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).     

A laboratory study on stone matrix asphalt using ground tire rubber

This research investigated the feasibility using asphalt rubber (AR), produced by blending ground tire rubber (GTR) with an asphalt, as a binder for stone matrix asphalt (SMA). Two different sizes of GTR produced in Taiwan were used. The potential performance of AR–SMA mixtures was also evaluated. The results of this study showed that it was not feasible to produce a suitable SMA mixture using an asphalt rubber made by blending an AC-20 with 30% coarse GTR with a maximum size of 0.85 mm. However, SMA mixtures meeting typical volumetric requirements for SMA could be produced using an asphalt rubber containing 20% of a fine GTR with a maximum size of 0.6 mm. No fiber was needed to prevent drain-down when this asphalt rubber was used. The AR–SMA mixtures were not significantly different from the conventional SMA mixtures in terms of moisture susceptibility from the results of AASHTO T283 tests. The results of the wheel tracking tests at 60 °C show that rutting resistance of AR–SMA mixtures was better than that of the conventional SMA mixtures.     

Effect of crumb rubber characteristics on crumb rubber modified (CRM) binder viscosity

Asphalt binder viscosity is of great importance during the production process of hot mix asphalt mixture as typically asphalt plants will store binders between 149 °C and 177 °C. SHRP guidelines state that asphalt binder viscosity must not exceed 3 Pa s. Therefore, given the documented increases in asphalt viscosity when modified with crumb rubber modifier (CRM) it is necessary to produce asphalt binder that fulfills the SHRP criteria while not exceeding plant mixing and storing requirements. This paper reports the results of an investigation of the importance of CRM properties on viscosity of CRM binder. Two binder sources were modified at four concentration levels using four different crumb rubber sources; the viscosities of the produced binders were evaluated by AASHTO T 316. Crumb rubber properties were evaluated by elemental analysis using a scanning electron microscope (SEM) and by determination of glass transition temperature (T_g) using a differential scanning calorimeter (DSC). In general, results indicate that processing procedure and tire type plays an important role in the determination of CRM binder viscosity.     

Prediction of bituminous mixture fatigue life based on accumulated strain

This research was aimed to predict the number of cycles that cause fracture of hot-mix asphalt (HMA) based on the number of cycles at which the slope of accumulated strain switched from decreasing to increasing mode. In addition, the effect of aggregate gradation and temperature on fatigue behaviors of HMA were evaluated.HMA specimens were prepared at optimum asphalt content using the Marshall mix design procedure. The specimens were prepared using crushed limestone aggregate, 60/70 penetration asphalt, and three different aggregate gradations with maximum nominal aggregate size of 12.5, 19.0, and 25.0 mm. Five magnitudes of load (1.5, 2.0, 2.5, 3.0, and 3.5 kN) were evaluated for their effect on fatigue behavior.Constant stress fatigue tests were performed using the Universal Testing Machine (UTM) at 25 °C. Other temperatures (10, 45, and 60 °C) were evaluated at a load of 3.5 kN.The tests results indicated that the slope of accumulated strain continued to decrease until the number of loading cycles approached 44% of the number of cycles that caused fracture of the HMA. Also, the initial stiffness of asphalt mixtures was found to increase as the magnitude of the load applied increased and as the aggregate gradation maximum nominal size decreased.     

Laboratory evaluation of the effects of short-term oven aging on asphalt binders in asphalt mixtures using HP-GPC

Both the RTFO (rolling-thin film oven) aging of asphalt binders and the STOA (short-term oven aging) of asphalt mixtures are designed to simulate aging during the construction of hot mix asphalt (HMA) pavements. Many studies have been conducted evaluating the aging effects on asphalt binders since their properties can be easily measured using many conventional tests, such as rotational viscometer, DSR (dynamic shear rheometer), and BBR (bending beam rheometer). However, studies on asphalt mixture aging have been limited to mechanical properties such as strength and fatigue characteristics because considerable effort is required to identify the aging of the asphalt binder in a mixture. This study evaluated the effects of short-term oven aging on asphalt mixtures using the GPC (gel-permeation chromatography) procedure. Nine asphalt mixtures, using three different binder sources, were prepared and five short-term aging methods were used to evaluate these mixes. For comparison, the RTFO aging was also conducted for nine asphalt binders. The aging of a binder within asphalt mixtures, including polymer-modified mixtures, could be identified under various short-term aging conditions. Statistical analysis of the GPC test results indicated that two commonly used short-term aging methods in the laboratory, a 154 °C oven aging for 2 h and a 135 °C oven aging for 4 h, are not significantly different, based on the increase in the large molecular size (LMS) ratios. The RTFO aging method was found to have less effect on binder aging than the short-term oven aging methods of asphalt mixtures.     

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.     

