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International Concrete Abstracts Portal

Showing 1-5 of 134 Abstracts search results

Document: 

19-406

Date: 

March 1, 2021

Author(s):

Anvit Gadkar and Kolluru V. L. Subramaniam

Publication:

Materials Journal

Volume:

118

Issue:

2

Abstract:

Self-leveling concrete is developed with low-calcium alkali-activated fly ash (AAF) binder paste. The rheological behavior of AAF pastes with different compositions is evaluated. AAF pastes are proportioned with alkali-silicate activating solutions to ensure specific reactive oxide ratios for comparable geopolymer strength. The yield stress and the viscosity of the AAF binder paste vary with the silica content and the silica modulus (SiO2/Na2O mass ratio) in the alkali-silicate activating solution. The slump and flow behaviors of concrete mixtures made with AAF paste are evaluated. The requirements of the AAF binder characteristics, paste content, and aggregate packing for achieving self-leveling flow characteristics under gravity-induced flow are assessed. The transition from a frictional to a flow-type behavior in concrete mixtures depends on the AAF binder paste content. Self-leveling is achieved without the use of admixtures with an AAF binder paste of low yield stress and at a paste content of 45%. Improving the aggregate packing using the Fuller-Thompson curve and reducing the yield stress of the AAF binder paste increase the flow achieved in concrete mixtures. The specifications for cement-based self-consolidating concrete (SCC) are closely applicable for self-leveling AAF-based concrete.

DOI:

10.14359/51729324


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: 

18-132

Date: 

January 1, 2021

Author(s):

Harun Tanyildizi

Publication:

Materials Journal

Volume:

118

Issue:

1

Abstract:

This work aims to decrease the damage in concrete caused by freezing-and-thawing. For this, concrete was healed using the polymer containing phosphazene after the freezing and thawing. The Taguchi method was used to decrease the experimental numbers. The experimental variables were determined as cement dosage, the phosphazene percentage, and curing time. 100 × 100 × 100 mm (3.94 × 3.94 × 3.94 in.) cubes were prepared for experiments. After demolding, the samples were cured in a water tank at 20°C ± 2°C (68°F ± 3.6°F) until the test ages (28, 60, 90, 180, and 365 days) were reached. These samples were then subjected to the freezing-and-thawing cycles. The healing process was conducted to the samples by impregnation with the polymer containing phosphazene after freezing-and-thawing cycles. Lastly, the compressive strength, ultrasonic pulse velocity, and weight change of concretes were determined. Scanning electron microscope, energydispersive X-ray spectroscopy, and X-ray powder diffraction analyses were performed to examine the microstructures of the samples. The results showed that the impregnation of polymer containing phosphazene after the freezing-and-thawing increased the strength and durability of the concrete.

DOI:

10.14359/51728147


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


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