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International Concrete Abstracts Portal

Showing 1-5 of 81 Abstracts search results

Document: 

SP170-17

Date: 

July 1, 1997

Author(s):

Z. Tian Chang and M. Marosszeky

Publication:

Symposium Papers

Volume:

170

Abstract:

The resistance to chloride penetration is one of the prime parameters in specifying concrete in marine applications and in a quality assurance scheme during construction. The aim of this research was to compare alternative accelerated laboratory test procedures for the assessment of chloride penetration into concrete containing supplementary cementitious materials. Three binder systems, a normal portland cement (PC), one with 30% fly ash and a third with 50% slag, were investigated under three curing conditions, 7 days water curing, air curing, and 12 hours 65 C water curing. Chlorides penetration was measured by static ponding (5% NaCl solution) and cyclic ponding (2%, 5% and 15% NaCl solutions with 12 hour wetting and drying cycles). The effect of the age at start of testing and the test duration were also investigated. The water absorption was tested by measuring weight gain, and the results were compared with that of the chloride penetration tests. It was found that the cyclic ponding test with 15% NaCl solution resulted in accelerated chloride penetration and a clearer chloride penetration front compared to the use of 2% and 5% NaCl solutions. Good correlation was found between the results from cyclic chloride ponding and static ponding. While the chloride penetration depth was found not vary significantly with test age from 7 to 56 days for all the three mixes, the increase of chloride penetration with the test duration from 3 to 14 days was much pronounced for the PC mix than the fly ash and slag mixes. The chloride penetration was highest in the air cured specimens and the lowest in the water cured specimens for all the three mixes, and the slag concrete had the lowest chloride penetration within the three mixes under each of the three curing conditions. It was also found that water absorption correlated poorly with chloride penetration.

DOI:

10.14359/6830


Document: 

SP170-54

Date: 

July 1, 1997

Author(s):

P. A. M. Basheer, A. McCauley and A. E. Long

Publication:

Symposium Papers

Volume:

170

Abstract:

This paper reports results of an investigation in which the effect of moisture condition of concrete at the time of application of silane on permeation and durability characteristics of concrete was determined. T h e permeation properties (i.e. air permeability and sorptivity) were measured with the Autoclam permeability system, an apparatus developed at Queen’s University of Belfast. The durability characteristics were determined in terms of chloride penetration and carbonation. Also, a comparison of the performance of silane was made with that of a controlled permeability formwork system. The results indicated that the moisture condition of concrete at the time of application of silane does not affect its protective properties to any significant degree. Silane’s performance was comparable with, or better than, that of the controlled permeability formwork in terms of sorptivity and chloride penetration at three moisture conditions included in the investigation. However, silane was found to have relatively little benefit in terms of carbonation resistance in accelerated tests, surface tensile strength and air permeability of the near surface concrete. The use of controlled permeability formwork resulted in improvements in these properties as well.

DOI:

10.14359/6867


Document: 

SP170-47

Date: 

July 1, 1997

Author(s):

H. Yamashita, K. Sakai and T. Kita

Publication:

Symposium Papers

Volume:

170

Abstract:

Frost damage of concrete gradually proceeds due to freezing and thawing of water in pore structure. The main cause is the expansion of frozen water, which is influenced by pore size distribution and air void spacing factor. This study focuses on the pore size distribution and the air void spacing factor. Freezing and thawing tests were conducted and the expansion was measured. Based on the test results, a strain model was proposed. Furthermore, the pore size distribution and the air void spacing factor were measured for different areas of an actual structure, and the degree of deterioration in the structures was compared with the expansion volume calculated using the model. It is found that the strain model represented the frost-resistance of concrete taking into account the difference of the pore size distribution and the air void spacing factor. That model also simulated the deterioration of an actual structure.

DOI:

10.14359/6860


Document: 

SP170-75

Date: 

July 1, 1997

Author(s):

Yves Lefebvre, Carmel Jolicoer, Monique Page and Phil T. Seabrook

Publication:

Symposium Papers

Volume:

170

Abstract:

The degradation of samples of cement pastes, mortars and concretes in acidic solutions (pH 2-4) ha s b een investigated over relatively short periods, e.g. -72 hours at 25°C. The degradation rate of the cementitious material is taken as the rate of alkali leaching at constant pH; the latter is obtained directly from the amount of acid required, as function of time, to maintain the pH at a preset value. The data allow the calculation of apparent rate constants, the magnitude of which is expected to be related to the durability of the materials investigated in acidic environments. Paste degradation rates were obtained at two W/C (0.35 and 0.45); the role of several additives (silica fume, superplasticizers, air entraining agents) and the influence of solution composition (pH, ionic strength, other electrolytes) were investigated. Kinetic data were also obtained for the acid reaction rate of several mortar and concrete samples of varying mixture compositions and in the presence of S0,-2. Under the conditions of this study, the acid degradation rate appears largely controlled by H+ diffusion through the leached zone of the matrix. The diffusional rates values are moderately influenced by changes in mixture compositions, in reasonable agreement with expectations from greatly enhance the acid degradation rate, an effect zone and the related studies. Sulfate ions which can be understood from pH gradients in the leached activity coefficients of the H+ in the presence of sulfates.

DOI:

10.14359/6888


Document: 

SP170-74

Date: 

July 1, 1997

Author(s):

N. Suzuki, T. lisaka, H. Umehara and S. Shiramura

Publication:

Symposium Papers

Volume:

170

Abstract:

At the early stages of development, RCD concrete often tended to be inferior in strength and durability to any other conventional dam concrete because RCD concrete had the properties of stiff consistency and lean mixture. In this research, a laboratory test was conducted to determine its optimum sand percentage, sand ratio and optimum mixture proportions in order to improve durability of RCD concrete. In addition, a field test was conducted to determine the optimum lift height and optimum compacting method. Furthermore, a new construction method was developed to improve durability of RCD concrete that any existing RCD concrete can be strengthened by casting one of the conventional types of dam concrete on the upstream or downstream slope of the dam. Hence the proposed method in combination with the recommended mixture proportions and construction method has enabled one to rebuild many of the dams and to keep then in serviceable condition for a long time.

DOI:

10.14359/6887


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