Electrical Conductivity Double Percolation in Portland Cement Mortar Incorporating Iron Sand as Fine Aggregate in Presence of Recycled Carbon Fibers

The new generation of multifunctional cementitious mixtures incorporating carbon fibers (CFs) with relatively low electrical resistivities is rapidly gaining importance in applications such as structural health monitoring and heated pavement deicing. In these mixtures, CFs are added to the paste, which occupies only a small volume fraction of concrete compared to that of the aggregates. Aggregates such as quartz and limestone that are commonly used for concrete production have high electrical resistivities. This can impede the electronic conduction in concrete mixtures and reduce the effect of the CFs. Increasing the paste volume of concrete has been previously proposed to overcome this issue. However, this method will increase the cost and greenhouse gas (GHG) emissions associated with producing concrete. In this regard, using conductive aggregates can provide a promising solution. This study aims to evaluate the effect of incorporating iron sand as the fine aggregate on the double percolation of mortars incorporating recycled CFs. The percolation of mortars incorporating up to 1 vol% CFs (pristine form or pre-dispersed) was investigated as the baseline. Iron sand was used to replace 25, 50, 75, and 100 vol% of standard quartz sand, separately and together with up to 0.6 vol% CFs. The synergistic effect of iron sand and CFs on the flow properties of mortars was studied through flow table test. The compressive strength (7-day and 28-day) and electrical resistivity (28-day) of the mortars were measured to evaluate the effect of CFs and iron sand as electrically conductive fillers in the mortar. The results showed that replacing standard quartz sand with iron sand reduced the electrical resistivity while maintaining the compressive strength and flow characteristics of mortars incorporating CFs.