Structural Engineering Research Centre

This paper presents the development of ambient temperature cured ultra-high-performance geopolymer concrete (UHPGPC). Ultra-high-performance concrete (UHPC) mixtures were developed by completely eliminating Portland cement and activating industrial by-product materials such as ground granulated blastfurnace slag and silica fume. Local standard sand (maximum size 2 mm), quartz sand (600 μm) and 0·16 mm diameter steel fibres of 13 and 6 mm length were used. Fresh properties (density and flowability) and mechanical properties (compressive strength) of the UHPGPC produced under ambient temperature curing conditions were evaluated. Four mixtures with fibres and one mix without fibre addition were studied as the UHPGPC mixtures. The highest average compressive strengths obtained were 175 MPa for UHPGPC with steel fibres (1% 6 mm and 2% 13 mm) and 124 MPa for UHPGPC without fibres. Prismatic specimens (100 × 100 × 500 mm) were cast to determine the flexural strength, which was found to be 10·3–13·5 MPa and 9·1 MPa for mixes with and without steel fibres respectively. The compressive and flexural strengths obtained in this work are comparable to UHPC strengths presented in the literature. Production of this innovative material with industrial by-products and without the conventional curing regimes used for UHPC will improve sustainability and lead to cast-in-situ applications of UHPC.

Li-rich oxides continue to be of immense interest as potential next generation Li-ion battery positive electrodes, and yet the role of oxygen during cycling is still poorly understood. Here, the complex electrochemical behavior of Li4FeSbO6 materials is studied thoroughly with a variety of methods. Herein, we show that oxygen release occurs at a distinct voltage plateau from the peroxo/superoxo formation making this material ideal for revealing new aspects of oxygen redox processes in Li-rich oxides. Moreover, we directly demonstrate the limited reversibility of the oxygenated species (O2(n-); n = 1, 2, 3) for the first time. We also find that during charge to 4.2 V iron is oxidized from +3 to an unusual +4 state with the concomitant formation of oxygenated species. Upon further charge to 5.0 V, an oxygen release process associated with the reduction of iron +4 to +3 is present, indicative of the reductive coupling mechanism between oxygen and metals previously reported. Thus, in full state of charge, lithium removal is fully compensated by oxygen only, as the iron and antimony are both very close to their pristine states. Besides, this charging step results in complex phase transformations that are ultimately destructive to the crystallinity of the material. Such findings again demonstrate the vital importance of fully understanding the behavior of oxygen in such systems. The consequences of these new aspects of the electrochemical behavior of lithium-rich oxides are discussed in detail.

Brain tumor is a serious disease occurring in human being. Medical treatment process mainly depends on tumor types and its location. The final decision of neuro-specialists and radiologist for the tumor diagnosis mainly depend on evaluation of MRI (Magnetic Resonance Imaging) Images. The manual evaluation process is time-consuming and needs domain expertise to avoid human errors. To overcome this issue, Faster R-CNN deep learning algorithm was proposed for detecting the tumor and marking the area of their occurrence with Region Proposal Network (RPN). The selected MR image dataset consists of three primary brain tumors namely glioma, meningioma and pituitary. The proposed algorithm uses VGG-16 architecture as a base layer for both the region proposal network and the classifier network. Detection and classification results of the algorithm demonstrate that it is able to achieve an average precision of 75.18% for glioma, 89.45% for meningioma and 68.18% for pituitary tumor. As a performance measure, the algorithm achieved a mean average precision of 77.60% for all the classes.

