Piezoresistive cement mortars and alkali-activated fly ash mortars

This study was carried out in the framework of the SensCrHEAT project (Self-SENSing conCretes for HEATing products). The research focused on two types of mortars: one based on ordinary Portland cement (OPC) and another on alkali-activated fly ash (AAF). For each type, three different mixes were developed: 1) a mix without any additions as reference, 2) a mix with commercial graphene nano-platelets (GNP) at 0.5 vol%, and 3) a mix with two recycled materials, i.e., biochar (BCH) at 0.5 vol% and recycled carbon fibers (RCF) at 0.05 vol%. Compressive strength (Rc) and electrical impedance during curing as well as during cyclic compressive strength tests were measured. Results showed that the addition of GNP reduced the Rc of mortars by over 10% after 28 days of curing, whereas BCH and RCF did not negatively affect the Rc. Furthermore, BCH and RCF significantly reduced the electrical impedance of mortars, achieving better performance than commercial GNP for self-sensing purposes. This was also reflected in the piezoresistivity of the mortars since mortars containing the combination of BCH and RCF demonstrated the highest sensitivity in both OPC (5.18∙10-4 με⁻¹) and AAF (7.91∙10-2 με⁻¹) formulations.