Investigation of engineering properties of normal and high strength fly ash based geopolymer and alkali-activated slag concrete compared to ordinary Portland cement concrete

Fly ash-based geopolymer (FAGP) and alkali-activated slag (AAS) concrete are produced by mixing alkaline solutions with aluminosilicate materials. As the FAGP and AAS concrete are free of Portland cement, they have a low carbon footprint and consume low energy during the production process. This paper compares the engineering properties of normal strength and high strength FAGP and AAS concrete with OPC concrete. The engineering properties considered in this study included workability, dry density, ultrasonic pulse velocity (UPV), compressive strength, indirect tensile strength, flexural strength, direct tensile strength, and stress-strain behaviour in compression and direct tension. Microstructural observations using scanning electronic microscopy (SEM) are also presented. It was found that the dry density and UPV of FAGP and AAS concrete were lower than those of OPC concrete of similar compressive strength. The tensile strength of FAGP and AAS concrete was comparable to the tensile strength of OPC concrete when the compressive strength of the concrete was about 35 MPa (normal strength concrete). However, the tensile strength of FAGP and AAS concrete was higher than the tensile strength of OPC concrete when the compressive strength of concrete was about 65 MPa (high strength concrete). The modulus of elasticity of FAGP and AAS concrete in compression and direct tension was lower than the modulus of elasticity of OPC concrete of similar compressive strength. The SEM results indicated that the microstructures of FAGP and AAS concrete were more compact and homogeneous than the microstructures of OPC concrete at 7 days, but less compact and homogeneous than the microstructures of OPC concrete at 28 days for the concrete of similar compressive strength

Callus inductions and Phytochemical Determination of Artichoke (Cynara scolymus) growing in Iraq

The artichoke (Cynara scolymus) belongs to Asteraceae family. It is included in British and European Pharmacopeia and has long–used in traditional medicine in several countries. The plant primarily grows in North Africa and Mediterranean; in addition, it is cultivated around the world. Artichoke is wildly distributed in Iraq at the watery lines and boundary of the field. The aim of study was to induce callus from leaves as explants, and to compare between contents of total phenolic and total flavonoids that extracted from the induced callus and from leaves. The induced callus was maintained on Murashige and Skoog (MS) medium supplemented with Naphthalene Acetic Acid (NAA) and Benzyl Adenine (BA). The highest percentage of callus (100%) was induced from the combination (5mg/l NAA plus 2 mg/l BA), followed by (86.67%) with the combination (3mg/l NAA plus 1mg/l BA). Two types of callus (friable and compact) were induced. The extract of friable callus produced 0.858 mg/g of total phenolic, while leaves extract produced 167.24 µg/ mg of total flavonoids. Auxins and cytokinins that added together in the culture medium seemed to be necessary for artichoke tissue culture

Effect of geogrid reinforcement on the drying shrinkage and thermal expansion of geopolymer concrete

2019 fib. International Federation for Structural Concrete The effect of triaxial geogrid reinforcement on the thermal expansion and drying shrinkage of geopolymer concrete (GPC) was experimentally investigated. Three groups of GPC prism specimens with a length of 280 mm and a cross-section of 75 mm x 75 mm were prepared and tested in this study. The first group included six unreinforced GPC specimens and was considered as the control group of specimens. The second group included six GPC specimens reinforced with one layer of geogrid. The third group included six GPC specimens reinforced with two layers of geogrid. The triaxial geogrid reinforcement was placed at a depth of 37.5 mm from the surface of the specimen. The tests were carried out by drying the GPC specimens in a controlled environmental chamber at a temperature of 27 ± 4°C and a relative humidity of 50 ± 10% for 98 days. It was found that the geogrid significantly reduced the thermal expansion and drying shrinkage of GPC specimens. The thermal expansion and drying shrinkage were less in the GPC specimens reinforced with two layers of geogrid compared to the GPC specimens reinforced with one layer of geogrid. It was also found that the rate of thermal expansion and drying shrinkage of the GPC specimens reinforced with geogrid was lower than that of the control unreinforced GPC specimens

From model-driven to data-driven : a review of hysteresis modeling in structural and mechanical systems

Hysteresis is a natural phenomenon that widely exists in structural and mechanical systems. The characteristics of structural hysteretic behaviors are complicated. Therefore, numerous methods have been developed to describe hysteresis. In this paper, a review of the available hysteretic modeling methods is carried out. Such methods are divided into: a) model-driven and b) datadriven methods. The model-driven method uses parameter identification to determine parameters. Three types of parametric models are introduced including polynomial models, differential based models, and operator based models. Four algorithms as least mean square error algorithm, Kalman filter algorithm, metaheuristic algorithms, and Bayesian estimation are presented to realize parameter identification. The data-driven method utilizes universal mathematical models to describe hysteretic behavior. Regression model, artificial neural network, least square support vector machine, and deep learning are introduced in turn as the classical data-driven methods. Model-data driven hybrid methods are also discussed to make up for the shortcomings of the two methods. Based on a multi-dimensional evaluation, the existing problems and open challenges of different hysteresis modeling methods are discussed. Some possible research directions about hysteresis description are given in the final section

