Pouring Driveways in Minnesota
Driveways in Minnesota are exposed to high levels of de-icing chemicals and high numbers of freeze/thaw cycles. Because driveways are exposed to these difficult conditions, it is essential that careful attention is paid to the practices and materials used for successful driveway installations. For driveway work in Minnesota we recommend the following:
- 4500 p.s.i concrete with a minimum of 6% air entrainment.
- Make sure the supplier uses ASTM materials and produces properly portioned mixes with industry accepted quality assurance.
- Maintain water:cement ratios at or below .45.
- Provide sufficient slope for drainage (1% minimum, 2% preferred)
- Do not over-finish the surface.
- Do not finish with steel tools.
- Cure the concrete promptly and properly.
- Pour driveways before October 15.
- Avoid the use of deicers in the first winter of service
Several years ago, Minnesota experienced an unusually high number of jobs with surface defects issues. In an attempt to understand what caused the surface defects, Marshall cored and tested dozens of jobs with surface defects. In almost every case, the concrete below the top surface of the slab was of high quality and could be expected to provide years of durable service.
However, the surfaces of the core samples told a different story. The surfaces showed at least one of the following:
- Ineffective curing (or no curing at all)
- Trapped bleed water
- Excessive surface density causing loss of air entrainment at surface (steel troweling)
- Higher water cement ratios on the surface.
Additional Practices to Employ
- Pour on damp sub-grades (never pour on standing water).
- Insure that screeding knocks rocks down below the surface.
- Pay attention to environmental factors like heat, wind, humidity and sun.
- Be prepared to protect the surface from rapid drying – have evaporation retardant on hand and/or erect wind shields to prevent rapid surface evaporation.
- Use super plasticizers instead of water when more workability is desired.
- Avoid trapping bleed water and prevent incorporating bleed water back into the slab.
- Don’t pour more than your crew can handle.
- Avoid adding water to the surface of the concrete during finishing.
Driveway surfaces in Minnesota are exposed to the most difficult environmental conditions. For a successful, durable driveway installation it is essential to use the best materials and the best practices, installed by experienced crews.