(Attachment)
ADVANCED TOOL TECHNOLOGY'S
"POWER VIBRATING SCREED"
OBJECTIVE:
Using Concrete Power Screed, to determine consolidation of concrete at varying slab depths with a low to medium slump (stiff).
PROCEDURES:
The concrete section was placed on July 25. 1998. The section was approximately 20 feet wide by 50 feet long with slab thickness ranging in depths of 4 inches, 8 inches, 12 inches. and 17 inches. The required compressive strength of the concrete was 4000 psi with a slump range of 2 inches to 4 inches (stiff to moderately stiff). GT&E, Inc. personnel were on-site to sample the concrete in accordance to ACl Standards and monitor the placement of concrete. The samples were obtained from each truck (2) that delivered the concrete. The concrete was placed directly from the chute of the concrete truck and spread with shovels. There was no effort to consolidate the concrete by mechanical or manual means. The finishers leveled the concrete (strike-off) with the "Power Vibrating Screed" and later applied a broom finish. Approximately one-half of the length of the slab was leveled with a pipe rail screed and the remaining half by eye. The results of the concrete field tests were as follows:
| Concrete (4000 psi) |
Truck #1 |
Truck #2 |
| Unit Weight (pcf) |
147.6 |
147.8 |
| Air Content (%) |
3.3 |
3.4 |
| Slump (in) |
3-3/4 |
2-1/2 |
| Concrete Temperature (°F) |
81 |
86 |
| Compressive Strength (7-Day psi) |
3790 |
3430 |
| Compressive Strength Average (28-Day psi) |
4380 |
4920 |
On July 31. 1998. GT&E. Inc. personnel was on site to perform core drilling of the concrete slab on-grade at random locations. The purpose of the cores was to perform a visual observation of the concrete matrix. Cores were removed from the following locations:
| 4-Inch Thick Slab |
- |
6 Cores |
| 8-Inch Thick Slab |
- |
1 Core |
| 12-Inch Thick Slab |
- |
1 Core |
| 17-Inch Thick Slab |
- |
2 Cores |
One of the cores was removed from a cold joint that was observed during the placement due to the concrete delivery time.
CONCLUSION:
GT&E. Inc. performed a visual observation of the concrete cores. The observation yielded very satisfactory results. The core surfaces indicated the concrete had a creamy paste on the surface without the use of a jitterbug, facilitating the finishing operations without additional labor. The concrete matrix appeared to have proper aggregate and cement distribution at all depths. The power-vibrating screed appears to have consolidated the concrete completely even in the area where the cold joint occurred with few voids present and the concrete well consolidated around the reinforcing steel. Despite that the concrete was not consolidated in accordance to ACI, the power-vibrating screed appeared to achieve similar results in consolidation. Compressive strength testing of a core from the 8-inch and 17-inch thick slab sections yielded strengths exceeding the 4000 psi concrete.
W.Scott Goodrich P.E.
 2215B Dunn Avenue · Nashville, Tennessee 37211 · (615) 256-3999 · Fax (615) 256-3987 |