Ultra High Performance Concrete (UHPC) is one of the recently emerging technologies in the construction industry. The strain hardening behavior, ductility, and toughness in UHPC are primarily contributed by the presence of the fibers. The major considerations adopted for the selection of fiber are: material properties should be compatible; fiber–matrix interaction must be sufficient to transmit stresses, and the aspect ratio must be optimal to ensure efficient post-cracking behavior. The efficiency of fibers is mainly dependent on their nature, fiber combination, fiber orientation, fiber mechanical properties, and fiber geometry. As detailed aforementioned, multiple criteria need to be satisfied for judicious selection of fibers. In view of the same, a critical review is presented in this study to provide a ready reference to the stakeholders regarding the effect of the fiber on the fresh and hardened properties of UHPC. In the first part, the fiber-to-binder interaction mechanism, geometrical and strength properties of metallic, inorganic, polymeric, carbon, and hybrid fibers adopted in UHPC are detailed. In the second part, the impact of fibers dosage and geometry is studied on workability, rheology, microstructure, compressive strength, tensile strength, and durability properties. Based on the findings, future potential applications, current challenges, and an overall summary are presented.

The effect of accelerated curing and steel fibre volume on ultra-high performance concrete (UHPC) is the focus of this paper. The compressive strength and microstructural properties of UHPC were evaluated under water, steam and heat curing. The results show that heat-cured samples have higher mechanical properties than those undergoing the other curing techniques. Experimental studies were conducted on heat-treated specimens with different steel fibre volumes and aspect ratios (2·5% and 2·0% of 13 mm and 6 mm length fibres of diameter 0·16 mm) to examine stress–strain behaviour, tensile behaviour and flexure behaviour. The stress–strain behaviour of UHPC was evaluated by uniaxial compression tests on cylinders to propose a new stress–strain model for UHPC under compression. Size-dependent and size-independent fracture energies were determined as per the Rilem procedure and the P–δ tail correction method. Flexural and residual strengths were evaluated under four-point bending.

Setting up a health monitoring system for large-scale civil engineering structures requires a large number of sensors and the placement of these sensors is of great significance for such spatially separated large structures. In this paper, we present an optimal sensor placement (OSP) algorithm by treating OSP as a combinatorial optimization problem which is solved using a swarm intelligence technique called particle swarm optimization (PSO). We propose a new hybrid PSO algorithm by combining a self-configurable PSO with the Nelder–Mead algorithm to solve this rather difficult combinatorial problem of OSP. The proposed algorithm aims precisely to achieve the best identification of modal frequencies and mode shapes. Numerical experiments have been carried out by considering civil engineering structures to evaluate the performance of the proposed swarm-intelligence-based OSP algorithm. Numerical studies indicate that the proposed hybrid PSO algorithm generates sensor configurations superior to the conventional iterative information-based approaches which have been popularly used for large structures. Further, the proposed hybrid PSO algorithm exhibits superior convergence characteristics when compared to other PSO counterparts.

One of the consequences of the state's inability to protect the life and property of all its citizens—especially in developing countries—is the formation of private alternatives to crime prevention and control. Gated communities, or enclosed neighbourhoods, are one such popular alternative. This article compares the phenomenon of gated communities in two developing countries: South Africa and Brazil. Both countries are plagued by violent crime and share key human development indicators. The article also explores key issues that have been raised around gated communities in both countries. Gated communities can contribute to spatial fragmentation in urban areas, and reflect increased polarisation, fragmentation and diminished solidarity within society. By excluding other urban residents and people from surrounding neighbourhoods, gated communities can contribute to social exclusion, inhibiting the construction of social networks that form the basis of social and economic activities.

Improved electrochemical performance of Na_0.67MnO₂ through Ni and Mg substitution.

(a) Photon absorption and exciton formation, (b) interstitial sulfur emission, (c) interstitial zinc emission, (d) blue emission, (e) electron trapping by Mn ions' d state, (f) orange light emission and (g) orange emission quenching by electrons trapped by the neighbouring Mn²⁺ ions.

