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International Concrete Abstracts Portal

Showing 1-5 of 46 Abstracts search results

Document: 

SP186-23

Date: 

May 1, 1999

Author(s):

M. N. Soutos, J. H. Bungey, M. J. Brizell, and G. D. Henderson

Publication:

Symposium Papers

Volume:

186

Abstract:

Attempts to study the effect of vibration of fresh concrete have mainly been based on visual observation of, for example the radius of influence of the insertion vibrator, or the rate of flow of concrete down a tube when vibration is applied. The reason for this has been the difficulty of measuring the sinusoidal wave form created by mechanical vibrators. Advances in electronic equipment have made devices for measuring this wave form commercially available, and they have therefore been used in this research project to gain a better understanding of the consolidation process. The amplitude of the sinusoidal signal was calculated from the acceleration measured at distances up to 250mm from the surface of the insertion vibrator. Preliminary tests indicate that the amplitude of the vibratory wave decays exponentially with distance. The damping coefficient is greater for superplasticized high-strength concrete mixtures with low W/C than it is for normal-strength concretes. An attempt was made to relate the damping coefficients to the rheological properties, yield (g) and plastic viscosity (h) values determined from tests carried out with Tattersall's two point test apparatus. Both the yield (g) and plastic viscosity (h) values were found to increase by decreasing the W/C, despite the concrete having an equal slump of 150 mm. This shows that the slump values obtained by the use of high dosages of superplasticizers, as is the case with low W/C, are not directly comparable to those resulting from high water contents, with respect to the rheological behavior of concrete.

DOI:

10.14359/5568


Document: 

SP186-37

Date: 

May 1, 1999

Author(s):

M. A. Aiello and L. Ombres

Publication:

Symposium Papers

Volume:

186

Abstract:

The present paper is devoted to the analysis of the behaviour of high performance concrete structures made with members reinforced with Fiber Reinforced Polymer (FRP) rebars. Models usually adopted for the evaluation of the deformability of steel reinforced concrete structures are described and their use for the analysis of FRP reinforced concrete structures is discussed. A theoretical model, developed taking into account both the real behaviour of materials and the interaction between the reinforcement and the concrete matrix is, thus, used to determine typical quantities that characterize the serviceability of reinforced concrete structures (moment-curvature and load-deflection diagrams). A large numerical investigation has been carried out in order to evidence the influence of predominating geometrical and mechanical parameters on the serviceability behaviour of FRP reinforced concrete beams. Finally, results of an experimental analysis, carried out by flexural tests on concrete beams reinforced with Aramidic Fiber Reinforced Polymer (AFRP) rebars, are described and a comparison between previsions of models and the experimental results has been made.

DOI:

10.14359/5582


Document: 

SP186-32

Date: 

May 1, 1999

Author(s):

J. Ambroise, S. Rols, and J. Pera

Publication:

Symposium Papers

Volume:

186

Abstract:

The goal of this project was to develop self-levelling concrete at lower cost than traditional self-levelling concrete. The concrete of this study was only 20% more expansive than usual concrete utilized for building concrete. Laboratory and on-site data proved that this objective could be reached if the mixture contained: 260kg/m3 normal portland cement,-140kg/m3 powdered limestone,-10kg/m3 chemical admixture composed of a superplasticizer and a viscosity agent. The production of this concrete was followed for one year and the main engineering properties investigated. The 28-day strength was higher than 30MPa and the water-permeability was low, 10-12m/s. 8,000m3 of such concrete were placed within one year and suggested that self-levelling concrete could be an interesting solution to improve the productivity on-site and the quality of buildings.

DOI:

10.14359/5577


Document: 

SP186-15

Date: 

May 1, 1999

Author(s):

G. Xu, J. J. Beaudoin, C. Jolicoeur, and M. Page

Publication:

Symposium Papers

Volume:

186

Abstract:

The effect of varying dosages of a polynaphthalene sulfonate (PNS) superplasticizer on the microstructure of a portland cement paste, and on the microstructural and transition zone characteristics of a portland cement mortar, was investigated using AC impedance spectroscopy. Interpretation of the impedance and resistivity data was carried out in conjunction with data from mercury intrusion porosimetry, scanning electron microscopy, and other techniques. The addition of the PNS superplasticizer influences both the cement paste/sand interfacial region and the bulk paste component in the mortar. The transition zone was more porous at early hydration (around 4 hours) for mortars with high dosages of superplasticzer. The dosage levels also influences the morphology of the hydrates. Larger high frequency arcs and higher electrical resistance values were obtained for all the superplasticized mortars one day and beyond. This suggests a modification in the pore structure and porosity of both the transition zone and the bulk past due to presence of the superplasticizer. Mercury porosimetry, thermogravimetry and conduction calorimetry measurements support the interpretation of the AC impedance spectra.

DOI:

10.14359/5560


Document: 

SP186-12

Date: 

May 1, 1999

Author(s):

M. Simon and J. Elih

Publication:

Symposium Papers

Volume:

186

Abstract:

The paper reports on the results of a research project aimed at assessing the applicability of aggregate from the NE region of Slovenia, where igneous rock is found, for the production of high-strength concrete with high abrasion resistance. A comprehensive investigation has been carried out into the mechanical properties and durability of such concrete, and the results of tests are presented for compressive and flexural strength, modulus of elasticity, abrasion resistance, freezing and thawing durability, shrinkage strain, creep and watertightness. The experimental study takes into account concrete mixtures with W/C varying from .30 to .70 and different chemical admixtures ensuing resistance to freezing and strength increase. No supplementary cementing materials have been used. The study has shown that the investigated aggregate can be used for the production of concrete meeting the requirements for strength and durability set by the relevant standards for concretes used in road pavements.

DOI:

10.14359/5557


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