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).     

Permeability of high-performance concrete subjected to elevated temperature (600 °C)

Permeability is one of the most important parameters to quantify the durability of high-performance concrete. Permeability is closely related with the spalling phenomenon in concrete at elevated temperature. This parameter is commonly measured on non-thermally damaged specimens. This paper presents the results of an experimental investigation carried out to study the effect of elevated temperature on the permeability of high-performance concrete. For this purpose, three types of concrete mixtures were prepared: (i) control high-performance concrete; (ii) high-performance concrete incorporating polypropylene fibres; and (iii) high-performance concrete made with lightweight aggregates. A heating–cooling cycle was applied on 160 × 320 mm, 110 × 220 mm, and 150 × 300 mm cylindrical specimens. The maximum test temperature was kept as either 200 or 600 °C. After the thermal treatment, 65 mm thick slices were cut from each cylinder and dried prior to being subjected to permeability test. Results of thermal gradients in the concrete specimens during the heating–cooling cycles, compressive strength, and splitting tensile strength of concrete mixtures are also presented here. A relationship between the thermal damage indicators and permeability is presented.     

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.     

Shear strength of RC beams subjected to cyclic thermal loading

The experiments were performed for assessing the influence of cyclic thermal loading on the shear strength of reinforced concrete (RC) beam specimens. One hundred eleven RC beams of 100 × 150 × 1200 mm size reinforced in tension zone with two bars of 8, 10 and 12 mm diameters were tested under four point loading. The beams were subjected to a number of thermal cycles varying from 7 to 28 cycles with peak temperature taken as 100, 200 and 300 °C. The effects of thermal cycles on the crack pattern, failure mechanism, first crack load and the shear strength of beams have been discussed. The shear strength of the beams has been found to increase by up to 10% at lower temperature cycles of 100 and 200 °C but reduces by up to 14% at higher temperature (300 °C) depending on the severity of thermal loading. The results of study emphasize the need for developing appropriate guidelines for the design of RC structural elements used in comparatively high temperature environment with cyclic thermal loading conditions.     

Thermography as a technique for monitoring early age temperatures of hardening concrete

The exothermal character of cement hydration reactions causes concrete to endure temperature changes during the first days after casting, with associated volumetric deformations that may induce undesired cracking. The capability to predict temperature evolution in concrete since casting is thus important to back decisions that avoid detrimental thermal cracking in concrete structures. Even though several approaches exist to model the early age behavior of concrete, the laboratory or in situ verification of numerical predictions is scarce, and mostly done with embedded temperature sensors, with limited sampling points. The present research intends to evaluate the performance of the thermography technique in the continuous monitoring of surface temperatures of a hydrating 0.40 × 0.40 × 0.40 m³ concrete cube, in which embedded thermal sensors are also used. By using thermography, simultaneous monitoring of the visible surfaces of the specimen is possible, thus providing comprehensive information regarding the evolution of surface temperatures. The temperatures monitored with the thermography, as well as with the embedded temperature sensors, are finally used as a benchmark example for validation of a 3D finite element numerical code for thermal analysis developed by the authors. The use of thermography images for validation of finite element results is rather more advantageous than the use of standard single point temperature measurements, in view of the large facility and wide range of comparison provided by the simultaneous visualization of temperature surface color maps (measured and simulated).     

Properties of Portland cement-modified asphalt binder using Superpave tests

This study investigates the effect of cement additive on some properties of asphalt binder using Superpave testing methods. Six cement-to-asphalt (C/A) ratios were considered in the study: 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30 by volume of asphalt binder. The experimental tests that were conducted in the study included the Superpave rotational viscosity (RV) test and the dynamic shear rheometer (DSR) test. The RV test was conducted at the Superpave-specified high temperature of 135 °C that represents the average mixing and laydown temperature, and at seven different rotational speeds of 5, 10, 20, 30, 50, 60, and 100 rpm. On the other hand, the DSR test was conducted at four test temperatures of 58, 64, 70, and 76 °C; one lower and two higher than the Superpave high performance grade (PG) temperature of the asphalt binder used in the study (PG 64). The loading frequency used in the DSR test was 10 rad/s (1.59 Hz) as specified by the Superpave system. Results of the study showed that the addition of Portland cement to asphalt binders increased the rotational viscosity (RV) of asphalt binders at 135 °C and different rotational speeds. The C/A ratio of 0.15 was found to be the optimum ratio that achieved a balanced increase in the rotational viscosity and the value of the DSR G^*/sin δ rutting parameter of asphalt binders. The C/A ratio had insignificant effects on the Newtonian behavior, the phase angle (δ), and the elastic behavior of asphalt binders. The increase in C/A ratio increased the stiffness of asphalt binders represented by the complex shear modulus (G^*) value. The increase in the C/A ratio improved the rutting parameter, G^*/sin δ value, at all temperatures. The increase in C/A ratio improved the Superpave high PG temperature (the high temperature at which the asphalt binder passed the Superpave criteria for G^*/sin δ value). It was also shown that the best function that described the relationship between each of RV, G^*, and G^*/sin δ and the C/A ratio was the exponential function with high coefficient of determination (R²).     

