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International Concrete Abstracts Portal

Showing 1-5 of 34 Abstracts search results

Document: 

SP119-20

Date: 

September 1, 1989

Author(s):

N. S. Berke and l. R. Roberts

Publication:

Symposium Papers

Volume:

119

Abstract:

Steel is used widely in reinforced concrete for its structural properties and because the alkaline environment normally protects the steel from corrosion. However, this alkalinity does not protect steel in the presence of chloride ions. Furthermore, in environments subjected to freezing and thawing, durability can also be affected severely. The corrosion resistance of embedded metals can be improved by the use of concrete admixtures. Calcium nitrite improves corrosion resistance by promoting passivity of metals in concrete. Superplasticizers reduce chloride ingress by allowing the use of lower water-cement ratios. Microsilica (silica fume) substantially increases concrete resistivities as well as lowering permeability to chloride. In this paper it is demonstrated how various combinations of these admixtures improve the corrosion resistance of steel in concrete, while giving greatly improved strengths, necessary freeze-thaw resistance, and handling properties conducive to rapid placement and consolidation.

DOI:

10.14359/2536


Document: 

SP119-21

Date: 

September 1, 1989

Author(s):

T. Nawa, H. Uchi, and Y. Fukaya

Publication:

Symposium Papers

Volume:

119

Abstract:

The influence of alkali sulfate on the viscosity of cement paste containing a superplasticizer was studied by using rotational viscometer. The mechanism of the action of superplasticizer on the fluidity of cement paste was also investigated. A larger amount of superplasticizer was rapidly adsorbed onto C3A and C4AF compared to that on C3S and C2S. The presence of alkali sulfate inhibited the adsorption of superplasticizer on C3A and C4AF, thus permitting increased adsorption on C3S and C2S. The reduction of viscosity of cement paste by superplasticizer is dependent mainly on its adsorption onto C3S and C2S. Therefore, an increase in alkali sulfate leads to an increase in the adsorption of superplasticizer on C3S and C2S, and results in reduced viscosity of cement paste. Excessive amount of alkali sulfate, however, compressed the electric double layer, providing an increase in viscosity of cement paste. Based on the results, it was concluded that there was an optimum alkali sulfate level with respect to the fluidity of cement paste containing the superplasticizer.

DOI:

10.14359/2541


Document: 

SP119-22

Date: 

September 1, 1989

Author(s):

M. Collepardi, S. Monosi, and M. Valenti

Publication:

Symposium Papers

Volume:

119

Abstract:

Purpose was to optimize the type and dosage of superplasticizer in concretes incorporating ASTM Class F fly ash, so that compressive strengths as high as those of superplasticized silica fume concretes could be obtained. Two types of high-range water reducers based on sulfonated naphthalene polymer (SNP) and sulfonated melamine polymer (SMP) both as 40 percent aqueous solution have been used in the presence of fly ash or silica fume to manufacture superplasticized flowing concretes containing ASTM Type I or Type III portland cements. The superplasticizer dosage and the pozzolan addition ranged from the 2 to 4 percent and from 12 to 20 percent, respectively, by weight of cement. The cement factor varied from 255 to 400 kg/m3. The results of the investigation work indicate that only in the presence of ASTM Type III portland cement, superplasticized fly ash concrete can be as strong as the corresponding silica fume concrete, particularly at relatively high cement factors ( ò 300 kg/m3).

DOI:

10.14359/2543


Document: 

SP119-23

Date: 

September 1, 1989

Author(s):

S. Nishibayashi, A. Yoshino, S. Hideshima, M. Takada, and T. Chikada

Publication:

Symposium Papers

Volume:

119

Abstract:

Describes an experimental study of mix designs and characteristics of fresh and hardened superplasticized concrete containing high volumes of blast furnace slag. Results show that using superplasticized concrete in a mix design with a large amount of blast furnace slag allows a lower water content than that of the base concrete, a lower superplasticizer dosage to attain the same increase in slump, and a somewhat lower percentage of fine aggregate. Also, the compressive strength of the hardened concrete was as high as that of the nonsuperplasticized concrete.

DOI:

10.14359/2545


Document: 

SP119-24

Date: 

September 1, 1989

Author(s):

C. Atzeni, G. Mantegazza, L. Massidda, and U. Sanna

Publication:

Symposium Papers

Volume:

119

Abstract:

Results of tests on modified cement mortars admixed with naphthalenesulfonate and acrylic latex used for repairs are presented. Theological and mechanical properties as well as durability have been measured. The combined use of polymer latex and naphthale

DOI:

10.14359/2546


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