The Strain Sensitivity of Coal Reinforced Smart Concrete by Piezoresistive Effect

The structures are challenged by earthquakes, material degradations and other environmental factors. In order to protect the lives, assets, and for maintenance planning, structural health monitoring (SHM) is important. In SHM applications, strain gages are widely used which have low durability, low sensitivity while they have high cost. To monitor a structure, large number of strain gages have to be used that increases the cost. In this study, seven coal reinforced concrete mixtures with 0, 0.35, 0.5, 0.8, 1, 1.5 and 2 volume % of coal were designed; three cubic samples for each mixture were fabricated. Simultaneous strain and electrical resistance measurement of the samples during the compression test was conducted. A strong linear piezoresistive relationship between strain and electrical resistance change with a correlation coefficient of 0.99 was determined. The concrete mixture having 0.8 volume % coal had the highest strain sensitivity of K=44, which was 22 times the strain sensitivity of commercial metal strain gages while it had a linearity error of LE=6.9% that was low. This mixture with 0.8 volume % coal is a candidate to be smart concrete which can sense its strain. As a contribution to the literature, a phenomenological model for the relationship between gage factor and coal volume % was explained in details. The multifunctional smart concrete will be used as a smart material, which can sense its strain in SHM applications while acting as a load bearing material.