleation, dilution and chemical reaction) were investigated to understand the microstructure property relationship of CACs systems. It was shown that the formation of hydration products rapidly levelled off. It appears that this levelling off is mainly determined by the space availability even though porosity was not completely filled and further hydration of reactants continued over several months of water curing. Subsequent densification of the matrix was partly attributed to the hydration of C2AS to C2ASH8. The addition of lithium sulphate allows the setting time to be controlled and contributes to the formation of stable hydrates (C3AH6 in the plain system and C2ASH8 in the blend). However there was also a noticeably inhibition of the hydration of CA. Self heating contributed to formation of distinct polymorphs of AH3 and their subsequent space filling. Microstructure property relationships depend on the density of hydrates but also their distribution. Detailed elucidation of the exact relationships is rendered difficult by the impact of drying methods on the measurement of porosity.

52 citations

Journal ArticleDOI
TL;DR: In this paper, the effects of lime addition on clay materials properties, in terms of mechanical and physico-chemical evolution, were investigated in order to explain the mechanical behaviors of lime-treated clay materials.
Abstract: This paper deals with the effects of lime addition on clay materials properties, in terms of mechanical and physico-chemical evolution. A coupling between these two aspects was undertaken in order to explain the mechanical behaviors of lime-treated clay materials. The study was performed on two different clays, a kaolin and a Ca 2 + -bentonite. Lime addition leads to an increase of mechanical properties of these clays. These improvements are faster with Ca 2 + -bentonite, even if at long term the performance reached for kaolinite is higher. The coupling between macroscopic and physico-chemical aspects shows that these improvements are linked to the development of secondary compounds such as calcium silicate hydrates, hydrogarnet and calcium carboaluminate hydrate phases.

48 citations

Journal ArticleDOI
TL;DR: In this article, a comprehensive program of isotropic consolidation tests and drained triaxial experiments were designed and carried out on saturated specimens of a silt treated with quicklime, and the chemical composition in hydrates, portlandite, and carbonates was determined using thermogravimetric analysis and differential thermal analysis.
Abstract: Lime treatment has been widely used to improve mechanical properties of soils. However, less has been done to account for the effect of the treatment on constitutive relationships. In this study, a comprehensive programme of isotropic consolidation tests and drained triaxial experiments were designed and carried out on saturated specimens of a silt treated with quicklime. The chemical composition in hydrates, portlandite, and carbonates was determined using thermogravimetric analysis and differential thermal analysis. The modifications to the mechanical parameters of the soil were evaluated in the framework of the Cam Clay elastoplastic model. The experimental results revealed that the addition of lime leads to the modification of the critical state. For concentrations in lime higher than 1%, the treated specimens displayed a different normal compression line compared to the untreated state. Chemical analysis revealed the production of cementitious compounds for every concentration tested. A constitutive model was proposed to describe the observed behaviour of lime treated soils in the framework of the Structured Cam Clay. The model accounts for the modifications on the mechanical parameters of the soil. A chemo-mechanical coupling was established between the yield stress and the mass concentration in cementitious compounds.

26 citations


Additional excerpts

  • ...Some studies have 170 shown that the decarboxylation processes of these three compounds were associated with 171 three temperature domains (Das et al., 1996; Saikia et al., 2002; Alarcon-Ruiz et al., 2005)....

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Journal ArticleDOI
TL;DR: In this paper, the authors investigated the hydration products and thermal decomposition mechanism of hydrated CaAl 2 O 4 and Ca 7 ZrAl 6 O 18 compounds by X-ray diffraction, SEM/EDS and thermal analysis.
Abstract: The hydration products and thermal decomposition mechanism of hydrated CaAl 2 O 4 and Ca 7 ZrAl 6 O 18 compounds were investigated by X-ray diffraction, SEM/EDS and thermal analysis. The processes of crystal hydrate nucleation and precipitation were preceded by the evolution of the X-ray amorphous phase during the first 24 h of hydration. DTA–TGA–EGA techniques allowed the study of the detailed decomposition and identification of intermediate and stable to be performed. The differential thermal analysis (DTA) curves of hydrated CaAl 2 O 4 and Ca 7 ZrAl 6 O 18 compounds show five similar endothermic peaks due to crystal water desorption. According to the quantitative TGA–EGA analyses performed on hydrated CaAl 2 O 4 and Ca 7 ZrAl 6 O 18 compounds, it was found that C 2 AH 8 , C 3 AH 6 and Al(OH) 3 phases are the main hydration products of CaAl 2 O 4 . Under the same laboratory conditions, the hydration of Ca 7 ZrAl 6 O 18 proceeds with the formation of mainly CAH 10 and AH 3 -gel phases. We provide the original illustrations of the hydrate crystals formation via amorphous phases.

