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The negatively charged nitrogen-vacancy (NV) center in diamonds is known as the spin defect and using its electron spin, magnetometry can be realized even at room temperature with extremely high sensitivity as well as a high dynamic range. However, a magnetically shielded enclosure is usually required to sense weak magnetic fields because environmental magnetic field noises can disturb high sensitivity measurements. Here, we fabricated a gradiometer with variable sensor length that works at room temperature using a pair of diamond samples containing negatively charged NV centers. Each diamond is attached to an optical fiber to enable free sensor placement. Without any magnetically shielding, our gradiometer realizes a magnetic noise spectrum comparable to that of a three-layer magnetically shielded enclosure, reducing the noises at the low-frequency range below 1 Hz as well as at the frequency of 50 Hz (power line frequency) and its harmonics. These results indicate the potential of highly sensitive magnetic sensing by the gradiometer using the NV center for applications in noisy environments such as outdoor and in vehicles. [ABSTRACT FROM AUTHOR]

• Sessile crusts (pro.) and algal filaments (con.) were investigated together. • Algal filaments cause concrete surface deterioration, resulting in chloride penetration. • The findings suggest that poor concrete finishing may promote surface deterioration. • Surface treatment has an indirect impact on chloride attack. This study investigates combined protective and negative effects of two sessile organism groups: calcareous-based sessile invertebrates, and root-spreading botanic life forms. A series of concrete cylinders were deployed on the testing site to check how surface properties and biological attachments contribute to chloride penetration. The study methods included chloride migration tests, EPMA (SEM-WDX), and image analysis of the specimen surfaces. The findings indicate that the smooth surface-controlled concrete with GGBS exhibited decent quantities of barnacle and oyster while limiting the area settled by algae. Thus, surface treatment could be a promising solution for recruiting more intertidal species with protective effects. [ABSTRACT FROM AUTHOR]

• A 3D non-linear finite element model for non-uniformly corroded RC beams was developed. • Effect of non-uniform rebar corrosion on the structural performance of RC beams was investigated by the experimental program. • Global behavior of RC structures subjected to non-uniform rebar corrosion was studied. The structural behavior of reinforced concrete (RC) beams subjected to non-uniform rebar corrosion is studied here by developing a simplified numerical approach using three-dimensional (3D) nonlinear finite element (FE) analysis and experimental study. In order to validate the proposed numerical model and to understand the influence of nonuniform rebar corrosion on the structural performance of RC beams, seven reinforced concrete beams with identical dimensions and reinforcement layout were tested under static loading. Out of the seven beams, six beams were subjected to a different level of corrosion using an electrochemical method, and another beam was used as a control specimen without corrosion. To further verify the accuracy of the numerical model, another experimental study from the literature was selected. Finally, to investigate the influence of non-uniform rebar corrosion on the global behavior of RC structures, a hypothetical building was modelled based on the experimental result, and non-linear structural analysis was carried out. Results from the experimental and numerical study demonstrated that non-uniform corrosion of steel bars led to a significant decrease in the ductility and load carrying capacity of the RC beams. Findings of this study will be useful in assessing the residual structural performance of the RC structures with non-uniform rebar corrosion. Therefore, this study will facilitate the optimization of the maintenance and repair strategies for the deteriorated RC structures. [ABSTRACT FROM AUTHOR]

This study aims to optimize the mechanical properties of one-part alkali-activated mortar (OPAAM) containing recycled plastic aggregates (RPA) and graphene nanoplatelets (GNP) using response surface methodology (RSM). Mixtures were prepared with RPA replacing fine aggregate in varying proportions from 0 % to 50 %, and GNP added in dosages ranging from 0.1 % to 0.4 % of the binder's weight. The results indicated that RPA substitution reduced the mechanical properties of OPAAM, with compressive strength decreasing by 27.5 % and 46.9 % for mixtures with 25 % and 50 % RPA, respectively, compared to the control mixture. However, the incorporation of GNP significantly improved the mechanical properties and microstructure of OPAAM, mitigating the negative effects of RPA. The maximum compressive strengths were 57 MPa, 38 MPa, and 31 MPa for mixtures containing 0 %, 25 %, and 50 % RPA, respectively, at 28 days, achieved with a 0.2 % addition of GNP. Predicted models were proposed based on RPA and GNP to estimate the strengths and water absorption of OPAAM. These models were found to be significant, with strong correlations in predicting the mechanical properties. The optimal OPAAM mixture was achieved with 10.7 % RPA and 0.2 % GNP. This result was validated experimentally, with the difference between predicted and experimental outcomes being less than 10 %. • RPA substitution reduced 28-day compressive strength of OPAAM by up to 46.9 %. • GNP addition improved mechanical properties and mitigated RPA's negative effects. • Maximum compressive strength achieved with 0.2 % GNP addition. • Predictive models for strength and water absorption showed strong correlations. • Optimal OPAAM mix achieved with 10.7 % RPA and 0.2 % GNP. [ABSTRACT FROM AUTHOR]

