Visual inspection has been the most widely used technique for monitoring concrete structures in service. Inspectors visually evaluate defects based on experience, skill, and engineering judgment. ...However, this process is subjective, laborious, time-consuming, and hampered by demanding access to numerous parts of complex structures. Accordingly, the present study proposes a nearly automated inspection model based on image processing and deep learning for detecting defects in typically inaccessible areas of concrete structures. Results indicate that using the Keras classifier combined with Otsu image processing can achieve superior classification accuracy of 97.63%, 96.5%, and 96.17% for training, validation, and testing data, respectively, along with low quantification error of 1.5%, 5% and 2% for the crack length, width, and angle of orientation, respectively. The type of structural damage and its severity are identified based on the allowed range of concrete crack width for different structures, including buildings and bridges based on different international standards and codes. The proposed method can deploy unmanned aerial vehicle image acquisition to offer a nearly automated inspection platform for the colossal backlog of aging concrete structures.
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Self-healing efficiency of cement-based materials has so far been evaluated mostly through the healing of surface cracks, without adequately capturing the dominant effects of environmental exposure ...or accurately quantifying the volume of cracks healed. In addition, the effects of diverse additions such as silica-based materials, swelling agents, and carbonating minerals on self-healing performance under different environmental exposure, remain largely unexplored. In this study, multiple test methods were used to investigate self-healing of cracks in cement mortar incorporating metakaolin, bentonite, and calcium carbonate microfiller in different environmental exposure. Change in crack width was monitored using optical microscopy. Backscattered electron microscopy coupled with energy disperse X-ray analysis was used to identify healing compounds. Mercury intrusion porosimetry and water absorption were employed to assess porosity. X-ray computed micro-tomography (X-ray μCT) with 3-dimensional image processing was used to segment and quantify cracks before and after healing. After one year of exposure, no significant self-healing occurred in all specimens exposed to cyclic T and RH. Conversely, all specimens submerged in water exhibited variable levels of self-healing, which depended on the type of mineral added. The healing efficiency was 32.26%, 27.27%, 25.6%, and 24.1% for specimens incorporating limestone microfiller, portland cement alone, bentonite, and metakaolin, respectively. The formation of calcium carbonate was found to be the main contributor to self-healing of surface cracks.
The use of recycled tire rubber in asphalt pavements to improve the overall performance, economy, and sustainability of pavements has gained considerable attention over the last few decades. Several ...studies have indicated that recycled tire rubber can reduce the permanent deformation of flexible pavements and enhance its resistance to rutting, reduce pavement construction and maintenance costs, and improve the resistance to fatigue damage. This paper provides a systematic and critical overview of the research on and practice of using recycled tire rubber in asphalt pavements in terms of engineering properties, performance, and durability assessment. This critical analysis of the state-of-the-art should enhance the understanding of using recycled tire rubber in asphalt pavements, define pertinent recommendations, identify knowledge gaps, and highlight the need for concerted future research.
The durability of zero-cement concrete or alkali-activated materials (AAMs) is a subject of controversy, especially when exposed to sulfate attacks. This can be due to the different elemental and ...microstructural compositions of the broad alkali-activated systems that exhibit different degradation mechanisms in sulfate-rich environments. Various parameters, such as properties of raw source materials (nature, fineness, and mineralogy), activators (type and concentration), mixture design, curing regime, types of sulfate salt and sulfate ion concentrations, and weathering conditions, are considered to have a significant impact on zero-cement concrete sulfate attack resistance. Furthermore, the adequacy of the standard sulfate immersion tests raises more concerns about the reported behavior. This paper presents a critical review of the current aging protocol associated with ordinary cement resistance and zero-cement concrete or AAMs to external sulfate attack.
Several studies have investigated the properties of alkali-activated materials (AAM), considering it as a substitute of cementitious concrete. However, the studies on alkali-activated ...self-consolidating concrete (AASCC) are extremely limited. This paper investigated the properties of AASCCs utilizing ground granulated blast furnace slag (GGBFS) as the main precursor. Single, binary, and ternary AASCCs were produced using fly ash Class-F (FA) and silica fumes (SF) as a replacement for GGBFS. The fresh properties including filing ability, passing ability and stability, as well as the hardened properties including unconfined compressive strength, ultrasonic pulse velocity, electrical resistivity, absorption, and sorptivity of the ambient cured one-part AASCC mixtures with different precursor blends were investigated. In addition, the microstructural properties of 90-day AASCC blends were studied by various microscale analysis methods. This paper demonstrated that the higher fraction of sodium carbonate/silicate activators, ranging from 20% to 25%, contributed to delayed reaction kinetics and satisfactory fresh and mechanical properties in all systems due to their nature. Slag replacement with variable SF or FA class-F ratios, instead, could indeed adjust the particle size distribution of the total binder material and improve the fresh concrete characteristics in binary and ternary systems. Finally, the formation of various reaction products and binding gels, i.e., C-(N)A-S-H, was found to have a significant impact on several transport mechanisms, including capillary sorptivity, permeable pores, and bulk electrical resistivity.
Little is known about the etiology of childhood diarrhea in the United Arab Emirates (UAE) especially after the introduction of rotavirus vaccines. This study aimed to identify gastrointestinal ...pathogens in children with diarrhea (cases) and the carriage rate of these pathogens in asymptomatic children (controls).
Stool samples were collected from 203 cases and 73 controls who presented to two major hospitals in Al Ain city, UAE. Samples were analyzed with Allplex™ Gastrointestinal Full Panel Assay for common entero-pathogens. The association between diarrhea and the isolated pathogens was calculated in a multivariate logistic regression model. The adjusted attributable fractions (aAFs) were calculated for all pathogens significantly associated with cases.
