Recycled Aggregate: A Viable Solution for Sustainable Concrete Production.

Construction and demolition activities consume large amounts of natural resources, generating 4.5 bi tons of solid waste/year, called construction and demolition waste (C&DW) and other wastes, such as ceramic, polyethylene terephthalate (PET), glass, and slag. Furthermore, around 32 bi tons of natural aggregate (NA) are extracted annually. In this scenario, replacing NA with recycled aggregate (RA) from C&DW and other wastes can mitigate environmental problems. We review the use of RA for concrete production and draw the main challenges and outlook. RA reduces concrete's fresh and hardened performance compared to NA, but these reductions are often negligible when the replacement levels are kept up to 30%. Furthermore, we point out efficient strategies to mitigate these performance reductions. Efforts must be spent on improving the efficiency of RA processing and the international standardization of RA.

Effect of TiO2 Nanoparticles on the Fresh Performance of 3D-Printed Cementitious Materials.

3D printing (3DP) of cementitious materials shows several advantages compared to conventional construction methods, but it requires specific fresh-state properties. Nanomaterials have been used in cement-based materials to achieve specific fresh and hardened properties, being potential candidates for 3DP applications. However, there are no reports on using TiO2 nanoparticles (nano-TiO2) in 3DP cementitious composites. Thus, the current work aims to assess the effect of nano-TiO2 on the fresh performance of 3DP cementitious materials. For this purpose, nano-TiO2 was incorporated in pastes and mortars from 0 to 1.5 wt.%. Time-resolved hydration (in situ XRD) and rheological and printing-related properties (buildability and printability) were evaluated. Results showed that nano-TiO2 particles enhanced the cement hydration kinetics, leading to further ettringite formation up to 140 min compared to plain cement paste. Rheological measurements showed that the nano-TiO2 incorporation progressively increased the static and dynamic stress, viscosity, and structuration rate of pastes. Furthermore, nano-TiO2 improved the buildability of the composites, progressively increasing the maximum number of successive layers printed before failure from 11 (0 wt.% TiO2) to 64 (1.5 wt.% TiO2). By contrast, the nano-TiO2 addition reduced the printability (i.e., the printable period during which the sample was able to be molded by the 3D-printing process) from 140 min (0% TiO2) to 90 min (1.5% TiO2). Thus, incorporating "high" nano-TiO2 contents (e.g., >1 wt.%) was beneficial for buildability but would require a quicker 3DP process. The adoption of nano-TiO2 contents of around 0.75−1.00% may be an interesting choice since it reduced the printability of paste by 30 min compared with the control mix but allowed for printing 24 layers (118% higher than plain mortar).

Influence of Ultrasonication of Functionalized Carbon Nanotubes on the Rheology, Hydration, and Compressive Strength of Portland Cement Pastes.

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.

Utilization of Thermally Treated SiC Nanowhiskers and Superplasticizer for Cementitious Composite Production.

Nanomaterials are potential candidates to improve the mechanical properties and durability of cementitious composites. SiC nanowhiskers (NWs) present exceptional mechanical properties and have already been successfully incorporated into different matrices. In this study, cementitious composites were produced with a superplasticizer (SP) and 0-1.0 wt % SiC NWs. Two different NWs were used: untreated (NT-NW) and thermally treated at 500 °C (500-NW). The rheological properties, cement hydration, mechanical properties, and microstructure were evaluated. The results showed that NWs incorporation statistically increased the yield stress of cement paste (by up to 10%) while it led to marginal effects in viscosity. NWs enhanced the early cement hydration, increasing the main heat flow peak. NWs incorporation increased the compressive strength, tensile strength, and thermal conductivity of composites by up to 56%, 66%, and 80%, respectively, while it did not statistically affect the water absorption. Scanning electron microscopy showed a good bond between NWs and cement matrix in addition to the bridging of cracks. Overall, the thermal treatment increased the specific surface area of NWs enhancing their effects on cement properties, while SP improved the NWs dispersion, increasing their beneficial effects on the hardened properties.

Materials for Production of High and Ultra-High Performance Concrete: Review and Perspective of Possible Novel Materials.

