This study investigated the mechanical, electrical, and piezoresistive performances of mortars made with Ordinary Portland cement (OPC) and limestone calcined clay cement (LC³), especially when reinforced with 0.1 wt% recycled carbon fibre (rCF) by weight of the binder. The results found that 0.1 wt% rCF failed to considerably enhance the electrical conductivity of OPC and LC³ mortars during the curing period, but the enhancement became apparent when these composites were 1 day-dried. With the increasing cement replacement ratio and the introduction of rCF, the mechanical properties deteriorated because of the dilutive effects together with the fragility of rCF. The OPC and LC³ mortars exhibited a certain degree of piezoresistivity under compression, which was amplified with added 0.1 wt% rCF. Additionally, the piezoresistive performance of the LC³ mortar was better than that of the OPC mortar, regardless of the presence of rCFs. The sensing capacity of composites is greatly weakened in terms of flexural stress. In terms of the two-probe method, because of the contact resistance, the resistivity usually decreases under compression, which results in larger fractional changes in resistivity values. This study aims to develop a low conductivity self-sensing cement-based composite (SSCC) filled with a small dosage of rCF.