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Showing 1-5 of 62 Abstracts search results

Document: 

SP179-07

Date: 

June 1, 1998

Author(s):

T. Yamato, Y. Emoto and M. Soeda

Publication:

Symposium Papers

Volume:

179

Abstract:

This paper presents the results of an investigation to determine the performance characteristics of concrete made with recycled coarse aggregate from a plant. Slump and air content of fresh recycled aggregate concrete are studied. The compressive strength, drying shrinkage and resistance to freezing and thawing were investigated experimentally when the types and combinations of coarse aggregate, admixture, air content and so on were varied. It was found that the recycled aggregate concrete decreased the compressive strength at 7 to 28 days as compared with those properties of the control concrete. The decrease in strength can be suppressed low by partial use of recycled coarse aggregate. Drying shrinkage of recycled aggregate concrete showed larger value than conventional crushed aggregate concrete. The use of shrinkage reducing agent can reduce the drying shrinkage of recycled aggregate concrete. The resistance to freezing and thawing of recycled aggregate concrete was lower than that of control concrete of similar composition. The decrease in resistance to freezing and thawing can be suppressed low by partial use of recycled aggregate, reducing W/C and increasing entraining air.

DOI:

10.14359/6034


Document: 

SP179-25

Date: 

June 1, 1998

Author(s):

K. Fujii. M. Kakizake, H. Edahiro, Y. Unisuga and Y. Yamamoto

Publication:

Symposium Papers

Volume:

179

Abstract:

Meeting the needs of urban development, high strength concrete has made remarkable progress where the standard concrete strength of 60 MPa level is attained with the help of high performance AE water-reducing agents. High strength lightweight concrete could be more advantageous with respect to the reduction of dead load and resulting construction cost reduction, and has been successfully applied to marine concrete constructions. This paper deals with the high strength, high fluidity lightweight concrete with bulk densities from 1.8 to 2.0 t/m3 and compressive strength from 60 to 90 MPa manufactured with belite-rich low heat cement and silica fume cement, and discusses the influences of materials and mixture proportions upon the properties of fresh and hardened concretes. Compressive strength with a water-cement ratio of 0.23 was 65 to 79 Mpa when silica fume blended cement was used, and was 59 to 68 MPa when belite-rich low heat cement was used.

DOI:

10.14359/6052


Document: 

SP179-14

Date: 

June 1, 1998

Author(s):

M. Shoya, S. Sugita, Y. Tsukinaga, M. Aba and M. Ohba

Publication:

Symposium Papers

Volume:

179

Abstract:

In recent years, especially in Japan, various types of chemical admixtures have been developed, with emphasis on making highly durable concrete and on developing the highly flowable concrete for labor-saving. In this paper, one kind of water-repellent admixture incorporating highly reactive silica powder, denoted as WRP, was examined to confirm its effect on various concrete properties. The concept is not only to prevent water penetration due to water repellency provided by the siloxane compound but also to compensate for the hindered hydration due to its adsorption to cement particles by the use of the highly reactive pozzolanic material. The efficacy of the admixture was confirmed as to its ability reducing the water permeability with little lowering of mechanical properties dependent on the dosage of WRP. From the tests for carbonation, drying shrinkage, resistance to freezing and thawing and the air-void systems, the effect of WRP was confirmed as satisfactory for those properties.

DOI:

10.14359/6041


Document: 

SP179-33

Date: 

June 1, 1998

Author(s):

T. Katayama

Publication:

Symposium Papers

Volume:

179

Abstract:

Thin-section petrography, coupled with quantitative electron-probe microanalysis, is very useful in identifying reactive constituents and alkali-aggregate reaction in concretes, as well as in characterizing the nature of cement constituents, reaction products and gel products in old deteriorated concretes. EPMA analysis made it possible to detect chemical compositions of the unhydrated cement phases alite, belite, tricalcium aluminate, and the ferrite phase in the original cement used in old structures from Canada and Japan, made even 100 years ago. Coupled with detailed petrography in thin section, this technique also enabled us to estimate the thermal histories and composition of cement clinkers in hardened concretes, variations of CSH gels which reflect the degree of cement hydration, leaching and weathering of concretes, as well as the process of migration and alteration of ASR gels in concretes. The results thus obtained can be used for the assessment of cement properties and the durability of old concretes.

DOI:

10.14359/6060


Document: 

SP179-56

Date: 

June 1, 1998

Author(s):

K. Fujii, T. Kemi, G. Shimizu, M. Sakuta and Y. Unisuga

Publication:

Symposium Papers

Volume:

179

Abstract:

High fluidity concrete has been used to meet requirements for the marine construction thanks to its superior durability and ease of placing. High-fluidity concrete is, however, so viscous and has less bleeding to have the cold joint that may harm the uniformity of the structure. We have executed series of experiments to study the effect of interval and method of making joints on the strength of placing-joint of 5 types of high-strength and high-fluidity concrete and high-fluidity lightweight concrete for the marine construction . The strength of the placing-joint has shown no substantial degradation compared to those without placing-joint by rodding the joint within 120 minutes after the first placing under an ambient temperature of 20 C, while specimens without rodding, cured under the standard water bath, have shown 2/3 of the strength of those without placing-joint at an interval of placement less than 60 minutes.

DOI:

10.14359/6082


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