This review article proposes the identification and basic concepts of materials that might be used for the production of high-performance concrete (HPC) and ultra-high-performance concrete (UHPC). Although other reviews have addressed this topic, the present work differs by presenting relevant aspects on possible materials applied in the production of HPC and UHPC. The main innovation of this review article is to identify the perspectives for new materials that can be considered in the production of novel special concretes. After consulting different bibliographic databases, some information related to ordinary Portland cement (OPC), mineral additions, aggregates, and chemical additives used for the production of HPC and UHPC were highlighted. Relevant information on the application of synthetic and natural fibers is also highlighted in association with a cement matrix of HPC and UHPC, forming composites with properties superior to conventional concrete used in civil construction. The article also presents some relevant characteristics for the application of HPC and UHPC produced with alkali-activated cement, an alternative binder to OPC produced through the reaction between two essential components: precursors and activators. Some information about the main types of precursors, subdivided into materials rich in aluminosilicates and rich in calcium, were also highlighted. Finally, suggestions for future work related to the application of HPC and UHPC are highlighted, guiding future research on this topic.

Pulmonary histoplasmoma: a disguised malady.

Histoplasmosis is a mycosis caused by the dimorphic fungus, Histoplasma capsulatum, which is transmitted via dust and aerosols. Lung involvement is the most common, with a varied clinical presentation. Although it is not the only source of infection, H. capsulatum is frequently found in bat guano, which is the reason why it is highly prevalent among caving practitioners. The solitary histoplasmoma of the lung is an unusual and chronic manifestation of this entity, which mimics, or at least is frequently misconstrued, as a malignancy. Almost invariably, the diagnosis of this type of histoplasmosis presentation is achieved after lung biopsy. The authors present the case of a young woman who sought medical care because of chest pain. The diagnostic work-up revealed the presence of a pulmonary nodule. She was submitted to a thoracotomy and wedge pulmonary resection. The histologic analysis rendered the diagnosis of histoplasmoma. This report aims to call attention to this diagnosis as the differential diagnosis of a pulmonary nodule.

Ultrasonometric evaluation of bone healing: Experimental study using a model of diaphyseal transverse osteotomy of sheep tibiae.

Noninvasive ionizing-radiation-free methods of evaluation, such as ultrasonometry, are desirable in any medical situation. An in vitro ultrasonometric study was undertaken to evaluate the bone healing process of sheep tibiae submitted to a diaphyseal transverse osteotomy at different times after the procedure. Fifteen sheep weighing an average of 37 kg had surgery for a transverse mid-diaphyseal osteotomy of the right tibia; they were divided postoperatively into three groups of five for periods of observation at 30, 45 and 60 days. The intact left tibiae of the 15 animals were used for control. The healing process was monitored with conventional radiographs taken at two-week intervals, and the animals were killed at the end of the period of observation of each group. Both surgical and intact tibiae were removed, their diameters were measured and they were submitted to measurement of underwater ultrasound propagation velocities (USPV) at the osteotomy sites in both the sagittal and frontal planes. The diameters of the surgical tibiae decreased with time in both planes (from 26.9 mm to 22.0 mm and to 20.9 mm in the sagittal plane, and from 29.3 mm to 23.9 mm and to 23 mm in the frontal plane), with significant differences between the periods of observation (p < or = 0.018 and p < or = 0.003 between 30 and 45 days and 30 and 60 days, respectively, for the sagittal plane and p < or = 0.006 and p < or = 0.003 between 30 and 45 days and 30 and 60 days, respectively, for the frontal plane) and between surgical and intact tibiae at all time points (p < or = 0.0005 for each comparison). USPV increased with time from 2290 m/s to 2399 m/s and to 2382 m/s in the sagittal plane, and from 2376 m/s to 2472 m/s and to 2466 m/s in the frontal plane, accounting for an approximate 5% difference between 30 and 60 days Differences between the surgical and intact tibiae were significant at all time points (p < or = 0.0005 for both sagittal and frontal planes) but not between periods for either plane. There was a strong negative correlation between diameter and USPV (Pearson's correlation coefficient of -0.8998 for the sagittal plane and -0.9192 for the frontal plane). It was concluded that ultrasonometric evaluation of the bone healing process is feasible, yielding precise and reliable results, with a potential for clinical application.