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Showing 1-5 of 31 Abstracts search results

Document: 

SP68-14

Date: 

January 1, 1981

Author(s):

Walter Lukas

Publication:

Symposium Papers

Volume:

68

Abstract:

Concretes display a chloride penetration which is dependent on several factors. The water-cement ratio exerts the most influence, the penetrated chloride content decreasing with a decrease in the ratio. High quality concrete with a low water-cement ratio has a considerably smaller chloride content than otherconcretes of the same consistency. Superplasticized concrete has a smaller tendency to absorb chloride than untreated concretes of the same water-cement ratio. Cements with pozzolanic additions show increased resistance to chloride diffusion into the concrete. If concretes are air entrained there is a considerable chloride concentration in the upper-most zone. This is due both to the greater segregation tendency and to the air voids themselves.

DOI:

10.14359/6475


Document: 

SP68-06

Date: 

January 1, 1981

Author(s):

Hiroshi Tokuda, Masami Shoya, Makoto Kawakami, and Makoto Kagaya

Publication:

Symposium Papers

Volume:

68

Abstract:

This paper describes the results of an investigation to improve the drying shrinkage, thermal diffusivity and coefficient of thermal expansion of comparatively rich-mix concrete by the use of admixtures. Three types of superplasticizers were examined. Shrinkage tests were performed on 100x100x400 mm prismatic speci-mens in a controlled room where the temperature and the humidity were kept at 20°C and at 50 % R.H.. Two series of tests were made, one to make clear the character of shrinkage of concretes of low water-cement ratio and another to examine the effect of dosage of superplasticizer on shrinkage. Thermal diffusivity tests and the tests for the coefficient of thermal expansion were carried out using 10x20 cm cylindrical specimens of gravel concretes having a maximum cement content of 700 kg/m3, and attempts were made to improve these thermal properties by reducing the unit water content by the addition of a certain superplasticizer. It was found that the addition of superplasticizer to reduce the unit water content by about 20 percent, while maintainingthe constant consistency of concrete, gave a maximum increase of thermal diffusivity of more than 14 percent, a maximum decrease of coefficient of thermal ex-pansion of about 7 percent and a maximum decrease of drying shrinkage of almost 12 percent at 350 days drying. It is concluded that a suitable choice and use of superplasticizers should be used more specifically to improve drying shrinkage and thermal properties.

DOI:

10.14359/6467


Document: 

SP68-01

Date: 

January 1, 1981

Author(s):

Kirsten Eriksen and Pal/e Nepper-Christensen

Publication:

Symposium Papers

Volume:

68

Abstract:

Use of a naphtalene-based superplasticizer at high dosages in concretes made with fly ash (100-150 kg/m3) and a moderate content of portland cement (250-300 kg/m3) results in great water reductions and high strengths (75-80 MPa after 28 days) for concretes with normal workability (slump 5-10 cm). Laboratory investigations concerning mixture proportions and pro-perties of the fresh and hardened concretes with a discussion of physical and chemical influences of the use of the superplasticizer are presented. Increasing problems with the supply of good, in-expensive, natural coarse aggregates may be solved through combined additions of superplasticizers and fly ash to the concrete. This paper further presents experimental evidence of mixture proportions and phy-sical data for socalled "sand-concrete", i.e. concrete without coarse aggregates but with "normal" contents of portland cement and water obtained by the addition of rather large amounts of fly ash and superplasticizers.

DOI:

10.14359/6462


Document: 

SP68-26

Date: 

January 1, 1981

Author(s):

Peter Bartos

Publication:

Symposium Papers

Volume:

68

Abstract:

The principle of a free orifice rheometer is used in a development of a device for site-tests of consistency of fresh superplasticized concretes. The new test is designed to complement the '2-point' test and to provide an alternative or even to replace the DIN Flow Table (1) test. Full scale prototype of the Orifice Rheometer was constructed and tests confirmed the capacity of the rheometer to detect differences between fresh flowing mixtures. Using an appropriate orifice the sensitivity of the device was sufficient to indicate excessive bleeding or segregation caused by an overdose of an admixture. Influence of factors such as the composition of a mixture, type and dosage of a superplasticizer on the consistency of a fresh flowing concrete and on its retention were also investigated. In its present form the Orifice Rheometer is a simple, rugged and easily portable apparatus which has provided encouraging results from its first site trials.

DOI:

10.14359/6487


Document: 

SP68-10

Date: 

January 1, 1981

Author(s):

D. H. H. Quon and V. M. Malhotra

Publication:

Symposium Papers

Volume:

68

Abstract:

The introduction of superplasticizers, or high-range water reducers as these are sometimes called, has made it possible to achieve very high slumps in normal portland cement concrete at very low water-to-cement ratios. It was considered that perhaps a similar approach may help to overcome the problems associated with concrete made with high-alumina cement. This report gives results of a brief investigation undertaken to determine the effect of superplasticizers on the consistency, compressive strength and degree of conversion of high-alumina cement concrete. Three commercially available superplasticizers were added to high-alumina cement concrete mixtures with a water-to-cement ratio of 0.36. The slump test was used as a measure of consistency. Compressive strength was obtained on 102 x 203~mm cylinders and the degree of conversion was determined using differential thermal analysis. In spite of dosages of 3% or more by weight of cement, concrete having flow characteristics was not obtained. In addition, there was extremely rapid slump loss, the concretes, reverting to their original slump in less than 20 minutes. At the ages of 10 hours, 1 and 2 days, the compressive strength of concrete incorporating superplasticizers was considerably lower than the strength of the control concrete. At 180 days 9 the strengths of the superplasticized and the control concretes were comparable, reaching a value of the order of 80 MPa. The addition of the superplasticizers to high-alumina cement concrete did not affect the rate of conversion of the high-alumina cement; the degree of conversion values for the superplasticized and the control concretes was less than 30% at 180 days.

DOI:

10.14359/6471


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