Is concrete waterproof?

Concrete is a widely used construction material known for its strength, durability, and versatility. It has been used for centuries in various structures, including buildings, bridges, and dams. While concrete is undoubtedly an excellent choice for many applications, many people pose the question, is concrete waterproof, or do we need to add a chemical to make it waterproof?

Understanding Concrete’s Composition

A basic concrete mix consists of cement, water and ballast (sand and stone mixture). In our vehicles, because we are volumetric concrete vehicles, we load all the materials separately onto the vehicle which allows the correct concrete mix to be created when we are on site.
Normal concrete, when hardened, has a mixture of tiny pores, voids and micro cracks which can allow the seepage of water through the concrete. Whilst normal concrete has the ability to resist water penetration, it is not considered waterproof.

Waterproofing Admixture

To enhance concrete’s resistance to water penetration, various waterproofing techniques and materials are commonly employed. At Axtell, we have an admixture called SIKA which we add in when all the materials are being are being mixed in the auger of the vehicle on site. This has been research and tested via our lab technicians who have calibrated our vehicles for the SIKA admixture so that the pour is perfect every time.

The SIKA admixture comprises of a powerful superplasticiser, which helps the concrete to be highly workable for ease of placement and compaction even at a low water to cement ratio, and a hydrophobic pore blocker to physically block any remaining voids or pores in the concrete to stop the movement of water.
For most concrete pours, it is not suggested that waterproof admixture is necessary as this is an expensive additive. However, if it is deemed as needed by the structural engineer or the application requires waterproofing, at Axtell, we use the SIKA admixture which is not premixed into the materials, hence, allowing the vehicle to travel straight to site from another job to speed up your pour.

In conclusion, it is important to dispel the notion that concrete is entirely waterproof by itself. While concrete exhibits a certain level of water resistance, it is not impervious to water penetration. Its inherent porosity and the presence of capillary pores and micro-cracks make it susceptible to water seepage under specific conditions. However, by adding the SIKA admixture, the water permeability of this concrete is reduced as much as possible.