Information regarding the early strength gain of fresh concrete determines the time for the removal of form work and the transfer of pre-stressing forces for pre-stressed concrete. An ultrasonic based non-destructive evaluation of early strength gain may not work for concrete in fluid and semi-solid phases. A possible alternative is a lead zirconate titanate (PZT)-based smart aggregate embedded in concrete, which can evaluate the micro-structural and rheological properties right from the fluid phase. A set of five smart aggregates embedded in a concrete cube were investigated for their suitability to evaluate electromechanical impedance (EMI) signatures. Cubes were loaded to failure and the EMI during progressive strength loss under compressive loads was studied. To show the generalized applicability of this, experimental results for the performance of typical smart aggregates on a larger specimen, namely a concrete beam, are also discussed. Different statistical metrics were examined computationally on a three peak admittance curve with a parametric variation of stiffness, damping and simple scaling. The root mean square deviation (RMSD), mean absolute percentage deviation (MAPD), cross correlation (CC) and modified cross correlation (MCC) were investigated, in addition to the rate of change of the RMSD. Variations between the reference and modified states were studied. Both stiffness and mass gains occur for the smart aggregates, resulting in an increase or decrease of frequency and amplitude peaks due to progressive C-S-H gel formation. The trend of increasing stiffness and the consequent rightward shift of the resonant peaks and decrease of damping, with the consequent upward shift of amplitudes that happens during curing and strength gain, was observed to be reversed during the application of damaging loads.

This work focuses on the use of copper slag, as a partial replacement of sand for use in cement concrete and building construction. Cement mortar mixtures prepared with fine aggregate made up of different proportions of copper slag and sand were tested for use as masonry mortars and plastering. Three masonry wall panels of dimensions 1 × 1 m were plastered. The studies showed that although copper slag based mortar is suitable for plastering, with the increase in copper slag content, the wastage due to material rebounding from the plastered surfaces increases. It is therefore suggested that the copper slag can be used for plastering of floorings and horizontal up to 50 % by mass of the fine aggregate, and for vertical surfaces, such as, brick/block walls it can be used up to 25 %. In this study on concrete mixtures were prepared with two water cement ratios and different proportions of copper slag ranging from 0 % (for the control mix) to 100 % of fine aggregate. The Concrete mixes were evaluated for workability, density, and compressive strength.

Porous carbon derived from silk cotton and heteroatom engineering is explored in this study for developing metal-free electrocatalysts for oxygen reduction (ORR). Individual and dual doping of N and F heteroatoms was conducted to regulate defects and the pore geometry to the porous carbon matrix. Microscopic analysis of N–F co-doped cotton carbon (N–F/CTC) undergoes morphological amendments in its textural properties and defects responsible in creating active sites for ORR. N–F/CTC catalyst exhibits excellent ORR catalytic activity and methanol and CO tolerance in the alkaline medium, which makes it a potential metal-free ORR catalyst for the polymer electrolyte membrane fuel cell. N–F/CTC catalyst is subjected to 10 000 repeated potential cycles with no degradation in its activity. XPS analysis of N–F/CTC catalyst revealed the presence of N in the form of pyridinic-N, pyrrolic-N, graphitic-N, active species, and F in the form of C–F ionic and C–F semi-ionic active forms. The maximum C–C bond polarization, charge redistribution, and high spin densities in the carbon matrices are attained by all these active forms present in the catalyst and synergistically enhance the ORR activity.

