Explore the vast range of titles available.

The influence of zinc oxide (ZnO) nanoparticles on the mechanical properties and photocatalytic degradation of methylene blue (MB) of ZnO-based geopolymer material was investigated under the illumination of ultraviolet (UV) radiations. In this work, ZnO-based geopolymer paste was manufactured using class F fly ash (FA) and ZnO nanoparticles powders with different mass percentages (0, 2.5, 5.0, 7.5 and 10 wt%). The FA-ZnO dry mix was activated by alkaline activator solution made from sodium silicate and sodium hydroxide with a ratio of 2.5. The mechanical properties were investigated by performing a compressive strength test at 28 days. The photocatalytic activity of ZnO nanoparticles was evaluated by measuring the photodegradation level of methylene blue under sunlight rays. The results showed a substantial influence of ZnO on the compressive strength, which decreased with the increase of ZnO amounts ranging from 2.5 to 7.5 wt% then a slightly increased at 10 wt% of ZnO. The addition of ZnO nanoparticles to a geopolymeric material showed a satisfactory efficiency of photocatalytic degradation of methylene blue after 150 min of exposure to sunlight. Phase analysis revealed that the addition of ZnO nanoparticles in the geopolymeric system develops a new ZnO crystalline phases. Graphic Abstract

This investigative study aims to study the mechanical and morphological properties of fly ash (FA)-based geopolymer paste as a repair material when applied on ordinary Portland cement (OPC) overlay concrete. The first part of this study investigates the optimal mix design of FA-based geopolymer paste with various NaOH concentrations of 8, 10, 12, and 14 M, which were used later as a repair material. The second part studies the bonding strength using a slant shear test between the geopolymer repair material and OPC substrate concrete. The results showed that a shorter setting time corresponds to the higher NaOH molarity, within the range of 53 and 30 min at 8 and 14 M, respectively. The compressive strength of FA-based geopolymer paste was found to reach 92.5 MPa at 60 days. Also, from the slant shear test results, prism specimens with 125 mm length and 50 mm wide have a large bond strength of 11 MPa at 12 M. The scanning electron microscopy/energy-dispersive X-ray (SEM/EDX) analysis showed that the OPC substrate has a significant effect on slant shear bond strength, where the presence of free cations of Ca2+ on the OPC substrate surface contributed to the formation of calcium alumina-silicate hydrate gel (C-A-S-H) by building various cross-links of Ca-O-Si.

Accurate and reliable prediction of Perfobond Rib Shear Strength Connector (PRSC) is considered as a major issue in the structural engineering sector. Besides, selecting the most significant variables that have a major influence on PRSC in every important step for attaining economic and more accurate predictive models, this study investigates the capacity of deep learning neural network (DLNN) for shear strength prediction of PRSC. The proposed DLNN model is validated against support vector regression (SVR), artificial neural network (ANN), and M5 tree model. In the second scenario, a comparable AI model hybridized with genetic algorithm (GA) as a robust bioinspired optimization approach for optimizing the related predictors for the PRSC is proposed. Hybridizing AI models with GA as a selector tool is an attempt to acquire the best accuracy of predictions with the fewest possible related parameters. In accordance with quantitative analysis, it can be observed that the GA-DLNN models required only 7 input parameters and yielded the best prediction accuracy with highest correlation coefficient (R = 0.96) and lowest value root mean square error (RMSE = 0.03936 KN). However, the other comparable models such as GA-M5Tree, GA-ANN, and GA-SVR required 10 input parameters to obtain a relatively acceptable level of accuracy. Employing GA as a feature parameter selection technique improves the precision of almost all hybrid models by optimally removing redundant variables which decrease the efficiency of the model.

This paper presents an experimental investigation on the post-repair flexural response of mortars with and without damage. In order to improve the mechanical properties of the damaged mortars, which were subjected to different loads ranging between 40 % and 90 %, the mortars specimens were reinforced and repaired using two different composite materials, the first with only epoxy resin, while the second consisted of a mixture of epoxy resin and glass fiber. The results show a significant improvement in the stiffness damaged. Therefore, the reinforced specimens by a layer of resin on the lower side surface increased the bending strength by 58 %, when compared to those control samples. The reinforcement using composite resin-fiber of glass exhibited considerable increases in the safety of constructions. The SEM images of damaged samples with and without repair, revealed the impact of reinforced glass fibers-mortar on the matrix-mortar by improving theirs mechanical performances.

Abstract Oil spillage, due to either direct or indirect accidents, can cause major environmental and economic issues if not detected and remedied immediately. In this study, the unique properties of carbon nanotubes have shown a substantial sensing capability for such a purpose when incorporated into a nanostructured composite material. A high-efficiency self-sensing nanocomposite sensor was fabricated by inserting highly conductive multi-walled carbon nanotubes (MWCNTs) into an elastomeric polymer substrate. The microstructure of the nanocomposite sensor was studied using scanning electronic microscopy and Raman spectroscopy. The response rate of the sensor was evaluated against different MWCNT concentrations, geometrical thickness and applied strains (causing by stretching). The results indicated that the response rate of the sensor (β) decreased with increasing MWCNT concentration and showed the strongest response when the sensor contained a 1.0 wt % concentration of MWCNTs. Additionally, it was found that the response time of the self-sensing nanocomposite sensors decreased in keeping with decreases in the sensor thickness. Moreover, when the sensor was subjected to strain, while immersed in an oil bath, it was found that the response rate (β) of the unstretched self-sensing nanocomposite sensor was significantly lower than that of the stretched one. The sensors given a 3% applied strain presented a response rate (β) ≈ 7.91 times higher than of the unstretched one. The self-sensing nanocomposite sensor described here shows good potential to be employed for oil leakage detection purposes due to its effective self-damage sensing capability and high sensing efficiency and low power consumption.

