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International Concrete Abstracts Portal

Showing 1-5 of 60 Abstracts search results

Document: 

18-347

Date: 

September 1, 2020

Author(s):

Song Wang and Mohamed A. ElGawady

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

In recent decades, concrete-filled fiber-reinforced polymer tube (CFFT) columns have gained increasing popularity in bridge construction as an alternative to conventional reinforced concrete columns. CFFT columns have excellent structural performance, which is attributed to the superior properties of the fiber-reinforced polymer (FRP) tubes. Furthermore, using FRP tubes eases the construction of CFFT columns. However, one obstacle hindering the greater acceptance of FRP as a common construction material in civil infrastructure application is the susceptibility of FRP to degradation during long-term exposure to a severe environment. The purpose of this study is to investigate the durability of CFFT columns subjected to seawater corrosion, which is the scenario for seashore bridges. CFFT stubs were immersed in simulated seawater with two different elevated temperatures for up to 450 days. Sustained axial loads were also applied to the stubs to simulate the real-life service load. Compression tests and hoop tensile tests were carried out on both pre- and post-conditioned specimens.

DOI:

10.14359/51724621


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: 

18-553

Date: 

January 1, 2020

Author(s):

Manuel A. G. Silva and Miguel Estêvão

Publication:

Materials Journal

Volume:

117

Issue:

1

Abstract:

Glass fiber-reinforced polymer rods, both bare and embedded in concrete or lime mortar, were immersed in an alkaline solution at 20°C for up to 6 months and tested to find the influence of the protective covers on the degradation of the rods. Diffusion and porosimetry studies were used to interpret the results. Reduction of the proportion of larger pores in the mortar cylinders altered the transport of contaminant to the reinforcing bars. Accelerated effects due to immersion in solution at 60°C caused marked degradation of the rods. SEM images revealed damage to the matrix and the interface fiber-resin, mostly noticeable on the resin matrix and in the peripheral region of the rods. Severe loss of capacity of energy absorption was found in low-velocity impact tests after exposure to solution at 20°C for more than 5000 hours. Globally, results showed that the embedment delayed the initiation of damage but did not shield the rods against the maximum intensity of degradation by the alkaline contaminant.

DOI:

10.14359/51719071


Document: 

17-433

Date: 

November 1, 2019

Author(s):

Er-yu Zhu and Ze-wen Zhu

Publication:

Materials Journal

Volume:

116

Issue:

6

Abstract:

A total of 16 pullout specimens were tested to investigate the effect of curing conditions on bond behavior of near-surface-mounted (NSM) carbon fiber-reinforced polymer (CFRP) strengthening concrete under curing temperatures from 35 to 65°C (95 to 149°F) and curing times from 6 to 12 hours. It was compared to that of specimens in ambient conditions (16°C [60.8°F]). On these bases, a nonlinear local bond-slip model was proposed. Two key parameters—A and B—are employed in the proposed bond-slip model, the specific expressions of which were mainly related to ultimate pullout load and peak shear stress of the specimen. The results show that the bond behavior of CFRP strip represents a negative quadratic curve with curing temperature and positive inverse tangent curves with curing time, respectively. The nonlinear local bond-slip model, considering the curing temperature-time, is deduced and validated.

DOI:

10.14359/51719148


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