Nitrogen and fluorine co-doped graphite nanofibers (N/F-GNF) and their cumulative effect with Fe and Co have been developed as an alternative non-precious metal catalyst for efficient oxygen reduction reaction (ORR) in acidic media. The synergistic effect between the doped hetero atoms and the co-ordinated Fe and Co towards ORR activity and durability of the catalyst is deeply investigated. A high ORR onset potential comparable with commercial Pt/C catalyst is observed with the Fe-Co/NF-GNF catalyst, which indicates that this catalyst is a potential alternative to Pt/C. A fivefold increase in mass activity is achieved by the Fe-Co/NF-GNF catalyst compared to the simple N/F-GNF catalyst, which endorses the significant role of transition metal atoms in enhancing ORR activity. The advanced Fe-Co/NF-GNF catalyst also exhibits complete tolerance to CH3OH and CO. The Fe-Co/NF-GNF catalyst also exhibits excellent durability towards the ORR with only a 10 mV negative shift in its half wave potential after a 10 000 repeated potential cycling test, whereas in the case of a commercial Pt/C catalyst there was an ∼110 mV negative shift under similar environmental conditions. More stringent corrosive test cycles were also performed by maintaining the cell as high as 1.4 V with a later decrease to 0.6 V vs. RHE for 300 cycles, which showed the excellent durability of the Fe-Co/NF-GNF catalyst in comparison with the Pt/C catalyst. XPS analysis of the Fe-Co/NF-GNF catalyst presents the ORR active chemical states of N (pyridinic-N and graphitic-N) and F (semi-ionic-F) and the co-ordinated sites of Fe and Co species with the dopants. The excellent performance and durability of the Fe-Co/NF-GNF catalyst is due to the synergistic effect between the hetero atoms dopants (N and F) and strong co-ordinating bonds of M-N-C, which protect the graphene layers around the metallic species and greatly mitigates the leaching of Co and Fe during the long term cycling test. The high activity and long term durability of the Fe-Co/NF-GNF catalyst make it a promising ORR electrocatalyst for the fuel cell cathode reaction.

This investigation is mainly focused on the effect of class F fly ash on the micro and macrolevel properties of self compacting concrete (SCC) after 28, 56 and 112 days of curing. The microlevel properties studied were the microcrack widths between aggregate and paste and atomic Calcium–Silica (Ca/Si) ratio. The macrolevel properties studied were compressive strength, modulus of elasticity and splitting tensile strength. A conventional concrete (CC) having an equivalent 28-day SCC compressive strength has also been examined at different ages. Scanning electron microscope (SEM) analysis was carried to examine the width of microcracks and energy dispersive X-ray analysis (EDAX) was carried out to determine the chemical elements of both SCC and CC. Studies revealed that pozzolanic action of class F fly ash improved the microlevel properties of SCC with age by reducing the microcracking width and Ca/Si ratio and thus enhanced the macrolevel properties.

This article describes an image processing based technique used to estimate the relationship between volume and mass of axi-symmetric fruits like apple, sweet-lime, lemon, and orange. The technique used a single camera to capture five different views of a fruit. The volume of the fruits was estimated based on its shape. The fruits were categorized into spherical, ellipsoid, and paraboloid shapes and an appropriate analytical model for calculating volume was used for each category. The volume computed was in accordance with the actual volume determined by water displacement method. The average densities measured were 0.808 g/cm3 for apples, 0.912 g/cm3 for sweet-limes, 0.912 g/cm3 for lemons, and 0.814 g/cm3 for oranges. As the density of a particular fruit within a batch was fairly constant, there was a good correlation between the volume and mass of fruits. This hypothesis was used to determine the mass of the fruits based on the estimated volume. Thus with a simple approach used to estimate the volume using a single camera, it was also possible to find the mass of the fruits. The proposed techniques were implemented using C++ language and open source computer vision library and the results were found to be reasonably accurate.

This article presents details of the experimental studies carried out on cement mortar using Bacillus cereus and Bacillus pasteurii in different cell concentrations. Test results showed that the addition of bacterial cultures of both species, enhanced the compressive strength of cement mortar due to the bio-mineralization of calcium carbonate in the cement mortar matrix. The test results revealed 38% increase in compressive strength using B. cereus and 29% increase in the case of B. pasteurii over the control cement mortar. The chloride ingress capacity of B. cereus incorporated concrete found through rapid chloride permeability test confirms the reduction of chloride penetration compared to control sample. Characterization studies have been performed to confirm the calcite precipitation through different experimental techniques, viz. X-ray diffraction, scanning electron microscope, thermogravimetric analysis and Fourier transform-infrared spectroscopy.

