1. Monitoring Stiffening Behavior of Conventional Concrete (CC) and SCC Using Ultrasonic Pulse Velocity by X. Wang, P. Taylor, K. Wang, M. Lim

2. Objectives Assess ultrasonic pulse velocity applications to observe concrete stiffening process Correlate features of ultrasonic compression wave (P-wave) development to set time and formwork pressure decay Provide an insight on surfacing, jointing, and formwork removal of concrete

3. Hydration related Stiffening Process

4. What does it affect? – Workability: Hydration Thixotropy Loss effectiveness of admixtures – Formwork pressure Filling rate – Jointing Saw cutting window

5. Materials Aggregates

6. Mixture Proportions CC – CC-a: Seven mixtures with two slag types (grade 100 and 120) at 20%, 35%, and 50% replacement level of cement by weight – CC-b: Eight mixtures with a Class F fly ash at 20% replacement level, which also contain lightweight fine aggregate, integral waterproofer (IWP), shrinkage reducing admixture (SRA), water reducer (WR), and air entraining admixture (AEA).

7. Mixture Proportions

8. SCC: based on ACI and ICAR proportioning methods – Three control mixes (CC): one for each size – 12 mixes designed for cast-in-place bridge construction applications, made with different aggregate sizes (¾”, ½”, and 3/8”) and different cementitious materials including ground limestone

9. Mix Proportions

10. Test Methods ASTM C403 – penetration resistance Formwork Pressure-ISU sacrificial formwork – Flush diaphragm pressure sensor – Loading rate of 6 in/min (9 m/h) – Constant room temperature (72˚F) – Applied pressure up to 30 psi to simulate 30 feet concrete

11. Test Methods Ultrasonic P-wave velocity measurement – Testing on 4 by 8 in. cylinder up to 1000 mins – Transducer central frequency: 54 kHz – Constant room temperature (72˚F) – Wave path length: 0.65 feet (7.8 inches)

12. Ultrasonic Wave Propagation Ultrasonic Pulse Velocity: – A stress wave propagation method that involves measurement of the travel time of compression wave pulse over a known path length Biot’s theory – The propagation of elastic waves in a porous elastic solid saturated with a compressive viscous fluid Longitudinal (compression) waves: related to dynamic modulus of elasticity, Poisson’s ratio, and density Transverse (shear) waves Surface (Rayleigh) waves

13. P-Wave (Vp) Transmission Ultrasonic pulse velocity (UPV) device – Commercial device: Proceq Pundit Lab plus – Vp = L/tp (length of the straight-wave-path through the specimen/travel time of the ultrasonic pulse)

14. P-Wave (Vp) Transmission Ultrasonic pulse velocity (UPV) device – Commercial device: Proceq Pundit Lab plus – Vp = L/tp (length of the straight-wave-path through the specimen/travel time of the ultrasonic pulse)

15. mixes

16. Discussion Initial Set Time

17. Results Summary C Ash mixes

18. Conclusion P-wave test can be used to monitor the stiffening process of various concrete mixtures Set time and formwork pressure decay of concrete are clearly related to P-wave development Potential to provide an insight on surfacing, jointing, and formwork removal of concrete – Planning to correlate with saw-cutting window of pavements in a forthcoming study