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International Concrete Abstracts Portal

Showing 1-10 of 262 Abstracts search results

Document: 

19-080

Date: 

March 1, 2020

Author(s):

Kangkang Tang

Publication:

Materials Journal

Volume:

117

Issue:

2

Abstract:

Steel fiber-reinforced concrete (SFRC) can be an ideal substitute for conventional steel reinforcement in railway tunnel lining construction due to its high strength and good fire resistance. On the other hand, it is still not clear whether discontinuous steel fibers can pick up and transfer stray current and lead to similar corrosive attack as that occurs in conventional steel reinforcement. These were evaluated through voltammetry tests and electrochemical impedance spectroscopy (EIS) before and after simulated railway stray direct current (DC) and alternating current (AC) interferences. In addition to instrumental methods in electrochemistry, numerical modeling based on the boundary element method (BEM) modeling indicates that discrete steel fibers can pick up and transfer stray currents. This was validated by the electrochemical investigations conducted using both aqueous and solid (mortar) electrolytes. It can be concluded that steel fibers have high corrosion resistance to stray AC and DC interferences even with the presence of a small amount of NaCl in the electrolyte.

DOI:

10.14359/51720303


Document: 

19-181

Date: 

March 1, 2020

Author(s):

Robert E. Melchers and Igor A. Chaves

Publication:

Materials Journal

Volume:

117

Issue:

2

Abstract:

This paper deals with long-term corrosion of steel reinforcement and how that is influenced by the presence of chlorides in the concrete. It provides experimental evidence that so-called “chloride-induced” long-term corrosion is the result of the accelerating effect of chlorides on the dissolution and loss of calcium hydroxide from concretes. This process progressively moves into the concrete, lowers its pH, increases its permeability, and facilitates inward diffusion of atmospheric oxygen. When these conditions reach the reinforcement, a high rate of reinforcement corrosion becomes thermodynamically possible and is observed in the experiments. It occurs earlier for concrete matrixes more open in structure. This can be attributed to greater internal surface area of exposed calcium hydroxide. The results also show that elevated concentrations of chlorides alone are not sufficient for causing long-term corrosion. The presented results throw a new light on chloride-induced corrosion under long-term exposures.

DOI:

10.14359/51722400


Document: 

19-161

Date: 

March 1, 2020

Author(s):

Sarah Mariam Abraham and G. D. R. N. Ransinchung

Publication:

Materials Journal

Volume:

117

Issue:

2

Abstract:

A comprehensive analysis on the effect that fine fraction of reclaimed asphalt pavement (RAP) aggregates can produce on the fresh properties, strength, and durability characteristics of cementitious mixtures—that is, mortar and concrete—when used as partial or full replacement of natural fine aggregates (NA) is represented in this study. The replacements of NA were done by volume at 25, 50, 75, and 100% catering to the difference in specific gravity between the aggregates. The cement was also partially replaced by volume using silica fume and activated sugarcane bagasse ash (SCBA). To achieve this objective, effect of RAP aggregates was studied in both mortar and concrete. Although recycling is not a novel concept, altering the conventional mixture design and testing methodology whilst using RAP aggregates were looked into. The application of this study was focused upon rigid pavements, where flexural strength is of great importance. The mixtures considered did achieve the design flexural strength and protected the reinforcement from corrosion due to basic pH and absence of carbonation.

DOI:

10.14359/51722398


Document: 

19-006

Date: 

January 1, 2020

Author(s):

Naga Pavan Vaddey, Mahmoud Shakouri, and David Trejo

Publication:

Materials Journal

Volume:

117

Issue:

1

Abstract:

The American Concrete Institute (ACI) specifies allowable admixed chloride limit (Climit) values to minimize the corrosion risk of steel reinforcement in concrete. The chloride concentration of concrete for new construction must not exceed this Climit value. While most ACI documents require the ASTM C1218 (watersoluble) test standard to measure chlorides, some documents allow the ASTM C1152 (acid-soluble) test standard. ACI documents that require ASTM C1218 report the same Climit value for different cementitious systems. Different cementitious systems, with similar chloride concentrations, could have different ASTM C1218 test outcomes due to differences in chloride binding capacities. This paper develops models to predict ASTM C1218 test outcomes. These models can assist in choosing appropriate concrete mixtures that can meet ACI Climit values. This paper also reports models to predict the ratio of ASTM C1218 and ASTM C1152 test outcomes to better correlate Climit values in ACI 222R, which allows both test methods.

