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| 2. |
- Emanuelson, Anna, et al.
(författare)
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A comparative study of ordinary and mineralised Portland cement clinker from two different production units Part I: Composition and hydration of the clinkers
- 2003
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Ingår i: Cement and Concrete Research. - 0008-8846. ; 33:10, s. 1613-1621
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Tidskriftsartikel (refereegranskat)abstract
- Portland cement clinkers from two production units were investigated; Plant 1: ordinary clinker (P1) and clinker mineralised with CaF2+CaSO4 (P1m); Plant 2: ordinary clinker (P2) and two clinkers mineralised with CaF2+CaSO4 (P2m, low SO3 and P2m', high SO3). The chemical composition of the clinkers was determined by X-ray fluorescence, ICP analysis, titration (free lime) and ion selective electrode measurements (F). Observed clinker parameters (LSF, SR, AR, R, wt.% MgO, F, SO3, free lime): P1 (0.96, 2.72, 1.27, 1.04, 0.78, 0.06, 0.64, 0.71); P1m (1.03, 2.21, 1.58, 2.18, 0.87, 0.23, 1.95, 0.69); P2 (1.00, 2.66, 1.72, 0.75, 4.06, 0.20, 1.38, 1.51); P2m (1.01, 2.91, 1.96, 0.90, 3.21, 0.39, 1.72, 2.06); P2m' (0.97, 2.70, 1.84, 1.15, 3.86, 0.42, 2.48, 0.89). The qualitative and quantitative phase compositions were characterised using X-ray powder diffraction, backscattered electron imaging, X-ray microanalysis and elemental mapping, plus optical reflection microscopy. Phases observed in all clinkers were: alite, beta-belite, cubic aluminate, ferrite and free lime. Additional phases observed were: aphthitalite (P1, P2, P2m, P2m'), calcium langbeinite (P1m) and periclase (P2, P2m, P2m'). The clinker composition and texture differ more between the two plants, than between ordinary and mineralised clinker from the same production unit. Laboratory cements were prepared by mixing ground clinker with CaSO(4)(.)2H(2)O. The cements were hydrated in an isothermal calorimeter at 20 degreesC (water/cement weight ratio = 0.5) during 33 h. After 12 h, the laboratory cement based on P1m reached a higher level of reaction than the one based on P1. The P2m and P2m' laboratory cements had a slower reaction than the P2 cement. (C) 2003 Elsevier Ltd. All rights reserved.
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| 3. |
- Emanuelson, Anna, et al.
(författare)
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A comparative study of ordinary and mineralised Portland cement clinker from two different production units Part II: Characteristics of the calcium silicates
- 2003
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Ingår i: Cement and Concrete Research. - 0008-8846. ; 33:10, s. 1623-1630
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Tidskriftsartikel (refereegranskat)abstract
- Portland cement clinkers from two production units were investigated in order to determine the effects of mineralisation on alite and belite; Plant 1: ordinary clinker (P1) and clinker mineralised with CaF2 + CaSO4 (P1M); Plant 2: ordinary clinker (P2) and two clinkers mineralised with CaF2 + CaSO4 (P2m, P2m'). The polymorphism of alite was studied using synchrotron X-ray powder diffraction (XRD), wavelength 1.5227 Angstrom, and electron diffraction (ED) in a transmission electron microscope. The substitutions of minor elements in alite and belite were determined using electron microprobe analysis. Clinkers P1 and P1m both contained apparent rhombohedral alite (XRD) with an incommensurately modulated structure (ED), while clinkers P2, P2m, and P2m' all contained monoclinic alite (XRD). The addition of mineralisers in the process caused increased content of fluoride in alite and increased substitution of Si(4+) by Al(3+) and S(6+) in both calcium silicates. The latter effect was most pronounced in clinker P1m due to its high molar SO3 to alkali oxide ratio (R = 2.18). The improved hydraulic activity of P1m compared to P1 was caused by substitutions rather than a change in symmetry. The decreased hydraulic activity of P2m and P2m' compared to P2 was explained by the high levels of fluorine, which had a retarding effect on the hydration. (C) 2003 Elsevier Ltd. All rights reserved.
