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Guidelines for Durable Concrete

POURING CONCRETE IN MINNESOTA 

Minnesota, with our weather and temperature fluctuations, can be very hard on exterior concrete. We’ve produced a guide, located below, on the best practices, as well as other considerations, when pouring ready mix concrete driveways, as well as other exterior applications, in Minnesota. Remember, we’ve been working with concrete in Minnesota for over 80 years, and we are here to help you!

Materials

When pouring a driveway in Minnesota, there are certain materials one is required to have on hand. We’ve made a little checklist of those materials and put that down below.

  • 4500 p.s.i concrete (the number of p.s.i indicates the strength of the 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 45:55.
Practices

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.


We suggest following these practices to avoid those problems:

  • 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
Cures & Sealers

All driveways in Minnesota must be cured as soon as the last finishing operation is completed.

Few topics cause more confusion for users of concrete than curing and sealing. We want everyone using our products to understand these vital steps in the concrete construction process.

Concrete is a mixture of cement, sand, coarse aggregate, water and admixtures. When the cement comes in contact with water, a chemical reaction called hydration occurs. It is this chemical reaction that changes concrete from a fluid to an inflexible, strong, stone-like substance.

Cement hydration is a long term process. After 28 days, 95% of the hydration is completed, so the concrete has gained most of the compressive strength that it will achieve. However, for hydration to continue for 28 days, two conditions must be maintained:

  1. Sufficient temperature (above 50 degrees F.)
  2. Sufficient moisture

If either of these conditions is not maintained, hydration will stop, and concrete will stop gaining strength at that time. Curing is maintaining sufficient moisture and temperature for hydration.

Sealing is applying surface protection on cured concrete. For exterior applications, especially areas exposed to road chemicals, sealing should be repeated every 3-4 years with high quality sealers.
Curing Methods

  • Air Cure - this means no cure at all - okay for a footing or a basement floor perhaps, but not too smart on a driveway or exterior concrete.
  • Water Cure - must keep concrete saturated - allowing it to dry out stops hydration
  • Membranes - poly will leave discoloration. Kraft paper is a two part system - wet under layer and poly outer layer.

Chemical cures - spray on chemicals - water based or solvent based.

Further Reading

We realize that our products are used for a variety of projects including sidewalks, decorative paths, pools, etc. Here are some additional practices to keep in mind when working with concrete in general no matter what the projects is.

  • 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.