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International Concrete Abstracts Portal

Showing 1-5 of 272 Abstracts search results

Document: 

19-306

Date: 

September 1, 2020

Author(s):

Rachel E. Henkhaus, Sandra Villamizar, and Julio A. Ramirez

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

The allowable range of epoxy coating thickness specified by ASTM A775/A775M is 175 to 400 μm (7 to 16 mils). This study investigates the impact on structural performance of increasing the upper limit of epoxy coating thickness to 460 μm (18 mils) with respect to deflections, cracking, and bond strength of tension splices. Twenty beam specimens containing single splices as well as splices of bundled bars were tested to failure. The experimental parameters were ranges of epoxy coating thicknesses (300 to 380 μm [12 to 15 mils] and 460 to 530 μm [18 to 21 mils]) and bar sizes No. 16 and 29 [No. 5 and 9]). Test results confirmed the applicability of current code requirements for development and splice length of epoxy-coated bars in tension in ACI 318-14 and AASHTO LFRD 2014, including bars in bundles, up to a coating thickness not to exceed 460 μm (18 mils).

DOI:

10.14359/51727018


Document: 

19-354

Date: 

September 1, 2020

Author(s):

Edward G. Moffatt, Michael D. A. Thomas, Andrew Fahim, and Robert D. Moser

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

This paper presents the durability performance of ultra-high-performance concrete (UHPC) exposed to a marine environment for up to 21 years. Concrete specimens (152 x 152 x 533 mm [6 x 6 x 21 in.]) were cast using a water-cementitious materials ratio (w/cm) in the range of 0.09 to 0.19, various types and lengths of steel fibers, and the presence of conventional steel reinforcement bars in select mixtures. Laboratory testing included taking cores from each block and determining the existing chloride profile, compressive strength, electrochemical corrosion monitoring, and microstructural evaluation. Regardless of curing treatment and w/cm, the results revealed that UHPC exhibits significantly enhanced durability performance compared with typical high-performance concrete (HPC) and normal concretes. UHPC prisms exhibited minimal surface damage after being exposed to a harsh marine environment for up to 21 years. Chloride profiles revealed penetration to a depth of approximately 10 mm (0.39 in.) regardless of exposure duration. Electrochemical corrosion monitoring also showed passivity for reinforcement at a cover depth of 25 mm (1 in.) following 20 years.

DOI:

10.14359/51727022


Document: 

18-339

Date: 

September 1, 2020

Author(s):

Morteza Khatibmasjedi, Sivakumar Ramanathan, Prannoy Suraneni, and Antonio Nanni

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

The use of seawater as mixing water in reinforced concrete (RC) is currently prohibited by most building codes due to potential corrosion of conventional steel reinforcement. The issue of corrosion can be addressed by using noncorrosive reinforcement, such as glass fiber-reinforced polymer (GFRP). However, the long-term strength development of seawater-mixed concrete in different environments is not clear and needs to be addressed. This study reports the results of an investigation on the effect of different environments (curing regimes) on the compressive strength development of seawater-mixed concrete. Fresh properties of seawater-mixed concrete and concrete mixed with potable water were comparable, except for set times, which were accelerated in seawater-mixed concrete. Concrete cylinders were cast and exposed to subtropical environment (outdoor exposure), tidal zone (wet-dry cycles), moist curing (in a fog room), and seawater at 60°C (140°F) (submerged in a tank). Under these conditions, seawater-mixed concrete showed similar or better performance when compared to reference concrete. Specifically, when exposed to seawater at 60°C (140°F), seawater-mixed concrete shows higher compressive strength development than reference concrete, with values at 24 months being 14% higher. To explain strength development of such mixtures, further detailed testing was done. In this curing regime, the seawater-mixed concrete had 33% higher electrical resistivity than the reference concrete. In addition, the reference concrete showed calcium hydroxide leaching, with 30% difference in calcium hydroxide values between bulk and surface. Reference concrete absorbed more fluid and had a lower dry density, presumably due to greater seawater absorption. Seawater-mixed concrete performed better than reference concrete due to lower leaching because of a reduction in ionic gradients between the pore solution and curing solution. These results suggest that seawater-mixed concrete can potentially show better performance when compared to reference concrete for marine and submerged applications.

DOI:

10.14359/51725973


Document: 

19-416

Date: 

September 1, 2020

Author(s):

Ali F. Al-Khafaji, John J. Myers, and Antonio Nanni

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

Corrosion in reinforced concrete (RC) represents a serious issue in steel-reinforced concrete structures; therefore, finding an alternative to replace steel reinforcement with a non-corrosive material is necessary. One of these alternatives is glass fiber-reinforced polymer (GFRP) that arises as not only a feasible solution but also economical. The objective of this study is to assess the durability of GFRP bars in concrete bridges exposed to a real-time weather environment. The first bridge is Southview Bridge (in Missouri) and its GFRP bars have been in service for more than 11 years; the second bridge is Sierrita de la Cruz Creek Bridge (in Texas State) and its GFRP bars have been in service for more than 15 years. To observe any possible mechanical and chemical changes in the GFRP bars and concrete, several tests were conducted on the GFRP bars and surrounding concrete of the extracted cores. Carbonation depth, pH, and chlorides content were performed on the extracted concrete cores to evaluate the GFRP-surrounding environment and see how they influenced certain behaviors of GFRP bars. Scanning electron microscopy (SEM) was performed to observe any microstructural degradations within the GFRP bar and on the interfacial transition zone (ITZ). Energy dispersive spectroscopy (EDS) was applied to check for any chemical elemental changes. In addition, glass transition temperature (TA) and fiber content tests were carried out to assess the temperature state of the resin and check any loss in fiber content of the bar after these years of service. The results showed that there were no microstructural degradations in both bridges. EDS results were positive for one of the bridges, and they were negative with signs of leaching and alkali-hydrolysis attack on the other. Fiber content results for both bridges were within the permissible limits of ACI 440 standard. Carbonation depth was found only in one of the bridges. In addition, there were no signs of chloride attack in concrete. This study adds new evidence to the validation of the long-term durability of GFRP bars as concrete reinforcement used in field applications.

DOI:

10.14359/51725980


Document: 

19-358

Date: 

September 1, 2020

Author(s):

Christoph Mahrenholtz and Akanshu Sharma

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

The world becomes ever smaller and thus the global construction industry moves closer together. For this reason, civil engineers are looking for possibilities to harmonize design—for example, in the field of reinforced concrete structures. The streamlining would ease working in an international context and could offer opportunities for optimization: harmonization allows the identification of the technically best and most economical solution. This also holds for the provisions to calculate the development length of deformed reinforcing bars which, to date, differ notably from code to code. It is not reasonable that local codes define different development lengths for identical situations in terms of geometry and material used. This paper analyzes the provisions for the calculation of the development lengths according to internationally selected national codes as a basis for this discussion.

DOI:

10.14359/51725782


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