When exposed to chloride-rich environments, reinforced concrete (RC) structures have serious concerns about rebar corrosion. In this study, a strengthening method was developed for RC columns with corrosion damage. Five full-scale RC columns with the same dimensions and rebar arrangements were experimented under reversed cyclic loading, where an axial stress equal to 1 MPa was applied to the specimens. Out of the five test specimens, two specimens underwent an average of 10 % rebar corrosion (Group 1), another two specimens underwent an average of 15 % rebar corrosion (Group 2), and one specimen acted as the sound specimen. One specimen from each group was retrofitted with 50 mm thick ultra-high-performance concrete (UHPC) layers. The experimental outcomes showed that reinforcement corrosion reduced ductility and maximum load-carrying capacity (MLC) significantly. The ductility and MLC of the specimen with 15 % rebar corrosion was decreased by 17 % and 9.2 %, respectively, compared to the sound specimen. However, the 15 % corroded specimen strengthened with UHPC layers displayed superior structural performance, for example, the MLC was increased by 24 % compared to the sound specimen. The performance of the strengthening scheme was evaluated using important performance indices, i.e., MLC, ductility, stiffness degradation, energy absorption, curvature distribution, etc. A simplified numerical model was developed and verified with experimental results. Experimental and numerical results revealed that the proposed approach can be very effective in strengthening corrosion-damaged RC columns. • A strengthening scheme was developed for full-scale corrosion-damaged RC columns using UHPC layers for the first time. • The strengthening effect of the UHPC layers in different corrosion ratios was investigated. • The maximum load-carrying capacity of a 15 % corroded RC columns with UHPC layers was increased by 24 % compared to the sound specimen. • Failure analysis of the strengthened specimens was carried out. • A simplified numerical model was developed. [ABSTRACT FROM AUTHOR]

Plastic waste (PW) generation continuously increases every year due to the growing population and demand for plastic materials. This situation poses a challenge to many countries, including developed ones, on how to dispose of PW. Accordingly, PW was utilized in this study to replace coarse aggregates partially in high-volume fly-ash (HVFA) concrete. However, PW decreased the strength and durability of concrete. To address this issue, graphene nanoplatelets (GNPs) were added to mitigate the negative consequences of PW and HVFA on concrete's properties. The objective of this study is to investigate the influences of PW and GNP contents on the durability and deformation of HVFA concrete. Response-surface methodology (RSM) was used to design and optimize a series of cement mixes to achieve the most desirable properties. Independent variables included PW content as partial replacement for coarse aggregates (0%, 15%, 30%, 45%, and 60% by volume), fly ash as partial substitute for cement (0%, 20%, 40%, 60%, and 80% by volume), and GNPs as additives (0%, 0.075%, 0.15%, 0.225%, and 0.3%). The considered responses were concrete unit weight, modulus of elasticity (MoE), and Cantabro abrasion loss at 300 revolutions. Results showed that PW and HVFA decreased concrete unit weight and MoE but increased Cantabro abrasion loss. By contrast, GNPs increased concrete unit weight and MoE but decreased Cantabro abrasion loss. PW and HVFA also increased the compressive toughness and porosity of concrete, while GNPs increased its stiffness but decreased its compressive toughness and porosity. The mathematical models developed to predict the unit weight, MoE, and abrasion resistance of concrete were significant, with errors of less than 6%. An optimized mix was achieved by partially replacing 12.44% of coarse aggregates with PW and 24.57% of cement with fly ash and adding 0.279% GNPs with a desirability of 100%. [ABSTRACT FROM AUTHOR]

