Now that the temperatures are dropping the pressure is off. It’s a different game. There’s little chance of the concrete “getting away” from you. In fact, as many of you will know, it’s quite the opposite. You’ve laid the concrete and then it’s a waiting game. And it can be a VERY boring waiting game.
As a general guide, the concrete that is ordered in the warmer weather has a (minimum) cement content of 320kgs per m3, a 10mm aggregate and a fairly high slump (i.e. it’s wet / workable). Makes life easier, you may use a bit more CSH, but hey ho, nice job, everybody happy.
Lower temperatures change the rules.
So, to reduce the number of hours spent on site getting freezing cold and bored stiff, waiting for the concrete to harden sufficiently to start imprinting, (and then ending up printing using the lights from your truck!), it is worth considering these options :
- Lower the slump. Yes, it will be physically harder work to install, but it’ll keep you warm and toasty and for sure you’ll be finishing earlier. Also, drier concrete is less likely to suffer from frost damage whilst it is hardening.
- Raise cement content. The concrete may cost a bit more to purchase with a higher cement content, but it’ll pay you back in spade fulls as you’ll be going home earlier. Also, you will produce a more durable concrete slab in the long term. Because of the higher cement content the concrete will harden quicker and also generate more heat. Therefore there will be less chance of frost damage whilst it is hardening.
- Order 20mm aggregate. (Be careful with this one though if you’re going to be imprinting a deep pattern). 20mm aggregate concrete will set faster than 10mm concrete. Also, for a given degree of set, 20mm aggregate will support the weight of a man earlier than 10mm aggregate. So, printing can start earlier and can be finished earlier. (FYI quite a number of installers successfully use 20mm aggregate, whatever the pattern, all through the winter and a few guys will use 20mm aggregate all year round.)
Even though the temperatures are lower, be aware that the sun does come out and we do have warm days, even in the winter. Installing a ‘large’ area of low slump concrete with a high cement content and 20mm aggregate can catch an inexperienced person out, even in the winter. So, for the new guys into the industry, if in doubt, stick with the concrete mix you are used to / are happy with, and don’t bite off more than you can chew (which, as you know, is Dr Concretes most valuable tip).
For the installers that do use the winter mix, they will be going home earlier, (often with a better quality print), and there will be less chance of frost damage while the concrete is hardening because:
- The concrete sets quicker.
- More heat is generated.
- Less water to freeze.
You have to learn to adapt to handle all the variables that the four seasons can throw at you and as the saying goes in this wonderful business, “you don’t know ‘nothing’ until you’ve done a year”.
Red Shute Hill Industrial Estate