Although concrete appears rock solid (pun intended) and is used to build everything from sidewalks to 150-story towers, under the microscope concrete looks a lot like a sponge. Concrete has an abundance of hydrated cementitious product, pores, and aggregate. Chloride ions reach reinforcing steel primarily by diffusion through concrete’s system of saturated pores. Diffusion is driven by a concentration gradient of chloride ions.
The details of concrete testing
Concrete testing gives an indication of how quickly a certain concrete allows chloride ions to diffuse through the pore structure. The pore structure is controlled by many factors, including water-to-cement ratio, quantity of supplemental cementitious materials (fly ash, slag, silica fume) in the cementitious portion of the concrete, and degree of hydration [of the cementitious materials].
Durable concrete develops a narrow, unconnected, tortuous pore structure that makes it difficult for chloride ions to reach the reinforcing steel. Non-durable concrete has a large, open pore structure that easily allows chloride ions to reach their target.
Beton can perform four different concrete tests that assess either the proclivity of chloride ion penetration or the rate of chloride ion penetration (diffusion coefficient). Referred to by their common names, these tests include rapid chloride (RCP), bulk diffusion, chloride migration, and resistivity.
A combination of ASTM testing can help overcome the limitations of any one test. Having more than one tool allows us to select the right ones for your job.
We welcome the opportunity to design, batch, and test your concrete for you.
Learn more about these concrete tests:
ASTM C1202: Rapid Chloride Permeability (Coulombs Passed)
ASTM C1556: Bulk Chloride Diffusion (Diffusion Coefficient)
ASTM C1760: Bulk Electrical Conductivity (Resistivity)
NT Build 492 Chloride Migration Coefficient from Non-Steady State Migration Experiments