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Shrinkage and Cracking Behavior of HPC Used for Bridge Deck Overlays

By Hasitha Seneviratne . Shrinkage and Cracking Behavior of HPC Used for Bridge Deck Overlays. Iowa State University, 2013. Objective To examine the shrinkage and cracking potential of HPC concrete overlay mixes Different cements Supplementary materials Shrinkage cracking potential.

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Shrinkage and Cracking Behavior of HPC Used for Bridge Deck Overlays

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  1. By Hasitha Seneviratne Shrinkage and Cracking Behavior of HPC Used for Bridge Deck Overlays Iowa State University, 2013

  2. Objective • To examine the shrinkage and cracking potential of HPC concrete overlay mixes • Different cements • Supplementary materials • Shrinkage cracking potential Introduction

  3. Shrinkage and Cracking Behavior of HPC Used for Bridge Deck Overlays εsh εauto εsh εring E, Fc & Fsplit Creep Research approach Materials Proportions Experimental work Modeling Stressanalysis σ t creep σ Split tensile σ t =Ecεsh σ t ring Cracking Behavior

  4. Types of shrinkage • Chemical • Autogenous • Plastic • Drying • Effects of constituent materials • Cementitious material • Aggregates • Admixtures • Factors affecting restrained shrinkage behavior • Creep prediction models • B3 • Modified NCHRP 496 model Literature review

  5. pore Literature review Waterevaporates Capillary Force Plastic shrinkage Chemical shrinkage Autogenous shrinkage Drying shrinkage

  6. Cement • Type IP, I/II and I • Fly Ash : Class C Fly Ash (Headwaters Resources) • GGBFS (Holcim) • Metakaolin : Davison Catalysts • Coarse aggregates • Crushed Limestone (2 gradations), Crushed Quartzite • Fine aggregates – River Sand • Admixtures • Air Entraining Agent: Daravair 1000, Retarder: Daratard 17, Mid-range Water Reducer (MRWR): Mira 62, Standard Water Reducer (NRWR): WRDA 82 Materials

  7. Mix proportions

  8. Test methods of concrete shrinkage • Autogenous shrinkage (ASTM C157) • Free Drying shrinkage (ASTM C157) • Restrained ring shrinkage (ASTM C1581) • Test methods of mechanical properties • Elastic modulus (ASTM C469) • Compressive strength (ASTM C39) • Split tensile strength (ASTM C496) Experimental work

  9. Shrinkage displayed by cements were as follows • Type IP < Type I/II < Type I • Autogenous shrinkage has a high correlation to the amount of cementitious material • Free shrinkage has a strong linear correlation to the mass loss • Coarser coarse aggregate displayed lesser restrained shrinkage Summary of results

  10. Discussion • Strength Parameters • Concrete mixtures with supplementary cementitious material display late age strength development • Elastic modulus is highly dependent on the amount of cementitious material used • Fly ash improved the strength parameters • Slag and combination of MK and fly ash had no significant impact on strength parameters • Combination of fly ash and slag reduced the early age strength but the strength grew with time. • Split tensile strength was greater with coarser aggregates while elastic modulus was greater with quartzite.

  11. Free drying stress calculated from the Hooke’s law and the stress calculated for the strain recorded on the steel ring display a linear relationship. discussion

  12. Mixes 4, 5 and 6 have high cracking potential, • Mixes 1, 7, 8, 9 and 10 have medium cracking potential and • Mixes 2, 3 and 11 have low cracking potential

  13. Concrete mixes with high shrinkage values may not always crack first and it is the combined effect of shrinkage and mechanical properties (elastic modulus, creep, and strength) that determines concrete cracking potential. • 20% fly ash which reduces shrinkage and 25% GGBFS which has little effect on the shrinkage and are recommended to be used in bridge deck overlay concrete either as singular replacements or in combination. • Type I/II Cement may be preferred over Type I cement and Type IP is preferred over Type I/II cement for the consideration of the shrinkage cracking resistance. • Type IP < Type I/II < Type I Conclusion and recommendation

  14. Since free drying shrinkage and mass loss have a strong correlation, mass loss can be used as a good indicator for free drying shrinkage. • Compressive strength is a good indicator to evaluate elastic modulus and split tensile strength. • Controlling the paste volume in concrete to maintain minimum paste volume is highly recommended. Cautions shall be taken when total cementitious material content in concrete of over 700lb/ft3 is used for bridge decks. • Results of the finite element analysis reveals that the mixes would not display cracking within the 56 day period of study. Conclusion and recommendation

  15. Thank You!Questions?

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