ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sun, 15 Sep 2024 07:51:24 GMT2024-09-15T07:51:24Z5091- Behavior analysis of asphalt mixtures using triaxial test-determined propertieshttps://scholarbank.nus.edu.sg/handle/10635/74079Title: Behavior analysis of asphalt mixtures using triaxial test-determined properties
Authors: Fwa, T.F.; Low, B.H.; Tan, S.A.
Abstract: The mix design procedure for asphalt mixtures by the Marshall method does not furnish material property parameters that can be used analytically for structural thickness design and performance analysis of pavements. This research illustrates that this missing link can be bridged by the use of laboratory triaxial test-determined properties to characterize asphalt mixtures. By means of finite element analysis using triaxial test-determined properties as input, it is illustrated that the stress-strain behavior of asphalt specimens up to failure can be simulated for the following three loading conditions: triaxial test, Marshall test, and indirect tension test. Laboratory tests involving four different asphalt mixtures are performed to provide the verification data.
Sun, 01 Jan 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/740791995-01-01T00:00:00Z
- Determination of Thermal Properties of Pavement Materials and Unbound Aggregates by Transient Heat Conductionhttps://scholarbank.nus.edu.sg/handle/10635/65421Title: Determination of Thermal Properties of Pavement Materials and Unbound Aggregates by Transient Heat Conduction
Authors: Tan, S.-A.; Fwa, T.-F.; Chuai, C.-T.; Low, B.-H.
Abstract: A laboratory procedure for determining the thermal conductivity (k) and diffusivity (α) of pavement materials and unbounded aggregate beds by means of a transient heat conduction experiment is described. It is first established that the plane-wall theory of heat conduction can be applied to a finite-slab problem provided that the thickness-to-width ratio is kept within 0.2. The procedure is to obtain the k and α values that would match the theoretical temperature-time history response with the measured response. An analytical curve-fitting technique is used to match the inflection points of the measured to the theoretical temperature- √t curves. The heat experiment is conducted in a controlled convection oven with parallel air flow at constant velocity over a horizontal test specimen bed. This allows for the testing of unbounded aggregate beds made into a slab by placement of aggregates in an insulated polystyrene box that fits into the base of the oven. The test method is first validated by comparing steady-state heat conduction results with the transient test predictions of k for a solid acrylic slab, two bituminous slabs, and four concrete slabs, with good agreement in the values of k determined by both methods. For the unbounded aggregates, it is observed that there is trend of decreasing values of k and α, with increase in particle size. Also, wet aggregates exhibit higher thermal conductive properties than dry aggregate beds. The test method will be useful for obtaining thermal properties of pavement materials to allow for thermal analysis in pavement layers subjected to solar heating.
Wed, 01 Jan 1997 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/654211997-01-01T00:00:00Z
- Determination of thermal conductivity and diffusivity by transient heating of a thin slabhttps://scholarbank.nus.edu.sg/handle/10635/65420Title: Determination of thermal conductivity and diffusivity by transient heating of a thin slab
Authors: Tan, S.-A.; Low, B.-H.; Fwa, T.-F.
Abstract: Transient heat conduction through a thin slab which is initially at a constant temperature, and subsequently heated by free convection in a thermal bath, is a well established theory. From the theory, it is deduced that a thickness to length ratio of 0.2 is adequate to achieve one-dimentional heat flow in the middle of a square slab. Using the theory, the non-dimensional temperature-time history for the midpoint of the slab is obtained. From these non-dimensional plots, a statistical scheme of finding the best fit between experimental data and the theory is described. By obtaining the best fit, the most probable values of the thermal conductivity and diffusivity are obtained directly. © 1992.