DOI:

10.14359/51719149


Document: 

18-461

Date: 

November 1, 2019

Author(s):

Chaomei Meng, Liangcai Cai, and Guanhu Wang

Publication:

Materials Journal

Volume:

116

Issue:

6

Abstract:

Continuously reinforced concrete pavement (CRCP) has superior durability and mechanical performance over jointed plain concrete pavement (JPCP) without preset joints. However, there are many small cracks in CRCP under environmental loading. Crack width of CRCP is the one of most important factors for pavement design, and it directly influences durability. Therefore, an approximate model is developed to predict crack width and stresses of CRCP under temperature loading. Furthermore, the effect of influenced parameters on crack width is discussed. The results show that axial components account for a great proportion of thermal stress, compared to curling stress. Reinforcement ratio and diameter of reinforcement have significant influence on crack width. Increasing reinforcement ratio, while decreasing diameter of reinforcement can decrease crack width. Adhesive strength between concrete and reinforcement influences crack width, too. Higher adhesive strength can reduce crack width. Moreover, thicknesses of pavement, tensile strength, and elastic modulus of concrete also have an effect on crack width. Improvement of the tensile strength of concrete would widen the crack width, but lengthen the spacing between adjacent cracks. Both thicker pavement and higher elastic modulus of concrete introduce wider crack widths but improve bearing capacity. Therefore, a larger reinforcement ratio but smaller diameter of reinforcement with deformation, and a lower elastic modulus of concrete pavement with larger thickness are recommended.

DOI:

10.14359/51718064


Document: 

18-010

Date: 

November 1, 2019

Author(s):

Konstantinos Sotiriadis, Eleni Rakanta, Maria Eleni Mitzithra, George Batis, and Sotirios Tsivilis

Publication:

Materials Journal

Volume:

116

Issue:

6

Abstract:

The development of environmentally friendly cementitious materials, efficient in preventing chloride ingress and decreasing reinforcement corrosion risk, is significantly important for structural applications exposed to corrosive conditions. This paper investigates the effect of natural pozzolana, fly ash, blast-furnace slag, and metakaolin on the behavior of portland-limestone cement concretes and mortars during storage in chloride-sulfate and chloride solutions at 5°C (41°F). Acid- and water-soluble chloride contents, and apparent chloride diffusion coefficients, were determined in concretes. Reinforcement corrosion half-cell potential and current density, mass loss of steel reinforcing bars, and carbonation depth were monitored in mortars. The employment of mineral admixtures decreased chloride ingress and reinforcement corrosion during specimens’ exposure to chloride solution; however, the presence of sulfates in the corrosive environment prevented their improving effect. Mineral admixtures increased chloride binding and the resistance of concrete against chloride diffusion, while they also showed similar efficiency in preventing reinforcement corrosion. Sulfates facilitated chloride ingress, hindered chloride binding, and promoted reinforcement corrosion.

DOI:

10.14359/51716820


Document: 

18-440

Date: 

November 1, 2019

Author(s):

Arturo D’Alessandro, David J. Corr, and Surendra P. Shah

Publication:

Materials Journal

Volume:

116

Issue:

6

Abstract:

Ferrocement is a construction material that (in comparison to traditional reinforced concrete) provides superior crack control, impact resistance, and toughness. However, while extensive literature exists on the deterioration mechanisms and maintenance of reinforced concrete structures, little attention has been given to the durability of ferrocement. In this study, the adoption of ethyl silicate, a newly developed nanomaterial, is investigated to improve durability of ferrocement. Such nanomaterials are expected to penetrate the cementitious matrix without changing the appearance of the surface. Once penetrated, pozzolanic behavior is displayed forming calcium silicate hydrate and consequently increasing durability and mechanical performance. Particular attention is given to the carbonation-induced corrosion of reinforcement, which should be considered a major concern in ferrocement due to the initially small diameter of the mesh wires and the thin mortar cover. Despite its importance, there is a limited amount of literature on carbonation-induced corrosion of ferrocement structural elements.

