Development of an automatic torque test to measure the shear bond strength between asphalt

This paper describes the development of a laboratory-based automatic torque bond test that is capable of quasi-static and repeated load interface testing. Results from quasi-static testing undertaken using either a controlled torque rate or a controlled rotation rate showed that the shear strengths and shear reaction moduli increased as the temperature decreased. Samples with interfaces treated with the cationic emulsion were found to display the highest shear strengths and those treated with no emulsion were found to display the lowest shear strengths. A reasonably good correlation was found between results from testing performed at 600 N m/min and testing performed at 180°/min. The nominal shear strength measured from a test performed at 180°/min was found to be approximately 1.9 times higher than the nominal shear strength measured from a test performed at 600 N m/min. The nominal shear reaction modulus from a test performed at 180°/min was found to be approximately 1.6 times higher than the nominal shear reaction modulus from the test performed at 600 N m/min. The effect of material compliance above and below the interface on the rotation of the interface and shear reaction modulus of the interface is likely to be relatively small unless the shear stiffness of these materials is very low and/or the thickness is large. Results from repeated load (fatigue) testing showed a higher fatigue life and greater sensitivity to shear stress level at the lower temperature.     

Effects of elevated water temperatures on interfacial delaminations,failure modes and shear strength in externally-bonded CFRP-concrete beams using infrared thermography,gray-scale images and direct shear test

This paper reports the results of a durability study of the effects of exposing externally-bonded CFRP-concrete beams to three elevated water temperatures (25 °C, 40 °C and 60 °C). The effects of the heated water environments on the adhesive bonding layer between the CFRP and concrete beams were evaluated by quantifying: (1) the changes of delaminations within the adhesive bonding layer, (2) the changes in resistance to direct shear force and (3) the changes of failure mode distribution. Before the exposure, the condition of the adhesive bonding layer was inspected by infrared thermography (IRT). After exposure, the deterioration of the same bonding layer and failure mode distributions were measured by analyzing the visual photos on the failed CFRP strips. The failure modes were found to be affected largely by the combined effect of elevated temperature and moisture ingress, in which three types were identified: failure at concrete beams, at adhesive bonding layer and interface between CFRP strip and concrete. With these methods, results of 54 specimens show that the adhesive bonding layers of all the specimens had gradually deteriorated in the 40 °C and 60 °C water baths. This deterioration was due to the weakening of the adhesive bonding layers when the glass transition temperature (T_g) or the heat distortion temperature (HDT) was approached or even exceeded, and gradual development of delaminations at adhesive bonding layer.     

Shear bond strength between asphalt layers for laboratory prepared samples and field cores

This paper describes the laboratory measurement of shear interface properties between asphalt layers using the Leutner test. Results are presented and compared for both laboratory prepared specimens and field cores. The standard Leutner test was modified by the introduction of a 5 mm gap into the shear plane to reduce edge damage caused by misalignment of the specimen and specimens that incorporate a thin surfacing material were extended using a 30 mm thick grooved metal cylinder to eliminate dependence of the shear strength on surfacing thickness. The laboratory produced surfacing/binder course combinations incorporating the 20 mm Dense Bitumen Macadam (20 DBM) binder course showed the highest average shear strengths when nothing was applied at the interface and the lowest average shear strengths when the tack coat was applied at the interface. The average shear strength from field cores was found to increase as the class of the road increases for both surfacing/binder course interfaces and binder course/base interfaces.     

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.     

Structural behavior and performance of water pipes rehabilitated with a fast-setting polyurea–urethane lining

This paper presents the structural behavior and performance of a fast-setting polyurea–urethane (PUU) lining as a structural lining material for rehabilitating water pipes. To this end, a series of experimental tests were carried out to assess the following: (1) bond strength; (2) hole and gap spanning capabilities; (3) angular displacement ability; (4) transverse shear resistance; and (5) fatigue cyclic loading resistance. First, pull-off bond tests were conducted to evaluate the bond characteristics of a fast-setting PUU lining bonded to steel specimens. Surfaces were dried to ensure adequate bond strength. Second, hole and gap spanning tests were carried out to investigate the spanning capability of the lining on the water pipes. From these tests, the hole spanning capability of water pipe with 5 mm hole was observed to be 11 MPa. Then, angular displacement and transverse shear tests on fast-setting PUU lined water pipes were also carried out to evaluate the behavior and performance in bending and shear of this material. Peel off failure of PUU occurred at an angular displacement capacity of 6.74° and no failure of PUU was observed at a transverse shear capacity of 25% of the diameter. Finally, fatigue cyclic loading test was conducted to investigate the fatigue behavior and performance of the water pipe lined with this PUU material. The fatigue resistance of PUU in the range of 10⁵ cyclic loadings was achieved.     

