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International Concrete Abstracts Portal

Showing 1-5 of 165 Abstracts search results

Document: 

SP-349_08

Date: 

April 22, 2021

Author(s):

David I. Stackelberg, Boris I. Wilge, Shimon V. Boiko and Felix A. Goldman

Publication:

Symposium Papers

Volume:

349

Abstract:

Hardening and strengthening of cement-concrete compositions (CCC) is a result of forming a moist capillary porous body. Physical water contained in pores and capillaries of the resulting structure is its most informative component. First, it is only the pore solution that is electrically conductive component, and, second, the liquid phase stays perpetually in a thermodynamic equilibrium with the solid surfaces by which it is adsorbed. Thus the physical-moisture state immediately responds to any change in the material’s solid skeleton of hardening CCC.

These effects serve as a physical basis for the CCC hardening and strengthening monitoring using the results ofcontinuous measurement of electric resistivity. Such monitoring is aimed at controlling various properties of the material: from the initial viscous fluid or viscous plastic state of fresh mixtures to the final elastic state of artificial stone. The results of measuring the electric resistivity are compared to those of standard tests. Thus established relationships “Electric resistivity ( ρ ) – Parameters ( i P )” (Parameters: W/C, Slump, Setting Time, Plastic strength, Compressive Strength) allow to carry out technological monitoring over the entire range of CCC hardening. All correlations Pi = f (ρ ) are described by linear relations with high correlation coefficients.

The linearity of the correlations “Strength – Electric Resistivity” is characteristic of various CCC: regular dense concrete, dry concrete mixtures (W/C ≈ 0.35), shotcrete, rising and plastic strengthening of aerated concrete at the stage of preautoclave hardening, etc.


Document: 

SP-345_19

Date: 

February 1, 2021

Author(s):

Egbert Müller, Sarah Bergmann, Manfred Curbach, Josef Hegger

Publication:

Symposium Papers

Volume:

345

Abstract:

Carbon Reinforced Concrete (CRC) can be used for new structures and to strengthen existing components. Carbon fibre rods and fabrics are used as reinforcement for new components. Besides CFRP-lamellas, grid-like carbon reinforcements and shotcrete are very suitable for strengthening. Due to the low concrete cover, thin strengthening layers can be realised, which minimise the additional dead load. Depending on the chosen fibre material and impregnation, different failure mechanisms can be observed. The fibre strand should preferably be able to reach the maximum stress under load, but at this stage, the bond behaviour has to be thoroughly considered to prevent failure due to pull-out or delamination. Two carbon reinforcement fabrics are currently being investigated in the research programme C³ - Carbon Concrete Composite.This paper presents the results of large-scale tests on reinforced concrete slabs strengthened with CRC. In addition to the strengthening procedure and the large-scale component tests that have been carried out, this paper deals mainly with the recalculation of the test results and the positional accuracy of the carbon reinforcement and its influence on the flexural strength.


Document: 

SP-346_05

Date: 

January 1, 2021

Author(s):

Mohit Soni

Publication:

Symposium Papers

Volume:

346

Abstract:

Alternative reinforcement such as Glass Fiber Reinforced Polymer (GFRP) and Basalt (BFRP) are gaining popularity due to their corrosion resistant properties in extremely aggressive environments. The Florida Department of Transportation was concerned with the long-term durability of fiber resin systems in wet marine environments and restricted its use in submerged marine locations. This paper demonstrates the implementation of a pilot project after the thorough evaluation of a Fiber Reinforced Polymer resin prior to broader deployment of the alternative reinforcement. The paper focuses on the successful construction implementation to provide an archival reference document for future study and comparison to look at the long-term performance and integrity of the strengthening systems. During the execution of this pilot project, several lessons were learned and are demonstrated in this paper.


Document: 

SP-343_06

Date: 

October 1, 2020

Author(s):

Juhasz, K.P.; Schaul, P.; Winterberg, R.

Publication:

Symposium Papers

Volume:

343

Abstract:

The design of fibre reinforced shotcrete (FRS) hard rock linings is commonly based on the Q-System or Barton charts. This performance based design approach assess the results of experimental tests, carried out on panel specimens according to existing standards or guidelines. This is different to the general methodology to assess and determine the performance of fibre reinforced concrete (FRC) using standardized beam tests. Panel and beam test results yield significantly different information on the performance of FRC and it is problematic to correlate them. The beam test yields a stress-strain relationship for a small displacement range only. Based on the significantly different working and failure mechanisms, structural tests to evaluate the post-crack performance and the ductility of FRS linings are typically conducted on different types of panels rather than on traditional beams. As a consequence, test results based on beam tests may lead to an overestimation of FRC performance in panels and vice versa. In order to avoid uneconomic designs the most appropriate material must be found using the most appropriate test methodology. This paper discusses the difficulty in correlating test results obtained from beams and panels as well as the discrepancy in performance of different FRC using different test methodologies and aims to provide guidance on materials, testing and design.


Document: 

SP-343_24

Date: 

October 1, 2020

Author(s):

Bernard, E. S.

Publication:

Symposium Papers

Volume:

343

Abstract:

Numerous investigations of the effect of fibre addition on the seismic performance of conventionally reinforced concrete members have been published. These generally show that fibres can improve robustness and survivability during reverse-cycle loading, but the dosage rate of fibre required to achieve significant improvements in performance is substantial. Recently, pure FRC members have increasingly been used in structures such as tunnel linings, including both fibre reinforced shotcrete and pre-cast FRC segments. Concerns have been raised about the absence of data on the seismic resistance of such members given that all previous research on seismic performance has essentially involved hybrid members incorporating both steel reinforcing bars and fibres. The present investigation has focused on the reverse-cycle flexural performance of FRC members in the absence of conventional steel reinforcing bars. Laboratory testing was performed on plain, bar-reinforced, and steel fibre reinforced concrete members, and their performance was compared. The tests indicate that steel fibres provide a small improvement in flexural capacity under reverse-cycle loading compared to plain concrete, but that the robustness of pure FRC members is relatively poor compared to steel bar-reinforced members incorporating steel stirrups. The data suggest that, when used at practical dosage rates, large hooked-end steel fibres cannot be relied upon to provide seismic performance in flexure comparable to steel bar reinforced concrete members.


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