I have been involved with concrete work for many years. First thing is that temperature makes a huge difference. On 90 degree or above days I won't pour. Concrete cures by a chemical process not drying as most people think. The higher the temp the faster it sets and then cures. I've been told of ice used in the trucks to cool down the load(at extra cost). Another problem is that it has to have adequate water to cure to full strength. That is why good concrete crews will pour jobs like this first thing in the morning. They will cover it to keep water in and excess heat out.
You will probably see this slab crack in numerous places in the next two weeks. Depending on how much it cracks and how soft the concrete feels( I test existing concrete with a geologists pick to get and idea of the strenght) you can then decide whether to pull it out or just pour over it.
When doing any kind of constuction work the 7 Ps always apply. Concrete trucks don't actually deliver a yardage. The ticket will really be for a tonnage. I always add 10% to the order because its better to have a bit left over. If there is limited manpower break the job into small manageable pours. Joints in a slab are not a problem if you use rebar and a properly designed joint. Use strong forms and set them so that you are pouring to the top of the forms. The top of the form should be smooth and unobstructed so that you can use it as a screed guide. This will save alot of time and labor. Use a vibrator when placing the concrete to prevent voids but do not over vibrate.
That slab size looked to me like there should have been atleast three men on the crew. I made the mistake of my wife and I trying to pour a 3 cy grout pour oursleves. It was too much. Fortunately the driver(a Marine) got out of the truck and gave a hand. Gary had been to our house(under constuction) many times because I used about 200 cy in our house.
Always get the ticket from the driver and read it before signing. In 2008 I poured about 700 truck loads and on atleast 5 trucks they had sent the wrong type of concrete. We were building bridges and needed the high strenght.
I was taught in the 1950s that it is cheaper and easier to work with nature. I prefer to pour concrete in cool weather. When the daytime high is around 70 is perfect. Higher or lower temperatures adds to cost and usually increases risks to the quality of the job. In you case, I would water and cover that slab. Check it several times a day to make sure it is wet. This may help reduce cracking and increase the strength. After a few weeks you can evaluate whether it is worth covering or should just be removed.
I realize that this has been long and complicated. Unfortunately, doing good concrete work is complicated. Good Luck, Rick
I looked at the pics again and realized that you are keeping it wet. That is great. You may be able to pour a topping on that but I would still wait to see how strong the slab is. Pressure wash it and you may be able to put welded wire mesh over the existing slab and pour over that.
Edited by boyscout862, August 29, 2013 - 07:15 AM.