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| 4. |
- Evju, Cecilie, et al.
(författare)
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Simulating the hydration of cementitious phases with an oscillating rate of reaction
- 1999
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Ingår i: Cement and Concrete Research. - 0008-8846. ; 29:9, s. 1513-1517
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Tidskriftsartikel (refereegranskat)abstract
- To investigate how an oscillating reaction rate might influence the hydration of cementitious solids, a simple iterative mathematical model that includes recurrent passivation of the surface has been constructed. The algorithm generates a wide variety of hydration curves with a limited number of input parameters: i.e.. V0 (volume of unreacted solid after initial reaction), a, (degree of reaction upon initial wetting), x0 (fraction of particle surface passivated after initial wetting); running index: n (cycle number, with an arbitrary unit of time per cycle); constants: m (number of cycles with constant x, the relative rate of the hydration and passivation reactions), k (maximum linear rate of reaction front), and lambda (range 0-1, determines the general passivation behaviour, modelled by the algorithm x(new) = 4 lambda xold[1 - xold]). The hydration process is described by the sequence: (1) Delta V = k(1 - x)V^2/3, (2) Vnew = Vold - Delta V, (3) alpha = 1 - (V/V0) + alpha0.
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| 5. |
- Hillerberg, Arne, et al.
(författare)
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Analysis of crack formation and crack growth in concrete by means of fracture mechanics and finite elements
- 1976
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Ingår i: Cement and Concrete Research. - : Elsevier BV. - 0008-8846. ; 6:6, s. 773-782
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Tidskriftsartikel (refereegranskat)abstract
- A method is presented in which fracture mechanics is introduced into finite element analysis by means of a model where stresses are assumed to act across a crack as long as it is narrowly opened. This assumption may be regarded as a way of expressing the energy adsorption GC in the energy balance approach, but it is also in agreement with results of tension tests. As a demonstration the method has been applied to the bending of an unreinforced beam, which has led to an explanation of the difference between bending strength and tensile strength, and of the variation in bending strength with beam depth.
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| 6. |
- Johannesson, Björn
(författare)
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Diffusion of a mixture of cations and anions dissolved in water
- 1999
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Ingår i: Cement and Concrete Research. - 0008-8846. ; 29:8, s. 1261-1270
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Tidskriftsartikel (refereegranskat)abstract
- In service life modeling of concrete, the ion transport in the pore solution is crucial. The main deterioration phenomena associated with ions in the pore solution are (1) corrosion due to external chloride ions reaching the embedded reinforcement bars; (2) carbonation due to presence of dissolved carbon dioxide (which will form carbonic acid with water) supplied from the surrounding air; and (3) leaching of hydroxide ions from the pore solution to the surrounding environment. Models dealing with diffusion of ions are usually based on the mass balance equations for the individual diffusing ions together with constitutive relations for the mass density flows and for the mass exchange among the constituents. The important consequences of electroneutrality among the diffusing ions, however, is often omitted in models dealing with diffusion of ions in the pore solution of concrete. Here a method will be examined that allows diffusion of different ions in water, which satisfies both the electroneutrality requirement and the mass balance laws. For simplicity the effect of built-up electric double layers on the charged pore walls will not be treated.
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| 7. |
- Johannesson, Björn, et al.
(författare)
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Microstructural changes caused by carbonation of cement mortar
- 2001
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Ingår i: Cement and Concrete Research. - 0008-8846 .- 1873-3948. ; 31:6, s. 925-931
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Tidskriftsartikel (refereegranskat)abstract
- The change of specific surface area and pore size distribution due to carbonation of an ordinary Portland cement mortar is investigated. The adsorption of water vapor on noncarbonated and well-carbonated cement mortar is measured in order to evaluate the difference in specific surface area for the two samples using the BET theory. From the measured desorption the pore size distribution is calculated using the Kelvin formula. A sorption balance is used to measure the sorption characteristics for the two studied sample qualities. In this method dry and saturated air are mixed in desired proportion in a closed system. One of the benefits of the method is that the samples not are exposed to carbon dioxide during testing, i.e., undesired effects caused by carbonation on the sorption can be eliminated. The specific surface area for a noncarbonated sample was calculated, using the measured adsorption data, to be 8% higher than for the well-carbonated sample. The difference in pore size distributions was more marked than the difference in specific surface area for the two samples. The well-carbonated mortar had about twice as much volume attributed to small pores as the noncarbonated cement mortar.
