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International Concrete Abstracts Portal

Showing 1-5 of 27 Abstracts search results

Document: 

SP159-14

Date: 

February 1, 1996

Author(s):

R. Narayan Swamy

Publication:

Symposium Papers

Volume:

159

Abstract:

Although the cement-paste matrix is intrinsically protective to steel, it also permits the ingress of deleterious agents that leads to its own progressive deterioration and consequent destabilisation of steel. Further, the development of a highly impermeable cement matrix, per se, may not ensure a high- performance concrete structure in practice, since the development of strength and pore structure are both time-dependent phenomena and aggressive elements somehow find a means of penetrating concrete and initiate a cumulative process of structural damage. This paper advocates an integrated design philosophy from concept to completion and during service life of a concrete structure. It is shown that by selecting concrete constituents that encourage synergic interactions, it is possible to develop a concrete matrix of high strength and excellent durability. However, concrete also needs to be protected from aggressive agents to enable it to attain its full potential and examples are given to show how such techniques can be adopted to ensure durable service life even in the most unfriendly environment. The application of this integrated design strategy is further illustrated with the design of columns exposed to alkali-silica reactivity and the production of cost-effective, fiber-reinforced thin sheets.

DOI:

10.14359/1528


Document: 

SP159-19

Date: 

February 1, 1996

Author(s):

Rajendra K. Navalurkar and Farhad Ansari

Publication:

Symposium Papers

Volume:

159

Abstract:

Properties of high strength concrete under uniaxial states of stress were studied. Main emphasis was given to tensile, compressive, and fracture properties of concrete with compressive strengths ranging from 6000 to 12000 PSI. Complete stress-deformation curves under uniaxial tension were obtained using a closed-loop servo-hydraulic testing system. Important mechanical and fracture properties such as moduli of elasticity, fracture energy, and the critical crack tip opening displacements, were evaluated from the experimental results. Fracture energies were evaluated from the descending branch of stress-crack separation curves using the direct tension test results. For the range of high-strength concretes studied, experimental results indicate that the relationship between tensile and compressive strengths are different from those of normal strength concretes. Comparison of stress-deformation curves in tension reveals a significant decrease in post peak compliance of the higher strength concretes.

DOI:

10.14359/1429


Document: 

SP159-24

Date: 

February 1, 1996

Author(s):

Antoine E. Naaman and Fadi M. Al-Khairi

Publication:

Symposium Papers

Volume:

159

Abstract:

This paper provides a summary of part of the results of SHRP project C-205 on the Fresh and Hardened Properties of High Early Strength Fiber Reinforced Concrete (HESFRC). HESFRC was defined as achieving a minimum target compressive strength of 5 ksi (35 MPa) in 24 hours. Fresh HESFRC properties included air content, inverted slump test, temperature, and plastic unit weight. Tests on the mechanical properties included compressive strength, elastic modulus, flexural strength, splitting tensile strength, and fatigue life. Seventeen different combinations of parameters were investigated for each type of test. The main parameters included: (1) three different matrix mixtures (one control, one with silica fume, and one with latex), (2) two different volume fractions of fibers (1 percent) and (2 percent), (3) two fiber materials (steel and polypropylene), (4) two steel fiber lengths corresponding to aspect ratios of 60 and 100 respectively, and (5) hybrid mixes containing either an equal amount of steel and polypropylene fibers, or an equal amount of steel fibers of different lengths. The compression and the bending tests also included a time variable; the compressive properties were measured at ages 1, 3, 7, and 28 days, and the bending properties at ages 1, 7, and 28 days respectively. Information from the compression tests comprised the compressive strength, the elastic modulus, and the strain capacity. Information from the bending tests included the modulus of rupture and the toughness indices as per ASTM standards. Optimum mixtures that satisfied the minimum compressive strength criterion, and showed excellent values of modulus of rupture, toughness indices in bending, and fatigue life in the cracked state are identified. Potential applications in repair, rehabilitation, or construction of transportation structures are suggested. In this paper a description is given of key results of the bending tests only.

DOI:

10.14359/1430


Document: 

SP159-10

Date: 

February 1, 1996

Author(s):

H. M. Cheyrezy

Publication:

Symposium Papers

Volume:

159

Abstract:

This paper reviews the developments of HPC in France for the past ten years in bridges, buildings, tunnels, offshore platforms, and nuclear containers. Different projects are presented wherein 55 to 80 MPa concretes were used. The motivation for using HPC are many. The future developments initiated by owners, public research institutes, consultants, and contractors are documented and innovative materials are introduced, as well as research program initiated by different laboratories.

DOI:

10.14359/1596


Document: 

SP159-20

Date: 

February 1, 1996

Author(s):

Pierre-Claude Aitcin and Moussa Baalbaki

Publication:

Symposium Papers

Volume:

159

Abstract:

High-performance concretes (HPC) characterized by a low water/binder ratio and generally high binder content which may include supplementary cementing materials, are used increasingly in the worldwide construction industry for technical or economical reasons as well as for their improved durability. The development and the use of such a high performance material necessitate some drastic readjustments within the construction industry. Concrete should not be envisaged as a commodity material that has to be produced with the cheapest materials and placed and cured in the cheapest ways. Concrete should rather be considered as an elaborate material for which constituents are carefully selected in order to achieve the desired performance. Of special importance are the selection of a compatible cement/superplasticizer combination and clean, strong, and well shaped aggregates. The use of cementitious materials should be considered not only because they can reduce the production cost of high performance concretes but also because they can be technically advantageous. Making and using HPC necessitate the implementation of a strong and efficient quality control program on the materials used to make the concrete, on the properties of the fresh and hardened concrete, and on the placing and curing techniques in order to be sure of obtaining a high performance final product. Testing high performance concrete necessitates great care and special attention.

DOI:

10.14359/1603


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