The Virginia Transportation Research Council has produced a research report detailing the use of crushed hydraulic cement concrete as an additive to base/subbase materials.
“The Evaluation of Use of Crushed Hydraulic Cement Concrete (CHCC) as an Additive to Base Course/Subbase Material,” is a 78-page report that details research conducted by George Mason University’s Sustainable Geotransportation Infrastructure research group.
Authored by George Mason University researchers, Dr. Burak F. Tanyu and Dr. Aiyoub Abbaspour, the report begins with the point that pavement systems constructed by the Virginia DOT require drainage systems, but currently do not allow the use of crushed hydraulic cement concrete (CHCC) as base course because of concerns the material might clog the geotextile used as a component of the drainage system.
The research used a gradient ratio (GR) test to evaluate the reduction in serviceability of geotextile, when placed adjacent to CHCC and blends of CHCC and virgin aggregate. The research also explored the effects of the stockpiling CHCC before used as base course in a pavement system to assess changes in the chemistry of CHCC.
The research results included:
- Stockpiling CHCC does not appear to create adverse effects when using CHCC as base course adjacent to geotextile.
- Chemical activity of CHCC stabilizes and so the potential for leaching of calcareous constituents precipitating in the underdrain structure appears to decrease with increasing age of stockpiled CHCC.
- Precipitation of calcareous tufa from CHCC leachate from the high release of alkali metals under favorable conditions is always a possibility. As such, the potential for precipitation was shown and characterized using geochemical analyses in this study. Based on the findings, the calcareous precipitate potential appears to be significantly reduced by blending CHCC with virgin aggregate.
- When tested with base material having 9% fines or less, the serviceability of the geotextile used in this study did not decrease to levels such that the system flow was impacted. However, when the fines content exceeded 9%, major reductions in aggregate/geotextile system permeabilities were observed. Therefore, the fines content of the material placed over the geotextile used in the edge drain should be limited to 9% as determined from the particles passing No. 200 U.S. sieve size.
Researchers noted the concerns about the use of CHCC were based on limited literature from the research conducted around the late 1990s. The researchers further recommended the findings of this study be evaluated in the field before implementing in highway construction.