Interaction effects of crumb rubber modified asphalt binders

The application of crumb rubber in asphalt mixtures is intended to improve the binder properties by reducing the binder’s inherent temperature susceptibility. This research investigated the interaction effects of CRM binders as a function of various blending treatments in the laboratory. For this study, CRM binders were produced using seven blending times (5, 30, 60, 90, 120, 240, and 480 min), three blending temperatures (177, 200, and 223 °C), and four rubber contents (5%, 10%, 15%, and 20% by weight of asphalt binder). The results from this study showed that (1) The interaction time and interaction temperature for CRM binders were observed to have significant effect on the binder properties; (2) The longer time and higher temperature for interaction of CRM binders resulted in an increase in the high failure temperature and the viscosity. This is thought to be due to the increase in the rubber mass through binder absorption. However, this study found that the control binder of PG 64-22 had little change of the binder properties as a function of interaction conditions; (3) The CRM percentage influence is statistically significant on the viscosity and G^*/sin δ values. Also, the asphalt binder with higher CRM percentage showed a higher large molecular size (LMS) value, and the increase in CRM percentage is considered to result in the additional loss of the low molecular weight in the asphalt binder to the CRM.     

Modeling temperature distribution and thermal property of asphalt concrete for laboratory testing applications

Material characterization from laboratory tests on asphalt concrete or predictions of pavement performance are meaningful only if temperature of the material is well taken into account. This paper discusses an analytical model to predict the transient temperature distribution within asphalt concrete and to determine its thermal properties. The paper also presents the laboratory test program designed to validate the model. Temperature measurements were carried out on a cylindrical specimen at different times after the specimen with a steady-state low temperature (3.5 °C) was placed inside an environmental chamber in a steady-state high temperature (36 °C). The temperature magnitude at different positions and its variation with time was recorded at a sampling rate of 1 min⁻¹. The analytical temperature models based on the classical planar wall and long cylinder were established to approximate the temperature distribution of asphalt concrete specimens with the geometry of a short cylinder or a beam. Thermal diffusivity as a function of thermal conductivity and heat convection is solved from the models, and then back-calculation was conducted to achieve the thermal properties using curve fitting. It was found that the analytical model could predict the measured temperatures reliably. For the materials used in this research, a thermal conductivity of 2.88 W/m °C and diffusivity of 1.42 × 10⁻⁶ m²/s were attained from the back-calculation. The time–temperature relationship, as determined from the prediction model, was found to be very sensitive to the geometric size and thermal properties of asphalt concrete.     

Modeling viscosity behavior of crumb rubber modified binders

Accurately predicting the viscous properties of crumb rubber modified (CRM) binders has proven difficult, especially as these properties tend to vary with changing crumb rubber concentrations and temperatures. This study explores the utilization of the statistical regression and neural network (NN) approaches in predicting the viscosity values of CRM binder at various temperatures (135 °C and greater). A total of 53 CRM binder combinations were prepared from two different rubber types (ambient and cryogenic), three different binder sources, four rubber concentrations (0%, 5%, 10%, and 15%), and five crumb rubber gradations (ADOT, SCDOT, 0.18 mm, 0.425 mm, and 0.85 mm). The results indicated that the regression model is easy to use and can be used for viscosity prediction, similarly NN-based models also provided accurate for predictions for the viscosity values of CRM binders regardless of rubber type and can easily be implemented in a spreadsheet. In addition, the developed NN model can be used to predict viscosity values of other types of CRM binders efficiently. Furthermore, the sensitivity analysis of input variables indicated that the changes of viscosity are significant as the changes of asphalt binder grade, test temperature, and rubber content. The results also show that these three independent variables are the most important factors in the developed NN models in comparison with other variables.     

废旧轮胎橡胶混合法改性沥青混合料的研究

运用包括湿法和干法两道工艺的混合法,在实验室成功开发了废旧轮胎橡胶改性沥青混合料.即先用细橡胶粉制备成橡胶沥青,然后在集料中加入粗橡胶粉拌制成废橡胶改性沥青混合料.试验结果表明,与类似级配的湿法工艺或干法工艺的改性沥青混合料相比,混合法改性沥青混合料显示出更加优良的高、低温性能,水稳定性完全满足要求,且消耗了相对多的废旧轮胎,达到了环保和工程双赢的目的.     

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.     

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.     

Strengths and flexural strain of CRC specimens at low temperature

Crumb rubber concrete (CRC) is made by adding rubber crumbs into conventional concrete. This study undertakes an experimental study on the cubic compressive strength, axial compressive strength, flexural strength and splitting tensile strength of CRC specimens at both ambient temperature 20 °C and low temperature ?25 °C. The flexural stress–strain responses were also recorded. The averaged size of rubber crumbs used in the study is about 1.5 mm. Four levels of rubber contents are investigated, which are 0%, 5%, 10% and 15% by volume, respectively. The mix design aimed at 40 MPa of compressive strength and 100 mm of slump for all the CRC specimens. The results show that CRC increases its magnitude in strengths when temperature decreases, which is similar to the case of conventional concrete, but still exhibits ductility in low temperature. The conclusion from this study is that CRC may be more beneficial in its application in low temperature environments than in ambient temperature environments.     

