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International Concrete Abstracts Portal

Showing 1-5 of 39 Abstracts search results

Document: 

SP121-02

Date: 

November 1, 1990

Author(s):

H. Aoyama, T. Murota, H. Hiraishi, and S. Bessho

Publication:

Symposium Papers

Volume:

121

Abstract:

A National Project lasting five years has been promoted by the Ministry of Construction of Japan since 1988 to develop super high-rise reinforced concrete buildings in seismic zones. The strength of concrete and reinforcing steel bars ranges from 30 to 120 MPa (4.3 to 17.4 ksi) and from 400 to 1200 MPa (58 to 174 ksi), respectively. The following is investigated in the Project: 1) production, quality control, and placement of high-strength concrete; 2) production of high-strength steel bars; 3) mechanical properties of high-strength concrete and steel bars; 4) behavior of members and subassemblages; and 5) structural design methodology.

DOI:

10.14359/3638


Document: 

SP121-20

Date: 

November 1, 1990

Author(s):

Magne Maage, Sverre Smeplass, and Randulf Johansen

Publication:

Symposium Papers

Volume:

121

Abstract:

Use of silica fume is important to produce high-strength concrete. Possible negative effects on long-term properties are, therefore, of vital interest for the future development of high-strength concrete. It has been reported that silica fume concrete stored in air showed strength loss from 90 days to 5 years, but courses are not discussed. The report was based on a limited number of results. Similar results are not found in high-strength concrete up to 10 years old either in laboratory tests or testing samples from existing structures in Norway. Results from two major research projects showed that, for laboratory-stored specimens, the strength increased or was constant for concrete stored in water or air, respectively. No difference was found between high- and normal strength concretes. The increase was somewhat higher for concretes without silica fume compared to concretes with up to 20 percent silica fume by weight of cement. Furthermore, the strength increase was somewhat higher for water-stored concretes than for air-stored. However, high-strength silica fume concrete was not more sensitive to early drying than concrete without silica fume. High-strength concrete from several existing structures did not exhibit the same consistent pattern in strength development, however. This is probably due to insufficient documentation at an early age. However, the results did not show any significant negative long-term strength development.

DOI:

10.14359/2552


Document: 

SP121-34

Date: 

November 1, 1990

Author(s):

M. Berra and G. Ferrerra

Publication:

Symposium Papers

Volume:

121

Abstract:

Reports on high-strength lightweight and normal weight concretes. Sintered fly ash lightweight aggregates, crushed limestones, and two types of cement with different contents were investigated. All the concretes contained silica fume and a high-range water-reducing admixture. To obtain high specific strengths (i.e., ratio of strength to relative density), lightweight concretes were prepared with only lightweight particles (coarse and fine), reaching strengths higher than 60 MPa with density of about 1700 kg/m3. The results of physical (permeability, thermal conductivity, thermal diffusivity, and thermal expansion coefficient) and mechanical (compression, direct tension, direct shear, modulus of elasticity, bond strength, fracture energy, and compression softening behavior) tests, carried out on specimens cured for different ages at two curing conditions (20 C and 95 and 50 percent relative humidity, respectively), are reported and discussed.

DOI:

10.14359/2576


Document: 

SP121-29

Date: 

November 1, 1990

Author(s):

Norio Marushima, Kenji Kuroha, and Kuniyiki Tomatsuri

Publication:

Symposium Papers

Volume:

121

Abstract:

High-strength concrete tends to mean small water-cement rations, implying poor workability. This tendency becomes more pronounced when much higher strength is required, and conventional concreting processes cannot sufficiently guarantee high-quality work. In current construction work, therefore, maximum use has been made of precast concrete (guaranteeing quality and minimizing the need for concrete cast in situ) and a new high-performance, air-entraining, and plasticizing admixture has been used for the necessary in situ concrete. The concrete prepared in this way exhibited a mix strength of 55 MPa at best. This value, in itself, is by no means high, but meaningful efforts to establish methods of concreting that insure still greater strength have been made. This construction work has demonstrated that combining the reinforced concrete (RC) layer method (which uses a large proportion of precast members) with high-strength concrete obtained from mixing with the new high-performance, air-entraining, plasticizing admixture is an extremely effective way to secure quality structures. Since this admixture is a novel product, the physical properties of the resulting concrete have been thoroughly checked to supplement the results of laboratory experiments and preliminary field tests.

DOI:

10.14359/3758


Document: 

SP121-38

Date: 

November 1, 1990

Author(s):

Kaare K. B. Dahl

Publication:

Symposium Papers

Volume:

121

Abstract:

Presents the results of an investigation undertaken at the Technical University of Denmark to determine the parameters that affect the ultimate load capacity of a concrete structure subjected to concentrated loads originating from reinforcement bars bent 90 deg. The following parameters have been found to have a decisive influence on the ultimate load capacity of the concrete bar: bar diameter, internal height of the specimen, side concrete cover, and concrete compressive strength. The results show that the relative load-carrying capacity of the concrete åc / fc decreases for increasing concrete compressive strength. However, the use of high-strength concrete (HSC) still results in an increase in the absolute load-carrying capacity of the concrete whencompared to normal strength concrete (NSC).

DOI:

10.14359/2870


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