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Highlights • Cementitious sensors were fabricated with electrostatic self-assembled fillers. • Sensors were embedded into concrete columns to develop smart components. • Self-sensing properties of sensor/smart column were evaluated under loading. Abstract In this paper, cementitious sensors were fabricated with electrostatic self-assembled carbon nanotubes (CNT)/nano carbon black (NCB) composite fillers, and embedded into concrete columns to develop smart structural components. Self-sensing properties of the sensor/smart column were evaluated under cyclic loading and monotonic loading through measuring the fractional change in resistivity (FCR) of sensor. The effect of sensor on the mechanical strength of column was also studied. Experimental results showed that whether the sensor is embedded in concrete column or not, its piezoresistivity presents high stability and repeatability under cyclic loading within the elastic regime. The relationship between stress/strain and FCR of the sensor under monotonic loading obeys polynomial formulas. As the sensor is embedded into column, regardless of the concrete strength grade is C30 or C50, the piezoresistive behavior of the embedded sensor undergoes two phases, which is different from that of the sensor before embedded. This difference between the output signal characteristics results from the Poisson's ratio and elastic modulus differences of sensor and concrete. In addition, the presence of sensor does not impact the bearing capacity of concrete column. The developed sensor is therefore suitable to be embedded into prefabricated components to make smart building products which can be calibrated for structural monitoring in real applications. [ABSTRACT FROM AUTHOR]

• Post-fire curing of cement composites was notably modified by carbon nanomaterials. • CBN and MWCNT improved rehydration and strength recovery of mortars exposed to 200–400 °C. • Recured nanomodified mortars exposed to 200–400 °C and 600 °C had relative residual factors higher than 85% and 40%, respectively. • Decomposition of CBN and MWCNT after 500 °C decreased strength recovery of rehydrated mortars. Concrete elements exposed to fire can partially recover strength and stiffness if recured in water or in a moist environment. This paper reports a pioneering investigation of the influence of post-fire curing on residual mechanical properties and microstructure of cement mortars containing different concentrations of carbon-black nanoparticles (CBN) or multi-walled carbon nanotubes (MWCNT). A total of 84 specimens were subjected to various maximum exposure temperatures (200, 400, or 600 °C) and post-fire curing (water-recuring for 1 day followed by air-recuring for 27 days). X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectrometry (EDS) were used to investigate the microstructure of different types of specimens. Experimental tests were carried out to determine the compressive strength, static modulus of elasticity, and dynamic modulus of elasticity of rehydrated specimens. Nanofillers enhanced the strength recovery of composites exposed to temperatures up to 400 °C, since they improved rehydration reactions. In this case, the rehydration process provided values of relative residual strength and elastic modulus factors higher than 85%. Composites containing 0.4% MWCNT and 3% CBN presented the best strength and stiffness recovery. Therefore, small contents of carbon nanomaterials provided additional nucleation sites for dehydration products to sediment and being rehydrated. Moreover, water adsorbed by the nanomaterials during the water-recuring process was used later to provide greater rehydration. Composites containing 1.2% MWCNT and 9% CBN presented lower mechanical properties recovery, as high contents of nanomaterials made it harder for water to reach decomposed C-S-H gel, hindering the development of rehydration reactions. After 600 °C, lower relative residual factors were obtained, but always higher than 40%. It happened because nanofillers were not able to provide those rehydration improvements, since their thermal decomposition started at about 500 °C. [ABSTRACT FROM AUTHOR]

• Electrical properties of mortars were tailored with carbon nanotubes (CNT) and carbon black (CB). • Saturation points were found to be 0.25% and 0.40% for CNT and CB, respectively. • Ambient-cured geopolymer composites had compressive strength more than 25 MPa. • Multifunctional large-scale reinforced geopolymer beams were achieved under shear and flexural failure mode. • CNT-based geopolymer beams were more responsive to change of strain compared to CB-based geopolymer beams. The investigation was performed on the self-sensing behavior of reinforced geopolymer concrete beams produced at ambient curing. Prior to investigation, carbon nanotubes (CNT) and carbon black (CB) were used in small-scale geopolymer specimens at different ratios and the electrical properties of the composites were tailored in the favor of self-sensing functionality. After characterization of mechanical and electrical properties, 150 × 150 × 750 mm3 (width × height × length) self-sensing reinforced geopolymer beams were produced with a span/effective depth ratio of 2.0. An experimental procedure was designed to obtain a mixed failure mode of shear and flexural. Engineering properties of large-scale beams were evaluated in terms of flexural strength, deflection capacities, initial stiffness and ductility ratios with the proposed design. Simultaneously, self-sensing assessments were performed continuously by the evaluation of relative factor in electrical resistivity of geopolymer beams at different loading levels. Microstructural and experimental results revealed that CNT-based beams significantly enhanced the load-carrying capacity and ductility that provided a high amount of energy dissipation capacity compared to CB-based beams. CNT-based beams exhibited 107.7%, 188.9%, 217% and 51% higher relative factor in electrical resistivity compared to CB-based beams at 25%, 50%, 75% and 100% of total applied load, respectively. Results indicate that applied load was continuously sensed by all geopolymer beams although CNT-based beams were more responsive to change of strain compared to CB-based beams at earlier stages of loading. [ABSTRACT FROM AUTHOR]

• Self-sensing capability of ECC with different carbon-based materials was assessed. • Carbon fibers (CF), carbon nanotubes (CNT) and carbon black (CB) were used. • Specimens cured for 7, 28, 90 and 180 days were used for self-sensing assessment. • Tests were performed under compression, splitting tension and four-point bending. • Self-sensing is valid for all curing ages and under different loading conditions. Self-sensing capability of 7-, 28-, 90- and 180-day-old Engineered Cementitious Composites (ECC) incorporated either with carbon fibers (CF/ECC-CF) at micro-scale or multi-walled carbon nanotubes (CNT/ECC-CNT) and carbon black (CB/ECC-CB) at nano-scale were investigated herein. Mechanical properties (compressive strength, splitting tensile strength/deformation, flexural strength/deformation) of different-age mixtures were evaluated. Control mixture (ECC-Control) without any carbon-based material was also produced and tested for comparison. Depending on the loading condition, equipment utilizing either direct current (DC) or alternating current (AC) was used for self-sensing assessments. Results showed that carbon-based materials generally improve the mechanical properties of ECC-Control specimens depending on the type of carbon-based materials, specimens' age and loading conditions. All specimens sensed different types of damage except 180-day-old ECC-Control specimens loaded under uniaxial compression and splitting tension due to abrupt increments in impedance results exceeding the limits of testing device which revealed the importance of presence of electrically-conductive materials for achieving enhanced self-sensing capability independent of aging, testing configuration/equipment, loading conditions and microcrack characteristics. CF is the best to improve self-sensing capability of ECC-Control specimens for all ages and loading conditions. Self-sensing performances of ECC-CNT and ECC-CB are comparable and utilization of nano-size carbon-based materials is suggested in cases where reversibility in self-sensing is needed. [ABSTRACT FROM AUTHOR]