ISSN: 1945-7553
CODEN: JTEVAB
Published Online: 31 January 2011
Page Count: 7

Influence of Feedback Control on Flexural Toughness of Fiber Reinforced Concrete in ASTM C1399 Tests

Banthia, Nemkumar
Professor of Civil Engineering, Univ. of British Columbia, Vancouver, BC

Mindess, Sidney
Professor Emeritus of Civil Engineering, Univ. of British Columbia, Vancouver, BC

Jiang, Zhengwu
Associate Professor, Key Laboratory of Advanced Civil Engineering Materials of Ministry of Education, Tongji Univ., Shanghai,

(Received 3 August 2010; accepted 6 December 2010)

Abstract

The influence of feedback control on the measured flexural toughness of fiber reinforced concrete (FRC) remains elusive. Some tests such as ASTM C1609/C1609M-07 require closed-loop control, while others such as ASTM C1399/C1399M-10 are considered control independent, and hence open-loop testing is allowed. Recent field experience has indicated that results from even ASTM C1399/C1399M-10 tests may be test control dependent. Towards this end, a test program was initiated to understand the influence of feedback control in ASTM C1399/C1399M-10 tests. Tests were performed on specimens of two different concrete strengths and one dosage of a polymeric fiber under both open-loop and closed-loop environments. In addition to performing the analysis using the ASTM C1399/C1399M-10 approach, R_i values as per the Canadian Highway Bridge Design Code (CHBDC-S06-16) were calculated. R_i values are derived from the Average Residual Strength (ARS) values obtained from ASTM C1399/C1399M-10 tests. The results indicate that while the influence of feedback control on the measured ARS values in the case of normal strength FRC is only marginal, its influence on high strength FRC is significant. The same applies to the R_i values calculated in CHBDC-S06-16, where the results indicate that based on the published minimum acceptance criteria, the choice of feedback control may in fact govern the acceptance or rejection of a given FRC material. In the context of these findings, it is recommended that beyond a certain compressive strength, ASTM C1399/C1399M-10 tests should only be performed in a closed-loop environment.

Keywords:
testing, fiber reinforced concrete, flexural toughness, feedback control, load instability

Paper ID: JTE103291
DOI: 10.1520/JTE103291
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