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Showing 1-5 of 46 Abstracts search results

Document: 

SP186-40

Date: 

May 1, 1999

Author(s):

J. Sebe and J. M. Calixto

Publication:

Symposium Papers

Volume:

186

Abstract:

The results of an experimental investigation on the water permeability of high performance concrete are presented. Several aspects were studied including different components for the concrete as well as the load history for the test specimens. The concrete was made with Brazilian Type CP V ARI cement (ASTM Type III), type different aggregates (limestone and gneiss) and silica fume. The concrete compressive strength was above 50 MPa at 28 days. For the water permeability test, the apparatus developed by Ludirdja et al. at the University of Illinois was employed. Permeability test were subjected to different load histories. In series 1, the applied load was equal to 40% of the ultimate compressive strength, while in series 2 this value was increased to 70%. The secant modulus of elasticity and the splitting tensile strength of the concretes at the start of the permeability test were also evaluated. The test results indicate clearly the effects of the load history on the value of the water permeability coefficient. As the load increases, the value of this coefficient also increases. The results also show that for high-performance concrete produced with Brazilian Type CP V ARI cement, the prescribed compressive strength may be reached in a short period of time, but the long-term water permeability coefficient seems to require a longer time to develop.

DOI:

10.14359/5585


Document: 

SP186-34

Date: 

May 1, 1999

Author(s):

R. C. A. Pinto and K. C. Hover

Publication:

Symposium Papers

Volume:

186

Abstract:

An investigation was performed to study the estimation of modulus of elasticity at early and later ages, as a function of compressive strength and by the maturity approach. The study includes extensive laboratory work, where compressive strength and modulus of elasticity were measured at different ages for a high performance concrete mixture made with two different types of coarse aggregate, and cured at various curing temperatures. Comparison with provisions to estimate the modulus of elasticity given by ACI 318 and the CEB model code are presented, together with the application of the maturity approach to model the development of the modulus of elasticity. It is concluded that the compressive strength-modulus of elasticity relationships in the international codes may be used to estimate the elastic modulus at later ages if correction factors to account for the type of coarse aggregate are used. These relationships, however, were not able to estimate reliable results at earlier ages. The maturity approach was seen to better estimate the modulus of elasticity at early ages.

DOI:

10.14359/5579


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: 

SP186-24

Date: 

May 1, 1999

Author(s):

M. Soeda, T. Yamato, and Y. Emoto

Publication:

Symposium Papers

Volume:

186

Abstract:

This paper presents the results of laboratory studies conducted to determine freezing and thawing and scaling resistance of high-performance concrete. High-performance concretes were made using a combination of different cementitious materials (Blast-furnace slag and silica fume). The water-to-cementitious materials ratio was .27, and the bulk volume of coarse aggregate and fine aggregate per unit volume of concrete were fixed at .50 and .60, respectively. All mixtures used a superplasticizer and were non-air-entrained. Test cylinders were cast for testing in compression at 1 and 28 days, and test prisms were cast for determining resistance to freezing and thawing cycles in accordance with ASTM C 666, Procedure A. and for resistance to scaling from deicing chemicals according to ASTM C 672. The curing methods were water curing and steam curing. The air-void parameters of the hardened concrete were determined on the sawn sections. The test results indicate that non-air-entrained, high-performance concrete with steam curing showed low durability factors. High-performance concrete with water curing performed satisfactorily when subjected to up to 1500 cycles of freezing and thawing. Water-cured, high-performance concrete showed no appreciable scaling after 100 freezing and thawing cycles, showing high resistance to scaling.

DOI:

10.14359/5569


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


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