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International Concrete Abstracts Portal

Showing 1-5 of 63 Abstracts search results

Document: 

20-085

Date: 

January 1, 2021

Author(s):

Mohammed Farooq and Nemkumar Banthia

Publication:

Materials Journal

Volume:

118

Issue:

1

Abstract:

The influence of factors such as cementitious matrix characteristics, fiber inclination, and temperature on the interfacial bond between fiber-reinforced polymer (FRP) fibers and cementitious matrix are studied herein. It was noticed that use of glass fibers in the form of glass FRP (GFRP) composite fiber greatly improved the bonding mechanism over using just constituent glass fibers. With matrix maturity, a steady increase in bond was observed with over 60% bond strength achieved within a day. Densification of the cementitious matrix with the addition of silica fume was found to greatly increase the interfacial bond and changed the failure mode from fiber pullout to fiber rupture and delamination. At inclined loading as well, a different failure mode in the form of fiber rupture after partial pullout was noticed. This change in failure mode from fiber pullout to fiber rupture was also accompanied by a lower apparent tensile strength at large inclination. At lower temperature of –20°C, the bond between FRP fibers and the cement matrix was found to improve, but increased brittleness in fibers was also noted. At higher temperatures, FRP fibers performed satisfactorily up to 80°C, after which a gradual degradation in bond was observed.

DOI:

10.14359/51725996


Document: 

19-295

Date: 

January 1, 2021

Author(s):

Yail J. Kim and Yongcheng Ji

Publication:

Materials Journal

Volume:

118

Issue:

1

Abstract:

This paper presents the infiltration of sulfuric acid (H2SO4) through concrete confined with carbon fiber-reinforced polymer (CFRP) sheets. Despite the popularity of such a rehabilitation method in upgrading the strength and ductility of existing reinforced concrete columns, scarce information is available when these members are exposed to H2SO4 as a result of changes in service environments after strengthening. In an experimental comparative study alongside plain concrete, the efficacy of CFRP confinement is elaborated in the context of durability. Concrete specimens with and without CFRP confinement are immersed in a 5% solution for up to 6 weeks and are used to examine their physical and chemical responses. In the concrete subjected to the acid, H2SO4 dissolves the cement binder, alters surface-level pH values, and lowers the electrical resistivity of the plain concrete. Although the resin of the CFRP allows the ingress of H2SO4, the influence was not as significant as that of its plain counterpart. The CFRP system impedes the progression of chlorides through the conditioned concrete, which is beneficial in mitigating the potential corrosion damage of strengthened concrete members, preserves the integrity of the conditioned concrete, and lessens the absorption and effective diffusivity of H2SO4.

DOI:

10.14359/51728148


Document: 

20-040

Date: 

January 1, 2021

Author(s):

R. Kampmann, S. Telikapalli, A. Ruiz Emparanza, A. Schmidt, and M. A. Dulebenets

Publication:

Materials Journal

Volume:

118

Issue:

1

Abstract:

Concrete infrastructure is deteriorating at a fast pace because of corrosion issues inherent to traditional black steel reinforcing bars. Alternative non-corrosive reinforcement materials for concrete structures have been developed and reinforcing bars made from fiber-reinforced polymers (FRP) are one of the most predominantly used non-corrosive materials for internal reinforcement. This research focused on basalt FRP reinforcing bars as this technology is still in development for the U.S. market and no standard specifications are available yet. In an effort to develop basalt specific acceptance criteria, two commonly available BFRP reinforcing bar sizes from five different sources and two different production lots were tested to quantify the tensile strength and stress-strain behavior of this emerging reinforcing bar technology. The obtained results were used to evaluate the performance of each reinforcing bar type in a relativistic comparison to existing benchmark values for glass FRP reinforcing bars given in AC454. The tensile strengths were consistent for all reinforcing bar types and the recorded values surpassed the strength measurements generally reported for comparable GFRP reinforcing bars. It was found that No. 3 reinforcing bars measured guaranteed tensile strengths between 760 and 1266 MPa (110 and 184 ksi), while No. 5 reinforcing bars ranged between 836 Pa and 1074 MPa (129 and 131 ksi). Though the fiber-to-resin ratio of all tested reinforcing bar types was similar, the tensile strength of these reinforcing bars varied due to differences in the raw materials and production. The elastic moduli were calculated according to AC454 and it was noted that this property varied significantly between the different reinforcing bar types because of irregular cross-sectional dimensions and the various proprietary (not standardized) manufacturing processes. It was determined that acceptance criteria for BFRP reinforcing bars can be conservatively defined according to the currently available GFRP values, but more specific criteria can be developed through further research to take advantage of the additional load capacity and potential improved stiffness of BFRP reinforcing bars.

DOI:

10.14359/51729288


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: 

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


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