Year round performance and potential of a natural circulation type of solar water heater in India

The system consists of a flat-plate collector and a storage tank. Flat-plate collector is made of galvanised steel tube and aluminium plate, with MAXORB selective surface, encased in a mild steel tray with top single glass cover, bottom has been provided with glass wool insulation. It is kept facing equator and at λ+15° tilt (λ latitude of the place).The double walled storage tank is of 100 l capacity. The inner drum is made of 18 gauge galvanised steel and outer of mild steel. Space (100 mm) between them is filled with glass wool insulation.Performance and testing of solar water heater has been carried out extensively. It has been found that the heater can provide 100 l of hot water at an average temperature of 60.6 °C at 16:00 h when tap water temperature was 23.6 °C, it can retain hot water till next day morning at an average temperature of 51.6 °C. The overall efficiency of the heater is 57%.Based on performance at Jodhpur, a model has been developed by using ambient temperature and solar radiation for the prediction of its performance at various Indian stations. The predicted performance at various Indian stations revealed that hot water is required at most places for domestic use only during winter season and it can provide 100 l of hot water at an average temperature of 50–70 °C that can be retained to 40–60 °C till next day morning use.     

Effects of thermal cycles on mechanical properties of an optimized polymer concrete

The aim of this study is the design, fabrication and experimentally characterization of an optimized polymer concrete (PC). To this end, three factors, namely: the aggregate size, epoxy resin weight percentage, and chopped glass fiber percentage; are considered as the influencing factors on the compressive strength, bending strengths and interfacial shear strength between the PC and steel. The number of tests which are necessary to simultaneously optimize three above strengths of the PC are reduced based on the design of experiment using the orthogonal array technique or so-called Taguchi method. Comparison of the predicted strengths based on the Taguchi approach with the measured experimental results shows a good correlation between them. Afterward, the effect of three freeze/thaw thermal cycles; 25 °C to ?30 °C (cycle-A), 25 °C to 70 °C (cycle-B) and ?30 °C to 70 °C (cycle-C) for 7 days; on the strengths of the optimized PC is experimentally investigated. Comparison of the experimental results for the mechanical strengths measured at room temperature (RT) and above thermal cycles shows that the compressive strength of the optimally designed PC is not affected by heating and cooling cycles. On the other hand, the bending strength is more affected by exposing PC to the thermal cycle-B. The interfacial shear strength becomes affected by exposing the PC to cycles-A and -B, whereas no changes are observed on this strength by exposing to the thermal cycle-C. In general, among the three thermal cycles, cycle-B exerted the most deteriorating effect on the strengths.     

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.     

Performance of fully encapsulated rebar bolts and D-Bolts under combined pull-and-shear loading

The performance of two types of rock bolts, fully encapsulated rebar and D-Bolt, under combined pull and shear loading were studied in the laboratory. A new test approach was developed to apply the pull and shear loads to the rock bolt at the same time so that the bolt is displaced in a direction different from the bolt axis. Five displacing angles between 0° (pure pull) and 90° (pure shear) were employed in the tests. The test results show that the linear elastic stiffness of both the D-Bolt and the rebar bolt is mobilised quickly after a small displacement. When the displacing angle is larger than 40°, grout crushing may occur underneath the bolt shank, resulting in reduction in the stiffness of the bolt. The ultimate load of the bolts remains approximately constant no matter what the displacing angle is for both the D-Bolt and the rebar bolt. The displacement capacity of the D-Bolt, however, is dependent on the displacing angle. The ultimate displacement of a 1-m long D-Bolt section varies from 140 mm under pure pull (0°) to approximately 70 mm when the displacing angle is larger than 40°. The ultimate displacement of the rebar slightly increases from 29 mm under pure pull to 53 mm under pure shear. In general, the displacement capacity of the D-Bolt is larger than that of the rebar bolt. It is approximately 3.5 times the rebar under pure pull and 50% higher than rebar under pure shear. The test results show that the displacing angle of the bolt is larger than its loading angle, which is also confirmed by the analytical solutions.     

