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International Concrete Abstracts Portal

Showing 1-5 of 55 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: 

20-040

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: 

20-079

Date: 

January 1, 2021

Author(s):

Prannoy Suraneni, Lisa Burris, Christopher R. Shearer, and R. Douglas Hooton

Publication:

Materials Journal

Volume:

118

Issue:

1

Abstract:

ASTM C618 and AASHTO M 295 specifications for fly ash represent the primary documents used by U.S. state and federal agencies to determine the suitability of a fly ash source for use in concrete. Other countries have broadly similar specifications for fly ash. The article compares specifications from the United States, Canada, Europe, Australia, and New Zealand, noting similarities and differences. Despite its common use, several criticisms of the ASTM C618 specification exist and are discussed in this document. Specifically, concerns exist regarding its dependence on strength activity index testing for determination of fly ash reactivity and strength generation potential, and loss on ignition for quantification of unburnt carbon content, as these tests relate somewhat poorly to performance of the fly ash in concrete. Recently developed test methods that could improve some of the most problematic components of the ASTM C618 specification are discussed.

DOI:

10.14359/51725994


Document: 

20-030

Date: 

November 1, 2020

Author(s):

Joseph J. Assaad and Marianne Saba

Publication:

Materials Journal

Volume:

117

Issue:

6

Abstract:

The development and use of geopolymers (GP) considerably increased in the construction industry. This paper assesses the suitability of metakaolin-based GP mortars for masonry plastering works, including their comparison to masonry cement (MC) mortars and compliance to relevant EN 413-1 and ASTM C91 specifications. Three classes of GP mortars prepared with different metakaolin-to-limestone ratios are tested; the sodium hydroxide and sodium silicate activators contained air-entraining molecules to secure approximately 10% ±2% air content. Test results showed that GP mortars exhibited excellent water retention and increased rheological properties, which was related to higher viscosity of alkaline solution that increases stickiness and overall cohesiveness. For given limestone concentration, the mechanical properties of GP mortars including the pulloff bond strength and sorptivity were remarkably better than MC mixtures. Almost 90% of ultimate compressive strength was achieved after 7 days for GP mortars cured at ambient temperature, while this varied from 55 to 80% for MC mixtures cured in moist conditions. This can be particularly advantageous in masonry applications to speed up construction operations while, at the same time, eliminate the hassle of moist curing normally required with cement-based plasters.

DOI:

10.14359/51725991


Document: 

18-338

Date: 

September 1, 2019

Author(s):

Karthik H. Obla

Publication:

Materials Journal

Volume:

116

Issue:

5

Abstract:

Past research showed a correlation between the measured apparent chloride diffusion coefficient determined in accordance with ASTM C1556 and the ASTM C1202 rapid indication of chloride ion penetrability test (RCPT) results. Based on that research, a combination of RCPT and strength criteria was proposed to categorize mixtures based on their resistance to chloride ion penetration. This article proposes specification criteria based on a formation factor to categorize mixtures. The efficacy of using both approaches to categorize 44 concrete mixtures prepared from different portland cements, types and dosages of supplementary cementitious materials, and w/cm is examined. It is found that either approach can be used to categorize mixtures based on their resistance to chloride ion penetration. Specimens from 10 mixtures, moist-cured for over 8 years, were tested for surface and bulk resistivity. The same specimens were immersed in chloride solutions in accordance with ASTM C1556, and chloride-ion contents at specific depths from the exposed surface were measured and compared with the later-age bulk resistivity, early-age RCPT, and estimated formation factor.

DOI:

10.14359/51716835


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