Green Land Reclamation Limited
(Now at Kingston University)

A novel rig has been developed to assess the shrinkage behaviour of building mortars. The rig induces cracking in the mortar if shrinkage occurs and measurement of crack width, without dismantling the specimen, gives a direct indication of shrinkage. Cracking may not necessarily appear in practical applications but a comparison can be made between different mortars. A study has been made of 1:1:5.5 mortars, with and without air entrainment, made with a range of commercial building sands. Plastic shrinkage was greater than drying shrinkage and it appeared that plastic shrinkage reduced the capacity of the mortar for later drying shrinkage. Sands having the highest clay content produced mortars showing most shrinkage. However, mortar made with a sand with low clay but high fines content also showed substantial shrinkage. Mortars applied to oven-dry brick substrates showed more plastic shrinkage than those applied to saturated bricks. Air-entrainment reduced mortar shrinkage considerably.