22 citations

Journal ArticleDOI
TL;DR: In this paper, the technical feasibility of reusing iron ore tailing (IOT) rich in iron in natura (sludge and dry), partially replacing cement in pastes by up to 15%.
Abstract: The present work aims at evaluating the technical feasibility of reusing iron ore tailing (IOT) rich in iron in natura (sludge and dry), partially replacing cement in pastes by up to 15%. Fluid, hydration and hardened state properties were investigated. IOT favored hydration of the aluminate phases due to the nucleation effect and the rheological behavior was affected by the morphology of the particles. The early age compressive strength of the cement paste is maintained when using 10% or less of sludge in the mixture. The use of higher contents or 10% of dry IOT reduced slightly the late age strength of the material.

22 citations

References
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Journal ArticleDOI
TL;DR: The chemistry of hydration of monocalcium aluminate, CA, has been studied at several temperatures using conduction calorimetry, X-ray diffraction and other techniques as discussed by the authors.
Abstract: The chemistry of hydration of monocalcium aluminate, CA, has been studied at several temperatures using conduction calorimetry, X-ray diffraction and other techniques. At 4 °C, hydration to the decahydrate CAH 10 occurs about 15 hours after mixing; this hydration time increases with increasing temperature up to 30 °C, and C 2 AH 8 appears as a hydration product. At 40 °C rapid hydration to C 2 AH 8 is followed over a period of weeks by the ‘conversion’ reaction producing C 3 AH 6 . The reaction of CA to form crystalline hydrates was monitored by X-ray diffraction analysis; the results indicate that hydration also produces significant amounts of noncrystalline material. The enthalpies of the reactions involved in hydration and ‘conversion’ were measured by conduction calorimetry.

63 citations

Journal ArticleDOI
TL;DR: In this article, the authors studied the hydration behavior of Secar 71 refractory aluminous cement using conduction calorimetry, X-ray diffraction and thermal analysis techniques.
Abstract: The hydration behaviour of Secar 71 refractory aluminous cement has been studied over a range of temperature using conduction calorimetry, X-ray diffraction and thermal analysis techniques. The first reaction is the hydration of monocalcium aluminate, CA, producing a sharp calorimeter peak within 12 hours of mixing. Following this reaction the other major component, calcium dialuminate (CA 2 ), undergoes slow hydration over a period of weeks. The enthalpies of these two reactions have been measured. The initial hydration products of both components are CAH 10 , or C 2 AH 8 with alumina gel. These can subsequently convert to C 3 AH 6 ; after one month significant conversion is observed even at room temperature. A method of estimating the degree of conversion based on X-ray measurement of C 3 AH 6 is proposed.

46 citations

Journal ArticleDOI
TL;DR: Differential scanning calorimetry (dsc) was used to investigate the freezing behaviour of hardened cement paste (hcp) subjected to nacl and cacl2 solutions containing up to 5.4 mol cl/l as mentioned in this paper.
Abstract: Differential scanning calorimetry (dsc) was used to investigate the freezing behaviour (-175 deg c to 20 deg C) of hardened cement paste (hcp) subjected to nacl and cacl2 solutions containing up to 5.4 mol cl/l. Thermograms were also recorded for samples dried to relative humidities (rh) between 61% and 96%. The low-temperature phase transition at -38 deg c exhibited the freezing behaviour of an aqueous solution in gel pores of approximately equal to 4 nm radius. Chloride ions strongly reduce the coupling forces between gel particles and structure the gel pore water. On desorption critical behaviour of the low-temperature transition energy was observed at 0.52 mol cl/l which is the concentration most damaging to hcp. Above 1.3 mol cl/l freezing of supercooled bulk water in macropores was observed at more than one temperature. (Author/TRRL)

31 citations

Journal ArticleDOI
TL;DR: In this paper, the hydration process of a high alumina cement was investigated through ultrasonic wave propagation techniques, and a correlation between wave amplitude and velocity and breaking strength of the cement was demonstrated.
Abstract: The hydration process of a high alumina cement was investigated through ultrasonic wave propagation techniques A correlation between wave amplitude and velocity and breaking strength of the cement is demonstrated The wave behaviour through hydrating cements was found to be a function of the cement-to-water ratio between values of 2 and 4 Changes in the temperature of the hydrating samples were found to exhibit a similar dependence

6 citations