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.     

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.     

Fatigue behavior of rubberized asphalt concrete mixtures containing warm asphalt additives

The long-term performance of pavement is associated with various factors such as pavement structure, materials, traffic loading, and environmental conditions. Improving the understanding of the fatigue behavior of the specific rubberized warm mix asphalt (WMA) is helpful in recycling the scrap tires and saving energy. This study explores the utilization of the conventional fatigue analysis approach in investigating the fatigue life of rubberized asphalt concrete mixtures containing the WMA additive. The fatigue beams were made with one rubber type (?40 mesh ambient crumb rubber), two aggregate sources, two WMA additives (Asphamin^® and Sasobit^®), and tested at 20 °C. A total of eight mixtures were performed and 29 fatigue beams were tested in this study. The test results indicated that the addition of crumb rubber and WMA additive not only reduced the mixing and compaction temperatures of rubberized asphalt mixtures offset by crumb rubber but also effectively extended the long-term performance of pavement when compared with conventional asphalt pavement. In addition, the exponential function forms are efficient in achieving the correlations between the dissipated energy and load cycle as well as mixture stiffness and load cycle.     

Creep behaviour of CFRP-strengthened reinforced concrete beams

The strengthening of reinforced concrete structures with externally bonded fibre reinforced polymer (FRP) laminates has shown excellent performance and, as a result, this technology is rapidly replacing steel plate bonding techniques. The numerous studies that have been carried out to date on FRP-strengthened concrete elements have mainly focussed on the static and short-term responses; very little work has been done regarding the long-term performance. This paper addresses this issue, and presents results from a series of experiments on the time-dependent behaviour of carbon FRP-strengthened concrete beams. Twenty-six reinforced concrete beams with dimensions 100 × 150 × 1800 mm, with and without bonded CFRP laminates, were investigated for their creep behaviour. Different reinforcement ratios were used to evaluate the contribution of the external reinforcement on the creep resistance of the beams. High levels of sustained load were used in order to determine the maximum sustained load that can be applied without any risk of creep failure. The applied sustained loads varied from 59% to 78% of the ultimate static capacities of the un-strengthened beams. For most of the long-term tests, the applied sustained loads were higher than the service loads. This was done to account for the fact that strengthening is typically required when a structure is expected to carry increased service loads. The main parameters of this study were (i) the level of sustained load and (ii) the strengthening scheme. The results confirm that FRP strengthening is effective for increasing the ultimate capacities of the beams; however, there is virtually no improvement in performance with regard to the long-term deflections.     

Study on thermal effects on fatigue behavior of cracked steel plates strengthened by CFRP sheets

Carbon fiber reinforced polymer (CFRP) sheets have been used to strengthen steel structures to enhance fatigue life. However there is very limited information on the influence of temperatures on the fatigue strengthening efficiency. This paper describes an investigation on the behavior of cracked steel plates strengthened with CFRP at different temperatures. Firstly, through cylinder coupon tests, mechanical properties of the resin were found to vary at different temperatures, especially when the temperature exceeds the glass transition temperature T_g. Secondly, three cracked bare steel plates and five cracked steel plates strengthened with high modulus CFRP sheets were tested under fatigue loading at different temperatures. The results prove the effectiveness of CFRP strengthening technology to increase fatigue life when the temperature ranges from −40 °C up to 60 °C. It is concluded that the variation of temperature has an obvious influence on properties of the resin, leading to influence on fatigue life. Finally, the existing analytical method to predict fatigue lives of CFRP strengthened steel plates at ambient temperature was modified by considering the temperature effect. Experimental and theoretical results are compared and reasonable agreement is achieved. The influence of the number of CFRP layers and CFRP modulus is also found based on the proposed analytical method.     

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.     

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.     

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.     

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.     

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.     

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.