Long-term bond performance of GFRP bars in concrete under temperature ranging from 20 °C to 80 °C

Eighty pull-out specimens were used to study the effect of temperature ranging from 20 °C to 80 °C in dry environment on bond properties between Glass Fiber Reinforced Polymer (GFRP) bars and concrete. The pullout-test specimens were subjected during 4 and 8 months to high temperatures up to 80 °C and then compared to untreated specimens (20 °C). Experimental results showed no significant reduction on bond strength for temperatures up to 60 °C. However, a maximum of 14% reduction of the bond strength was observed for 80 °C temperature after 8 months of thermal loading. For treated specimens, the coefficient β in the CMR model, which predicts the bond–stress–displacement behavior, seems to be dependant with the temperature.     

Laboratory evaluation of WMA mixture for use in airport pavement rehabilitation

The concept of warm mix asphalt (WMA) gives a promise for rehabilitating airport pavement to realize quick turnover to traffic after construction, however, laboratory and field data in terms of the performance-related properties are significantly lacking for using WMA in airfield in Japan. To fill this gap, three WMA mixtures (different gradations) were systematically investigated compared with the conventional airfield used hot mix asphalt (HMA) through a series of laboratory tests in terms of wheel tracking test, submerged wheel tracking test, raveling test, static bending and fatigue bending test. These WMA mixtures were made at two production temperatures (30 and 50 °С lower than the normal, respectively) by incorporating a commercially sold additive. Results showed that overall, the WMA mixture with a coarse gradation produced at the temperature 30 °С lower than the normal exhibited a comparable performance compared with the control HMA mixture, and it was further recommended for use in airport pavement rehabilitation.     

Self-ignition of natural fuels: Can wildfires of carbon-rich soil start by self-heating?

Carbon-rich soils, like histosols or gelisols, cover more than 3% of the Earth's land surface, and store roughly three times more carbon than the Earth's forests. Carbon-rich soils are reactive porous materials, prone to smouldering combustion if the inert and moisture contents are low enough. An example of soil combustion happens in peatlands, where smouldering wildfires are common in both boreal and tropical regions. This work focuses on understanding soil ignition by self-heating, which is due to spontaneous exothermic reactions in the presence of oxygen under certain thermal conditions. We investigate the effect of soil inorganic content by creating under controlled conditions soil samples with inorganic content (IC) ranging from 3% to 86% of dry weight: we use sand as a surrogate of inorganic matter and peat as a surrogate of organic matter. This range is very wide and covers all IC values of known carbon-rich soils on Earth. The experimental results show that self-heating ignition in different soil types is possible, even with the 86% inorganic content, but the tendency to ignite decreases quickly with increasing IC. We report a clear increase in ambient temperature required for ignition as the IC increases. Combining results from 39 thermostatically-controlled oven experiments, totalling 401 h of heating time, with the Frank-Kamenetskii theory of ignition, the lumped chemical kinetic and thermal parameters are determined. We then use these parameters to upscale the laboratory experiments to soil layers of different thicknesses for a range of ambient temperatures ranging from 0 °C to 40 °C. The analysis predicts the critical soil layer thicknesses in nature for self-ignition at various possible environmental temperatures. For example, at 40 °C a soil layer of 3% inorganic content can be ignited through self-heating if it is thicker than 8.8 m, but at 86% IC the layer has to be 1.8 km thick, which is impossible to find in nature. We estimate that the critical IC for a ambient temperature of 40 °C and soil thickness of 50 m is 68%. Because those are extreme values of temperature and thickness, no self-heating ignition of soil can be expected above the 68% threshold of inorganic content. This is the first in-depth experimental quantification of soil self-heating and shows that indeed it is possible that wildfires are initiated by self-heating in some soil types and conditions.     

Determinants of winter indoor temperatures in low income households in England

The objective of this study is to quantify the extent to which variation in heating season indoor temperatures is explained by dwelling and household characteristics and increased by energy efficiency improvements in low income households. A survey of dwellings in the Warm Front home energy efficiency scheme was carried out in five urban areas of England. Half-hourly living room and main bedroom temperatures were recorded for 2–4 weeks over two winters. For each dwelling, regression of indoor on outdoor temperature was used to obtain estimates of daytime living room and night time bedroom temperatures under standardized conditions (outdoor temperature of 5 °C). The results indicate that the median standardized daytime living room temperature was 19.1 °C and the median standardized night time bedroom temperature 17.1 °C. Temperatures were influenced by property characteristics, including its age, construction and thermal efficiency and also by the household number of people and the age of the head of household. Dwellings that received both heating and insulation measures through the Warm Front scheme had daytime living room temperatures 1.6 °C higher than pre-intervention dwellings, night time bedroom temperatures were 2.8 °C higher. Warm Front energy efficiency improvements lead to substantial improvements of both living room and bedroom temperatures which are likely to have benefits in terms of thermal comfort and well-being.     