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.     

Comparison of fibrous insulations – Cellulose and stone wool in terms of moisture properties resulting from condensation and ice formation

Cellulose fibres are often used as thermal insulation in buildings. The organic nature of cellulose fibres, however, makes the insulation sensitive to high moisture content. This study investigates the moisture performance of cellulose insulation when exposed to a subzero environment. The paper is focused on the condensation and freezing in the material and includes comparison with the authors previous studies on stone-wool insulation. While the used stone-wool samples were water-repellent due to resin binders, cellulose is a typical representative for hydrophilic thermal insulation to which any contact with water condensate can be crucial.Test specimens of loose-fill cellulose were placed in a special laboratory device providing high moisture load. During a period of 100 h the specimens were subjected to a continuous load of moisture at atmospheric conditions on one side while the other side of the specimen faced a surrounding temperature of 0, −10 and −20 °C and the laboratory tests were repeated three times for each set of the specific thermal conditions (T_i = +20 °C, T_e = 0, −10 and −20 °C). The results indicate that there are minor changes in the water vapour permeability of the specimens. The experimental data from the investigation is compared with a mathematical model that simulates moisture diffusivity of cellulose together with accumulation due to sorption and freezing, using the actual climatic data.     

Field experiments on thermal comfort in campus classrooms in Taiwan

This paper presents the results of the ASHRAE methodology for thermal comfort study applied in Taiwan. Field experiments conducted in 10 naturally ventilated and 26 air-conditioned campus classrooms used survey questionnaires and physical measurements to collect data. A total of 944 individuals in seven universities completed 1294 questionnaires. The chi-square tests were applied to find the significant aspects that affect students’ thermal sensations. The results show that air temperature, air movement and mean radiant temperature have significant influence, but humidity has no statistical significance. By using probit regressive analyses, the thermal neutrality and thermal preference of students occurred at 26.3 °C ET^* and 24.7 °C ET^*, respectively. Responses from those students suggest a wider acceptable temperature range for occupants in Taiwan. The margins of the acceptable zones obtained from direct and indirect acceptability assessing methods are 21.1–29.8 °C ET^* and 24.2–29.3 °C ET^*, respectively. When compared with similar studies elsewhere, this finding supports the sentiments on climatic adaptation.     

Behavior of FRP-confined concrete after high temperature exposure

This paper presents the results of an experimental program to investigate the effect of high temperature on the performance of concrete externally confined with FRP sheets. For this purpose, a two-phase experimental program was conducted. In the first phase, 42 standard 100 × 200 mm concrete cylinders were prepared. Out of these specimens, 14 cylinders were left unwrapped; 14 specimens were wrapped with one layer of CFRP sheet; and the remaining 14 specimens were wrapped with one layer of GFRP sheet. Some of the unconfined and FRP-confined specimens were exposed to room temperature; whereas, other cylinders were exposed to heating regime of 100 °C and 200 °C for a period of 1, 2 or 3 h. After high temperature exposure, specimens were tested under uniaxial compression till failure. The test results demonstrated that at a temperature of 100 °C (a little more than the glass transition temperature (T_g) of the epoxy resin), both CFRP- and GFRP-wrapped specimens experienced small loss in strength resulting from melting of epoxy. This loss of strength was more pronounced when the temperature reached 200 °C. In the second phase of the experimental program, three 100 × 100 × 650 mm concrete prisms were prepared and then overlaid by one layer of CFRP and GFRP laminates for conducting pull-off strength tests as per ASTM D4541 – 09. The objective of this testing was to evaluate the degradation in bond strength between FRP and concrete substrate when exposed to elevated temperature environments. One prism was exposed to room temperature whereas the other two specimens were exposed to heating regime of 100 °C and 200 °C for a period of 3 h. It was concluded that a significant degradation in the bond strength occurred at a temperature of 200 °C especially for CFRP-overlaid specimens.     

