What Is Concrete Permeability? Does Concrete Have High Permeability?
What Is Concrete Permeability?
Concrete permeability is a measure of how easily water or other liquids can pass through the concrete.
It is determined mainly by the amount and type of paste or cement and aggregate used, as well as the porosity of the hardened cement paste.
Good concrete permeability requires good workmanship during placement, compacting, curing and finishing processes to ensure longevity and durability of the concrete structure, allowing moisture to escape from within the mix and not linger on the surface.
While there are different ways to measure concrete permeability, one of the most common methods is known as AASHTO T-277 – a standard quantitative test technique that measures how easily water can penetrate through a moist-hardened sample over a 15 minute period.
Does Concrete Have High Permeability?
Concrete is a mixture of cement, aggregates (usually sand and gravel) and water that hardens over time.
It has low permeability due to its highly compacted structure which resists the movement of water and other fluids, making it an ideal material for walls, floors and foundations.
The low permeability of concrete also makes it a good choice for buildings in areas that are prone to flooding or have high levels of groundwater.
In addition to its resistance to fluid movement, concrete’s ability to block odors also makes it attractive for use in structures located near sources of unpleasant smells such as food processing plants or garbage dumps.
Why Is Permeability Important In Concrete?
Permeability is an important property of concrete as it affects the amount of water infiltration and therefore the durability of concrete structures.
Permeable concrete has better resistance to freeze-thaw cycles, chemical attack, cracking due to volume changes, and scaling or spalling caused by moisture accumulation.
It also reduces moisture related problems such as mold growth that can cause structural damage.
In addition, permeable concrete can provide a more effective drainage system which improves overall safety and comfort in spaces where water infiltration is an issue.
What Affects Concrete Permeability?
Concrete permeability is affected by several factors, including the water-cement ratio of the concrete mix, the size and type of aggregate used, the curing process, and any contaminants that may be present.
The water-cement ratio will determine the porosity of the concrete which directly affects its permeability; using too little or too much water in a mix can create weak points in concrete that are more susceptible to permeation.
Aggregates with larger particle sizes result in lower porosity while smaller particles increase permeability; thus, it’s important to properly select the type and size of aggregate when pouring concrete.
Additionally, adequate curing is necessary to ensure a higher quality product; leaving a fresh pour exposed to dry out too quickly without proper planning could leave weak spots that are easily penetrated.
Lastly, if contaminants such as salt are accidentally added during mixing, this can reduce concrete strength and make it more permeable.
How Is Permeability Of Concrete Determined?
To assess the permeability of concrete in a structure, core samples of around 100-150mm in height and 100mm in diameter can be taken and tested using pressure and volume controllers for accurate measurements.
However, this method may have limitations when testing large volumes of weakly permeable concrete.
Another method, flow pump testing, involves maintaining a constant level of hydraulic head and controlling the flow rate under a given pressure.
This approach allows for reproducing the conditions used to measure the depth of water penetration under pressure in accordance with EN 12390-8.
The short testing time of the flow pump technique eliminates the influence of other factors on the permeability coefficient, making it possible to determine the permeability coefficient of concrete within a specific time period, which can be useful in testing the effect of additives and determining their optimal time of effectiveness.
