A test specimen of the 0/2 mm fraction of a sand is placed in a transparent, graduated cylinder, together with a small quantity of flocculating solution (containing calcium chloride, glycerine and formaldehyde). The mixture is agitated to loosen the clay coatings from the sand, and irrigated with more flocculating solution to force the fine particles into suspension. The cylinder is left standing upright for 20 minutes, during which time the coarser particles settle to form a sediment at the bottom of the cylinder but the finer particles remain in suspension in the flocculant. Two measurements are then made:
h1 = the height of the upper level of the flocculant above the base of the cylinder;
h2 = the height of the upper level of the sediment above the base of the cylinder;
The Sand Equivalent value is calculated as:
SE = 100 × h2 ÷ h1
The test is carried out on sand with a moisture content (w %) in the range 0 <= w <= 2 %. The moisture content of a separate test specimen of the 0/2 mm fraction of the sand is determined and used to calculate the test specimen mass that contains 120 g of the dry 0/2 mm fraction.
With a clean sand containing very few clay particles, the upper level of the flocculant will be close to the upper level of the sediment, so an SE value close to 100 SE units is obtained. Sands that contain substantial amounts of clay can give SE values as low as 20 or 30 SE units.
The CEN test method has been developed from the French Standard P 18-598 (AFNOR, 1991. P 18-597 Détermination de la propreté des sables: équivalent de sable à 10 % de fines (ES10).). In the French method the test is carried out on a 0/5 mm fraction. It is mainly used to check the cleanliness of natural sands used in concrete. The test is also commonly used in Denmark to measure the cleanliness of the 0/4 mm fraction of natural all-in aggregate.
Participants in the cross-testing experiment were sent copies of the method that was prepared in August, 1996, to be sent to CEN members for CEN enquiry. Some laboratories may have used the version prepared in their own language, and may have been given additional information by their National Co-ordinator.