Challenges and strategies involved in designing and constructing a 6 km immersed tunnel: A case study of the Hong Kong–Zhuhai–Macao Bridge

A 6 km immersed tunnel of the Hong Kong–Zhuhai–Macao Bridge (HZMB) has been designed and funded. Once completed in 2016, the HZMB Tunnel will break the record of the 5.8 km BART Tunnel in the United States, although it will soon be overtaken by the ∼20 km Fehmarn Tunnel between Denmark and Germany that is to be completed in 2020. Construction of the HZMB Tunnel was started in 2011 and more than ten elements thus far have been installed on the site. This paper presents details about the challenges and solutions for the design and construction of the HZMB Tunnel on a strategic level. Special features of the HZMB Tunnel include a long length of 6 km, a deep water depth of almost 45 m, and a thick backfill of 23 m. Challenges include severe marine environment, strict requirements for waterproofing, construction of sections connecting the tunnel with artificial islands, and tunnel stability after future excavation of fairway trenches. Moreover, the HZMB Tunnel is challenged by possible sand liquefaction in seismic events, conservation of white Chinese dolphin, and waterway dispersion during construction. Details about the strategies are given in order to improve the immersed tunnel design and construction methods.     

Effects of calcination temperature of kaolinite clays on the properties of geopolymer cements

The aim of this work is to determine the most convenient calcination temperature of kaolinite clays in view of producing geopolymer cements. In this light, the clay fractions of three kaolin minerals were used. The clay fractions were characterized (chemical and thermal analyses and X-ray diffraction) and then calcined in the temperature range of 450 and 800 °C. The obtained amorphous materials were dissolved in a strongly alkaline solution in order to produce geopolymer cements whose pastes were characterized by determining their setting time, linear shrinkage and compressive strength. Hardened geopolymer cement paste samples were also submitted to X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy analyses. The setting time of geopolymer cement pastes produced from the clay fractions calcined at 450 °C was very long (test samples could be handled easily only after 21 days at the ambient atmosphere of the laboratory). For the clay fractions calcined between 500 and 700 °C, the setting time of geopolymer cement pastes reduced with increasing temperature and varied between 130 and 40 min. Above 700 °C, the setting time began to increase. The linear shrinkage of the hardened geopolymer cement paste samples aged between 21 and 28 days attained its lowest value around 700 °C. Above 700 °C, the linear shrinkage began to increase. The compressive strength of the hardened geopolymer cement paste samples was between 11.9 and 36.4 MPa: it increased with samples from the clay fractions calcined between 500 and 700 °C but dropped above 700 °C.It can be concluded that the most convenient temperature for the calcination of kaolinite clays in view of producing geopolymer cements is around 700 °C.     

Suppression of sodium fires with liquid nitrogen

Sodium has unusual fire hazards, including autoignition when heated in air or exposed to liquid water. Owing to limitations of existing suppression agents for sodium pool fires, suppression using liquid nitrogen (LN₂) is examined here. Sodium pools of 5–80 g were heated in stainless steel beakers. At about 290 °C, pool surface autoignition occurred and caused a rapid pool temperature increase. Vapor phase combustion occurred when the pools reached 320–450 °C, ultimately leading to pool temperatures up to 700 °C. For suppression tests, LN₂ delivery (at 2.7 g/s) began when the fires became fully-developed, near a pool temperature of 600 °C. Liquid nitrogen was found to be an effective suppression agent. The minimum amount of LN₂ required to suppress a fully-developed sodium pool fire was found to be about three times the initial sodium pool mass.     