Performance of thermally damaged fibre reinforced concretes

Mechanical characteristics of Fibre Reinforced High Performance Concrete (FR-HPC) subjected to high temperatures were experimentally investigated in this paper. Three different concretes were prepared: a normal strength concrete (NSC) and two High Performance Concretes (HPC1 and HPC2). Fibre reinforced concretes were produced by addition of steel or polypropylene fibres in the above mixtures at dosages of 40 kg/m³ and 5 kg/m³, respectively. A total of nine concrete mixtures were produced and fibres were added in six of them. At the age of 120 days specimens were heated to maximum temperatures of 100, 300, 500 and 700 °C. Specimens were then allowed to cool in the furnace and tested for compressive strength, splitting tensile strength, modulus of elasticity and ultrasonic pulse velocity. Reference tests were also performed at air temperature (20 °C). Residual strength of NSC and HPC1 was reduced almost linearly up to 700 °C and 500 °C, respectively whereas the residual strength of HPC2 was sharply reduced up to 300 °C. Explosive spalling was observed on both HPC. Addition of steel fibres increased the residual strength up to 300 °C, but spalling still occurred in HPC1 and HPC2. Such an explosive behavior was not observed when polypropylene fibres were added in the mixtures; however, in this case the residual mechanical characteristics of all concretes were significantly reduced.     

Development of mechanistic–empirical design method for an asphalt pavement rutting model using APT

This paper describes the study of accelerated pavement testing (APT) with test variables of temperature and air void ratio, which are important factors that influence rutting. The purpose of the study was to use the APT results to calibrate a laboratory rutting model for asphalt concrete (AC) mixtures and to develop an appropriate rutting model for AC pavements. The test specimen for the APT was prepared as a pavement system with an AC layer of 30 cm, subbase of 30 cm, and subgrade of 180 cm. The experimental variables were chosen to be the important factors that influence the rutting of AC pavement: temperature (50 °C) and air void ratios (7.31% and 10.57%). A multi-depth deflectometer was installed at depths of 12 and 30 cm from the AC pavement surface to measure the plastic and resilient strains, which are necessary for the development of the rutting model. The result was used to examine the rutting models of AC pavement layers suggested by the AASHTO 2002 model as well to calibrate a laboratory rutting model.     

Modeling mechanical performance of lightweight concrete containing silica fume exposed to high temperature using genetic programming

In this study, the mechanical performance of lightweight concrete exposed to high temperature has been modeled using genetic programming. The mixes incorporating 0%, 10%, 20% and 30% silica fumes were prepared. Two different cement contents (400 and 500 kg/m³) were used in this study. After being heated to temperatures of 20 °C, 200 °C, 400 °C and 800 °C, respectively, the compressive and splitting tensile strength of lightweight concrete was tested. Empirical genetic programming based equations for compressive and splitting tensile strength were obtained in terms of temperature (T), cement content (C), silica fume content (SF), pumice aggregate content (A), water/cement ratio (W/C) and super plasticizer content (SP). Proposed genetic programming based equations are observed to be quite accurate as compared to experimental results.     

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.     

Study on properties of recycled tire rubber modified asphalt mixtures using dry process

To minimize waste tires pollution and improve properties of asphalt mixtures, properties of recycled tire rubber modified asphalt mixtures using dry process are studied in laboratory. Tests of three types asphalt mixtures containing different rubber content (1%, 2% and 3% by weight of total mix) and a control mixture without rubber were conducted. Based on results of rutting tests (60 °C), indirect tensile tests (−10 °C) and variance analysis, the addition of recycled tire rubber in asphalt mixtures using dry process could improve engineering properties of asphalt mixtures, and the rubber content has a significant effect on the performance of resistance to permanent deformation at high temperature and cracking at low temperature.     

