1 / 18

Fourth International Seminar on Self-desiccation and Its Importance in Concrete Technology

1. The Effect of Autogenous Shrinkage on Flexural Cracking Behavior of Reinforced HSC Beams and Improvement by Using Low-shrinkage HSC. Masahiro SUZUKI P.S. Mitsubishi Construction Co., Ltd., Japan Makoto TANIMURA Taiheiyo Cement Corporation, Japan Ryoichi SATO Hiroshima University, Japan.

adanne
Download Presentation

Fourth International Seminar on Self-desiccation and Its Importance in Concrete Technology

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 1 The Effect of Autogenous Shrinkage on Flexural Cracking Behavior of Reinforced HSC Beams and Improvement by Using Low-shrinkage HSC Masahiro SUZUKI P.S. Mitsubishi Construction Co., Ltd., Japan Makoto TANIMURA Taiheiyo Cement Corporation, Japan Ryoichi SATO Hiroshima University, Japan Fourth International Seminar on Self-desiccation and Its Importance in Concrete Technology 20/June/05, Gaithersburg, Maryland, USA

  2. 2 Background • Autogenous shrinkage (AS) properties of HSC using various materials • Comprehensive approach for reducing AS ----- well studied!! However, few investigations on the effect of AS on structural performance. Only a few reports on evaluation method for cracking behavior considering AS Objectives • Evaluation of AS effect on cracking performance of RC flexural beams, effectiveness of low shrinkage-HSC on the improvement of cracking performance • Calculation method for crack width of RC beam considering shrinkage/expansion effect before loading

  3. 3 (Unit; mm) • Dimension; 200x250x2700 mm • Two-point loading; span:2100mm, pure flexural zone:800mm RC beam specimen • Sealed curing period;30-50 days • Crack width • Steel strain • Evaluations • Before loading Steel strainRestrained stress on bottom fiber • Under short-term loading - Crack width; Contact-type strain gauge

  4. 4 Mixture investigated • Reference HSC • Low-shrinakge HSCs • W/(C+EX); 0.3 • EX content; 40 kg/m3 • SRA content; 6 kg/m3 • Targeted concrete strength; 70 N/mm2 at 28 days

  5. 5 Equation for calculating restrained stress on extreme bottom fiber • Equilibrium of the force between concrete and rebar • Navier’s assumption

  6. Restrained-shrinkage/expansion stress 6 1.5 N/mm2 Tension Compression －1.5 N/mm2 • Low-shrinkage HSCs are obviously effective in reducing AS-restrained stress.

  7. 7 Flexural cracking moment • AS-restrained stress affects cracking load significantly. • LS-HSC markedly improve cracking load.

  8. 8 Maximum crack width/crack spacing • LS-HSCs improve cracking performance significantly. --Decrease in crack width, while increase in crack spacing!!

  9. 9 General evaluation method for crack width considering shrinkage/expansion effect before loading • Diferrenec in elastic strain component between steel and concrete; affect crack width This concept incorporated into JSCE CODE-2002

  10. 10 JSCE Code Equation for maximum crack width

  11. 11 Verification of proposed concept for evaluating maximum crack width (1) JSCE CODE-1996 JSCE CODE-2002 • Improved accuracy Reinforcement stress (N/mm2) Reinforcement stress change(N/mm2) Significant effect of AS on crack width; Reference HSC has 250x10-6 of steel stress at zero stress state; this means the influence of 25% for the steel stress of 200MPa(=1000x10-6)

  12. 12 Verification of proposed concept for evaluating maximum crack width (2) Range of conventional theory Range of Proposed concept Conventional theory Proposed concept Measured • Conventional RC theory cannot evaluate the tendency of crack width of RC beams with AS and expansion. • Proposed concept has acceptable accuracy for evaluating crack width.

  13. Conclusions 13 • AS decreases significantly the cracking performances of Reinforced HSC flexural beams. • LS-HSCs markedly improve the flexural cracking performances; the combined use of Belite-rich low heat Portland cement and expansive additive is particularly effective. • It is verified that a new concept can evaluate crack widths of the RC beams with wider range of early age deformation with acceptable accuracy. This concept was adopted into JSCE Code equation. Time-dependent structural performance of LS-HSC beams will be presented by TANIMURA, at 7th HS/HPC symposium.

  14. Thank you !!

  15. Unit; mm Specimen for autogenous shrinkage measurement

  16. Autogenous shrinkage/expansion strain

  17. Additional performance Necessity of low-shrinkage HSC • Significant autogenous shrinkage • Tensile restrained-stress before loading • Deterioration of serviceability performance of RC members Low shrinkage Low-shrinkage HSC-High cracking resistance-Durable RC structure High-strength High-flowability generalization Assignment High-mechanical performance and high-durability

  18. Approach for low-shrinkage HSC Low-shrinkage cement Special admixtures Belite-rich Portland cement Expansive additive Low-heat Portland cement Shrinkage reducing agent EX+SRA Autogenous strain Age Autogenous strain LPC EX SRA Conventional HSC Combination Control of autogenous shrinkage Expansion rather than shrinkage

More Related