Effect of various rebar types and crushed glass coating onto BFRP rebar on the bond strength to concrete

This study demonstrates the bond-slip behaviour of steel, BFRP, CFRP and GFRP rebars to concrete obtained from a series of pull-out tests. Results show that CFRP can achieve higher bond strength than steel, whereas BFRP attains half of the bond strength of steel. The bond strength was decreased by 23–28% in steel and BFRP due to an increase in bar diameter. However, the CFRP and GFRP showed a 73–78% reduction in bond strength due to the increase in bar diameter. Steel had the steepest slope in the bond-slip curve, followed by CFRP, BFRP and GFRP. Since BFRP attained optimum performance, the surface coating was applied onto BFRP using natural sand and recycled crushed glass to evaluate the roughness of FRP on the bond performance. Sand and glass coated BFRP demonstrated 37% and 75% higher bond strength compared to uncoated BFRP, while bond stiffness was increased by 14 and 11%, respectively. Compared to the sand coated BFRP, crushed glass coated BFRP exhibited approximately 20% and 10% more bond strength for the 6 mm and 10 mm diameter rebars, respectively. However, the glass coated BFRP exhibited more brittle behaviour compared to its sand coated counterparts. Based on the analytical results, surface roughness and embedment length are found to have a significant influence on the ultimate bond strength (p-value < 0.05) at a 5% level of significance. Additionally, the interaction effect of diameter*embedment and diameter*coating was found to have a significant effect on bond strength

Stainless steel top-seat angle beam-to-column connection: Full-scale test and analytical modelling

Stainless steel (SS) is increasingly used for structural applications in the construction industry as its beneficial properties outweigh initial material costs when sustainability aspects and the whole life cycle of structures are appropriately accounted for in the structural design. Despite the well-recognised significance of connections in bare metallic construction, experimental research on SS beam-to-column connections, especially full-scale test results, are scarce. This paper presents a full-scale experimental investigation on the semi-rigid behaviour of top-seat bolted connection (also known as ‘flange cleat’ connection) made from austenitic SS. Deformation characteristics of various elements of the connection were carefully investigated and subsequently used to calibrate nonlinear FE models for parametric analysis. Obtained numerical results were used to develop a four-parameter power model that relies on simplified expressions for key input parameters to predict the semi-rigid behaviour of bolted top-seat connections. Results predicted using the proposed model and those obtained using currently available techniques based on carbon steel behaviour were compared. Outcomes of the current research highlighted the significance of appropriate inclusion of stain hardening offered by austenitic grade to capture the semi-rigid response of such connections

Recent trends in the use of electrical neuromodulation in Parkinson's disease

Purpose of Review: This review aims to survey recent trends in electrical forms of neuromodulation, with a specific application to Parkinson’s disease (PD). Emerging trends are identified, highlighting synergies in state-of-the-art neuromodulation strategies, with directions for future improvements in stimulation efficacy suggested. Recent Findings: Deep brain stimulation remains the most common and effective form of electrical stimulation for the treatment of PD. Evidence suggests that transcranial direct current stimulation (tDCS) most likely impacts the motor symptoms of the disease, with the most prominent results relating to rehabilitation. However, utility is limited due to its weak effects and high variability, with medication state a key confound for efficacy level. Recent innovations in transcranial alternating current stimulation (tACS) offer new areas for investigation. Summary: Our understanding of the mechanistic foundations of electrical current stimulation is advancing and as it does so, trends emerge which steer future clinical trials towards greater efficacy

A framework for understanding shared substrates of airway protection

Deficits of airway protection can have deleterious effects to health and quality of life. Effective airway protection requires a continuum of behaviors including swallowing and cough. Swallowing prevents material from entering the airway and coughing ejects endogenous material from the airway. There is significant overlap between the control mechanisms for swallowing and cough. In this review we will present the existing literature to support a novel framework for understanding shared substrates of airway protection. This framework was originally adapted from Eccles' model of cough28 (2009) by Hegland, et al.42 (2012). It will serve to provide a basis from which to develop future studies and test specific hypotheses that advance our field and ultimately improve outcomes for people with airway protective deficits

The Effect of Alkali to Fly Ash Ratio on the Durability of Geopolymer Mortar Against the Coupled Actions of Chemicals and High Thermal Cycles

The present study investigates the performance of fly ash (FA) based geopolymer (GP) mortar (3 and 28-day old) under the combined effect of aviation oils and high thermal cycles. Cubic specimens of GP mortar were repeatedly exposed to both aviation oils and high thermal cycles simultaneously. After a couple of cycles of exposure, all GP specimens underwent saponification process, which possibly weakened the compressive strength of the GP mortar. Upon the 60th cycle of exposure, the 3 and 28-day old GP lost a maximum of 44.23% and 33.72% of the compressive strength compared to the original values, respectively. However, the GP mortar did not suffer scaling on the surface even after 60 cycles of exposure in 5 months. The FA to alkali liquids (AL), (FA/AL), ratio plays an important role in the compressive strength degradation process of GP mortar. The study also reports a suitable AL/FA ratio for GP mix that could be used to patch repair for scaled concrete at military airbases

