Testing of industrial products - Aggregates for construction

The Magnesium Sulfate test method

The principle of the method

A laboratory sample of aggregate is used to produce two test specimens of mass 425+/-5g of the 10/14mm fraction of aggregate that has been washed with distilled water and oven-dried at 110+/-5C. A saturated solution of magnesium sulfate is produced with a density of 1.292+/-0.008g/mL. The test specimens are then subjected to five 48-hour immersion and drying cycles in which they are:

The saturated solution is maintained at 20+/-2C during the test, and its density is checked at the beginning of each cycle. After completion of the five cycles, the test portions are washed free from magnesium sulfate with tap water, oven-dried, and hand-sieved on the same 10.0mm sieve as was used for their preparation. The magnesium sulfate value is calculated as:

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

where

M1 = the initial mass of the test specimen

M2 = the mass of the test specimen retained on the 10.0mm sieve after the five cycles.

The proposed CEN method

The CEN test method (Proposed prEN 1367-2 Tests for thermal and weathering properties of aggregates. Part 2 Magnesium sulfate test. CEN/TC 154 committee document, 1997.) has been developed from the British Standard (BS 812 Testing aggregates Part 121 Method for determination of soundness.). It is identical to the British method in all important respects with one exception. In the British method the magnesium sulfate result is calculated by expressing the mass retained on the 10.0mm sieve after the five cycles as a percentage of the initial test specimen mass (i.e. as 100 - MSV).

Participants in the cross-testing experiment were sent copies of the method that was prepared in 1997, 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.

It would be helpful if the CEN method contained a timetable that showed how to fit the various operations into a weekly cycle. A suggestion is given below in Table 1, which would also clarify two points of detail in the method: according to this timetable, specimens are stored over weekends in the desiccator; and the Cycle 5 includes the oven-drying operation.


Table 1. Proposed timetable for the Magnesium Sulfate test.
Week 1MondayPrepare specimens
Tuesday11.30 Place specimens in oven
Wednesday 11.30 Remove specimens from oven and place in desiccator
Wednesday 16.30 Remove specimens from desiccator and sieve
Thursday Wash specimens
Thursday 11.30 Place specimens in oven
Friday 11.30 Remove specimens from oven and place in desiccator
Friday 16.30 Remove specimens from desiccator and sieve
WeekendLeave specimens in the desiccator
Cycle 1
Week 2Monday 16.30 Place specimens in Magnesium Sulfate solution
Tuesday 09.30 Remove specimens from Magnesium Sulfate solution and allow to drain
Tuesday 11.30 Place specimens in oven
Wednesday 11.30 Remove specimens from oven and place in desiccator
Cycle 2
Wednesday 16.30 Place specimens in Magnesium Sulfate solution
Thursday 09.30 Remove specimens from Magnesium Sulfate solution and allow to drain
Thursday 11.30 Place specimens in oven
Friday 11.30 Remove specimens from oven and place in desiccator
Weekend Leave specimens in the desiccator
Cycle 3
Week 3Monday 16.30 Place specimens in Magnesium Sulfate solution
Tuesday 09.30 Remove specimens from Magnesium Sulfate solution and allow to drain
Tuesday 11.30 Place specimens in oven
Wednesday 11.30 Remove specimens from oven and place in desiccator
Cycle 4
Wednesday 16.30 Place specimens in Magnesium Sulfate solution
Thursday 09.30 Remove specimens from Magnesium Sulfate solution and allow to drain
Thursday 11.30 Place specimens in oven
Friday 11.30 Remove specimens from oven and place in desiccator
Weekend Leave specimens in the desiccator
Cycle 5
Week 4Monday 16.30 Place specimens in Magnesium Sulfate solution
Tuesday 09.30 Remove specimens from Magnesium Sulfate solution and allow to drain
Tuesday 11.30 Place specimens in oven
Wednesday 11.30 Remove specimens from oven and place in desiccator
Wednesday 16.30 Remove specimens from desiccator and wash
Test
Thursday 09.30 Place specimens in oven
Friday 09.30 Remove specimens from oven and place in desiccator
Friday 16.30 Hand-sieve specimens