Drought analysis via the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI) is necessary for effective water resource management in Sarawak, Malaysia. Rainfall is the best indicator of a drought, but the temperature is also significant because it controls evaporation and condensation. This study examined drought periods in the state of Sarawak using the SPI and SPEI based on monthly precipitation and temperature data from thirty-three rainfall stations during a forty-year period (1981–2020). This analysis of drought conditions revealed that both the SPI and SPEI were able to detect drought temporal variations with distinct time scales (3, 6, 9, and 12 months). Taking precipitation and evapotranspiration data into account, the SPEI was able to identify more severe-to-extreme drought in the study area over longer time periods and moderate droughts over shorter time periods than the standard drought index. According to Pearson correlation coefficients, a substantial association existed between the SPI and SPEI during hydrological dryness. Based on the results, the temperature is a decisive factor in drought classification, and the SPI should only be used in the absence of temperature data.

Geopolymer has received great attention in recent years as a new material that could replace Ordinary Portland cement (OPC) for producing concrete. Geopolymer uses the raw materials rich in aluminium and silicon, which are activated by alkaline solutions to formulate the binder. It has been proven that the geopolymer could be a material capable of providing high-quality properties and having less environmental impact. This research project aims to investigate the capability for producing a geopolymer concrete (GPC) mainly based on the combination of various by-product materials (fly ash, (FA), ground granulated blast-furnace slag (GGBS) and high-magnesium nickel slag (HMNS)) at ambient temperature. The characteristics of the precursor materials such as the chemical compositions, particle size and shape, unburned carbon content (LOI), and amorphous and crystalline phases were characterized using various technical methods. These included Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), X-ray fluorescence spectrometer (XRF), X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy analysis (FTIR), to identify the different functional groups. In addition, a mix design procedure has been proposed in order to manufacture the FA-GGBS-HMNS-based geopolymer concrete, which is mainly based on the selection of the sodium silicate to sodium hydroxide (alkaline activator solution) ratio and the binder-to-liquid and binder-to-aggregate ratios. The effects of the selected materials and their characteristics on the properties of the fresh GPC at a room temperature of 25±2oC and a relative humidity of 85-90% were later evaluated by performing workability and setting time tests. The fresh FA-GGBS-HMNS based geopolymer concrete showed excellent workability which maintained for at least 240 minutes, without any sign of setting or stiffness before starting to harden. The mechanical properties of the hardened FA-GGBS-HMNS based geopolymer concrete, e.g. the compressive strength, the splitting tensile strength and modulus of elasticity, are similar or better when compared to those of OPC concrete. A strong relationship between the compressive strength and the theoretical modulus of elasticity was shown by a true correlation with an approximate R2 ≈ 0.997. The microstructure analysis of the GPC produced exhibits the formation of an aluminosilicate amorphous phase in a three-dimensional network. The SEM images reveal a fully compact and cohesive geopolymer matrix, which explains why the mechanical properties of the FA-GGBS-HMNS based GPC are improved, both with GGBS and with HMNS. The thermal stability and durability of the designed GPC were investigated by performing both a thermal residual test at elevated temperatures up to 900oC and a Rapid Chloride Permeability Test (RCPT) respectively. The results confirmed that the manufactured GPC showed great resistance to high temperatures, with residual strength ranged from 48.4 to 20.56 MPa. Moreover, it was found that FA-GGBS-HMNS based GPC could have the capability of resisting the migration of chloride ions and showed good behaviour against the diffusivity of chloride ions at 75 days after casting. It was also observed that, at 210 days after casting, the chloride migration coefficient increased due to the influence of different parameters such as the fineness of precursor materials, the continuation of the geopolymerization process and the pH of the pore solution of the mixture. To evaluate the dynamic behaviour of the designed FA-GGBS-HMNS GP further, an impact test was implemented using a SHPB system. The results showed that the dynamic compressive strength increased with the strain rates. A linear relationship between the dynamic increase factor (DIF) and the logarithmic strain rates experimentally, demonstrated the strain rate sensitivity of the GP paste–like material. From the aspects of damages, different failure patterns were observed under various strain rates ranging from 24.1 to 176 s-1. Furthermore, the synthesised GPC achieved good mechanical and microstructure properties at ambient curing temperature, which are sufficient for the quality of concretes, and hence it can provide the construction industry with a feasible technology which could be used for on-site and off-site applications. The main significant findings of this investigative study are: - A high compressive strength and splitting strength were achieved at 28 days with about 55.6 MPa and 4.57 MPa, respectively, with a high workable mix design. - The microstructure analysis showed the formation of dense and compact gels such as Quartz, Calcium Beryllium Praseodymium Oxide, and Magnesium Vanadium Molybdenium Oxide. - A strong relationship between the dynamic compressive strength and strain rate, which increases as the strain rate increase. - The continuity of the geopolymerization process negatively affects chloride diffusion coefficient. - The residual compressive strength increased by 3% after exposing the samples to 200 oC, then it showed different degradation trends with the temperature up to 900 oC.