Determination of bond strength in glass fibre reinforced cement using petrography and image analysis

The reinforcement in glass fibre reinforced cement (grc) is not present as discrete fibres, but as 'strands' of about 200 filaments each. This configu ration greatly complicates determination of the 'perimeter' of the reinforc ing elements, a crucial parameter in bond strength determination. Previous investigators have attempted to quantify strand perimeters but their method s have always involved at least one subjective step and are prone to operat or bias. This paper describes an objective method of determining strand per imeters using digital analysis of images captured from petrological thin se ctions. The measured perimeters were found to be sensitive to the "threshol d value" chosen for the analysis, and consideration of perimeter vs. thresh old value curves eliminated subjectivity involved in the analysis. The peri meter value obtained, together with microscopic analysis of the crack patte rns produced during tensile testing, were used for calculating bond paramet ers 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 si milar problems in a wide range of materials. (C) 2000 Kluwer Academic Publi shers.