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Engineering Properties of Ambient Cured Alkali-Activated Slag-Fly Ash Concrete Reinforced with Different Types of Steel Fiber

This paper investigates the influence of different types of steel fibers on the engineering properties of ambient cured alkali-activated slag-fly ash concrete. The engineering properties investigated include workability, compressive strength, splitting tensile strength, flexural strength, direct tensile strength, and stress-strain response under axial compression. Three types of steel fibers, i.e., straight micro steel fiber, deformed macro steel fiber and hybrid steel fiber, were added to the alkali-activated slag-fly ash mixes. It was found that the workability of the alkali-activated slag-fly ash concrete mixes decreased with the increase in the volume fraction of steel fibers. It was also found that the compressive strength, splitting tensile strength, flexural strength, and direct tensile strength of alkali-activated slag-fly ash concrete mixes increased with the addition of steel fibers. The stress-strain response of alkali-activated slag-fly ash concrete mixes changed from brittle to ductile by the addition of steel fibers. Significant improvements in the mechanical properties of alkali-activated slag-fly ash concrete were observed for the addition of 2% by volume of all three types of steel fiber. The addition of hybrid steel fiber (1% straight micro steel fiber plus 1% deformed macro steel fibers) showed the highest improvement in the mechanical properties of ambient cured alkali-activated slag-fly ash concrete

Design of geopolymer concrete with GGBFS at ambient curing condition using Taguchi method

In this paper, the Taguchi method has been used to design optimum mix proportions for geopolymer concrete with ground granulated blast furnace slag (GGBFS) as aluminosilicate source at ambient curing condition. The influences of binder content, alkaline activator to binder content (Al/Bi) ratio, sodium silicate to sodium hydroxide (SS/SH) ratio, and sodium hydroxide (SH) concentration on the geopolymer concrete were investigated. A total of nine mix designs were evaluated. It was found that specimens with a binder content of 450 kg/m3, Al/Bi ratio of 0.35, SS/SH ratio of 2.5, and SH concentration of 14 M produced the highest 7-day compressive strength (60.4 MPa). However, the setting time was found to be short. Hence, fly ash (FA), metakaolin (MK), and silica fume (SF) were used as partial replacement of GGBFS in different proportions to increase the setting time. It was found that the setting time improved for the partial replacement of GGBFS with FA, MK, and SF

Experimental Investigation on the Effect of Corrosion on the Bond Between Reinforcing Steel Bars and Fibre Reinforced Geopolymer Concrete

This paper investigates the effect of corrosion on the bond between reinforcing steel bars and fibre reinforced geopolymer concrete. An accelerated corrosion method was used to corrode the reinforcing steel bars embedded in geopolymer concrete. Three types of steel fibres including straight micro steel fibre, deformed macro steel fibre, and hybrid steel fibre were used in this study. A total of ten geopolymer concrete mixes were used to evaluate the effect of corrosion of steel bar on the bond between steel bar and fibre reinforced geopolymer concrete. The pull-out test specimens were composed of concrete cubes with a side length of 160mm and reinforced with a deformed steel bar of 16 mm diameter located at the centre of the specimens. The test results showed that the addition of steel fibres in geopolymer concrete (fibre reinforced geopolymer concrete) significantly enhanced the bond strength of reinforcing steel bar. The bond strength of reinforcing steel bars embedded in steel fibre reinforced geopolymer concrete specimens reduced due to corrosion of reinforcement. However, the reduction of bond strength in steel fibre reinforced geopolymer concrete specimens was less than the reduction of bond strength in plain geopolymer concrete specimen

Behaviour of Ambient Cured Steel Fibre Reinforced Geopolymer Concrete Columns Under Axial and Flexural Loads

This study investigates the behaviour of ambient cured geopolymer concrete column specimens reinforced with steel fibres under different loading conditions. Three types of steel fibres (straight micro steel fibre, deformed macro steel fibre and hybrid steel fibre) were used in reinforcing the geopolymer concrete column specimens. Also, geopolymer concrete column specimens without steel fibre were tested as reference column specimens. Sixteen circular geopolymer concrete column specimens of 150 mm diameter and 600 mm height were cast and tested. The influences of the addition of different types of steel fibres and the loading conditions (concentric axial load, eccentric axial load and four-point bending) on the performance of the geopolymer concrete column specimens were investigated. The test results showed that the peak axial load and bending moment of fibre reinforced geopolymer concrete column specimens were higher than those of the geopolymer concrete column specimens without steel fibres under different loading conditions. Also, the addition of different types of steel fibres resulted in significant improvements in the ductility of the geopolymer concrete column specimens. The addition of hybrid steel fibre showed the highest improvement in the peak axial load, bending moment and the ductility of ambient cured geopolymer concrete column specimens