Over the years in this business, I’ve often encouraged people to ask questions that might pertain to their current or future concrete placement and finishing projects .. It’s always a good thing to help, if possible, I feel, and as a result, my mailbag (email box) is found filled to the brim on some days.
As soon as I get a bit more time, I’m going to add a new category to this blog .. I’ll call it “From the Mail Bag” .. and it will address the concerns and/or the questions that others might have with regard to anything having to do with concrete.
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From the mailbag today, Joe (Roanoke, Texas) writes:
Is it too hot right now in Texas to pour a concrete driveway. It has been averaging 101 degrees at my house. I have half driveway in Sun. Other half in shade trees. I also want to use a 5-sack mix. Would you recommend that in this heat?
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Dear Joe
Thanks for contacting me with your question.
5 Sack Mix (3,000 psi) is fairly common in Texas .. more because it’s cheaper, than due to any kind of heat issues.
I could recommend 5 sack mix on house foundations, sidewalks, and patio’s .. but for the sake of durability, I would suggest a 5 1/2 to 6 sack mix (3,500 psi – 4,000 psi) for a driveway.
In the heat, 5 sack mix will set up about as fast as 5 1/2 sack mix .. added *flyash and adequate base *moisture can slow the setup time on nearly any mix design you use.
The mix setup can also be slowed by shade. If you are pouring this yourself, I would suggest pouring the shady portion first, and then pouring the sunny section last. By doing this, you stand to even the odds between the setup times of the two. The slab will set more uniformly.
It’s okay to use a 5 sack mix for what you are wanting to do .. If you have concerns about the heat, simply ask the batch plant to bump the percentage of flyash up a bit, and be sure that your subgrade contains adequate moisture .. you should be fine.
Because sun and shade are proven to move throughout the course of the day, you might do well to consider the best time to pour during that particular day. The earlier, the better, is usually the rule, but if it can’t be poured early, you’ll have your logistics to fall back on .. i.e. mix design, flyash, base prep moisture and a pour plan.
