Rigid pavements at military airfields experience surface deterioration within 6–18 months of construction. The cause of this degradation is mainly due to combined exposure to repeated heat shocks from jet engine exhaust and spilled aviation oils (hydrocarbons). Surface degradation occurs in the form of disintegration of aggregates and cement paste into small pieces that pose severe risks of physical injury to maintenance crews or damage to an aircraft engine. Since coarse aggregates typically occupy 60–80% of the concrete volume, aggregates’ thermal properties and microstructure should play a crucial role in the degrading mechanism. At high temperatures, concrete with lightweight aggregates is reported to have better performance compared to concrete with normal-weight aggregate. Thus, the present study carried out a detailed investigation of the mechanical and thermal performance of lightweight aggregate concrete exposed to the combined effects of high temperatures and hydrocarbon oils simultaneously. To replicate harsh airfield operating conditions, standard-sized concrete cylinders were exposed to elevated temperatures using an electric oven. Additionally, a mixture of equal parts of aircraft engine oil, hydraulic oil, and kerosene was applied before each exposure to high temperatures. To identify the resistance of different concrete with various lightweight coarse aggregates, pumice, perlite, lytag (sintered fly ash), and crushed brick were used as lightweight coarse aggregates in concrete. Also, basalt aggregate concrete was used as a reference. After curing, cylinders were tested for the ultimate strength. Later, after every 20 cyclic exposures, three cylinders from each aggregate type were tested for residual comprehensive strength, thermal, chemical, and microstructural (SEM) properties. Overall, concrete with crushed brick aggregate and lytag used in this study showed superior resistance to the simulated airfield conditions. The findings of this study will provide valuable insights to select an appropriate coarse aggregate type for military airfield pavement construction, aiming to effectively minimize surface spalling.

Surface degradation at parking aprons of military airfields concerns jet aircraft safety. It is caused by the disintegration of coarse aggregates in concrete. This study aims to understand the effects of repeated exposure to various aviation oils and high-temperature on concrete constituent materials. An airfield exposure condition was created to expose samples made with different water to cement ratios (w/c). Samples were tested for residual mechanical properties, thermal conductivity, specific heat, thermogravimetric and microstructural analysis. Results show that the w/c ratio of concrete significantly influences the residual strength of the exposed samples. Moreover, aviation oils react with ordinary concrete at higher temperatures and produce harmful salts. Besides, thermal incompatibility between the aggregates and cement paste triggers microcracks in cement paste and thermal cracks in the coarse aggregate. Due to the simultaneous thermal and chemical attack, concrete suffers the disintegration of aggregates and flake-like concrete pieces on the top surface.

Due to routine maintenance of aircraft on the concrete pavement at army airbases, a large part of the pavement surface is often found saturated with different hydrocarbon-based oil, fuel, and fluid. In addition, the pavement concrete is subjected to the aircraft’s exhaust temperature during operation. This study examined the resistance ability of 3 different cementitious materials: (i) epoxy, (ii) fly ash (FA) based geopolymer with various alkali to fly ash (AL/FA) ratios and (iii) Portland cement (PC) mortar under a simulated airfield circumstance. The mortar specimens were repetitively exposed to a mixture of synthetic engine oil, hydraulic fluids, jet fuel and elevated temperatures (175 °C) for 5 months simultaneously. During the exposures, geopolymer and PC mortar both suffered saponification. The degree of saponification of geopolymer samples is found to be highly reliant on the AL/FA ratios. On the contrary, the epoxy mortar was found to be resistant to saponification. It was also found that the PC mortar developed numerous thermal cracks but epoxy and geopolymer did not experience any visual thermal cracks under the same conditions.

This paper presents an experimental study on the behaviour of bolted flanged structural steel pipe joint subjected to bending. The sample was prepared by welding a flange to an end of a pipe segment and then joining the two segments of pipe by placing the flanges face to face and fastening using structural bolts through holes in the flanges. The whole assembly was then subjected to flexure by placing on a simple support arrangement and applying two-point loading. Total 16 flanged pipe joint samples were tested having different pipe diameter, flange thickness, bolt diameter etc. The deformation characteristics of the joint demonstrated two different kinds of behaviour: thin flange behaviour and thick flange behaviour. Thin flange behaviour is characterised by local flexural deformation of the flange accompanied by prying action and some bending of the bolts while thick flange behaviour is characterised by contact separation between flanges accompanied by tensile elongation of the bolts.

