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International Concrete Abstracts Portal

Showing 1-5 of 267 Abstracts search results

Document: 

18-247

Date: 

July 1, 2020

Author(s):

Nattapong Paewchompoo, Wanchai Yodsudjai, and Prinya Chindaprasirt

Publication:

Materials Journal

Volume:

117

Issue:

4

Abstract:

The objective of this research was to clarify the mechanism of concrete cover cracking time due to reinforcement corrosion in steel fiber-reinforced concrete. An experimental study and analytical study were conducted. For the experimental study, 3 in. (76.2 mm) diameter and 6 in. (152.4 mm) length cylindrical concrete specimens with reinforcement placed in the middle were prepared. Conventional and steel fiber-reinforced concrete with three levels of compressive strength were used in the study. A strain gauge was installed along the specimen’s circumference and the corrosion of reinforcement was accelerated using anodic DC current. Concrete surface strain and impressed anodic current were recorded via a data logger and a multimeter, respectively. Concrete cover cracking time was also investigated. After corrosion acceleration, reinforcement weight loss was evaluated and internal pressure due to the reinforcement corrosion product was calculated. The analytical study was conducted using finite element with four-node bilinear plane strain in a two-dimensional (2-D) model. In the finite element method (FEM) model, the reinforcement was removed and the internal pressure result from the expansion of corrosion products was applied, similar to the problem of cylinder under constant internal pressure. The relationship between concrete surface strain and internal pressure from the analytical study was compared with the experimental study. It was found that corrosion current density of the reinforcement embedded in the fiber-reinforced concrete was higher than that of conventional concrete. Concrete cover cracking time increased with increase of concrete tensile strength. In addition, the relationship between concrete surface strain and the internal pressure could be predicted by the FEM results within an acceptable margin of error.

DOI:

10.14359/51724620


Document: 

18-280

Date: 

July 1, 2020

Author(s):

Vishakha Bisht, Leena Chaurasia, and L. P. Singh

Publication:

Materials Journal

Volume:

117

Issue:

4

Abstract:

This paper investigates and compares the potential of ureolytic and non-ureolytic bacteria in resisting corrosion due to chloride penetration and carbonation. The concrete specimens with and without reinforcement were treated with ureolytic and nonureolytic bacterial strains and exposed to 3.5% NaCl and 2% CO2, respectively, for 90 days. The bacteria-treated reinforced concrete (RC) specimens showed approximately 32% lower corrosion rate, more positive value of Ecorr, and an approximately 26% increase in pullout strength than the control. Field emission scanning electron microscopy (FESEM) of the treated RC revealed thick mineral deposition by bacteria at interfacial transition zone (ITZ), leading to overall densification of the concrete. Moreover, ureolytic and non-ureolytic bacteria-treated concrete showed approximately 60% less carbonation. X-ray diffraction (XRD) revealed additional formation of hydration products and quantification by thermogravimetric (TG) analysis, validating approximately 40% higher CH in carbonated bacterial concrete. Besides calcite, the bacteria mediated additional formation of hydration product (CH) instead of reduction during carbonation, which is believed to be the definite reason of improved ITZ and thus the durability of treated concrete.

DOI:

10.14359/51724610


Document: 

18-320

Date: 

May 1, 2020

Author(s):

Colin B. Van Niejenhuis, Ibrahim G. Ogunsanya, and Carolyn M. Hansson

Publication:

Materials Journal

Volume:

117

Issue:

3

Abstract:

The pore solution expressed from 28-day cement pastes was analyzed as part of a wider research program investigating the corrosion behavior of stainless-steel reinforcing bars in concrete, using inductively coupled plasma and ion chromatography techniques. The pastes were prepared with different water-cementitious materials (binder) ratios (w/cm), portland cement with and without supplementary cementitious materials (SCMs), and with admixed sodium chloride in the range typical of the threshold values for stainless steel reinforcement. The major anion and cation concentrations are given, showing the influence of admixed chloride on the amount of chloride retained in solution and of sulfate released into the pore solution. The results are discussed in terms of the initial compositions of the cementitious materials and their effect on chloride binding.

DOI:

10.14359/51724590


Document: 

18-307

Date: 

May 1, 2020

Author(s):

M. M. Al-Zahrani, K. A. Alawi Al-Sodani, M. Maslehuddin, O. S. Baghabra Al-Amoudi, and S. U. Al-Dulaijan

Publication:

Materials Journal

Volume:

117

Issue:

3

Abstract:

One of several methods used to minimize reinforcement corrosion is the use of service-life prediction models to calculate mixture design and construction variables for the desired service life of a structure. Although several models are available for this purpose, very few incorporate the effect of environmental temperature on chloride diffusion. Moreover, most of the earlier studies were conducted under laboratory conditions and they are not based on actual field data. In the reported study, chloride diffusion in Type V and silica fume cement concretes was evaluated under laboratory and field conditions. Large-size concrete specimens were exposed in the tidal zone of a marine exposure site for 1, 2, 5, and 10 years while the laboratory specimens were exposed to a chloride solution maintained at 22, 35, 50, and 60°C (71.6, 95, 122, and 140°F) for 1 year. The coefficient of chloride diffusion (Da) for Type V cement concrete specimens placed in the field was noted to be much more than that of silica fume cement concrete specimens at all exposure periods. However, the Da for both Type V and silica fume cement concrete specimens decreased by 1.3 to 3 times with increasing period of exposure. The Da for the laboratory concrete specimens increased by 2.2 to 3.8 times as the exposure temperature was increased from 22 to 60°C (71.6 to 140°F). Furthermore, the Da for Type V cement concrete specimens was 2.9 to 5 times more than that of silica fume cement concrete specimens. Empirical models correlating the field and laboratory data were developed. These models could be useful for calculating the Da for field conditions from the laboratory data.

DOI:

10.14359/51724589


Document: 

19-240

Date: 

May 1, 2020

Author(s):

Carolina Boschmann Käthler, Ueli Michael Angst, Karla Hornbostel, and Bernhard Elsener

Publication:

Materials Journal

Volume:

117

Issue:

3

Abstract:

Cracks in concrete are expected to accelerate the degradation of reinforced concrete—mainly reinforcement corrosion. Previous literature studies have shown that the initiation time can decrease due to cracks, whereas the accelerating effect on corrosion propagation has no clear experimental evidence. This paper critically assesses how different common experimental setups may influence the test results. It is found that, particularly, the exposure duration and condition, the water-binder ratio (w/b), and the crack width have an impact on the outcome of the experimental study about corrosion rates in cracked concrete. Hence, these parameters should be carefully considered when designing experiments to study the influence of cracks. Recommendations for future research work are given.

DOI:

10.14359/51722408


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