Hamza ALLAM, doctorant à l’IUSTI, a reçu le prix ‘Best paper award’ à la conférence de la fédération internationale du béton.


Présentation. – Proceedings : https://phdsymp2020.sciencesconf.org/data/pages/Proceedings_phdsymp_2021.pdf
– Youtube presentation : https://www.youtube.com/watch?v=TosfqmLU9oo

Self-sensing concrete, also known as “Smart concrete”, is obtained by including electrically conductive fibers in cement-based materials. These fibers may allow to reduce electrical resistivity and develop a piezoresitive behaviour. Smart Concrete could therefore be simultaneously both a structural and a sensing material, which eliminates the need for external instrumentation in Structural Health Monitoring.
By increasing the fiber volume fraction within the cement matrix, the electrical resistivity  of the material is reduced once percolation threshold is reached. Above this percolation threshold, the fiber content is high enough to allow conductive particles to be in contact or very close to each other, thus creating a continuous conductive network within the insulative matrix. Sand’s presence was stated to have an influence on resistivity in case of fibred mortar: a high sand content may prevent the network of conductive fibers from percolating. This phenomenon is referred to as “double percolation”: the cement paste needs to be a continuous phase between sand aggregates in order to allow fibers to maintain their efficiency in reducing the electrical resistivity of composites.
However, little attention has been given to the impact of the size of sand grains on the electrical percolation. This work intends to study the effect of the grain size distribution and volume fraction of sand within mortars containing various fiber volume fractions. The results confirm. the “double percolation” phenomena: when the volume fraction of sand is close to its maximum packing density, the addition of fibres was not as effective in reducing the electrical impedance of mortar samples. In addition, sand’s grain size distribution proved an influence on impedance of mortar: fine sand showed higher impedance compared to standard sand, especially in case of high sand volume fraction. This could be related to the smaller maximum packing density in case of fine sand, where distance between particles would be in average reduced. This effect, combined with the higher number of insulative particles, could probably disrupt the continuity of the conductive network of fibres within mortar.