Over the years, leaked fluids from aircraft have caused severe deterioration of airfield pavement. The combined effect of hot exhaust from the auxiliary power unit of military aircraft and spilt aviation oils have caused rapid pavement spalling. If the disintegrated concreted pieces caused by spalling are sucked into the jet engine, they may cause catastrophic damage to the aircraft engine or physical injury to maintenance crews. This study investigates the effectiveness of incorporating hybrid fibres into ordinary concrete to improve the residual mechanical and thermal properties to prevent spalling damage of pavement. Three fibre-reinforced concrete samples were made with micro steel fibre and polyvinyl alcohol fibre with a fibre content of zero, 0.3%, 0.5% and 0.7% by volume fraction. These samples were exposed to recurring high temperatures and aviation oils. Tests were conducted to measure the effects of repeated exposure on the concrete's mechanical, thermal and chemical characteristics. The results showed that polyvinyl alcohol fibre-, steel fibre- and hybrid fibre-reinforced concrete suffered a 52%, 40% and 26.23% of loss of initial the compressive strength after 60 cycles of exposure to the conditions. Moreover, due to the hybridisation of concrete, flexural strength and thermal conductivity was increased by 47% and 22%. Thus, hybrid fibre-reinforced concrete performed better in retaining higher residual properties and exhibited no spalling of concrete.

Strain rate sensitivity and deformation mechanisms of closed-cell aluminium foams under low-velocity impact loadings are investigated in this study. Instrumented drop-weight impact experiments and Finite Element (FE) modelling were conducted to explore the deformation rate dependency of aluminium foams (manufactured by CYMATTM corporation). An X-ray micro-Computed Tomography (XCT) reconstructed foam geometry was used in the FE modelling approach to explore actual deformation mechanisms and strain rate sensitivity of foams. The deformation and pore collapse mechanisms were explored through investigating the stress and plastic strain contours. Our results show that the FE modelling with rate-dependent material properties agreed with the dynamic experimental results. The foam showed significant rate sensitivity within the examined range of strain rates. Our modelling and experimental results collectively indicate that the rate sensitivity of the base material is the primarily responsible for enhancing strength during impacts. Furthermore, the FE modelling with rate-independent material properties and unique foam topology confirms the negligible inertia effect at low velocity impacts.

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. (C) 2020 Elsevier Ltd. All rights reserved.

Conventional concrete at military airbase is reported to experience premature scaling damage due to repeated exposures to hydrocarbon fluids (HFs), rainwater and high thermal shocks simultaneously. The present study examines the performance of amine cured epoxy and reactive silica fume (SF) modified Portland cement (PC) mortar and unmodified PC mortar under laboratory simulated military airbase operating conditions, which simultaneously applied HFs, water and high temperature on the surfaces of the considered mortar specimens repeatedly. Unmodified PC mortar was observed to experience saponification, thermal cracks and scaling when exposed to the combined actions of HFs and thermal cycles; however, the modified PC mortar sustained those adverse conditions. After 80 cycles of exposure to the simultaneous actions of HFs and high temperature, the unmodified plain mortar lost 80.48% of the compressive strength. Whereas, the 3-day and 28-day old epoxy and SF modified PC mortar lost 41.70% and 36.15% of the compressive strength showing considerable resilience against the military airbase working conditions, respectively. Epoxy and SF modified PC mortar retained more than the required minimum compressive strength for military airbase even after 80 cycles of exposure, however, the unmodified PC mortar failed to do so. FTIR and XRD analyses, showed that compounds created by interactions amongst epoxy, SF and PC did not react with HFs even at high temperature. Epoxy notably protected crystalline mineral compounds such as ettringite, portlandite, quartz, alite, belite mullite and calcite in PC from hydrocarbon attacks but failed to prevent their thermal decomposition, as epoxy in mortar was observed to deform, swell and plasticized after thermal exposures. Mass loss characteristics, depths of HFs attack, effect of epoxy to cement (E/C) ratio on the durability, residual compressive strength and microstructures after the considered exposures are also reported.