Concrete in Cold Weather Guidelines
Pouring concrete in cold weather can be quite difficult compared to normal times.
After these days of cold weather that we have been, it seems that we have had to dust in some areas the concrete notes to know what measures to take to concrete in cold weather .
Neither is that it has been anything exaggerated, in my area we have not lowered of 0 degrees, but since I have put to review the conditions to concrete in cold weather I thought that what better to share them with you.
Surely, if you are in areas colder than mine, you will be used to both you and the equipment of structures that are executing the work, but here it is not usual to have to be aware of the thermometer to take into account these conditions of concreting in cold weather .
The truth is that both the manager of the work and I have gone ass watching the forecasts, not only the day of concreting, but the next 2 days.
But you better get to the point, do not you think?
Consequences of concreting in cold weather?
As you know, for the concrete to acquire resistance, a chemical process must be produced by which the cement is hydrated in combination with the water of the mixture , but of course, for that the water has to be in liquid state, that is, that does not serve us frozen.
The cement needs a certain amount of water to achieve complete hydration and hardening, but if part of the water is frozen it does not intervene in the process and the hydration of the cement remains incomplete, therefore the expected resistance is not reached.
It is not necessary to reach the freezing point of the water to cause damage to the concrete, since below 5º there is already a delay in the setting speed due to the slowing down of the chemical process due to the temperature.
When it takes to set, the water that remains free could evaporate before reacting with the concrete, especially in dry wind environments, which directly affects the hardening of the mixture .
Obviously this is more pronounced in the outer layers of the piece , which increases the external porosity, which will directly affect the durability of the concrete and the possibility of that in the future these pores could cause damage in freezing processes when they are filled with water.
On the other hand, in the event that the temperature drops when the mixture has already set to freeze, the water that has not yet hydrated the cement is free, will increase its volume and may break internally the concrete .
This is especially serious in the first hours after pouring , as there is still a lot of free water that can freeze and increase its volume within the pores of the dough.
It can also happen that there is water in the solid state within the mass of the concrete, but if it returns to liquid when the piece has hardened, it will be trapped inside the concrete and, what is worse, it will have prevented the volume that occupied frozen is occupied by concrete mass, thus creating a cavity within the mass. It is not necessary to specify that leaving a concrete with holes in the interior is not the most appropriate, although we will have invented the “Gruyere Concrete”
There are more consequences that can damage the concrete placed in cold weather, but I do not think it is a matter here of messing up to specify all the cases.
When is it considered that it is going to concrete in cold weather?
This is a subject that is perfectly defined in the instruction , in which it is said that the temperature, at the moment of pouring the concrete into the mold, will not be less than 5º.
It also prohibits pouring concrete when the temperature of the elements on which it is poured is lower than 0ºC .
Does this mean that in these cases we have to go home and wait for the time to be more favorable?
Well, in theory, yes, but in real life nobody believes it. Of course, we must take into account certain measures to avoid the consequences of concreting in cold weather that we have discussed before.
So let’s see what things we can do to be able to concrete in cold weather without negative consequences for the concrete we are running.
Measures to take into account to concrete in cold weather
We have seen that the main problem of concreting in cold weather is the presence of water in the equation, which is the one that suffers most from the consequences of temperature, so it seems logical that the main actions we have to undertake will have to be directed to influence this material in several ways.
The main problem of concrete in cold weather is the presence of water, which is the most affected by low temperatures.
One of the first actions we can do is to reduce the amount of water in the dough. A smaller amount of water less water may be affected by the temperature conditions, so a low ratio water cement in the dosage of concrete can improve the behavior of concrete at low temperatures.
For this, the use of fluidifiers can be interesting , so that despite obtaining a dry paste, due to the low amount of water, it can maintain the workability of the dough.
Once we have reduced as much as possible the amount of water in the dough, there is still the possibility that it is affected by the temperature, so we must make it disappear as soon as possible , that is, we must accelerate the setting and hardening so that the mixing water, which is free and susceptible to freezing, becomes water combined with the cement.
This can be achieved with the use of setting accelerating additives , which will reduce the time during which the water is free and can be affected by the cold.
We can also combine the water more quickly using cements with a greater amount of fines , which have a higher initial resistance because they combine more quickly, making the free water disappear.
Making the water mix as soon as possible with the cement is a good measure to take into account in concreting in cold weather.
Already put to speak of cements, we can use those that have a high heat of hydration , so that they help that the temperature is not so low as to affect the mass.
We can also influence the temperature using antifreeze additives , so that the water lowers its freezing temperature and therefore is not affected by the action of cold to a significantly lower temperature, but enough to work with a certainty that it does not the final characteristics of the concrete element will be modified.
All this is very good, but we can not only act on the mass of fresh concrete that we are going to pour, modifying its dosage or chemical characteristics, but we can also act directly on the temperature at which the piece is once concreted.
A good measure to concrete in cold weather is to shelter the concrete to limit the temperature to which it is during the hardening process.
But how can we shelter the concrete?
There are several ways to do it, depending on the element, since it will not be the same to shelter a pillars plant than a recently concreted floor.
For the case of singular elements, such as pillars, wood formwork can be used, which greatly limits the passage of cold to the interior, or polystyrene formwork. Of course it is not good practice to use metal formwork.
In addition to using formwork that maintains the temperature better, it is advisable to allow more time until the demoulding, at least those first 48 critical hours until the free water of the dough has been almost completely reduced, so that these formworks are responsible for maintaining constant the proper temperature of the dough.
In the case of surface elements, such as a floor slab or a slab, things get a little more complicated, but basically it’s about the same thing, protecting the concrete from the cold.
We can achieve this by covering the concreted surface with polystyrene sheets that maintain the temperature . You can also use wooden planks or cover with earth, but I think it is more practical to do it with polystyrene because of the ease of placement and low weight.
There are other measures that can be taken into account when concreting in cold weather, such as preheating the materials, but the truth is that as far as I know I do not see the concrete plants doing this, so we will have to try to minimize the effect of the cold with the measures that I have mentioned.
As I told you at the beginning, what I have told you only I have been able to put into practice on one occasion when I directed a work in Teruel, so my experience is limited, so if you are one of those brave people who work in cold areas and that you face this problem every winter, surely you can contribute your experience to concrete in cold weather.
Please share your comments and suggestions with us. Thank you for your interest…