Testing of industrial products - Aggregates for construction

The Freeze/Thaw test method

The principle of the method

Aggregate used for the Freeze/Thaw test is single-sized production material from which the oversized and undersized aggregates have been removed. If a sieve of aperture size d mm is used to remove the undersize, then a sieve of aperture size d/2 mm should be used as the test sieve referred to below.

A laboratory sample of the aggregate is used to produce three test specimens that have been washed and oven-dried at 110+/-5C. (Note that the method does not specify what should be used to wash the aggregate.) For aggregate size fractions within the range 8mm to 16mm, such as those used in the experiment, the mass of the test specimens should be 2.0+/-0.1kg. The test specimens are placed in cans, covered with distilled or demineralised water, and stored at 20+/-3C for 24+/-1h. The cans full of aggregate are subjected to ten 24h freeze/thaw cycles in which they are:

The freezer cabinet should be controlled so that the requirements shown in Figure 1 are met. After completion of the ten cycles, the test portions are washed and sieved on the test sieve by hand. (Again note that the method does not specify what should be used to wash the aggregate.) The aggregate retained on the sieve is oven-dried and weighed, and the Freeze/Thaw value calculated as:

FTV = 100 x (M1 - M2) / M1 %

where

M1 = the initial mass of the test specimen

M2 = the mass of the test specimen retained on the test sieve after the ten freeze/thaw cycles.

The proposed CEN method

The proposed CEN method is derived from a method that has been used for many years in Germany. Participants in the cross-testing experiment were sent copies of the method that was prepared in 1996 for submission to CEN members for CEN enquiry.


Figure 1. Requirements for the freezing period of the freeze/thaw test: temperatures in the centre of a filled can located in the middle of the cabinet.