Determination of the optimum conditions for tire rubber in asphalt concrete

The Taguchi method was used to determine optimum conditions for tire rubber in asphalt concrete with Marshall Test. The tire rubber in asphalt concrete was explored under different experimental parameters including tire rubber gradation (sieve #10–40), mixing temperature (155–175 °C), aggregate gradation (grad. 1–3), tire rubber ratio (0–10% by weight of asphalt), binder ratio (4–7% by weight of asphalt), compaction temperature (110–135 °C), and mixing time (5–30 min). The optimum conditions were obtained for tire rubber gradation (sieve #40), mixing temperature (155 °C), aggregate gradation (grad. 1), tire rubber ratio (10%), binder ratio (5.5%), compaction temperature (135 °C), mixing time (15 min).     

Shaking table test on reinforcement effect of partial ground improvement for group-pile foundation and its numericalsimulation

In this paper, particular attention was paid to the seismic enhancement effect of group-pile foundation with partial ground improvement method that is used for existing pile foundations in practical engineering. A model test on a full system with a superstructure, a nine-pile foundation and a sandy ground was conducted with the shaking table test device. The model pile is made from aluminum and the model ground is made from Toyoura Sand. The shaking table test device is 120 cm in width and 160 cm in length. The maximum acceleration is 1 g and the maximum displacement is 5 cm. The maximum payload is 16 kN and the highest frequency is 10 Hz. The model ground is carefully prepared to obtain a ground with controllable unified density. Before the shaking table test, the pattern of the partial ground improvement for an existed group-pile foundation is carefully selected using numerical tests with a 3D elastoplastic static finite element analysis. In the analysis, the nonlinear behavior of ground and piles are described by the cyclic mobility model (Zhang et al., 2007) and the axial force dependent model (AFD model) proposed by Zhang and Kimura (2002) can take into consideration of axial-force dependency in the nonlinear moment–curvature relations. The applicability of the numerical analysis has been verified in previous works by comparing the numerical results with a real-scale field tests (Kosa et al., 1998). Based on the results from the numerical tests on seismic enhancement effect of group-pile foundation with ground improvement, an optimum pattern of partial ground improvement of an existing pile foundations has been picked out for shaking table test. A numerical analysis using the program DBLEAVES (Ye, 2007) is also conducted for the same optimum pattern for comparison purposes. The effectiveness of the partial ground improvement method has been proved by both the shaking table test and the numerical analysis.     

Effects of CaO addition on lightweight aggregates produced from water reservoir sediment

Lightweight aggregates were produced from water reservoir sediment with various amounts of CaO at calcining temperatures of 1170 °C–1230 °C. It was found that C–S–H gel did not form with CaO addition. The bulk density and compressive strength of the lightweight aggregates meet the regulations for lightweight structural concrete. The properties of samples with 1% CaO by weight calcined at 1200 °C match those of a commercial product. Water adsorption and compressive strength decreased with increasing CaO addition since more of the glassy phase formed, which sealed pores and led to few connections between pores.     

The effect of reflective coatings on building surface temperatures,indoor environment and energy consumption—An experimental study

This paper presents an experimental study on the impact of reflective coatings on indoor environment and building energy consumption. Three types of coatings were applied on identical buildings and their performance was compared with three sets of experiments in both summer and winter. The first experiment considers the impact of coatings on exterior and interior surface temperatures, indoor air temperatures, globe temperature, thermal stratification and mean radiant temperatures for non-conditioned buildings (free-floating case); the second one focused on the impact of coatings on reduction of electricity consumption in conditioned spaces; in the third experiment, the impact of different envelope material properties equipped with different coatings was investigated. The results showed that, depending on location, season and orientation, exterior and interior surface temperatures can be reduced by up to 20 °C and 4.7 °C respectively using different coatings. The maximum reduction in globe temperature and mean radiant temperature was 2.3 °C and 3.7 °C in that order. For the conditioned case, the annual reduction in electricity consumption for electricity reached 116 kWh. Nevertheless, the penalty in increased heating demand can result in a negative all-year effect in Shanghai, which is characterized by hot summers and cold winters.     