Wed, 01 Jan 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/654201992-01-01T00:00:00Z
- Thermal properties of concrete from transient conduction of a thin slabhttps://scholarbank.nus.edu.sg/handle/10635/66304Title: Thermal properties of concrete from transient conduction of a thin slab
Authors: Tan, Siew-Ann; Low, Boon-Hwee; Fwa, Tien-Fang
Abstract: The thermal properties of concrete, such as its thermal conductivity, thermal diffusivity, and specific heat, are important in some applications of concrete. The rate at which heat flows into, through, or out of a concrete structure is governed by the thermal conductivity of the concrete. The ease of difficulty with which the concrete undergoes temperature change as a result of heat loss or gain depends also on the thermal diffusivity and heat capacity. Established methods for determining the thermal conductivity of concrete invariably use steady-state heat conduction from which the conductivity under a constant thermal gradient can easily be calculated. Such methods suffer the disadvantage that the time taken to reach thermal equilibrium may be inconveniently long, especially for concrete, which is a poor conductor of heat. The long period to reach steady-state also restricts its use for measurements on damp materials because of redistribution and drying out of moisture within the specimen. Transient heat conduction methods are less well known and seldom used. This paper describes the use of transient heat conduction through a thin slab that is initially at a constant temperature and subsequently heated by free convection in a thermal bath to determine the thermal conductivity (k) and diffusivity (α) of the slab. From the transient heat conduction theory, it is deduced that a thickness-to-length ratio of 0.2 is adequate to achieve one-dimensional heat flow in the middle of a square slab. Using the theory, the nondimensional temperature-time history for the midpoint of the slab is obtained. From these nondimensional plots, a statistical scheme of finding the best fit between experimental data and the theory is described. By obtaining the best fit, the most probable values of the thermal conductivity and diffusivity are obtained directly. Repeated tests on several slabs of different compositions illustrate the usefulness of the method of obtaining k and α of concrete materials. Good comparison with published values of k and α obtained experimentally using similar materials serve to validate the method.
Tue, 01 Dec 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/663041992-12-01T00:00:00Z
- Behavior of asphalt concrete mixtures in triaxial compressionhttps://scholarbank.nus.edu.sg/handle/10635/65207Title: Behavior of asphalt concrete mixtures in triaxial compression
Authors: Siew-Ann, Tan; Boon-Hwee, Low; Tien-Frang, Fwa
Abstract: The triaxial compression test is one of the most common standard tests for determining the stress-strain behavior and strength parameters of soils under drained and undrained conditions. This paper describes the use of the triaxial compression tests for asphaltic mixtures for determining their engineering properties such as the friction angle Φ, the cohesion, c, and the elastic compression modulus, E. Effects of test temperatures, strain rate, and confining pressures on the compressive behavior of asphalt concrete were studied.
Sun, 01 May 1994 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/652071994-05-01T00:00:00Z
- Analysis of Marshall test behavior with triaxial test determined material propertieshttps://scholarbank.nus.edu.sg/handle/10635/65137Title: Analysis of Marshall test behavior with triaxial test determined material properties
Authors: Low, Boon-Hwee; Tan, Siew-Ann; Fwa, Tien-Fang
Abstract: The Marshall test is one of the most common methods used for mix design and quality control of asphalt concrete mixtures. However, this method is empirical in nature and does not provide fundamental engineering properties. Fundamental engineering properties provide a basis for rational analysis and design of asphalt concrete pavements. The triaxial test method described in this paper allows engineering properties such as internal angle of friction, φ, cohesion, c, and elastic modulus, E, to be determined. The method of specimen preparation and the triaxial test setup are briefly described. A numerical simulation of the Marshall test is performed using a plane-stress finite element analysis with triaxial test determined properties as input parameters. A constitutive plasticity model based on the Drucker-Prager yield condition is used to describe the elasto-plastic behavior of the specimen. Analysis shows that the model very well describes the deformation progression before failure and can predict experimental Marshall stability value very closely. There is some underprediction of the Marshall flow, probably due to the idealization of an elastic-perfectly-plastic stress-strain relationship for asphalt concrete.
Sat, 01 May 1993 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/651371993-05-01T00:00:00Z
- Data reduction for k and α from transient heating of slabhttps://scholarbank.nus.edu.sg/handle/10635/65379Title: Data reduction for k and α from transient heating of slab
Authors: Tan, S.-A.; Low, B.-H.; Fwa, T.-F.
