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International Concrete Abstracts Portal

Showing 1-5 of 23 Abstracts search results

Document: 

SP131-07

Date: 

March 1, 1992

Author(s):

Sidney Diamond and Michael Penko

Publication:

Symposium Papers

Volume:

131

Abstract:

Among the important stages of the overall SR process as it occurs in concrete is the conversion of alkali sulfate dissolved from the cement to alkali hydroxide. The results of laboratory studies are presented to provide an understanding of this process and its effects. This conversion process depends on continued formation of ettringite and does not take place until the cement gypsum is exhausted. Provision of a large excess of gypsum or interference with early ettringite production by high-temperature exposure may postpone or prevent it, thus reducing the OH - ion concentration and the possibility of ASR reaction.

DOI:

10.14359/1206


Document: 

SP131-01

Date: 

March 1, 1992

Author(s):

V. Ukraincik and D. Bjegovic

Publication:

Symposium Papers

Volume:

131

Abstract:

The greatest threat to the durability of reinforced concrete structures is the reinforcement corrosion. The paper presents the importance of the concrete protective cover and the conditions causing the reinforcement corrosion under the action of chlorides and carbonic acid. Processes of absorption, diffusion and flow, i.e. of transport of media through concrete depend on the pore system and the amount of water in the pores.Physical laws describing the penetration of aggressive agents into concre-te can serve as a basis for engineering calculations of reinforcement durability in the concrete as well as for the designing of the concrete cover. Physical laws and corresponding material parametars are briefly reviewed in the paper. For engineering purposes, in calculating the durability, four typical tasks can be solved. The processes of degradation depend on the pore system in the concrete structure, and the paper indicates some possible technological measures of structure modifications.

DOI:

10.14359/10025


Document: 

SP131-05

Date: 

March 1, 1992

Author(s):

F. R. Montgomery, P. A. M. Basheer and A. E. Long

Publication:

Symposium Papers

Volume:

131

Abstract:

Good curing is now recognized as essential to achieving good durability of concrete and other cementitious material surfaces. However, it has not been easy to judge whether or not it has been achieved on site, so surface failures continue to occur. The Department of Civil Engineering at the Queen's University of Belfast is developing a number of test techniques to allow the measurement of surface strength, surface absorption and permeability, and surface abrasion-resistance of structures on site. These have been used to assess the performance of various curing regimes for concrete and mortar, first to see if the test methods can extract meaningful measurements of durability-related properties, and secondly to get an indication of the magnitude of the changes in these properties for different curing regimes and water-cement ratios. It is hoped that they may eventually provide a means to assess a surface in terms that could allow an objective judgment of its durability.

DOI:

10.14359/1204


Document: 

SP131-11

Date: 

March 1, 1992

Author(s):

A. A. Ramezanianpour

Publication:

Symposium Papers

Volume:

131

Abstract:

A laboratory study on the durability of OPC and trass-OPC mortars and concretes is presented. A natural pozzolan of volcanic origin obtained from the Demavend area in Iran and known as "trass" is used to substitute 20 percent of the OPC content of mortar and concrete. The performance of the material is evaluated by measurements of total porosity. Pore-size distribution and permeability are given in relation to their response to aggressive chloride and sulfate concentrated solution, and also CO 2 gas. The carbonation data is used to formulate a performance-time function, which is proposed as a model to assess durability of the mortars and concretes.

DOI:

10.14359/1210


Document: 

SP131-04

Date: 

March 1, 1992

Author(s):

M. J. Simon, R. B. Jenkins, and K. C. Hover

Publication:

Symposium Papers

Volume:

131

Abstract:

Experiments were conducted to determine the influence of immersion vibration on the air-void system parameters of air-entrained concrete, as a function of both radial distance and depth from the point of vibrator insertion. For a 1½ in. (40 mm) diameter immersion vibrator, one could conclude that vibration has little or no effect on air-void systems at distances of 5, 8, or 10 in. (125, 200, or 250 mm) from the point of insertion. The same vibrator in the same concrete can reduce the total air content by 50 percent, and increase specific surface by as much as 100 percent directly at the point of vibrator insertion. Which particular effect one may observe in hardened concrete, therefore, depends on the selection of core location relative to point of vibrator insertion. These observations have implications for specifying, casting, and testing air-entrained concrete.

DOI:

10.14359/1203


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