Effect of pre-heating duration and temperature conditioning on the rheological properties of bitumen

It is well known that overheating asphalt bitumen can lead to oxidation and stiffening. While heating bitumen is an essential protocol in sample preparation, it is important to identify the oven setting time and temperature for lab testing. Current AASHTO standards do not specify exact oven settings for bitumen sample preparation prior to laboratory testing. This study is evaluating the effect of oven heating duration and pouring temperature during sample preparation in the rheological properties of neat and polymer-modified bitumen (PMB). Rheological properties are measured using Rotational Viscometer, Dynamic Shear Rheometer and Bending Beam Rheometer at grade-specific testing temperatures. A neat bitumen PG64-22 and two PMB PG70-22 and 76-22 in un-aged (original) and aged conditions were tested at two temperatures: 143 °C and 185 °C for 1/2, 2 and 4 h. The effect of short-term aging by rolling thin film oven was also investigated. To investigate the rheological properties over a wide range of temperatures, temperature sweep testing was conducted from 35 °C to 110 °C at a 10 rad/s frequency. The results suggest that there was no significant difference in the viscosity, complex modulus and creep stiffness for the tested bitumen. The RTFO aging index, absolute drop of complex viscosity and temperature aging indices were used to evaluate the bitumen preparation settings. The study recommends using the 143 °C and 2-h heating for proper preparation prior to standard lab testing. The study also investigated the aging influence in rheological properties for neat and PMB using the black diagram, DSR function map, and critical-stiffness temperature.     

Concrete cover effect on reinforced concrete bars exposed to high temperatures

The mechanical properties of structural reinforcement steel have been investigated after the exposure to high temperatures. Plain steel, reinforcing steel bars embedded into mortar and plain mortar specimens were prepared and exposed to 20, 100, 200, 300, 500, 800 and 950 °C temperature for 3 h individually. The S420 deformed steel bars with diameters of ∅10, ∅16 and ∅20 were used. The mortar was prepared with CEM I 42.5 N cement and fly ash. The tension tests on reinforcements taken from cooled specimens were performed, and the variations in yield strength, ultimate strength and in resilience of three different dimensioned reinforcements were determined. A cover of 25 mm provides protection against high temperatures up to 400 °C. The high temperature exposed plain steel and the steel with 25-mm cover has the same characteristics when the reinforcing steel is exposed to a temperature 250 °C above the exposure temperature of plain steel.     

Temperature effects on mechanical behaviour of engineered stones

In this research, three types of artificial or engineered stones were compared against two types of natural stones (a limestone and a granite) in what concerns to temperature, thermal ageing and thermal shock effects on flexural strength and Young’s modulus. Temperatures of the thermal treatments, in the range from 20 to 200 °C, were intentionally chosen to simulate some practical applications of this kind of materials, for example, when they are used as kitchen tops. The results reveal the different characteristics of the materials. When tested at temperatures up to 100 °C, engineered stones show much higher values of flexural strength compared to the natural stones; and when tested at ambient temperature after being submitted to rapid cooling (thermal shock) from 200 °C down to 20 °C, engineered stones continue to show higher values of flexural strength compared to the natural stones. For the temperature range from 20 to 200 °C, thermal shock and thermal ageing effects on Young’s modulus are not very pronounced. Young’s modulus (E) of each of the materials was determined at ambient temperature, and the engineered stones keep almost the same value of E after thermal ageing or thermal shock up to 160 °C.     

Influence of temperature on fresh performance of self-consolidating concrete

The results of a study dealing with the influence of temperature on the fresh performance of self-consolidating concretes (SCC) made with slump flow of 508, 635 and 711 mm are presented. Seven different temperatures, namely: 43, 36, 28, 21, 14, 7, and −0.5 °C, to simulate hot and cold temperatures were used to evaluate the unconfined workability, the rate of flow ability or viscosity per inference, and the dynamic stability of the trial matrices. The fresh performance of SCC was significantly affected by hot temperatures (i.e. 43, 36, and 28 °C) and marginally influenced by cold temperatures (14, 7, and −0.5 °C). The remediation method by way of admixture overdosing was successful to reverse the change in fresh properties of the self-consolidating concretes in elevated temperatures. The selected matrices did not require any remediation in cold temperatures.     

Mechanical properties of normal and high strength concretes subjected to high temperatures and using image analysis to detect bond deteriorations

The effect of high temperatures, up to 250 °C, on mechanical properties of normal and high strength concretes with and without silica fume was investigated, and image analysis was performed on split concrete surfaces to see the change in bond strength between aggregate and mortar. Specimens were heated up to elevated temperatures (50, 100, 150, 200, 250 °C) without loading and then the residual compressive and splitting tensile strength, as well as the static modulus of elasticity of the specimens were determined. For normal strength concrete residual mechanical properties started to decrease at 100 °C, while using silica fume reduced the losses at high temperatures. In terms of percent residual properties, high strength concrete specimens performed better than normal strength concrete specimens for all heating cycles. Image analysis studies on the split surfaces have been utilized to investigate the effect of high temperatures on the bond strength between aggregate and mortar. Image analysis results showed that reduced water–cement ratio and the use of silica fume improved the bond strength at room temperature, and created more stable bonding at elevated temperatures up to 250 °C.     

