Scales and accessories

Following Louis Vicat’s research into concrete in the early 19th century, around 1850 the first tests to measure the tensile strength of lime and cement mortars were devised. H. Fruhling and W. Michaëlis, who sought to standardise these measurements, showed a small-scale traction machine at the Universal Exposition in 1878. The Commission on Methods of Testing Construction Materials adopted it in 1895, and the Conservatoire acquired one from the precision instrument makers Ponthus & Therrode in 1907. To determine a mortar’s tensile strength, a sample of the mortar to be tested is first mixed in a standardised figure-8-shaped mould. When the mortar has hardened, the sample is placed between two claws then progressively stretched by a lever lowered by a container filled with lead pellets. The weight required to rupture the sample gives a precise measurement of the sample’s tensile breaking strength.