Durability of Acrylic Latex and Silica Fume Modified Cement Mortar under Harsh Circumstances

Acrylic latex (AL) is a polymer that is often used in resurfacing as a thin layer coating on the degraded surface of concrete structures. The study presented in this paper aims to investigate the suitability of using AL and silica fume (SF) modified Portland cement (PC) mortar to repair the scaled concrete at military airbases’ apron those are regularly exposed to high thermal cycles and is often found saturated by the aviation oils. For this purpose, PC mortar was modified by 15% of AL (by parts) and was replaced by 10% of SF, and the performance of the modified mortar was experimentally investigated. Both the unmodified original PC mortar and the modified PC mortar was repeatedly exposed to both the aviation oils and high thermal cycles simultaneously, until the scale formation on the surface of the mortar. During the experimental investigation, the compressive strength degradation and loss of mass of the mortar were recorded. Chemical analyses of the mortar and aviation oils are also conducted. The study reveals that AL and SF modified PC mortar is more durable than the unmodified conventional PC mortar under army airbase circumstances

Residual properties of conventional concrete repetitively exposed to high thermal shocks and hydrocarbon fluids

The rapid degradation of traditional concrete at aprons in army airbases is a major problem for the operation of jet aircraft safely. Aprons are often saturated by rainfall water and hydrocarbon fluids (HFs) and are frequently subjected to heat shocks from jet exhaust. The current study investigates the causes of rapid degradation of airbase concrete and the effects of that on concrete properties. Standard sized concrete cylinders (w/c ratio = 0.35, 0.45 and 0.55) using Australian general-purpose cement were prepared and repeatedly exposed to both high thermal shocks and HFs, separately and combined until degradation becomes obvious in term of surface scaling. Surface scaling was developed when cylinders were subjected to the coupled effects of high thermal shocks and HFs, cylinders did not form scaling when subjected to high thermal shocks and HFs individually. However, significant changes in residual properties were identified for all exposure types. The considered cylinders showed 40% of decrease in the compressive strength and more than 27% of decrease in the splitting tensile strength. In addition, the elasticity of concrete was reduced by more than 63% after the formation of scaling on the surface. The crystal lattices of minerals in cylinders, such as alite, belite, quartz, ettringite, portlandite, and mullite were significantly decomposed owing to the repetitive actions of both thermal shocks and HFs combined, which resulted in the deterioration of mechanical properties. Deterioration of mechanical properties of cylinders highly depended on w/c ratio. Cylinders with a lower w/c ratio retained the higher percentage of residual strength when subjected to the coupled effects of high thermal shocks and HFs. This study also reports the influence of w/c ratio on mass loss characteristics and microstructures of conventional concrete subjected to both thermal shocks and HFs simultaneously

Resistance of fly ash based geopolymer mortar to both chemicals and high thermal cycles simultaneously

Geopolymer has already been used at a commercial airport, Brisbane West Wellcamp Airport (BWWA), and in mainline railway sleepers in Australia. It has also been proposed for use at military airbases to repair degraded concrete or any other special construction needs. Rigid pavements at military airbases, especially aprons, are frequently exposed to high thermal shocks by jet exhaust, and often get saturated by chemicals such as hydrocarbon fluids (HFs): aircraft's engine lubricating oil, hydraulic fluid and jet fuel. To promote wider and reliable use of geopolymer at military airbases, the resistance of geopolymer to both HFs and high thermal cycles should be thoroughly assessed. The present study investigates the resistance of fly ash (FA) based 3-day and 28-day old geopolymer mortars to both HFs and high thermal cycles simultaneously and separately. This study has identified that irrespective of the age of the geopolymer mortar, they experience saponification when expose to both HFs and high thermal cycles simultaneously. Soap and salt compounds, e.g., sodium carboxylate and sodium phosphates were identified in the geopolymer mortar after the saponification occurrence. The crystal lattices of the 3-day old geopolymer mortar were significantly affected and decomposed when exposed to HFs and high thermal cycles simultaneously. Upon 60 cycles of heat exposure, 3-day and 28-day old geopolymer mortar treated with HFs lost 42.52% and 33.85% of their compressive strength, respectively. The geopolymer mortar exposed to HFs at ambient temperature did not suffer from saponification process, and the reduction in the compressive strength was almost insignificant. The effect of high thermal cycles in reducing the compressive strength of the geopolymer mortar was substantial. This paper also reports mass loss characteristics, microstructures and degrading mechanisms of geopolymer mortar after exposure to HFs and high thermal cycles