Tension in geomembranes on landfill slopes under static and earthquake loading—Centrifuge study

Geomembranes are some of the most commonly used geosynthetics in landfill liner systems. Geomembranes may experience harsh environmental conditions such as extreme temperatures or earthquake loading. Earthquake loading can be an extreme loading case for landfills located in seismic regions. This study, based on dynamic centrifuge testing, investigates the effects of simulated earthquake loading on the tension experienced by the geomembrane on a landfill slope. The landfill modelled in the dynamic centrifuge tests was a 7 m high municipal solid waste (MSW) landfill with a single geomembrane-clay liner system (45° side slope and 10 m slope length). Results show that moderate earthquake loading (base acceleration between 0.1 and 0.3 g) can result in a permanent increase in geomembrane tension of 5–25%.     

Thaumasite formation in sugary solutions: Effect of temperature and sucrose concentration

Thaumasite formation in cementitious environments is attributed to sulphate attack (internal or external). Thaumasite is characterized by the presence of octahedrally coordinated silicon, but is formed from the silicate phases of cement, (mainly C–S–H gel), whose silicon atoms are tetrahedrally coordinated. Thaumasite formation is favoured at low temperatures and from recent studies sugar solutions increases calcium solubility and also increases the velocity of formation of thaumasite. The aim of the present study is to explore the effect of temperature (5 °C and 25 °C) and sucrose concentration (5%; 10% and 20% wt) on thaumasite formation from lime and sodium carbonate, sulphate, silicate sugary solutions. Precipitates formed different ages were characterized by XRD and FTIR. At 5 °C larger proportions of thaumasite were formed in 10% sucrose however at 25 °C, the 20% sugary solution generates more thaumasite at shorter times.     

An experimental investigation of mechanical properties of structural cast iron at elevated temperatures and after cooling down

This paper presents the results of an extensive experimental investigation of the mechanical properties of structural cast iron at elevated temperatures and after cooling down to room temperature. A total of 135 tests were carried out. The specimens were subjected to tension (83 tests), compression (48 tests) or were heated for measurement of the thermal expansion (4 tests). The tests in tension include 35 steady-state tests up to 900 °C, 32 transient tests (5 °C/min and 20 °C/min heating rates, applied stress from 20% to 80% of 0.2% proof stress) and 16 tests after cooling down (heated up to 800 °C and cooled down with two different methods: quenching and air flow cooling). 32 steady-state tests (up to 900 °C) and 16 transient tests (5 °C/min and 20 °C/min heating rates, applied stress from 50% to 120% of 0.2% proof stress) were carried out for specimens in compression. The paper evaluates and proposes elevated temperatures material models.     

Multiaxial tensile–compressive strengths and failure criterion of plain high-performance concrete before and after high temperatures

Multiaxial tensile–compressive tests were performed on 100 mm × 100 mm × 100 mm cubic specimens of plain high-performance concrete (HPC) at all kinds of stress ratios after exposure to normal and high temperatures of 20, 200, 300, 400, 500, and 600 °C, using a large static–dynamic true triaxial machine. Friction-reducing pads were three layers of plastic membrane with glycerine in-between for the compressive loading plane; the tensile loading planes of concrete samples were processed by attrition machine, and then the samples were glued-up with the loading plate with structural glue. The failure mode characteristic of specimens and the direction of the crack were observed and described, respectively. The three principally static strengths in the corresponding stress state were measured. The influence of the temperatures, stress ratios, and stress states on the triaxial strengths of HPC after exposure to high temperatures were also analyzed respectively. The experimental results showed that the uniaxial compressive strength of plain HPC after exposure to high temperatures does not decrease completely with the increase in temperature, the ratios of the triaxial to its uniaxial compressive strength depend on brittleness–stiffness of HPC after different high temperatures besides the stress states and stress ratios. On this basis, the formula of a new failure criterion with the temperature parameters under multiaxial tensile–compressive stress states for plain HPC is proposed. This study is helpful to reveal the multiaxial mechanical properties of HPC structure enduring high temperatures, and provides the experimental and theory foundations (testing data and correlated formula) for fire-resistant structural design, and for structural safety assessment and maintenance after fire.