An Investigation of Prediction Model for Autogenous Shrinkage/Expansion Strain of Low-shrinkage HSC

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