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Showing 1-5 of 31 Abstracts search results

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


Document: 

SP68-15

Date: 

January 1, 1981

Author(s):

M. Kobayashi, E. Nakakuro, K. Kodama, and S. Negami

Publication:

Symposium Papers

Volume:

68

Abstract:

First, the paper shows the results of microscope analyses of concretes using three high-range water-reducing admixtures of different chemical compositions and having different water-cement ratios and air contents in order to determine the air-void systems of concretes containing high-range water-reducing admixtures, and also discusses the selection of the air-entraining admixture to be jointly used. Secondly, the paper deals with the relation between frost resistance and spacing factor based on the results of rapid freezing and thawing tests on concretes made with high-range water-reducing admixtures and further gives air contents or spac-ing factors required to give concrete adequate resistance to severe frost action. The results of tests on the effects of different kinds of high-range water-reducing admixtures on surface tension, foaming, and stability of air bubbles are given.

DOI:

10.14359/6476


Document: 

SP68-24

Date: 

January 1, 1981

Author(s):

K. Kishitani, F. Tomosawa, and S. Oka

Publication:

Symposium Papers

Volume:

68

Abstract:

In order to consider the workability of superplasticized concrete, it is necessary first to evaluate rheologically the effect of a superplasticizer on fresh cement paste. The authors conducted a series of experiments measuring the resist-ances met by a sphere in motion at various constant speeds in cement pastes, and calculated their rheological constants. It is indicated that the rheological constant of a paste to which superplasticizer has been added is completely different from that of plain paste and also different from pastes with conventional chemical admixtures, and as a result, the superplasticizer can be rheologically defined. Further, in order to clarify the reason for the comparatively rapid slump loss after superplasticizing, the variations in rheological constants due to elapse of time after mixing of cement paste are measured, and it is found that when the addition of the superplasticizer is delayed, the increase in the yield value (rheological constant) is hastened, and it is thus substantiated that the rate of slump loss of concrete is increased when the timing of superplasticizer addition is delayed.

DOI:

10.14359/6485


Document: 

SP68-16

Date: 

January 1, 1981

Author(s):

V. M. Malhotra

Publication:

Symposium Papers

Volume:

68

Abstract:

This investigation was undertaken to determine whether or not the use of superplasticizers can help in the manufacture of semi-lightweight concrete having compressive strengths in excess of 30 to 40 MPa at early ages. Further, the investigation was extended to find if the combined use of superplasticizers and fly ash can produce high strength concrete with moderate cement contents. Three series of concrete mixtures were made using normal portland cement, lightweight coarse aggregate and natural sand. All mixtures were air-entrained and superplasticized except the con-trol mixture which was only air-entrained. In the four mixtures of Series A, cement content ranged from 406 to 443 kg/m3, and test cylinders and prisms were used for strength and durability studies. In the three mixtures of Series B, cement content ranged from 422 to 445 kg/m3, and test cylinders were used for strength determination only. In the two mixtures of Series C, part of the cement was re-placed by fly ash and test cylinders and prisms were cast for the determination of compressive and flexural strengths. The investigation revealed that the use of superplasti-cizers allows the manufacture of semi-lightweight concrete having compressive strengths of the order of 30 and 40 MPa at one and three days respectively. The unit weight of the fresh concrete ranged from 1835 to 1961 kg/m3. In the durability test, the appearance of the test prisms was characterized by a number of aggregate popouts after 300 cycles of freezing and thawing; in one instance, these became numerous after 400 cycles. Notwithstanding the above, the changes in the length of prisms after 400 to 500 cycles of freezing and thaw-ing were well within the accepted limit of 0.07 per cent and the relative durability factors were greater than 99 per cent. It was indicated that the combined use of superplasti-cizers and fly ash can produce high strength semi-lightweight concrete at moderate cement contents. Compressive strengths of 47.6 and 50.7 MPa at 28 and 365 days were obtained for concrete with cement and fly ash contents of 393 and 60 kg/m3 respectively.

DOI:

10.14359/6477


Document: 

SP68-03

Date: 

January 1, 1981

Author(s):

Jiro Murata, Tadashi Kawai, and Katsuro Kokubu

Publication:

Symposium Papers

Volume:

68

Abstract:

The studies reported were concerned with the application of high-strength concrete to structural members as related to some aspects of their design, construction and behavior. With regard to construction, tests were performed on the consistencies and strengths of concretes of low water-cement ratios using superplasticizers. The superplasticizers used were the 5 brands being marketed in Japan. The influence on consistency of fineness of cement was also studied. In examinations made by design calculations, monorail piers were used as case studies. The relation between concrete strength and cross-sectional dimensions, and quality of reinforcing bars required when applying high-strength concrete to structural members were investigated. In structural tests, the stresses, bending strengths and ductilities of model piers using high-strength concrete were studied.

DOI:

10.14359/6464


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