RCP Test (ASTM C 1202); Should be specified in a project specification in GCC region?

Rapid chloride permeability test (ASTM C1202) is a well-known test in American standards related to testing of concrete durability. It is usually one of the tests that specified in a project specification to evaluate and assess the durability of the concrete. The title of the test standard ASTM C1202 is “Standard Test Method for Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration” . The abbreviation “RCP” will be used in this article since it is a well-known abbreviation in GCC region.

Project specifications usually specify figures such as less than 2000 coulombs for what so called “a regular durable concrete”, less than 1000 coulombs for “a high durable concrete” and sometimes less than 500 coulombs for “Ultra-high durable” concrete.

Regardless the specified figures, from mix design point of view: achieving a lower RCP value is a function of three main parameters: The first one is W/CM, the second and the third ones belong to supplementary cementitious materials:?The type of the cementitious materials used and the replacement percentages. Other components such as aggregate and admixtures have usually less effects in lowering RCP test results. Some admixtures increase RCP test results without a real change in concrete permeability. (This claim is based on thousands of RCP tests done by the author which conducted either for product development purposes to serve many construction projects or for research purposes).

RCP is a widely-used testing method in GCC for the assessment of the concrete durability. Although RCP test is somehow an easy test method for the assessment of the durability, it has many limitations such as:

·???Low inherent repeatability and reproducibility. AASHTO T277 states that the results of companion samples tested by the same operator should not vary by more than 19.5%. This is an extremely large variation in allowable results. The ASTM method shows that the results of two properly conducted tests by the same operator on concrete samples from the same batch may differ as much as 42%. On companion samples tested by different laboratories, this percentage is raised to 51%. This large variability in test results indicates the relative inaccuracy of the test method while maintaining that concrete samples which lie within this large acceptable range are essentially equal in quality. “GCP applied technologies – Technical Bulletin”

·???????RCP test might be a misleading test in the evaluation of some chemical admixtures such as hydrophobic or crystalline admixtures. Such admixtures might increase or have little effects on RCP test results while they reduce the concrete permeability significantly. Author believes that the use of RCP test method for evaluation, qualification, or comparison purposes of a concrete containing hydrophobic or crystalline admixtures is just a waste of time, effort and money. Water Absorption and Water Permeability tests offer a better and more reliable evaluation in this case.

·???????The presence of ionic salts increases the amount of coulombs passed. It is theorized that the ionic salts act as additional transport medium for the charge. This results in a higher coulomb level even though the concrete’s permeability has not changed. Admixtures that contain ionic salts are primarily accelerators composed of the following materials (Calcium Nitrite, Calcium Nitrate,?Calcium Chloride,?Sodium Thiocyanate)?“GCP applied technologies – Technical Bulletin”

·???????It can be used to show the effect of the cementitious materials on concrete durability during a design process or research activities, but it should not be used alone as a testing method tool for qualifying or disqualifying a concrete mix containing cementitious materials or in a comparison between two or more cementitious materials.

·???????The electric current used to pass through the sample during the test indicated the movement of all ions and not just the chloride ions.

·???????It measures the electrical conductance of concrete (concrete resistivity) rather than the concrete permeability.

·???????The high voltage (60V) can lead to an increase in the temperature which it may affect the accuracy of the test results. The test does not replicate actual conditions that concrete would experience in the field. There is no condition where concrete is exposed to a 60-volt potential.

·???????High potential of human errors which it may affect the accuracy of the test results.

The limitations of RCP test and the non-reliability of its test results raise requests of either withdrawing the test from ASTM standards or replacing it by similar but more robust tests such as bulk resistivity and/or surface resistivity tests.

The question is: Should RCP test be specified in a project specification in GCC region?

From the author point of view, Specifiers of concrete durability in GCC region should:

·???????Never specify RCP test as the only test in the specification for evaluating and assessing the durability of the concrete. The test might be a misleading test in case of severe and very sever exposure conditions or where “ultra-high” durable concrete is required. Specifying RCP test only might let ultra-performance concrete that uses advanced hydrophobic admixtures to fail in complying with the project requirement related to RCP.

·???????Do not remove RCP test from the specification: one of the main methods in lowering RCP test results is the use of supplementary cementitious materials. Specifying of RCP in a project specification in GCC region usually force the contractor to use binary, ternary or even quaternary mix design. The replacement percentages of cement by supplementary cementitious materials might be high too. This has many benefits such as a better durability, an improved strength, a lower environmental impact and a lower CO2 emissions.

The author recommends RCP test to be dealt as a supportive tool to lower CO2 emissions of concrete mixes in GCC region. Under the current level of concrete technology nowadays, specifying RCP in the project specification results “in most cases” in the use of the supplementary cementitious materials in the mix design which consequently results in lower CO2 emissions.?Most of GCC countries set plans and limits for CO2 emissions during the coming decades. Specifying RCP in a project specification might be an efficient supportive tool to reduce CO2 emissions in the construction sector. The specifier may specify alternative tests such as bulk resistivity or surface resistivity for the same purpose.

Author recommends that the specifier to put a limit “not less than 1500 coulombs” as a minimum requirement for lowering CO2 emissions. This limit offers a good reduction of CO2 emissions without a significant effect on the cost of the concrete since a binary mix might be enough to comply with this limit in most cases. A more restrict limit such as “less than 1000 coulombs” offers an excellent reduction of CO2 emissions but the cost of the mix should be evaluated when the concrete is not in sever or very sever exposure conditions.

Source of picture: RCP device: Perma? | Rapid Chloride Permeability | Giatec Scientific Inc.