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Aerial additive manufacturing (AAM) represents a paradigm shift in using unmanned aerial vehicles (UAVs, often called 'drones') in the construction industry, using self-powered and untethered UAVs to extrude structural cementitious material. This requires miniaturisation of the deposition system. Rheological properties and known hydration times are important material parameters. Calcium aluminate cement (CAC) systems can be advantageous over purely ordinary Portland cement (OPC) binders as they promote hydration and increase early strength. A quaternary OPC/pulverised fuel ash (PFA)/CAC/calcium sulphate (CS) system was combined with polyvinyl alcohol (PVA) fibres and pseudoplastic hydrocolloids to develop a novel AAM material for miniaturised deposition. CAC hydration is affected by environmental temperature. Intending material to be extruded in situ, mixes were tested at multiple temperatures. OPC/PFA/CAC/CS mixes with PVA fibres were successfully extruded with densities of ≈1700 kg/m 3 , yield stresses of 1.1–1.3 kPa and a compressive strength of 25 MPa. Pseudoplastic OPC/PFA/CAC/CS quaternary cementitious systems are demonstrated to be viable for AAM, provided mixes are modified with retarders as temperature increases. This study can significantly impact industry by demonstrating structural material which can be extruded using UAVs in challenging or elevated in situ construction, reducing safety risks. [ABSTRACT FROM AUTHOR]

[Display omitted] • Higher water to cement ratio mixes showed more rapid changes in their EMI response. • Impedance signature amplitudes were related to the mortar damping properties. • The higher frequency impedance peaks shift more rapidly through the curing stage. • The PZT actuation range withdraws as the actuation frequency increases. • Higher frequency EMI response was related to the mortars' outer layers' response. Lead Zirconate Titanate (PZT) based electromechanical impedance (EMI) sensors were used to monitor the mechanical properties development of different water to cement ratios (w/c) cementitious mortar mixes, during the first 28 days of curing under water. Through using the analytical procedure proposed in this study to analyse the EMI data, the different mixes mechanical properties development through the curing period were detected, and the EMI response was able to provide a more detailed interpretation regarding the difference between the surface and the bulk material mechanical properties development. Both the peaks from the impedance signature (Z) and the first difference of the impedance signature (dZ) showed shifts to higher frequency ranges as the age of the samples increased, indicating an increase in the material stiffness. Furthermore, the compressive and the flexural stresses showed an R2 > 0.8 and > 0.9, respectively in relation to the frequency shifts. The relationship between the PZT-EMI response through the curing period and the sample's mechanical properties was shown to be frequency-dependent; hence a numerical analysis using ANSYS Workbench 18.1 was undertaken to understand this frequency-dependence phenomenon. From the numerical model, the impedance signature response at higher frequency ranges was shown to be dominated by the response from the surface of the hosting material, whereas the response from the specimen's interior dominated the lower frequencies EMI response. The analytical approach proposed in this study is expected to assist in differentiating between internal cementitious materials processes, such as internal curing, and those originating at the surface, such as aggressive chemical agents penetration. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of dewatering on the strength and microstructure of mortars manufactured from Portland cement, hydrated calcium lime (CL90), and natural hydraulic limes of classification 2, 3.5, and 5 with binder/aggregate/water ratios of 1:2:0.78. Dewatering was achieved by placing the mortars on a high porosity brick. Dewatered and nondewatered specimens were exposed to an atmosphere containing 400 ppm carbon dioxide with a relative humidity of 65%, at 20°C for periods of 14, 28, and 56 days. Following hardening for these periods, compressive strengths were compared with evaluate the mechanical performance. The structural morphology of the samples was determined using scanning electron microscopy and chemical composition by Raman spectroscopy. Results showed CL90 mortars are unaffected by dewatering. However, dewatering resulted in an increase in the compressive strength for the hydraulic limes and cement mortars tested. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents results about the characterisation of the biomass fly ashes sourced from a thermal power plant and from a co-generation power plant located in Portugal, and the study of new cement formulations incorporated with the biomass fly ashes. The study includes a comparative analysis of the phase formation, setting and mechanical behaviour of the new cement–fly ash formulations based on these biomass fly ashes. Techniques such as X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), thermal gravimetric and differential thermal analysis (TG/DTA), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and environmental scanning electron spectroscopy (ESEM) were used to determine the structure and composition of the formulations. Fly ash F1 from the thermal power plant contained levels of SiO2, Al2O3 and Fe2O3 indicating the possibility of exhibiting pozzolanic properties. Fly ash F2 from the co-generation plant contained a higher quantity of CaO (∼25%). The fly ashes are similar to class C fly ashes according to EN 450 on the basis of chemical composition. The hydration rate and phase formation are greatly dependant on the samples’ alkali content and water to binder (w/b) ratio. In cement based mortar with 10% fly ash the basic strength was maintained, however, when 20% fly ash was added the mechanical strength was around 75% of the reference cement mortar. The fly ashes contained significant levels of chloride and sulphate and it is suggested that the performance of fly ash–cement binders could be improved by the removal or control of these chemical species. [Copyright &y& Elsevier]