DOI:

10.14359/51716821


Document: 

18-271

Date: 

September 1, 2019

Author(s):

Claus Vestergaard Nielsen

Publication:

Materials Journal

Volume:

116

Issue:

5

Abstract:

Corrosion of reinforcement related to the ingress of chlorides is responsible for damage and degradation of reinforced concrete all over the world. In Europe, the exposure to chlorides is categorized into six exposure classes, depending on the origin of the chlorides (deicing agents, marine environment) and the severity of the environment. At present, the Eurocode for concrete structures is under revision and the possibility of introducing performance-based exposure resistance classes instead of deemed-to-satisfy prescriptive requirements is being investigated. This work includes the use of service life modeling by means of the fib Model Code probability-based approach. The paper presents a novel and versatile methodology for carrying out modeling of chloride ingress and predicting the initiation period for depassivation with a certain safety level. The main input parameters are discussed and the challenges to be overcome are presented together with examples of the proposed model.

DOI:

10.14359/51716823


Document: 

18-283

Date: 

September 1, 2019

Author(s):

Aditya Singh Rajput and Umesh Kumar Sharma

Publication:

Materials Journal

Volume:

116

Issue:

5

Abstract:

Increasing cases of reinforcement corrosion in reinforced concrete (RC) elements raise serious concerns for achieving desired strength and ductility despite following the relevant seismic guidelines. The present study is an experimental attempt to evaluate the seismic behavior of corroded RC columns and thereby to examine the effectiveness of advanced composite materials in restoring the seismic behavior of such corroded columns. To this end, seven full-scale RC columns were cast and tested. Six column specimens were corroded using a precalibrated, accelerated corrosion regime, while one specimen acted as a control uncorroded column. Columns were corroded at two nominal degrees of corrosion: 10% and 20%. These corroded columns were then tested for evaluating their seismic behavior, while companion columns with the same degree of corrosion were retrofitted. Retrofitting was aimed at restoring the ductility and strength of corroded columns as well as to achieve increased durability against future corrosion. Advanced composite materials such as ultra-high-performance fiber-reinforced concrete (UHPFRC) and glass fiber-reinforced polymer (GFRP) were employed for retrofitting of columns. The results show an alarming reduction in seismic performance of columns due to corrosion of reinforcement. Corroded specimens when retrofitted with only UHPFRC jacket yielded satisfactory recovery of strength and ductility for 10% corrosion but showed insufficient improvement against 20% corrosion. For columns with 20% corrosion, a combination of UHPFRC and two layers of GFRP worked well in improving ductility and strength.

DOI:

10.14359/51716825


Document: 

18-293

Date: 

September 1, 2019

Author(s):

Robert E. Melchers and Igor A. Chaves

Publication:

Materials Journal

Volume:

116

Issue:

5

Abstract:

Many cases of high-quality reinforced concrete structures in marine environments show little or no corrosion despite very high chloride contents in the concrete. To explain this, it is necessary to separate initiation from active corrosion because they are governed by different mechanisms. The present paper considers corrosion initiation. It reports observations for realistic model concrete specimens at intervals for up to 12 years of exposure in a high-humidity environment. Initiation of reinforcement corrosion occurred soon after first exposure and was predominantly localized (pitting) on the side away from the casting direction. The localized corrosion was consistent with air voids at the concrete steel interface. After 2 to 3 years, the rate of corrosion declined very considerably owing to oxygen depletion within the concrete. To explain these observations, a model involving electrochemical differential aeration at the air voids at the concrete-steel interface is proposed. Numerous practical implications are discussed.

DOI:

10.14359/51716827


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