About the research
In the past, the Iowa Department of Transportation (DOT) has had a number of pavements placed from 1986 to 1994 that exhibit vibrator trails. Many of these pavement sections exhibited cracking in the vibrator trails and investigation shown high air loss in those areas. Research was conducted on vibration in concrete pavement placements. The research found that at 12,000 vibrations per minute (vpm), aggregate distribution and air content was greatly affected. This research led to specification changes on vibration, reducing the vibration from a minimum of 7000 vpm to 5000 to 8000 vpm. Another research project led to the implementation of vibration monitoring on projects greater than 50,000 square yards. Newer paving machines have a tablet based system for inspectors to monitor vibration during the project. Older paving equipment typically have the old system of vibration monitoring, which requires occasional checks of the vibrators on the paving equipment.
This research was conducted on concrete mix designs with only coarse and fine aggregates and likely were gap graded. Since 1999, the Iowa DOT has been utilizing well graded aggregate combinations on quality management concrete (QMC) mix designs. It is not known what effect vibration has on well-graded aggregate mix designs. Perhaps, these mix designs may allow a higher tolerance on vibration or perhaps less is required. The Iowa DOT has been experimenting with reduction in cement content in QMC mixes, validated with the performance engineered mix (PEM) testing procedures.
Even with research conducted in the past, we do not have a full understanding of the vibration energy impact on durability and consolidation. Frequently, it has been noted that there are still a fair amount of voids found in concrete pavement cores. Iowa State University has conducted a small study on the effect of vibration on concrete mixtures. The study noted localized changes in w/c ratio and air movement within the concrete. It is not known if this could lead to localized durability issues. This project will investigate the impact of vibration on concrete pavement mix designs. In particular the QMC mixes and those reduced cement content mixes validated with PEM test procedures. Lab research will be validated on a concrete paving project.