Quality Control

QUALITY CONTROL - In Situ Crushing Resistance - BS 8204 – 1:2002


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Annex C

Method for the determination of in situ s=crushing resistance of bonded and unbonded levelling screeds

NOTE
For floating screeds see Annex D.

C.1 Principle
The screed is subjected to repeat impact by dropping a weight vertically down a guide onto a hardened steel anvil in contact with the screed surface. The depth of the indentation from the resulting impact after four blows is measured.

C.2 Apparatus
C.2.1 BRE Screed Tester, of the form shown in Figure C.1.
It consists essentially of a cylindrical guide rod along which an annular weight of mass (4.00 + 0.01) kg travels vertically through a distance of (1 000.0 + 0.5) mm after its release by pressing a lever. At the end of its travel the weight strikes the casehardended anvil, which has its cylindrical face of (25.23 + 0.05) mm diameter in contact with the screed and thereby transmits the required impact to the screed.

C.2.2 Depth Measuring device, for measuring the depth of the indentation in the screed surface, capable of reading depths from 0mm to 10mm to an accuracy of +0.1mm.

C.3 Sampling

The method sampling will vary depending upon the size and shape of the floor area and the nature of the base, such as positions of joints.

Carry out not less than three tests in areas less than 20m² and on each 20m² to 25m² of screed laid in larger areas. Test corridors at 3m to 5m intervals. Select the positions at which tests are made at random, but include areas vulnerable to traffic damage such as doorways. Avoid testing within 300mm of joints and cracks as the test can cause further cracking. When test indentations in excess of those given in Table 5 are measured, carry out additional tests to ascertain the area of non-conformity.

NOTE For detailed guidance on the sampling and testing of screeds for in situ crushing resistance using the screed tester and interpretation of test results.

C.4 Procedure
Select a reasonably flat, smooth area of screed and ensure that it is free from loose dirt and grit. Locate the anvil of the screed tester at the test position in contact with the screed. With the guide rod held vertically, deliver four successive blows of the test weight to the anvil at the same position on the screed, dropping each time freely from the trigger point. After the fourth blow, measure the depth of the final indentation in the screed with the depth-measuring device.

NOTE When carrying out this procedure on a slope (which should not exceed 1 in 2) the guide rod should be held vertically. The average indentation should be recorded.

C.5 Expression of results
Record the measured indentations on a plan of the floor area and compare with the relevant limit shown in Table 5.