Influence of loading rate and specimen geometry on lime mortar strength

Abstract

Compressive and flexural strength are important properties because they relate to the quality and durability of a material, and its suitability for a particular design or application. In addition, compressive strength is a principal parameter used to classify and compare materials and establish their requirements in building standards. Therefore, it is important to establish the parameters that affect these properties so that results are comparable. It is known that specimen size and shape, water content, curing conditions, aging and compaction determine the strength of mortars and concrete. This paper sets out the influence of loading rates, increasing from 5 to 900 Newton per second, a n d s p e c i me n g e o me t r y ( c u b e s a n d h a l f p r i sms ) on the compressive and flexural strengths of hydraulic lime mortars. The limes used are NHL5, NHL2 and FL2 which develop strength as a result of hydration and carbonation. The paper concludes that compressive and flexural strength are a function of the loading rate, increasing significantly as the loading rate increases; and that the possible reason for this is that, at high strain rates, micro-cracks do not have sufficient time to search for paths of minimum energy but are forced to propagate along the shortest paths with higher resistance, and this increases the peak load at which the material fails thus increasing its strength. In addition, the results indicate that the shape and size of the specimens also impact strength (half prisms being on average 37% stronger than cubes). The ratio of length to height which determines how strains build up in the specimen is probably one of the main shape parameters that affect the strength measured.