Masonry: Assessing Strength and Condition
The strength of existing masonry is frequently required when modifications are to be made to a building (be it creating an opening, inserting a padstone to support a beam or adding extra floors to a building).
There is no British Standard for testing existing brickwork, however indicative results for testing brick strength can be obtained using the test method for new bricks. A set of ten whole bricks is required for specification compliance purposes but recognising the difficulties in obtaining bricks from existing masonry this number is sometimes reduced for this type of assessment work.
Mortar mix proportions can be determined by chemical analysis. However it is not always possible to distinguish with certainty between Portland cement and lime binders or between hydraulic and non-hydraulic limes. Complimentary microscopical examination can usually ascertain the presence or otherwise of Portland cement in the mortar and of calcareous material in the aggregate.
Approximate Basic Compressive Stress for brickwork incorporating lime/sand mortars can then be estimated from historical Codes of Practise whilst the Characteristic Compressive Strength of cement/sand mortar masonry is given in BS 5628.
Sandberg can also test masonry cores for compressive strength but it must be recognised that testing core samples taken perpendicular to the surface of a masonry wall or arch may not replicate the loading conditions of the wall/arch.
In addition to estimating strength of masonry, Sandberg also carries out condition surveys, investigating causes of deterioration and likely future performance including repair options.
Test specimens can be taken to represent the range of exposure conditions and brick types (original/spalled/replaced). A testing programme could comprise:
- Preliminary visual examination
- Microscopical examination of both bricks and mortar
- Compressive strength and Water absorption of bricks
- Brick soluble salts content
- Chemical analysis of mortar to determine mix proportions and sulphate content
For further information contact: Richard Rogerson, Partner
Direct Tel: 020 7565 7080