Abstract In a recent study, Agrahari and Kapuria (J Int Mater Sys Struct, 27 , 1283–1305, 2016) presented a Lamb wave based refined time reversal method (RTRM) for baseline-free damage detection in thin plate structures. In this method, it was proposed to conduct the probe at the frequency of best reconstruction and to use an extended wave packet ranging between two side bands accompanying the main mode of the reconstructed signal for computing the damage index. The method showed excellent sensitivity to damage in a single actuator-sensor path scenario. In the present work, the RTRM is integrated with a damage imaging algorithm called the reconstruction algorithm for probabilistic inspection of defects (RAPID) to develop an accurate baseline-free damage localization technique using a network of piezoelectric wafer patch transducers. Its performance is tested experimentally in an aluminium plate with a block mass damage. It is found that the proposed RTRM conducted at the best reconstruction frequency of the sensor network-plate system is able to predict the damage location with very good accuracy, whereas the other existing baseline-free methods such as the conventional TRM with single mode tuning and the reciprocity principle based method are either ineffective in localizing or give highly erroneous prediction of the damage location.

The effect of amorphous nanosilica particles on the mechanical properties and durability of two high-strength concrete (HSC) mixes was investigated. Nanosilica in powder form was used as a partial replacement of cement at dosages of 1 wt% and 2 wt%, and significant improvements in performance were observed for 2 wt% replacement of cement by nanosilica. Micromechanical studies were performed on the nano-modified HSCs to determine the impact of nanosilica on pozzolanic reactivity. Durability assessments such as the rapid chloride penetration test, water sorptivity test and water absorption test revealed significant resistance to chloride penetration, sorptivity and water absorption. These improvements can be mainly attributed to the larger specific surface area of nanosilica, which effectively stimulates both pozzolanic reactivity and the filler effect over the cementitious matrix.

In the process of evaluating the green levels of cold-chain logistics providers, experts may hesitate between several linguistic terms rather than give precise values over the alternatives. Due to the potential profit and risk of business decisions, decision-making information is often based on experts’ expectations of programs and is expressed as hesitant fuzzy linguistic terms. The consistency of evaluation information of an alternative can reflect the clarity of the alternative in the mind of experts and its own controversy. This paper proposes a method to use the value transfer function in the cumulative prospect theory to convert the original hesitant fuzzy linguistic terms into evaluation information based on reference points. We also introduce the parameters related to the disorder of the system in the hesitant fuzzy thermodynamic method to describe the quantity and quality characteristics of the alternatives. In these kinds of multi-criteria decision-making problems, the weights of criteria are of great importance for decision-making results. Considering the conflicting cases among criteria, the weights were obtained by utilizing the PROMETHEE method. An illustrative example concerning green logistics provider selection was operated to show the practicability of the proposed method.

Knowledge about the strength gain of reinforced concrete structures facilitates speedy and accurate decision making in formwork removal and transfer of prestressing forces for prestressed concrete. In the current study, a set of two smart aggregates embedded in concrete cubes have been investigated for their suitability in evaluating the strength gain during the initial curing regime, through electromechanical impedance (EMI) signatures. Correlation of EMI signature from these embedded smart aggregates with progressive strength loss is also established. Different statistical metrics have been evaluated to quantify the variations between the reference and modified states. A relation between root-mean-square deviation (RMSD) and strength parameter is developed, which potentially could be used for arriving at the characteristic strength gain. The novelty is the proposed serial/parallel connected multisensor configuration with a cluster of lead zirconate titanate (PZT) sensors to monitor early-stage characteristics and later-stage strength evolution under a large-scale sensor deployment scenario. The experimental investigation on PZT-bonded concrete shear wall looked for variations in EMI signature under crack opening conditions. Experimental studies on PZT-bonded metal structures have also been carried out to study the variation in modal density characteristics and the effect of low-frequency vibration on the resulting EMI signature.