Variability of the mechanical properties of hemp concrete

The focus of this study is on statistical analysis of hemp concrete properties. The main objective is to determine statistically the variability of the three main properties, which are: material density, compressive strength and Young’s modulus. The analysis is done with respect to four main parameters, namely: the testing laboratory equipment and procedure, the hemp shiv type, the batch elaboration and finally the specimen size
Two types of hemp shiv have been used with two batches for each type. Two cylindrical specimen sizes have been considered: 11x22 cm and 16x32 cm. All the specimens were manufactured and dried in the same laboratory in order to ensure the repeatability and homogeneity of studied material. After 90 days of drying under the same conditions, the specimens were transported to ten different laboratories for compressive testing. Before testing, a drying protocol during 48 hours was applied by all laboratories for all specimens. Then, a unique protocol for compressive testing has been applied using the compressive testing machine in each laboratory. Finally, all data have been collected for statistical analysis. In this study, the results obtained by different laboratories show low variability for compressive strength and dry density; which is not the case for Young's modulus. Three probability distributions, namely: normal, log-normal and Weibull, have been proposed to fit the experimental results.