Every question asked by our customers is important and one of these is whether moisture damages cement and if so, what can be done to manage the risk of water getting into the bag. In this article we set out points that point out key considerations and we begin by exploring the baseline question, “Why does cement go hard?”
According to a group of researchers from the Massachusetts Institute of Technology (2019), “Although it is used to construct some of the world’s largest structures, it turns out that cement actually has something in common with a sponge.” Their study of the effects of moisture and drying on cement confirmed that as a highly porous material, cement tends to absorb water from precipitation and even ambient humidity. Just as the shape of a sponge changes depending on water saturation, so too, does cement. Tingtao Zhou, a Ph.D. student in the Department of Physics and the lead author of the paper explains:
“During cement hydration, the cement hydrate’s nanograins aggregate with each other, forming a network that glues all constituents together. While this gives cement its strength, the spaces between the cement hydrates to create an extensive pore network in the cement paste. … You have numerous pores of variable sizes that are interconnected. It becomes very complex and since they are so small, you don’t even need rain to fill them with water. Even ambient humidity can fill these pores.”
Why does cement set when water is added to it? Gharpedia shares good points:
“When water vapour passes through the multi-layer paper/ jute / polyethylene sacks, cement gets hardened to form lumps and this damages the quality of the stored cement. Hence, cement should be stored in such a manner that no moisture or dampness is allowed to reach cement either from the ground or from the environment. Extra precautions should be taken both at site and at a warehouse while storing the cement.”
On the subject of the hydration dynamics between cement and water, in an article in the Cement and Concrete SA publication titled Concrete Beton, David Samson talks about the love/hate saga between cement, concrete and water. He says, “To manufacture cement for production of concrete the base ingredients are heated to drive off water. Ancient cements were prepared by firing kilns made out of limestone and then crushing the anhydrous limestone into powder. The powder would then be proportioned with sand, stone and of course, the key ingredient – water. Now the complexity begins.” While he continues his commentary by addressing how to find, what he calls, the “Goldilocks zone” with “just right” curing, his reference to inherent complexities is spot on even before the cement reaches the mixing phase.
Put another way, “Cement, like sugar, is a hygroscopic (tending to absorb moisture from the air) material which reacts with water (either in liquid or even in vapour form). Cement must be kept away from both wetness (actual water such as leaks, flooding, etc. which can be seen with the naked eye) and dampness (moisture in the air which cannot be seen but which is always present to some extent). Moisture is a great enemy of the cement.”
The guideline from South African industry body Cement and Concrete SA is that the shelf life of cement is estimated to be six months inland and three months in coastal areas. However this guide would depend on the condition of the storage and how well moisture ingress is prevented. The entity indicates:
“Cement should be stored in a building which is dry, leak-proof and as moisture-proof as possible. There should be as few windows as practical in the storage building. Stack the cement bags off the floor on wooden planks in such a way, that they are about 150 mm to 200 mm above the floor and away from the walls. … Always store the cement in such a way that it can be used in a first in, first out basis.”
To help you store cement for optimal usage, we found additional advice in our Sephaku Cement blog archives. Here are some other hard and fast tips that stand true to how best to store your cement today:
- When stacking cement bags on the pallets or wooden planks, adding a plastic sheet underneath the pallets or planks will help to keep moisture out.
- Keep the cement bags away from any exterior walls (at least 60cm all-round).
- Stack the cement bags as close to each other as possible. This reduces the amount of air flowing around the bags and reduces the chance of the bags absorbing any moisture.
- It is best to keep the width of the stack to about 3m (or the length of four bags) and the height to no more than 10 bags when storing cement bags. Also, keep in mind that the cement bags should be packed alternately length-wise and cross-wise to prevent the stacks from falling over.
- You could also stick labels on the stacks to keep track of when the cement was purchased.
- Another great tip on how to store cement bags on site is to keep different types and strengths of cement separate.
- If you absolutely have to store cement for long periods of time, it is a good idea to cover the stack in a waterproof layer such as plastic or tarp.
In conclusion, we can say with confidence that moisture must and can be managed to optimise the shelf life of stored cement and to protect the integrity of its strength.