Influence of soaking and polymerization conditions on the properties of polymer concrete

An experimental investigation was conducted to study the effect of soaking time and polymerization temperature on the mechanical and physical properties of polymer-impregnated concrete. Soaking time was controlled in 4, 8, 12, 16, 20 and 24 h, polymerization temperature was set at 70, 80 and 90 °C for 0.5, 1, 2, 4, 6, 12 and 24 h in impregnation process, respectively. Cylindrical concrete specimens with water/cement ratios of 0.45 and 0.65 were impregnated with methyl methacrylate (MMA) and benzoyl peroxide (BPO) mixtures. The polymer loading increases as immersion time increases until 12 h. Based on compressive strength and surface absorption, optimum polymerization temperature is 70 °C for Mix A (high cement content) and 80 °C for Mix B (low cement content). Polymer impregnation not only increases concrete strength and resistivity but also greatly decreases surface absorption comparing with normal concrete. SEM and MIP observations indicate that the micro-pores and meso-pores of PIC specimens are filled with PMMA and the total pore volume and maximum pore size are reduced significantly.     

Mechanistic-empirical mixture design for hot mix asphalt pavement recycling

Mixture design of six asphalt mixtures containing Reclaimed Asphalt Pavement (RAP) were evaluated by using a mechanistic-empirical approach. The testing methodology involved determination of the key mechanical properties and durability of wearing course and base course materials containing RAP at three different levels of addition (i.e. 10%, 30% and 50%), manufactured to a supplied specification, and the rheological properties of binder used in, and recovered from, these materials. In order to optimise both rutting and fatigue resistance, the recycled mixtures were manufactured by using 80/100 pen virgin bitumen (which is one grade softer than the 60/70 pen bitumen conventionally used for the respective parent asphalt materials), with or without added rejuvenating oil. This paper demonstrates that the asphalt mixtures containing RAP performed at least similar to, or better than, that of conventional asphalt materials.     

Effect of crumb rubber modifiers on high temperature susceptibility of wearing course mixtures

This paper investigates the effects of different sizes of crumb rubber modifier (CRM) on the high temperature susceptibility of three gradations (AC-10, AC-20 and PA) of wearing course mixtures. A wet process and 10% CRM by total weight of binders were used in these studies and the control variables for these studies included three CRMs of sizes 0.15 mm, 0.30 mm and 0.60 mm. The evaluations were twofold. Firstly, a comparison of the properties of those modified and unmodified binders at a wide range of testing temperatures and ageing conditions was conducted. Secondary, a comparison of the rutting resistance of the CRM and conventional mixtures was made. The results show that all the CRMs have overall contributed to better performance of both binders and mixtures at high temperatures. In addition, among these three CRM sizes, mixtures modified with 0.15 mm CRM exhibited the best effect on the dense-graded mixture (AC-10 and AC-20) whereas mixtures modified with 0.60 mm CRM exhibited the best effect on the open-graded mixture of porous asphalt (PA).     

Experimental behaviour of RACFST stub columns after exposed to high temperatures

The experimental studies on the behaviour of recycled aggregate concrete-filled steel tube (RACFST) stub columns after exposed to high temperatures are reported in this paper. Forty specimens, including 32 RACFST stub columns and 8 normal concrete-filled steel tube (CFST) stub columns as reference, were tested, and the failure pattern, load versus strain relation and ultimate strength of the specimens were presented and analysed. Five types of concrete were produced: one reference concrete with natural aggregates, two concrete mixes with recycled coarse aggregate (RCA) replacement ratios of 50% and 100%, and two concrete mixes with recycled fine aggregate (RFA) replacement ratios of 50% and 100%. The specimens were exposed to 300 °C, 600 °C and 800 °C for 3 h. The test results showed that, due to the existence of the recycled aggregates, the post-fire performance of RACFST stub columns was lower than the corresponding normal CFST specimens under the same maximum temperature suffered, and the RACFST specimens with RCA had a better behaviour than those with RFA under the same recycled aggregate replacement ratio.     

Laboratory investigation of indirect tensile strength using roofing polyester waste fibers in hot mix asphalt

The vast quantity of waste materials (such as roofing polyester waste fibers) accumulating throughout the world is creating costly disposal problem. The use of these materials was proved to be economical, environmentally sound and effective in increasing the performance properties of the asphalt mixture in recent years. The primary objective of this research was to determine whether homogeneously dispersed roofing waste polyester fibers improve the indirect tensile strength (ITS) and moisture susceptibility properties of asphalt concrete mixtures containing various lengths and percentages of the fiber in various aggregate sources. The experimental design included the use of three aggregate sources, two lengths (0.635 cm (1/4 in.) and 1.270 cm (1/2 in.)) of this fiber, and two fiber contents (0.35% and 0.50% by weight of total mixture). The results of the experiments found that, in general, the addition of the polyester fiber was beneficial in improving the wet tensile strength and tensile strength ratio (TSR) of the modified mixture, increasing the toughness value in both dry and wet conditions, and increasing the void content, the asphalt content, the unit weight, and the Marshall stability.     

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.