The functionalization process usually increases the localized defects of carbon nanotubes (CNT). Thus, the ultrasonication parameters used for dispersing non-functionalized CNT should be carefully evaluated to verify if they are adequate in dispersing functionalized CNT. Although ultrasonication is widely used for non-functionalized CNT, the effect of this dispersing process of functionalized CNT has not been thoroughly investigated. Thus, this work investigated the effect of ultrasonication on functionalized CNT + superplasticizer (SP) aqueous dispersions by ultraviolet-visible (UV-Vis) spectroscopy, dynamic light scattering (DLS), and Fourier transform infrared spectroscopy (FTIR). Furthermore, Portland cement pastes with additions of 0.05% and 0.1% CNT by cement weight and ultrasonication amplitudes of 0%, 50% and 80% were evaluated through rheometry, isothermal calorimetry, compressive strength at 1, 7 and 28 days, X-ray diffraction (XRD), and thermogravimetric analysis (TGA). FTIR results from CNT + SP dispersions indicated that ultrasonication may negatively affect SP molecules and CNT graphene structure. The increase in CNT content and amplitude of ultrasonication gradually increased the static and dynamic yield stress of paste but did not significantly affect its hydration kinetics. Compressive strength results indicated that the optimum CNT content was 0.05% by cement weight, which increased the strength of composite by up to 15.8% compared with the plain paste. CNT ultrasonication neither increases the degree of hydration of cement nor the mechanical performance of composite when compared with mixes containing unsonicated CNT. Overall, ultrasonication of functionalized CNT is not efficient in improving the fresh and hardened performance of cementitious composites.

The ornamental stone industry generates large amounts of waste thus creating environmental and human health hazards. Thus, pastes with 0–30 wt.% ornamental stone waste (OSW) incorporated into ordinary Portland cement (OPC) were produced and their rheological properties, hydration kinetics, and mechanical properties were evaluated. The CO₂ equivalent emissions related to the pastes production were estimated for each composition. The results showed that the paste with 10 wt.% of OSW exhibited similar yield stress compared to the plain OPC paste, while pastes with 20 and 30 wt.% displayed reduced yield stresses up to 15%. OSW slightly enhanced the hydration kinetics compared to plain OPC, increasing the main heat flow peak and 90-h cumulative heat values. The incorporation of OSW reduced the 1-, 3-, and 28-days compressive strength of the pastes. Water absorption results agreed with the 28 days compressive strength results, indicating that OSW increased the volume of permeable voids. Finally, OSW incorporation progressively reduced the CO₂ emission per m³ of OPC paste, reaching a 31% reduction for the highest 30 wt.% OSW content. Overall, incorporating up to 10 wt.% with OSW led to pastes with comparable fresh and hardened properties as comported to plain OPC paste.