Porous geopolymers have been extensively developed as adsorbent materials for wastewater treatment. Display of a good mechanical strength on porous adsorbent would indicate an effective practicality in applications. In this work, we prepare geopolymeric cubes from coal fly ash by potassium-activation at different ratios of silicate: hydroxide, all of which were tested for the removal of cationic dye from aqueous solution. All samples exhibited open-cell macropores ranging from 1 to 10 μm in diameter, great durability, and reusability for multiple times without a substantial loss of mass. At the ratio 3.5: 1 silicate: hydroxide, the geopolymer cube displayed a high compression strength at about 1.7 MPa, which is much higher than other similar geopolymers prepared by sodium-activation. Surprisingly, our geopolymeric cube at the ratio 0.3: 1 demonstrated a high adsorption capability of methylene blue at 84 mg/g after about 6 h contact time. Electron and vibrational spectroscopies suggested that the incorporation of potassium within the aluminosilicate structure of geopolymers was responsible for the adsorption of methylene blue. Image 1 • Highly open-cell macropore absorbent from fly ash by simple and mild fabrication. • High durability and high compression strength owing to K+-driven geopolymerization. • Higher adsorption capacity than other previously reported fly ash-based geopolymers. • Repeated use is possible with less than 7% mass loss. • Potassium-incorporated-aluminosilicate species are responsible for the adsorption. [ABSTRACT FROM AUTHOR]

Following an idea derived from the concrete-filled steel tube (CFT), this research aims to enhance the structural responses of a damaged hollow steel tube by filling it with concrete. A series of experiments are conducted to investigate the effectiveness of this technique, simulating repair but more importantly retrofitting after the tube is damaged by accidental loads such as earthquakes. To this end, loading tests are performed on the modeled specimens. The level of damage induced on the steel tube by loading is one of the parameters investigated. Concrete filling is found to improve the load-carrying capacity as well as the stiffness and ductility of a damaged hollow steel tube even with severe local buckling. The load-carrying capacity of the retrofitted steel tube is more than 1.5 times that of a hollow steel tube and was 72–89% of that of a traditional concrete-filled steel tube calculated using the design codes presented by Japan Society of Civil Engineers. From these experimental results, concrete filling promises to be an effective means of enhancing the structural response of a damaged hollow steel tube. [ABSTRACT FROM AUTHOR]

[Display omitted] • In situ observation of the cement-based materials under hydraulic pressure with image analyses revealed the volumetric strain development due to hydraulic pressure varied greatly with location, owing to heterogeneous water infiltration in the mortar specimens. • The behavior of strains and the resultant internal damage to a mortar specimen under hydraulic pressure are strongly influenced by hydraulic pressure as a confinement mechanism and water infiltration as a stress-relaxation mechanism. • In situ observation and fluorescent imaging of the small cylindrical mortar specimens showed no visible damage within the spatial resolution (50–172 μm) up to 20 MPa whilst the reduction in Young's modulus suggested the occurrence of microcracks. The influence of hydraulic pressure (max. 20 MPa) on the internal damage of cement-based materials is experimentally studied. In order to observe in situ the internal damage of cement-based materials under hydraulic pressure, a new testing apparatus equipped with an X-ray micro-computed tomography (X-μCT) scanner is developed. The behaviors of water infiltration and strain development are evaluated for mortar specimens with different water-to-cement ratios. Although the internal damage of the mortar specimens under hydraulic pressure was not detected by the X-μCT scanner and fluorescent imaging, the mechanical properties tested after hydraulic pressure loadings were altered, indicative of the occurrence of microcracks (<50 μm) below the resolution of these observation techniques. It is concluded that the internal damage of mortar specimens under hydraulic pressure is strongly influenced by two mechanisms: hydraulic pressure as a mechanism of external confinement and water infiltration as a mechanism of stress relaxation. The volumetric strain development due to hydraulic pressure varies greatly with location, owing to heterogeneous water infiltration in mortar. Therefore, the balance of these two mechanisms must be taken into account to assess the risk of internal damage of cement-based materials under hydraulic pressure. [ABSTRACT FROM AUTHOR]

• GNP was used to enhance properties of HVFA concrete containing plastic waste (PW). • GNP reduces the negative effects of PW and HVFA on the properties of concrete. • Response Surface Methodology (RSM) was used to optimize experimental variables. • Equations were developed based on RSM to predict mechanical properties of concrete. Effect of plastic waste (PW) and graphene nanoplatelets (GNP) on properties of high-volume fly ash (HVFA) concrete was investigated. Response surface methodology has been used for designing experiment, modelling, and optimization. The variables were PW, HVFA, and GNP, and the responses were strengths and water absorption. PW and HVFA reduce the strengths and absorption while GNP enhances them. The proposed models developed were significant with high level of correlation. Optimized mix was achieved by substituting 15.3% of coarse aggregate using PW, 6.07% of cement using HVFA, and adding GNP at 0.22%, and was experimentally validated with error less than 5%. [ABSTRACT FROM AUTHOR]