The reinforcement in glass fibre reinforced cement (grc) is not present as discrete fibres, but as 'strands' of about 200 filaments each. This configuration greatly complicates determination of the 'perimeter' of the reinforcing elements, a crucial parameter in bond strength determination. Previous investigators have attempted to quantify strand perimeters but their methods have always involved at least one subjective step and are prone to operator bias. This paper describes an objective method of determining strand perimeters using digital analysis of images captured from petrological thin sections. The measured perimeters were found to be sensitive to the "threshold value" chosen for the analysis, and consideration of perimeter vs. threshold value curves eliminated subjectivity involved in the analysis. The perimeter value obtained, together with microscopic analysis of the crack patterns produced during tensile testing, were used for calculating bond parameters for different cement matrices. The development of bond with both ageing time and temperature were also studied. The method uses fundamental image analysis concepts and as such is readily adaptable to solve conceptually similar problems in a wide range of materials.