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International Concrete Abstracts Portal

Showing 1-5 of 817 Abstracts search results

Document: 

SP-361_06

Date: 

March 1, 2024

Author(s):

Michelle L. Hendrickson, Christine A. Langton, and Joan Q. Wu

Publication:

Symposium Papers

Volume:

361

Abstract:

Sixty percent of the nation's highly toxic and radioactive mixed wastes are stored at Hanford in 177 deteriorating underground storage tanks. To close or remove these storage tanks from service and place them in a condition that is protective of human health and the environment, the tanks must be physically stabilized to prevent subsidence once wastes have been retrieved. Remaining residual liquid waste in the tanks that cannot be removed must be solidified and the solid wastes encapsulated to meet the Nuclear Regulatory Commission, Department of Energy, Environmental Protection Agency, and the State of Washington requirements. The Department of Energy has developed cementitious flowable concretes to restrict access and provide chemical stabilization for radionuclides. Formulation, laboratory, and field testing for application at Hanford began with flowable, self-leveling structural and non-structural fills. A slump flow equal to or greater than 610 mm, 0% bleed water, and 0.1% (by volume) shrinkage measurements were key parameters guiding reformulation efforts that resulted in highly flowable, self-consolidating concretes that met Hanford 241-C Tank closure short- and long-term regulatory and engineering performance requirements.

DOI:

10.14359/51740608


Document: 

SP-360_45

Date: 

March 1, 2024

Author(s):

C. Barris, F. Ceroni, A. Perez Caldentey

Publication:

Symposium Papers

Volume:

360

Abstract:

Serviceability checks in Reinforced Concrete (RC) elements involves the verification of crack width mainly aimed to limit the exposure of the steel reinforcement to corrosion and chemical attack and, thus, improve durability. Classical approaches for assessing the crack width in RC elements provide the calculation of two terms: 1) the average crack spacing, and 2) the average difference between the strain in the steel reinforcement and in the concrete in tension referred to the average crack spacing. A similar approach can be assumed valid also for RC elements strengthened with externally bonded Fiber Reinforced Polymer (FRP) materials, taking into account the additional tension stiffening effect provided by the external reinforcement.

This paper presents the comparisons of some existing code formulations for predicting crack spacing and crack width in RC elements with the experimental results of a database collected by the Authors and concerning tests on RC beams and ties externally bonded with different types and configurations of FRP materials. The paper is mainly aimed to check the reliability of the existing equations provided by codes in order to address the future assessment of reliable design provisions for cracking verifications in RC elements strengthened with FRP materials. The comparisons have evidenced, indeed, some useful issues for the design provisions: 1) larger scatter in the predictions of crack width than in crack spacing and, in particular, for ties, 2) limited effect of shrinkage on crack width, 3) necessity of taking into account the external reinforcement in crack spacing formulations, 4) good reliability of mechanical models for calculating cracks width.

DOI:

10.14359/51740657


Document: 

SP-360_42

Date: 

March 1, 2024

Author(s):

Luciano Ombres, Pietro Mazzuca, Alfredo Micieli and Francesco Campolongo

Publication:

Symposium Papers

Volume:

360

Abstract:

This paper presents experimental and theoretical investigations on the residual tensile and bond response of polypara-phenylene-benzo-bisthiazole (PBO) fabric reinforced cementitious matrix (FRCM) composites after the exposure to elevated temperatures ranging between 20 °C [68 ºF] and 300 °C [572 ºF]. Experimental results obtained from direct tensile (DT) and single-lap direct shear (DS) tests carried out respectively on PBO FRCM specimens and PBO FRCM-concrete elements were reported and discussed. Overall, specimens exposed to temperatures up to 200 °C [392 ºF] did not present significant reductions of both bond and tensile properties. This result can be attributed to the thermal shrinkage underwent by the inorganic matrix, which may enhance the bond between the fibers and the matrix. On the other hand, when the specimens were heated at 300 °C [572 ºF], marked reductions were observed, primarily stemming from the degradation of both mechanical properties of the FRCM constituent materials and the fiber-to-matrix bond. Subsequently, the experimental results were used for the following purposes: (i) to assess whether the Aveston–Cooper–Kelly (ACK) theory is able to describe the tensile behavior of FRCM materials at elevated temperatures; (ii) to define temperature-dependent local bond stress vs. slip law and (iii) to evaluate the ability of degradation models to simulate the variation with temperature of the FRCM tensile and bond properties. The results obtained from the theoretical analyses showed that, for all the tested temperature, the relative differences between predicted and experimental results are very low, confirming the accuracy of the proposed approaches.

DOI:

10.14359/51740654


Document: 

SP357_05

Date: 

April 1, 2023

Author(s):

Simone Ravasini, Francesca Vecchi, Beatrice Belletti, and Nicolo Bonati

Publication:

Symposium Papers

Volume:

357

Abstract:

During an extreme event occurring on a reinforced concrete structure, characterized by the loss of a load-bearing element, the remaining resisting members may develop alternate load paths to resist gravity loads. However, it is recognized that reinforced concrete flat slabs are prone to punching shear failure. This issue is particularly relevant for existing reinforced concrete structures where creep, shrinkage, and corrosion effects due to environmental conditions play a fundamental role before the occurrence of the extreme event. In this paper, nonlinear pushdown and dynamic analyses were performed on an existing continuous reinforced concrete flat slab to investigate the structural response in the case of an interior column loss. Firstly, the flexural and membrane action resisting contributions were in-deeply analyzed. Secondly, the crucial effects of creep, shrinkage and corrosion on the dynamic response and punching shear resistance of the system were critically evaluated. Finally, useful insights for the structural robustness assessment of existing RC structures subjected to material deterioration were provided.

DOI:

10.14359/51738761


Document: 

SP356_07

Date: 

October 1, 2022

Author(s):

Mahmut Ekenel, Hossein Roghani, Francisco De Caso y Basalo, and Antonio Nanni

Publication:

Symposium Papers

Volume:

356

Abstract:

Advances in technology have opened doors for building construction with new materials that are lightweight, efficient, noncorrosive, and reliable in terms of durability without a sacrifice in strength and performance. One of these technologies is the use of FRP bars and meshes in concrete members as internal reinforcement. Although FRP bars as structural reinforcement in concrete members have been successfully utilized in building and bridge projects (i.e., slabs, beams, etc.) for the past three decades; recently, there has been an interest in using FRP bars and meshes as secondary reinforcement for non-structural concrete members such as plain concrete footings, concrete slabs-on-ground, and plain concrete walls in lieu of code-compliant conventional temperature and shrinkage steel reinforcement. Because the use of FRP bars and meshes as secondary reinforcement is not within the provisions of the International Building Code (IBC), the predominant building code in the United States, an acceptance criterion (AC521) has been developed under IBC Section 104.11. This paper explains the requirements of AC521, and how FRP bars and meshes as secondary reinforcement of nonstructural concrete members are evaluated to show compliance with the provisions of the IBC.

DOI:

10.14359/51737250


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