1 / 22

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

1. An Investigation of Prediction Model for Autogenous Shrinkage/Expansion Strain of Low-shrinkage HSC. Makoto TANIMURA, Yuji MITANI Taiheiyo Cement Corporation, Japan Ryoichi SATO Hiroshima University, Japan.

vivi
Télécharger la présentation

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 An Investigation of Prediction Model for Autogenous Shrinkage/Expansion Strain of Low-shrinkage HSC Makoto TANIMURA, Yuji MITANI 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. Background 2 • Importance of autogenous shrinkage in HSC • Necessity of reducing autogenous shrinkage ----- well known!! (JCI committee 1996 & 2002) • Effectiveness of expansive additive, shrinkage reducer, High C2S and low C3A-cement • Effectiveness for reduction of restrained-shrinkage stress, improvement of structural performance of RC members (Tazawa & Miyazawa, at least in 1994) (by authors, presented by SUZUKI) Objectives • Influence of dosage of Expansive additive and/or shrinkage reducer • Prediction model for autogenous shrinkage/expansion strain of low-shrinkage/expansion HSCs (required in practice)

  3. 3 Combinations of key-materials • EX; Lime-based expansive additive • SRA; Lower-alcohol alkyleneoxide adduct-based shrinkage reducer Mixture proportioning • W/(C+EX)= 0.3, W= 175 kg/m3 • Slump flow value; 500-700 mm • Targeted concrete strength; 70 N/mm2

  4. 4 Polyester film Formwork Polystyrene sheet Polyester film Concrete specimen (100×100×400mm) Displacement transducer Polytetrafluoroethylene sheet Gauge plug Measurement of autogenous length change JCI method 20oC (originally proposed by Tazawa & Miyazawa) • Before demolding Testing Method for Autogenous Shrinkage/Expansion of Concrete • After demolding JIS A 1129 (contact-type strain gage) Autogenous shrinkage/expansion strain= (Measured strain) – (thermal strain) coefficient of thermal expansion of concrete; assumed to be 10 x 10-6/oC

  5. 5 Definition of strain in this study According to JSCE Design Code 2002 • Investigation on autogenous shrinkage : autogenous shrinkage strain from initial setting time : drying shrinkage strain : total shrinkage strain from initial setting time ( ) : total shrinkage strain from start of drying : autogenous shrinkage strain from start of drying

  6. Effectiveness of Berite-rich low heat Portland cement 6 Initial set (by Miyazawa et al.) ‐40% JSCE0.4 LPC +40% ‐40% JSCE Code-2002 OPC +40% • AS of LPC-HSC is obviously small compared with OPC-HSC. • Prediction by JSCE Code is in good agreement with measurement.

  7. Effectiveness of shrinkage reducing agent(SRA) 7 Initial set Ras=0.0008SRA2-0.035SRA+1 始発 OPC LPC Ras=0.0024SRA2-0.094SRA+1 Age: 91days LPC OPC • SRA is obviously effective in reducing AS. • AS of LPC-based HSC is almost cancelled by adding SRA.

  8. (Expansion) (Expansion) (Shrinkage) (Shrinkage) Effectiveness of expansive additive (EX) 8 OPC LPC Initial set 80% 50% • EX effectively compensate AS. • Absolute expansion strain is dependent upon AS behavior of reference HSC. • Combination of LPC & EX; achievement of expansive HSCs

  9. Description of the effect of expansive additive (EX) 9 Definition of compensation of AS compensation of AS from final set of EX-added HSC LPC Expansion Age: 91days OPC (Final setting) AS from initial set of EX-added HSC εex∞=0.144EX2+4.47EX Age εex∞=0.061EX2+5.82EX (Initial setting) Shrinkage • Compensation of AS is more significant for LPC-based HSC. Reason; difference in early-age mechanical property, etc.

  10. Effectiveness of combined use of EX and SRA 10 OPC LPC SRA=6～12 kg/m3 SRA=6～12 kg/m3 Age: 91days Age: 91days Synergistic effect εex+sra∞=0.278EX2 +0.039EX εex+sra∞=0.142EX2 +3.08EX Synergistic effect No SRA No SRA • Significant synergistic effect is observed when EX content of more than 40 kg/m3 Reason; delicate change of hydration reaction of EX and cement by adding SRA, etc. --- further investigations is needed for detailed explanation, from both chemical and mechanical point of view.

  11. Definition of compensation of AS for EX+SRA-added HSC 11 compensation of AS from final set of EX+SRA-added HSC Expansion AS from initial set of EX+SRA-added HSC (Final setting) Age (Initial setting) AS from initial set of SRA-added HSC Shrinkage

  12. Prediction model for autogenous shrinkage/expansion strain, considered effect of EX and/or SRA 12 Basic equation; JSCE Code equation for AS Development property a=0.6, b=0.5 for W/C=0.3 End value Initial set

  13. 13 Prediction model considering SRA effect Same as that of JSCE Code OPC Reduction of end value LPC JSCE Code Average of “a” & “b” obtained from least square method for SRA-added HSC; a=0.62，b=0.48

  14. 14 Prediction model considering EX effect Development property of compensation of AS According to values below OPC End value of compensation of AS LPC OPC; c=0.8, d=0.5 Average of “c” & “d” obtained from least square method for EX-added HSC; c=0.8，d=0.5 for OPC c=0.5, d=0.6 for LPC LPC; c=0.5, d=0.6

  15. 15 Prediction model considering EX+SRA effect Development property of compensation of AS Same as that of EX-HSC OPC End value of compensation of AS for EX+SRA-HSC LPC Average; c=0.8, d=0.5 Average; c=0.5, d=0.6 OPC LPC Age (days) Age (days)

  16. +20% +20% -20% -20% -20% +20% Accuracy of prediction model 16 SRA-added HSC Prediction accuracy; 20 % EX-added HSC EX+SRA-added HSC

  17. Conclusions 17 • It is surely confirmed that HSCs with various low shrinkage/expansion strain properties can be produced by sole/combined use of investigated materials. • It is demonstrated that the investigated equations have accuracy of 20 % for predicting autogenous shrinkage /expansion strain of low-shrinkage/expansion HSCs. • (Further investigation is needed for temperature effect) On the other hand, addition of EX and/or SRA influence the strength of HSC. Therefore, suitable dosage of EX and/or SRA as well as W/C should be determined by considering both low-shrinkage performance and high-strength performance.

  18. Thank you !!

  19. 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

  20. 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

  21. Autogenous shrinkage of cement paste with W/C of 0.3 (x10-6) = 2.15＊(C3S%) – 5.49＊(C2S%) + 68.7＊(C3A%) + 48.5＊(C4AF%) where, (C3S%): Content of C3S (mass%) ………………… [by Miyazawa, Tazawa, 1996] Influence of mineral compositions of cement on autogenous shrinkage Mineral compositions of Portland cement in Japan Calculated value 1000x10-6 400x10-6 High C2S, Low C3A • LPC has lower autogenous shrinkage and resultant-induced stress

  22. Prediction model for autogenous shrinkage/expansion strain, considered effect of EX and/or SRA 22 Basic equation; JSCE Code equation for AS Development property a=0.6, b=0.5 for W/C=0.3 End value Initial set Approach for investigating prediction equation; • SRA effect -- Reduction of end value of AS • EX effect – Superposition of compensation of AS and AS of reference HSC based on JSCE-code equation • EX+SRA effect –Superposition of compensation of AS for EX+SRA-added HSC, including synergistic effect , and AS of SRA-added HSC

More Related