At least one pathogen was identified in 87 samples (42.8%) from cases and 17 (23.3%) from controls (P < 0.001). Rotavirus, norovirus GII and adenovirus were significantly more prevalent in cases. Their aAFs with 95% ci are 0.95 (0.64, 1.00) for rotavirus, 0.86 (0.38, 0.97) for norovirus GII and 0.84 (0.29, 0.96) for adenovirus. None of the 13 bacteria tested for were more commonly found in the cases than in controls. Cryptosporidium spp. were more significantly detected in cases than in controls. Co-infections occurred in 27.9% of the children. Viruses and parasites were significantly more likely to occur together only in the cases.
Multiplex PCR revealed high positivity rates in both cases and controls which demand a cautious interpretation. Rotavirus remains the main childhood diarrhea pathogen in UAE. Effective strategies are needed to better control rotavirus and other causative pathogens.
During their service life, concrete structures are subjected to combined fluctuations of temperature and relative humidity, which can influence their durability and service life performance. ...Self-healing has in recent years attracted great interest to mitigate the effects of such environmental exposure on concrete structures. Several studies have explored the autogenous crack self-healing in concrete incorporating superabsorbent polymers (SAPs) and exposed to different environments. However, none of the published studies to date has investigated the self-healing in concrete incorporating SAPs under a combined change in temperature and relative humidity. In the present study, the crack width changes due to self-healing of cement mortars incorporating SAPs under a combined change of temperature and relative humidity were investigated and quantified using micro-computed tomography and three-dimensional image analysis. A varying dosage of SAPs expressed as a percentage (0.5%, 1% and 2%) of the cement mass was incorporated in the mortar mixtures. In addition, the influence of other environments such as continuous water submersion and cyclic wetting and drying was studied and quantified. The results of segmentation and quantification analysis of X-ray µCT scans showed that mortar specimens incorporating 1% SAPs and exposed to environments with a combined change in temperature and relative humidity exhibited less self-healing (around 6.58% of healing efficiency). Conversely, when specimens were subjected to cyclic wetting and drying or water submersion, the healing efficiency increased to 19.11% and 26.32%, respectively. It appears that to achieve sustained self-healing of cracks, novel engineered systems that can assure an internal supply of moisture are needed.
Conventional cross-laminated timber is an engineered wood product consisting of solid-sawn lumber panels glued together. In this study, the structural behavior of solid wood panels of ...Nail-Cross-Laminated Timber (NCLT) panels connected with nails instead of glue was studied. The failure mode and nail deformation of the novel NCLT panels under axial compression load using eight full-scale NCLT panels was investigated. The effects of four key design parameters, namely, the nail type, number of nails, nail orientation angle, and nail slenderness ratio on axial compression performance of NCLT panels were also analyzed. In addition, a formula for predicting the axial compression bearing capacity of NCLT panels was developed. For calculation of the slenderness ratio, the moment of inertia of the full section or the effective section was determined based on the nail type, number of nails, angle of nail orientation and number of layers of the plate. Results showed that specimens connected by tapping screws had best compressive performance.
The Bacillus Calmette-Guérin (BCG) preparations are live-attenuated derivatives of Mycobacterium bovis. These products are used to vaccinate infants at birth, a practice that may result in a ...disseminated infection in those patients who have an unidentified immunodeficiency.
Patients who were immunized at birth with BCG and who developed a disseminated infection are reported here to emphasize the importance of taking an extensive medical history before giving the BCG vaccine. Patient 1 has a sibling who had familial hemophagocytic lymphohistiocytosis. Patient 2 has a severe immunodeficiency with profound lymphopenia. Patient 3 has a sibling who had a disseminated BCG infection. Patient 4 has two siblings with an immunodeficiency disorder; one sibling passed away in infancy and one is receiving regular immunoglobulin infusions. Patient 5 has profound lymphopenia and his brother had cytomegalovirus (CMV) pneumonitis and passed away in infancy.
These unfortunate events could have been avoided by compiling the relevant clinical and laboratory information. These cases also underscore the importance of a strict adherence to the BCG vaccine policies. Local and international registries that estimate the birth prevalence of primary immune deficiencies are needed prior to implementing universal BCG vaccination administration.
Crack self-healing in bio-green concrete Zhang, Lei V.; Nehdi, Moncef L.; Suleiman, Ahmed R. ...
Composites. Part B, Engineering,
12/2021, Volume:
227
Journal Article
Peer reviewed
Eco-efficient concrete produced by alkali-activation of recycled by-products has increased susceptibility to cracking. This study investigates the potential of S. pasteurii bacteria to impart crack ...self-healing in such green concrete. Porous expanded glass granules made from recycled glass were used, for the first time, as bacterial and nutrient carriers. Scanning electron microscopy, Raman spectroscopy, capillary water absorption, and inductively coupled plasma optical emission spectroscopy were deployed to investigate self-healing efficiency in the bio-green concrete under various environmental exposure. Crack widths up to 111 μm for moist-dry cured specimens incorporating bacteria were completely healed within 90 days, while no self-healing was observed in the control specimens. The sorptivity coefficient in specimens incorporating S. pasteurii bacteria was also much lower. SEM-EDS combined with Raman spectroscopy indicated that the dominant self-healing product was calcite. This study elucidates crack remediation in AAMs and demonstrates the potential of this novel biogenic self-healing system in green concrete structures.
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