10/18/2013 7:58:00 AM Ask the contractor: Special mix saves concrete from winter freeze/thaw damage
Yavapai County Contractors Association
Q: I am contemplating a rather large concrete project and have interest in using a superior type of concrete mix that will hopefully not have scaling and flaking issues. Is there anything available here in our local market? Tom, Sedona, Ariz.
A: Hanson Concrete has a high performance water proof mix which has been used locally on several projects both new and for replacement repairs on concrete that is scaling and spalling (where surface comes off due to ice melt usage and in locations where the concrete never sees sunlight). What is so special about this mix you ask? The main thing is that it is very resistant to water migration and is extremely resistant to ice melt usage. Hanson Concrete is the only source available for this mix. The mix contains a product called hydramix, which densifies and waterproofs the concrete from within. This is not a topical sealer like most contractors have to use to seal their concrete. This mix does it from within so there is no more efflorescence (which is residue that comes to concrete surfaces later on due to moisture migration through the slab).
Randy Wohlwend of Hanson Concrete said that Hanson has provided 24,000 yards of the high performance mix to hundreds of customers and contractors over the last four years. Randy stated, "This mix was created because of a desperate need to improve the quality of concrete mixes available to the public and due to the variety of applications concrete finds itself in."
The standard of 3000 psi concrete is not strong enough to withstand the freeze/thaw cycles our area experiences and the use of inferior ice melt products that so many homeowners use. Most of the driveways and patios in homes are poured with a 3000psi mix, but they are at a higher slump (wetter) during placement. The wetter the concrete the weaker the concrete.
We have seen driveways and sidewalks that should have lasted a lifetime, but only last a few years, so Hanson manufactured this mix that is becoming more and more popular for not just commercial use, but for the homeowner as well, and they are proving to be more and more reliable, and this mix is affectionately being called the "no call back concrete."
To prevent freeze/thaw damage, use quality materials and sound construction methods and concrete should be able to withstand the winter months. According to Wohlwend, "the mixes should be a minimum of a 4000psi to 4500psi strength."
We are labeled a moderate climate, but what we get in Prescott are many freeze/thaw cycles, which takes a toll on the concrete. When "ice mel" products are applied to concrete in winter, then the amount of freeze/thaw cycles increase because the ice melt products melt the ice while it is still freezing, and now that water along with the chemical has a chance to be absorbed into the concrete and then starts to naw away and attack the concrete.
If you are building a new home or adding concrete, you should be a good boy scout and take a compass to see if your patios or driveways and sidewalks are facing north to northeast and if they will be in the shade for long durations. If this is the case you should consider using a 4500pso mix. If the concrete areas are facing south and west without shade, a 3000psi mix will work and you should not have to use ice melt products.
Yavapai County Contractors Association (YCCA) is a professional association representing licensed, bonded and insured contractors, suppliers, distributors and business entities. Call YCCA for information on hiring a contractor at 778-0040. Submit questions to firstname.lastname@example.org or through www.ycca.org.
Posted: Saturday, October 19, 2013
Article comment by:
from The Portland Cement Association:
Concrete surfaces can flake or spall for one or more of the following reasons:
In areas of the country that are subjected to freezing and thawing the concrete should be air-entrained to resist flaking and scaling of the surface. If air-entrained concrete is not used, there will be subsequent damage to the surface. The water/cement ratio should be as low as possible to improve durability of the surface. Too much water in the mix will produce a weaker, less durable concrete that will contribute to early flaking and spalling of the surface. The finishing operations should not begin until the water sheen on the surface is gone and excess bleed water on the surface has had a chance to evaporate. If this excess water is worked into the concrete because the finishing operations are begun too soon, the concrete on the surface will have too high a water content and will be weaker and less durable.
and from the National Ready Mixed Concrete Association:
In general, concrete strength of 3500 psi for freezing and thawing exposure and 4000 psi when deicers are used should be adequate to prevent scaling.