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A TRIAL OF REDUCING AUTOGENOUS SHRINKAGE BY RECYCLED AGGREGATE

This study investigates the use of saturated recycled aggregate to control the risk of early-age cracking in high-strength concrete. The experiment examines the effects on compressive strength, Young's modulus, splitting tensile strength, autogenous shrinkage, and self-induced stress. Results show that while autogenous shrinkage can be reduced, the use of recycled aggregate decreases compressive strength and Young's modulus. Further research is needed to optimize early-age cracking risk and compressive strength for efficient use of recycled aggregate.

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A TRIAL OF REDUCING AUTOGENOUS SHRINKAGE BY RECYCLED AGGREGATE

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  1. A TRIAL OF REDUCING AUTOGENOUS SHRINKAGE BY RECYCLED AGGREGATE Ippei Maruyama Ryoichi Sato

  2. Objective High-Strength Concrete has a risk of early age cracking due to authogenous shrinkage. How to control the risk of early-age cracking?

  3. Background • Countermeasures: • -Expansive additive • -Shrinkage-reducing agent • -C2S rich cement • Some people try to compensate the self-desiccation: • Porous lightweight aggregate • Super adsorbent polymer particle

  4. Objective 2 We use saturated recycled aggregate. Because… It is important to enhance the rate of use. -limitation of resources(natural aggregate) -shortage of dump yards -decrease of reusing for pavement or back filling

  5. Concrete Conventional High Strength Concrete 0.25 0.25 High Strength Concrete with recycled aggregate Recycled fine aggregate: 10% absorption, 30% paste in mass. Recycled coarse aggregate: 6% absorption, 40% mortar in mass.

  6. Experiment -Compressive strength -Young’s modulus -Splitting tensile strength -Autogenous shrinkage (drying shrinkage after 28 days) -Self induced stress test by beam specimen Reinforcement ratio: 1.06%, 2.39%

  7. Experiment Self-induced stress of concrete at extreme bottom fiber is calculated from the strain of rebar according to the linear strain distribution:

  8. Results (Compressive Strength, Young’s modulus) 71.2 33.3 66.1 28.3 (93%) (85%) Using recycle aggregate reduce the compressive strength and Young’s modulus.

  9. Results (Splitting Tensile strength) About 70%

  10. Results (Deformation) (40%) (120%) Using recycle aggregate reduce the autogenous shrinkage remarkably. But total shrinkage after drying of recycled concrete exceeds conventional high-strength concrete.

  11. Results (Self-induced stress) (75%) (70%) 80 1.06% 2.39% Using recycle aggregate reduce the self induced stress efficiently. This can be explained by smaller shrinkage, Young’s modulus, and larger creep.

  12. Conclusion • Using saturated recycled aggregate can reduce autogenous shrinkage. • Using recycled aggregate decrease compressive and splitting tensile strength and Young’s modulus. • Further study for optimizing the early-age cracking risk and compressive strength is necessary for efficient use of recycled aggregate.

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