The mechanical performance of cementitious materials can be improved by incorporating carbon nanotubes (CNTs). Nevertheless, some challenges must be overcome, such as reducing the agglomeration trend of CNTs and minimizing their negative effect on the fresh state of the cementitious matrices. In this study, early-age portland cement (PC) hydration and the rheological behavior of cementitious composites with nonsilanized, 3-aminopropyltriethoxysilane (APTES)-functionalized CNTs were investigated. The APTES-functionalized CNTs were incorporated into PC pastes in contents of 0.05% and 0.1% by cement weight. The rotational rheometry of the CNT cementitious composites was carried out during the first hour of hydration. The effect of CNT silanization on cement hydration was assessed using isothermal calorimetry and in situ X-ray diffraction (XRD) for 48 h. The functionalization of CNTs with APTES offset the negative effect of nonsilanized CNTs on the fresh properties of the cementitious matrix, reducing the dynamic yield stress up to 39%. Calorimetry and in situ XRD results revealed that nonsilanized CNTs hindered early cement hydration, while the APTES-treated CNTs allowed proper hydration. At 28 days, the XRD and thermogravimetric analysis (TGA) results indicated that nonsilanized and silane-treated CNTs showed an equivalent hydration degree compared to the plain cement paste. Overall, CNT silanization improved the early age performance of cement pastes, enhanced the fresh properties of cement pastes, and did not affect the early hydration of PC.

The concept of self-healing materials and the development of encapsulated curing agents represent a cutting-edge approach to enhancing the longevity and reducing the maintenance costs of cementitious structures. This systematic literature review aims to shed light on the parameters involved in the autonomous self-healing of cementitious materials, utilizing various encapsulated healing agents such as pellets, granules, and capsules. This review also identifies and selects studies that offer additional insights into the efficacy of the self-healing process in cementitious materials and the influence of these specific encapsulated healing agents on the physical mechanical properties of mortars. This comprehensive approach provides a deep understanding of the interplay between self-healing and the physical–mechanical properties of mortars containing these encapsulated healing agents. The main findings indicate that the cement-to-sand ratio, characteristics of fine aggregates, and encapsulation methods significantly impact crack control, self-healing efficiency, and properties of mortar in both fresh and hardened states. The content of encapsulated healing agents within the cementitious matrix affects both the initial workability or flow and subsequent mechanical properties. While pellets coated with PVA film typically reduce workability in the fresh state and compressive strength, capsules coated with Portland cement and sodium silicate mitigate these effects and improve crack sealing in fresh and hardened states without compromising the self-healing capacity of cracks. The three-point flexural test has emerged as the preferred method for a pre-crack assessment over 28 days, with variations depending on the type of healing agent used. As noted in the literature, water has been identified as the optimal environment for autonomous healing. These findings underscore the potential of encapsulation techniques to enhance self-healing capabilities through the controlled release of agents within the cementitious matrix, thereby advancing the research on and development of intelligent construction materials and increasing the durability of cement-based structures.

The application of carbon nanotubes to produce cementitious composites has been extensively researched. However, the dispersion of this nanomaterial remains a technical limitation for its use. Thus, initially, this study assessed the stability of carboxyl-functionalized CNT on aqueous suspensions and simulated cement pore solution for 6 h through UV–visible spectroscopy. Subsequently, a CNT content of 0.1% by cement weight was incorporated into the cement pastes, and the compressive strength after 7, 14, 28, and 91 days was evaluated. In addition, the porosity of the CNT cementitious composites at 28 days of hydration was investigated by mercury intrusion porosimetry (MIP), and the microstructure was evaluated via scanning electron microscopy (SEM). The simulated cement pore solution’s alkaline environment affects the CNT stability, progressively reducing the dispersed CNT concentration over time. CNT reduced the cementitious matrix pores < 50 nm by 8.5%; however, it resulted in an increase of 4.5% in pores > 50 nm. Thus, CNT incorporation did not significantly affect the compressive strength of cement pastes. SEM results also suggested a high porosity of CNT cementitious composites. The CNT agglomeration trend in an alkaline environment affected the CNT performance in cement-based nanocomposites.

This paper significantly extends investigations into internal damping ratios in both undamaged and damaged conditions for normal-strength concretes (NSCs) and high-strength concretes (HSCs). This study examines concretes with compressive strengths ranging from 42 to 83 MPa. Cyclic loads were applied using a servo-controlled hydraulic testing machine, and for each cyclic step, the dynamic elastic modulus ($E_d$) and internal damping ratio ($\xi$) were determined through acoustic tests. The results show that the normal-strength concretes ($f_c=42$ MPa) exhibited an undamaged internal damping ratio of $\xi =0.5\%$, reaching a maximum of $\xi =2.5\%$ at a damage index of 0.8. Conversely, the high-strength concrete mixtures ($f_c=83$ MPa) showed an undamaged internal damping ratio of $\xi =0.29\%$, with a peak value of $\xi =0.93\%$ at a damage index of 0.32. The initial internal damping values are influenced by porosity and transition zones, which affect the material behavior under cyclic loads. Progressive damage leads to increased Coulomb damping due the cracking process. Few studies have quantified and comprehended the internal damping ratio under cyclic loading-induced damage, and this research advances our understanding of NSC and HSC behavior under dynamic excitation and damage evolution, especially in impact scenarios.