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| 8. |
- Johannesson, Björn
(författare)
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Prestudy on diffusion and transient condensation of water vapor in cement mortar
- 2002
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Ingår i: Cement and Concrete Research. - 0008-8846. ; 32:6, s. 955-962
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics of sorption of water vapor in mature cement mortar are examined experimentally by the use of a sorption balance (DVS1000). The relative humidity in the sample chamber is obtained by mixing dry and saturated air using flow regulators with very high accuracy. A predefined change of relative humidity in the sample chamber can be obtained in about 30 s. The time needed for equilibration in terms of the mass of a finely grained mortar sample is shown to be in the order of 2500 min for a 0-96% step in relative humidity at 25 degreesC. This fact calls for a refinement of modeling of diffusion of water vapor in materials such as mortar to take into account the kinetics of sorption. The established model involves a transient mass exchange term that explicitly describes the rate of condensation at internal material surfaces. This function becomes zero when located at the equilibrium sorption isotherm. The 'global' mass diffusion velocity of water vapor in the air-filled porosity is assumed to be significantly affected by the mass concentration of liquid water in the pore space. A satisfying match between the proposed model and measurements presented by U. Daian [Transp. Porous Media 4 (1989) 1.] was obtained by using nonlinear diffusion and sorption characteristics. In order to get a satisfying match, the sorption kinetics was, however, forced to be much slower than the recorded values obtained by the sorption balance. Some speculations as to the reason of this marked difference are performed. (C) 2002 Elsevier Science Ltd. All rights reserved.
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| 9. |
- Persson, Bertil
(författare)
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A comparison between mechanical properties of self-compacting concrete and the corresponding properties of normal concrete
- 2001
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Ingår i: Cement and Concrete Research. - 0008-8846. ; 31:2, s. 193-198
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Tidskriftsartikel (refereegranskat)abstract
- An experimental and numerical study on mechanical properties, such as strength, elastic modulus, creep and shrinkage, of Self-Compacting Concrete, SCC, and the corresponding properties of Normal Compacting concrete, NC, is outlined in this article. The study included eight mix proportions of sealed or air-cured specimens with water-binder ratio, w/b, varying between 0.24 and 0.80. Half of the mixes studied were based on NC. The age at loading of the concretes in the creep studies varied between 2 and 90 days. Four different stress to strength levels were studied. Parallel studies were performed on strength, fc, and relative humidity, RH. The results show that elastic modulus, creep and shrinkage of SCC did not differ significantly from the corresponding properties of NC. The ongoing study was started in 1997.
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| 10. |
- Persson, Bertil
(författare)
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A NORDTEST Method for Verification of Self-desiccation in Concrete
- 2001
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Ingår i: Cement and Concrete Research. - 0008-8846. ; 31:2, s. 199-203
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- This article outlines a new NORDTEST method for verification of self-desiccation in concrete. The method involves measurements of the internal relative humidity, RH, on pieces of concrete at one month’s age. The measured RH is then compared with the requirements according to the owner. The new NORDTEST method for self-desiccation permits requirements to be made of the self-desiccation of HPC in accordance with present demands on strength. During the development of the test method experimental studies were carried out on nine concretes with w/c varying between 0.32 and 0.50. Half of the concretes contained five per cent silica fume. The experiments showed a significant effect of cement type, silica fume and w/c on the self-desiccation in concrete. The test method was also verified in the field, both when manufacturing the concrete and on site. The method was developed after co-operation between the Technical University of Denmark and Lund University. The experimental studies were performed at Division of Building Materials, Lund Institute of Technology, Lund, 1995-1999.
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