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Showing 1-5 of 11 Abstracts search results

Document: 

SP139-06

Date: 

September 1, 1993

Author(s):

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

Publication:

Symposium Papers

Volume:

139

Abstract:

Numerous methods are available to improve the surface durability of concrete. The most commonly used techniques are improved curing practices and the application of surface treatments. A new technique that employs a controlled permeability formwork liner (CPF) has been introduced in the U.K. This paper describes the results of an investigation to compare the effect of the controlled permeability formwork liner with that of various curing techniques and the absorption of silane in relation to the air permeability, sorptivity, water permeability, and strength of the cover concrete. Also, the resistance to carbonation has been studied. Results indicate that, in general, the use of CPF improves the surface properties compared with conventional steel formwork. The effect of variation of curing methods was marginal for concrete with CPF.

DOI:

10.14359/3899


Document: 

SP139-03

Date: 

September 1, 1993

Author(s):

B. A. Clark, E. A. Draper, R. J. Lee, J. Skalny, M. Ben-Bassat, and A. Bentur

Publication:

Symposium Papers

Volume:

139

Abstract:

Laboratory concrete made under different curing conditions was evaluated using electron-optical techniques. Differences in microstructure and strength were observed in relationship to water-cement ratio, wet/dry curing, temperature of curing, presence of supplementary materials, and mode of preheating. This presentation highlights the partial results of the microstructural evaluation.

DOI:

10.14359/3895


Document: 

SP139-09

Date: 

September 1, 1993

Author(s):

C. T. Tam

Publication:

Symposium Papers

Volume:

139

Abstract:

Concreting of thick sections involves large volume placements for cases such as foundation rafts and beams of exceptional dimensions, which frequently occur in highrise construction in Singapore. The heat of hydration generated in using concrete of structural grade is much higher than that associated with mass concreting of dams. For any thick section, The temperature differential between the warmer interior and the cooler surfaces gives rise to different thermal strains which may be sufficiently high to result in cracking. In hot climates, it also leads to very high peak temperatures (often above 70 C). Typical case histories of such placements in tropical climates are presented, including the mixtures used and the overall dimensions of the members. For two of the cases, the measured temperature histories are compared with those from numerical simulation using finite elements. The requirements of concrete mix design and precautions to be considered in relation to the planning and execution of large placements as well as the use of insulation to control temperature differentials are discussed.

DOI:

10.14359/3902


Document: 

SP139-04

Date: 

September 1, 1993

Author(s):

J. G. Cabrera, T. A. H. Dodd, and S. O. Nwaubani

Publication:

Symposium Papers

Volume:

139

Abstract:

Presents an evaluation of the effects of temperature and type of superplasticizer--high-range water-reducing admixture) (HWRA)--on there rate of chloride-ion diffusion through hydrated superplasticized ordinary portland cement (OPC) pastes and opc + fly ash (PFA) pastes. OPC pastes and OPC/PFA pastes with a water-cementitious materials ratio of 0.31 containing a HRWRA were prepared in the laboratory and cured at 21, 30, and 45 C for different lengths of time, so as to obtain approximately identical compressive strengths. Five different types of HRWRA were used in the study. At the end of the curing period, the specimens were placed in diffusion cells maintained at 30 C and the amount of chloride passing through the pastes was measured. Measurements of total porosity and pore-size distribution were made using helium pycnometry and mercury-intrusion porosimetry. The variations of chloride diffusion coefficients arising from changes in the temperature of curing and type of HRWRA are presented and discussed.

DOI:

10.14359/3916


Document: 

SP139-10

Date: 

September 1, 1993

Author(s):

R. Huyke-Luigi

Publication:

Symposium Papers

Volume:

139

Abstract:

Concrete quality and strength are strongly affected by the curing procedures used in the initial days after concrete is cast. The relative advantage of any particular method and the strength-gain relations must be understood to assess concrete strength and quality adequately. In the present study, the strength gain with age of concrete up to 1 year with different compressive strengths and under different initial and subsequent curing conditions in warm and high-humidity climates was determined. The initial curing techniques evaluated were those most widely used in practice and were intended to represent actual, imperfect construction practice. The subsequent curing conditions were artificially modeled to simulate dry and rainy climates. Of the curing methods evaluated, ponding was found to be the most effective, followed by intermittent sprinkling, unsealed plastic covers, and curing compound. An initial period of three days can develop adequate concrete strength in Puerto Rico's climate; this has a good influence on concrete strength gain with age. Slabs that were kept indoors, and had no contact with water, showed in all cases a decrease in strength under saturated conditions at an age of 1 year, while those maintained outdoors with a rainy climate showed a continuous gain in strength with increasing slope at all times and developing strengths higher than the 28-day strength.

DOI:

10.14359/3903


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