Investigating Factors That Affect Air Entrainment During Fabrication of Concrete Railroad Ties

Transcription

1 Investigating Factors That Affect Air Entrainment During Fabrication of Concrete Railroad Ties Kyle A. Riding, Ph.D., P.E. Mohammed Albahttiti Ahmad Ghadban Kansas State University David Lange, Ph.D. University of Illinois at Urbana-Champaign US DOT Federal Railroad Administration

2 Outline Introduction In-situ concrete vibration attenuation measurements Concrete vibration response and performance 2

3 Air Entrainment Mechanisms No Air Entrainment Air Entrainment When Pores are >91.7% saturated 3

4 Air Content Measurement Pressure Meter (ASTM C231) Hardened Air Void Analysis (ASTM C457) Total air content Spacing factor farthest distance an water in a pore would have to travel to reach an air void during freezing 4

5 Air Content Need 9% by volume of mortar, 18% by volume of paste to protect concrete Air Spacing factor in Damage Prevention Minimize exposure to moisture Low water-cement ratio Adequate entrained air Suitable aggregates Adequate curing before freezing 5

6 Concrete Consolidation 6

7 Variables that Could Affect Air Factors that might affect air entrainment: Concrete slump and rheological properties Temperature Unit Weight Air Content Vibration 7

8 Variable Measurement Plants Testing: Two plants were visited to understand the entire manufacturing process. Slight differences in the manufacturing process is noticed. A month was spent at each plant to perform some testing on concrete ties. 8

9 Introduction Concrete Railroad Tie Manufacturing Concrete Vibration mechanisms in two manufacturing facilities: Cavity 1 Cavity 2 Cavity 3 Cavity 4 a) Vibrator b) Plant A vibration rods attached to the casting machine. a) Plant B vibrator schematics with the cavities labeled, and b) actual vibrator in position. 9

10 Plant A Stiff Concrete, Immersion Vibrator Accelerometers could only be rigidly attached to form and casting machine surface because immersion vibrators would destroy cables 10

11 Plant B, Fluid Concrete, Submersible Accelerometer 11

12 Immersion Vibrators Frequency 110 Hz on average frequency Frequency (Hz) Hz Time (seconds) Detected Frequency Upper Limit Lower Limit Average Frequency Average frequency in an 80 seconds interval at the end of Bed 2 of Plant A 12

13 Immersion Vibrators Acceleration Acceleration was 0.5 g on average, when attached to the forms at 1ft away from the casting machine. Maximum recorded acceleration was 2.5 g. Acceleration with the maximum acceleration envelope recorded over 1 second at the end of Bed 2 with the accelerometer attached to the casting machine of Plant A 13

14 Concrete Tie Vibration Form Vibrators Average vertical acceleration along the length of the form at 2ft intervals. Frequency = 75 hz Average peak acceleration vs. location along the length of Cavity 1 at 4.25 in deep with 2ft intervals without the off periods 14

15 Concrete Tie Vibration Form Vibrators Average vertical acceleration along the length of the form at 2ft intervals. 10 Acceleration (g) Location (in) Vertical Transverse Longitudinal Average peak acceleration vs. location along the length of Cavity 1 at 4.25 in deep with 2ft intervals without the off periods 15

16 Concrete Tie Vibration Form Vibrators Average vertical acceleration along the width of the form. 10 Acceleration (g) Location (in) Vertical Transverse Longitudinal Average peak acceleration vs. location across the width of Cavity 2 at 1in from the edge of the cavity 16

17 Acceleration (g) Concrete Tie Vibration Form Vibrators Average acceleration at the beginning of the form with the vibration source moving away Submersible Vertical Submersible Longitudinal Distance from Accelerometer (ft) Submersible Transverse Form Accelerometer Vertical Average peak concrete and form acceleration vs. location across the length of the entire bed in Cavity 1 at 1in from the start of the bed 17

18 Plant A Temperature of Fresh Concrete Temperature of fresh concrete was measured twice for each bed at the mixer. Temperature (of) Temperature (oc) Date, Batch and Location 18

19 Plant A Slump Slump was measured twice for each bed at the mixer and once for each bed at QC Lab (after concrete delivery and before vibration). Slump (inches) Batch Slump QC Slump Slump (mm) Date, Batch and Location 19

20 Plant A Fresh Air Content Air Content of Freshly Mixed Concrete by the Pressure Method: Air content was measured twice for each bed at the mixer and once for each bed at QC Lab (after concrete delivery and before vibration) Air content (%) 10% 9% 8% 7% 6% 5% 4% 3% 2% 1% 0% Air Content at Mixer End Batch Air Content at QC Lab Gravimetric Air 20

21 Plant B Temperature of Fresh Concrete Temperature of fresh concrete was measured twice for each bed at QC Lab (after concrete delivery and before vibration) Temperature (of) Temperature (oc) Date and Bed# 21

22 Plant B Slump Slump was measured twice for each bed at QC Lab (after concrete delivery and before vibration) Slump (in) Slump (mm) Date and Bed# 22

23 Plant B Fresh Air Content Air Content of Freshly Mixed Concrete by the Pressure Method: Air content was measured once for each bed at the mixer and twice for each bed at QC Lab (after concrete delivery and before vibration) Air content (%) 14% 12% 10% 8% 6% 4% 2% 0% Before Vibration From mixer Gravimetric Air 23

24 Summary of Air Results Hardened Air Content: Average Air Content (%) Average Spacing Factor (in) Spacing Factor: Mixer Before Vibration After Vibration Mixer Before Vibration After Vibration Location in the Manufacturing Process Location in the Manufacturing Process Plant A Plant B Standard Deviation Plant A Plant B Standard Deviation 24

25 Summary of Air Results Plant A B Calculation Average Standard Standard Average Deviation Deviation After Vibration Air Content (%) (AV) Spacing Factor (in) Before Air Content (%) Vibration (BV) Spacing Factor (in) Mixer (M) Air Content (%) Spacing Factor (in) Mixer Fresh Air (%) QC Fresh Air (%)

26 Conclusion The obtained results show a correlation between the concrete yield stresses and the air loss from the fresh concrete during handling. Variation in the batch-to-batch concrete rheology was observed. These variations could be because of: Small adjustments made to the mixture by the operator Variation in the aggregate moisture content Different air content 26

27 Conclusion Vibration also occurred for a longer period of time than needed to just consolidate the concrete. Immersion vibrators were found to vibrate the concrete for a shorter, more concentrated and effective period of time with less unwanted ongoing vibration from neighboring crossties. 27

28 Conclusion The hardened air content on average decreased by 4% and 3.4% between leaving the mixer and finishing vibration for Plant A and Plant B, respectively. Once the concrete left the mixer, each stage in the process was found to decrease the air content. The concrete air void spacing factor was found to increase more during handling with a more workable mixture and extended vibration. 28

29 Acknowledgements Federal Railroad Administration for funding this work Cameron Stuart, Hailing Yu and David Jeong for their valuable discussions 29

30 Thank you for listening. ANY QUESTIONS? 30