Assessing concrete durability requires reliable permeability testing. Among various laboratory methods, the Water Permeability Test to BS EN 12390-8 stands out as a direct measure of resistance to water ingress under hydrostatic pressure. This standard, alongside its equivalent DIN 1048 Part 5, measures the depth of water penetration into concrete samples subjected to 0.5 MPa (72.5 psi) of hydrostatic pressure. The test provides quantitative insight into how concrete performs when exposed to sustained water pressure—critical for structures such as basements, tunnels, reservoirs and marine installations.

Why Permeability Matters for Concrete Durability

Permeability plays a critical role in concrete durability. High permeability allows ingress of water and harmful chemicals, accelerating deterioration of the concrete matrix and corrosion of supporting rebar. Durability failures often stem from substandard materials, improper mix designs, inadequate construction practices and insufficient curing. These shortcomings can significantly reduce a concrete structure's expected lifespan and performance. Unlike strength testing, which is straightforward and uniform, durability testing requires a nuanced understanding of the concrete's interaction with its environment.

How the BS EN 12390-8 Test Works

The water permeability testing process follows a defined protocol:

  • Concrete samples are cast and cured for 28 days under controlled conditions
  • Samples are then subjected to hydrostatic pressure in a testing apparatus
  • After three days of sustained pressure exposure, specimens are removed and cracked vertically
  • The depth of water penetration is measured along the split surface

A lower depth of penetration indicates higher resistance to water pressure, suggesting superior durability. This direct measurement approach contrasts with indirect methods that rely on electrical conductivity or weight gain as proxies for permeability.

Comparing Water Permeability Testing to Alternative Methods

The Absorption Test, such as BS 1881-122:2011, measures the amount of water that penetrates into concrete samples when submersed. The test is intended to determine the susceptibility of unsaturated concrete to penetration for both surface and interior concrete. However, this method has inherent limitations: short submersion duration compared to potential long-term service conditions, failure to account for reactive processes that tie up water, and the assumption that all weight gain is water rather than reactive processes.

The Rapid Chloride Permeability (RCP) test to ASTM 1202 has gained wide acceptance as a relatively easy and quick method. Yet it measures concrete resistivity rather than permeability directly. The test monitors electrical current passed through cylindrical specimens for six hours, with total charge in coulombs relating to chloride ion resistance. The RCP test should not be used to accurately determine permeability of a concrete mix containing supplementary cementitious materials or chemical admixtures. High voltage applied can cause temperature increases and physical changes resulting in unrealistic values. The electric current indicates movement of all ions in the pore solution, not just chloride ions, meaning misleading results can stem from pore solution chemistry rather than true permeability.

Limitations of BS EN 12390-8

While Water Permeability Testing offers high reliability, it has constraints. For dense, low-permeable mixes, comparing penetration depths can be challenging when differences are minimal. The test is best suited for evaluating concrete designed for environments with sustained hydrostatic pressure. For conditions not involving such pressure—such as façades, floors or pavements exposed to intermittent wetting—the Absorption Test may provide more relevant insight. Additionally, the test requires careful sample preparation and three-day exposure duration, making it more time-intensive than rapid methods.

Specification Guidance for Water-Resistant Structures

When specifying concrete for water-resistant structures, durability assessments must consider the specific environmental conditions, intended application, and expected lifespan. Water permeability testing provides critical data for structures exposed to hydrostatic pressure, but a comprehensive approach should supplement this with tests evaluating resistance to environmental factors and propensity to crack. Testing at 28 days provides baseline performance; for certain admixture types—particularly hydrophilic crystalline waterproofing admixtures—testing at later ages such as 56 or 90 days yields more realistic results as the crystallization process continues.

Integrating Water Permeability Data into Mix Design

Water permeability results directly inform concrete mix design decisions. Lower penetration depths correlate with denser pore structures, typically achieved through optimized water-cement ratios, supplementary cementitious materials such as ground granulated blast-furnace slag or fly ash, and appropriate curing regimes. For projects requiring water-tight construction—such as below-grade structures in high water tables—specifying maximum penetration depths based on BS EN 12390-8 results provides enforceable, quantifiable performance criteria.

By prioritizing durability testing that matches the structure's exposure conditions, engineers and specifiers ensure construction of long-lasting concrete that meets lifespan expectations and contributes to more sustainable, resilient infrastructure. Related reading: Chloride resistance of concrete: Limits, test methods and protective measures and Exposure classes for concrete: Classification to SIA 262 and DIN EN 206.