Frost Resistance test on Aggregates with and without Salt (FRAS) (NT TR 566)

  • Report #: NT TR 566
  • Approved: November 2004
  • Author(s): Pétur Pétursson, Björn Schouenborg
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  The main objective of the project was to test aggregates from different sources throughout Europe at different laboratories in Europe, with both pure water and salt water freeze/thaw test methods, to widen the applicability of the freeze/thaw test method in 1 % NaCl. A part of this objective was to demonstrate that different freeze/thaw cabinets can be used to obtain comparable results, as long as the desired sample temperature is adhered to. Another objective was to gain reliable repeatability and reproducibility values for frost resistance test methods with and without salt (NT BUILD 485 and EN 1367-1). Thirdly, to produce and suggest to the relevant task group of CEN/TC 154, a revised method for testing aggregate freeze/thaw resistance with 1 % NaCl to be included in the European Standards. The first step involved inter-comparative, frost resistance testing of eighteen aggregate samples both using fresh water and a 1 % NaCl solution. The second step involved statistical evaluation of the test results for both methods used. Additionally, water absorption and particle density of the aggregates tested was measured to compare with freeze/thaw test results. Correlation was established between laboratories in frost resistance test results for both test methods, i.e. with and without salt. Correlation between test results when testing in fresh water and a salt solution was also established, although the numerical values are not comparable between the two test methods. The fresh water method (based on EN 1367-1) produced frost resistance values less than 2 % for all the aggregates tested (mean value of all laboratories) and thereof values less than 1 % for 15 out of 18 aggregate samples, including aggregates of known poor quality. Bearing in mind requirement categories in the product standards of CEN/TC 154, it was concluded that the fresh water method does not distinguish adequately between frost resistant and frost susceptible aggregates. The salt water method (based on NT BUILD 485) gives a wide spread in values between aggregates, leaving the frost resistant aggregates generally intact but causing degradation of the poorer ones, up to 33 % for the poorest aggregate sample tested (mean value of all laboratories). The ranking of aggregates according to frost resistance values obtained is generally according to predicted quality. Therefore it is possible, by using the salt solution, to introduce new requirement categories in the product standards of CEN/TC 154, based on the connection between test results and known quality of the aggregates tested in this project as well as previous, practical experience.  
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