Lead zirconium titanate (PZT) has recently emerged as a low-cost material for non-destructive monitoring for civil structures. Despite the numerous studies employing PZT transducers for structural health monitoring, no studies have assessed the effects of both damage and repair on the electromechanical impedance response in cementitious materials. To this end, this study was conducted to assess the effects of the damage and repair of mortar samples on the electromechanical response of a surface-mounted PZT transducer. When damage was introduced to the specimen in stages, the resonance frequencies of the admittance signature were shifted to lower frequencies as the damage increased, and an increase in the peak amplitude was detected, indicating an increase in the damping and a reduction in the material stiffness properties. Also, increasing the damage in the material has been shown to decrease the sensitivity of the PZT to further damage. During the repair process, a noticeable difference between the after-damage and the after-repair admittance signatures was noted. The root-mean-square deviation (RMSD) showed a decreasing trend during the repair process, when compared to the before repair RMSD response which indicated a partial recovery for the material properties by decreasing the damping property in the material. [ABSTRACT FROM AUTHOR]

• • Novel inorganic fullerene tungsten disulfide (IF-WS 2) CEM1 nanocomposite. • • Formation of CaWO 4 interface layer between IF-WS 2 and hydration products. • • 1 wt% addition of IF-WS 2 provides highest energy adsorption capability. • • 86% improvement in flexural strength of IF-WS 2 enhanced 3D printed specimens. An original cement based material enhanced with inorganic fullerene tungsten disulfide (IF-WS 2) nanoparticles has been engineered with superb shock absorbing properties. Physical properties were attributed to the IF-WS 2 nano-hollow multiple layered onion-like structure. The effect of IF-WS 2 concentration at 0.1 wt%, 1 wt% and 5 wt% on the hydration kinetics of ordinary Portland cement (CEM1), electrical impedance, thermal stability, rheology and strength development was thoroughly evaluated. X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and X-ray diffraction (XRD) studies confirmed the formation of the new phase, calcium tungstate (CaWO 4), at the nano-particle/cement matrix interface during early hydration. 1 wt% IF-WS 2 additions enhanced the impact energy of CEM1 by 89% compared to the control. An IF-WS 2 cementitious mixture was developed for 3D printing based on the 1% WS 2 -CEM composition. The mix exhibited excellent workability and buildability enabling the creation of a layer-by-layer printed component. Intimate interlayer adhesion minimized the presence of voids leading to a high flexural strength of 6.7 MPa, which equated to an over 86% improvement compared to plain CEM1 printed components. This study showcases IF-WS 2 nanoparticles as a new ground-breaking additive enabling the production of high-performance cementitious construction materials, for use under extreme environments demanding high strength and impact resistance. [ABSTRACT FROM AUTHOR]