Composite modelling of enlarged expansion movement strain of clay brickwork walls

The vertical movement strains of full-scale single-leaf clay brickwork walls (18 brick wide x 13 high) exhibiting enlarged expansion (cryptoflorescence) were monitored in the laboratory over a duration of 90 days, so that a composite model could be developed that would accurately predict the moisture movement strain. Previous studies have failed in their ability to predict the enlarged expansion of clay brickwork walls. Two brickwork walls were con-structed, one with ‘kiln fresh’ and one with 28-day old Fletton clay bricks.

Using the vertical moisture movement composite model developed by Brooks resulted in a significant underestimation of the amount of measured moisture movement strain. Using the measured strains, equations were developed for the vertical enlarged expansion movement of walls built from ‘kiln fresh’ and 28-day-old Fletton clay bricks. Along with a mortar modification factor, which was applied to the unbonded mortar strains to allow for a better representation of the shrinkage within the masonry to be acknowledged, these equations were used to enhance Brooks’ vertical moisture movement composite model. Whereas previously the composite model failed to predict the movement of masonry exhibiting enlarged expansion (its pre-dictions underestimated the ‘kiln fresh’ and 28-day-old brickwork walls, with a percentage difference of 110% and 177%, respectively), the predictions of the modified model presented in this paper were within 17% and 15%, respectively, of the measured ‘kiln fresh’ and 28-day old brickwork vertical strains. This is the first time that this accuracy of prediction has been achieved, ultimately resulting in the movements of a greater range of masonry types being predicted.