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The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.

Showing 1-5 of 31 Abstracts search results

Document: 

SP68-22

Date: 

January 1, 1981

Author(s):

V. S. Ramachandran

Publication:

Symposium Papers

Volume:

68

Abstract:

a few as Ca-acid, concre Of the slump in mor Superpla hours. The e lignosulfonat Na-heptonate te containing se admixtures loss; the inf tars was also sticized concrete 1 ffect of different , sucrose, Na-glut and Na-boroheptonat sulfonated melamin Na-gluconate prov luence on setting t examined. oses its workability within amounts of admixtures, such onate, citric acid, salicylic, on the slump loss of formaldehyde is reported. to be the best retarder of times and strengthdevelopment

DOI:

10.14359/6483

Document: 

SP68-23

Date: 

January 1, 1981

Author(s):

James S. Hampton

Publication:

Symposium Papers

Volume:

68

Abstract:

Normally in hot weather, it is difficult to maintain the workability of concrete containing high-range water-reducing admixtures (H-R W-RA) as the concrete temperatures approach 85 - 90°F(29 to 32oC). The loss of fluidity and workability often occurs within 30 min. after the introduction of the adrnix-ture making placement and pumping very difficult if there are delays. This paper discusses how certain modified H-R W-RA may be used to provide fluidized concrete with prolonged work-ability.

DOI:

10.14359/6484

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: 

SP68-25

Date: 

January 1, 1981

Author(s):

Shinzo Nishibayashi, Kiyoshi Yamura, and Shoichi lnoue

Publication:

Symposium Papers

Volume:

68

Abstract:

Generally the flow of fresh concrete is assumed to represent distortion as a Bingham body. In this study, in order to clarify the effects of chemical ad-mixtures on the flow of fresh concrete, rheological values such as the plastic viscosity and yield value (shearing stress) of fresh paste and mortar with superplasticizer were experimentally investigated both with and without vibration, Four types of chemical admixtures, sulfonated naphthalene-formaldehyde condensates, sulfonated melamine-formaldehyde conden-sates, poly-condensed aromatic sulfonate and a conventional water reducing agent (modified lignosulfonate) were used, and various water/cement ratio, sand/cement ratio, and consistencies, with and without chemical admixture, were selected for the mix pro-portions of test samples. The apparatus used in this study was designed to conduct experiments on the rheological phenomenon of fresh concrete under vibration. The frequencies of vibration em-ployed were 0, 100, 120, 150 and 180 Hz with accelerations of 0, 2, 4 and 6g. The plastic viscosity and yield value of vibrating cement paste and mortar through which a sphere moves can be calculated from Stokes's law. The results obtained have provided useful in-formation for identifying the fundamental rheological properties of the plasticizing concrete.

DOI:

10.14359/6486

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

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