Post-fire residual mechanical properties of concrete made with recycled rubber aggregate

This study investigates the effects of elevated temperatures on the residual mechanical performance of concrete produced with recycled rubber aggregate (RRA). Four different concrete compositions were prepared: a reference concrete (RC) made with natural coarse aggregate and three concrete mixes with replacement rates of 5%, 10% and 15% of natural fine and coarse aggregate by RRA from used tyres. Specimens were exposed for a period of 1 h to temperatures of 400 °C, 600 °C and 800 °C, after being heated in accordance with ISO 834 time–temperature curve. After cooling down to ambient temperature, the compressive strength and the splitting tensile strength were evaluated and compared with reference values obtained prior to fire exposure. For the replacement rates used in the present experiments, the obtained results show that concrete made with recycled rubber aggregate (CRRA) present a thermal response that is roughly similar to that of RC; in addition, although residual mechanical properties of CRRA are noticeably more affected than those of RC, particularly for higher exposure temperatures, the relative reduction should not prevent it from being used in structural applications.     

Beam test on bond behavior between high-grade rebar and high-strength concrete after elevated temperatures

In this paper, post-heating bond behavior between high-grade rebar and C80 high-strength concrete (hereafter, HSC) is studied. The high-grade rebar is HRBF500 fine grained steel with a yield strength of 500 MPa and the concrete grade C80 denotes compressive strength not lower than 80 MPa. First, the residual mechanical behavior of both high-grade rebar and HSC were tested after fire exposure. Second, the beam bond test was carried out to study the bond behavior between high-grade rebar and HSC after exposed heating at 200 °C, 400 °C, 500 °C and 600 °C, respectively. During the bond test, the influence of temperature, bond length, and some construction measurements on the bond–slip behavior were compared and evaluated. The investigation demonstrates that (1) the bond strength between high-grade rebar and HSC decreases while the peak slip increases with the elevated temperature, especially when the temperature exceeds 400 °C and (2) the confinement effect of steel wire mesh can help to improve rebar׳s bond behavior. Third, the bond–slip model between high-grade rebar and HSC for post-heating is proposed.     

Kinetic and mechanism of the thermal degradation of a plywood by using thermogravimetry and Fourier-transformed infrared spectroscopy analysis in nitrogen and air atmosphere

The thermal degradation of plywood was investigated using thermogravimetric analysis (TGA) device. The TGA experiments were conducted between ambient temperature and 1000 °C for seven different heating rates: 5, 10, 15, 20, 30, 40 and 50 °C min⁻¹. The experiments were realized under inert and air atmospheres in order to characterize the plywood thermal decomposition occurring during the pyrolysis and oxidative processes. Throughout all the tests, the gaseous emissions were continuously monitored using a Fourier transformed infra-red spectrometer (FTIR). The progress in the mass, the mass-loss rate (MLR) and gas emissions data allow to propose a mechanism of the thermal decomposition of plywood with six different stages. The reactions (stages) of this mechanism is of a rate represented by a modified Arrhenius law containing four unknown kinetic parameters (A, E_a, n and ν) for each reaction. These 24 unknown parameters are determined by using the inverse optimization method of the genetic algorithms. The model developed is validated regardless of the heating rate and atmosphere (inert or air) chosen. A very good agreement is obtained between the experimental and the numerical mass loss rate evolutions.     

Lime based steam autoclaved fly ash bricks

About 10 million tonnes of fly ash are produced yearly as waste from coal fired thermal power plants in Turkey. Only a small portion of this waste is utilized as a raw material in the production of cement and concrete. In this study, Seyitömer power plant fly ash was investigated in the production of light weight bricks. Fly ash, sand and hydrated lime mixtures were steam autoclaved under different test conditions to produce brick samples. An optimum raw material composition was found to be a mixture of 68% fly ash, 20% sand and 12% hydrated lime. The optimum brick forming pressure was 20 MPa. The optimum autoclaving time and autoclaving pressure were found 6 h and 1.5 MPa, respectively. The compressive strength, unit volume weight, water absorption and thermal conductivity of the fly ash–sand–lime bricks obtained under optimum test conditions are 10.25 MPa, 1.14 g/cm³, 40.5% and 0.34 W  m⁻¹ K⁻¹ respectively. The results of this study suggested that it was possible to produce good quality light weight bricks from the fly ash of Seyitömer power plant.