A N Fried, J J Roberts and A Yool Kingston University


The use of the methylene blue dye test to determine the extent of harmful material in building sands is now included in draft European Standards [I]. When the test is carried out on building sands it indicates the potential danger of clays in the sands to cause deterioration of the mortar. The test does not extend to hardened mortars. In this programme of work, the use of methylene blue dye adsorption tests for harmful clay fines in aggregates for concrete and mortar has been extended to aggregate that has been recovered from laboratory specimens of hardened building mortar and to a limited extent to hardened samples of site mortar Results of tests on the laboratory specimens of mortar suggest that testing aggregate recovered from hardened mortar for methylene blue dye adsorption is a practical proposition worthy of further investigation. Tests on failed mortar recovered from site suggest that the sand used had a high methylene blue dye adsorption that may have contributed to the failure.