Abstract: For the transient heat conduction of a thin slab, the temperature-time history of its mid-point can be determined from a plane wall theory, provided that a slab thickness to length ratio of 0.2 or smaller is used in the experiments. Using the theory, two data reduction methods are described for deducing the thermal properties of conductivity (k) and diffusivity (α) simultaneously from a single transient heating experiment. The first method uses an analytical technique to fit the inflection point on the temperature-√t, history plot to the theoretical inflection point. The second method, which was earlier proposed by the authors, uses a statistical curve fitting procedure to obtain the best fit between theory and experiment over seven points on the temperature-time history. Comparisons of the k values obtained by these methods against steady-state heat conduction measurements of the same slabs for various building construction materials indicate good agreement, and give support to the validity of these procedures. The values of k and α obtained by these procedures also compare favourably with reported literature data. © 1994.
Sun, 01 Jan 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/653791995-01-01T00:00:00Z
- Laboratory wheel tracking apparatus for bituminous pavement studieshttps://scholarbank.nus.edu.sg/handle/10635/65750Title: Laboratory wheel tracking apparatus for bituminous pavement studies
Authors: Tan, Siew-Ann; Fwa, Tien-Fang; Low, Boon-Hwee
Abstract: Rutting deformation is one of the most common forms of pavement distress found on bituminous pavements, especially in the hot, tropical climate of Singapore. These deformations are usually found in the wheel track on roads carrying heavy, slow moving, channeled traffic, such as in the city and industrial areas at traffic light junctions. To aid our investigation into the nature of pavement rutting, a laboratory wheel-tracking apparatus was used to simulate channeled wheel traffic loading under controlled conditions. It was upgraded with automated temperature and rut profile measurement capability. This article describes the features of the apparatus, which include temperature control of test specimens from ambient (27°C) to 70°C via a water bath with an adjustable weir, speed control of 0 to 80 wheel passes per minute, and variable wheel loading from 18 to 54 kg giving approximate equivalent tire pressures of 175 to 530 kPa. The apparatus can be used to simultaneously test three standard specimens of dimensions 405 mm by 135 mm by 90 mm-thickness. Single tests of two other sizes, which are two or three times the width of the standard specimen, are permissible. The rut depths are monitored by means of three linear variable displacement transducers (LVDTs), which measure the vertical displacements of each of the three wheel axles independently as rutting progresses. Due to errors induced by machine vibrations, accurate rut profile measurements can be made only under static conditions at selected intervals of wheel passes. With the use of a 200-ton-capacity static press, uniform dense asphaltic concrete beam specimens can be made, giving reasonably repeatable rutting test data on the apparatus, thus making it a valuable tool for evaluating the rutting potential of various mixes.
Sun, 01 Nov 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/657501992-11-01T00:00:00Z
- Compaction of asphalt mixtures for laboratory testing: evaluation based on density profilehttps://scholarbank.nus.edu.sg/handle/10635/84543Title: Compaction of asphalt mixtures for laboratory testing: evaluation based on density profile
Authors: Fwa, T.F.; Low, B.H.; Tan, S.A.
Abstract: Cylindrical specimens are commonly used in laboratory testing of asphaltic paving mixtures. This paper describes a study that examined the influence of different compaction methods on the resulted density distributions of cylindrical specimens using a laboratory twin-probe nuclear density gage. Two common sizes of 102 mm (4 in.) cylindrical specimens, namely 64-mm (2.5-in.) high Marshall-size specimens, and 200-mm (7.87-in.) high triaxial test specimens, were considered in the test program. Four compaction methods were studied: drop-hammer compaction, kneading compaction, single-plunger compression, and double-plunger compression. In the case of 200-mm-tall specimens, the effect of compaction in layers was also examined. Test results show that, except for the kneading compaction method, the other three methods could all produce 64-mm-tall Marshall-size specimens of relatively uniform density distributions with density variation within 0.05 g/cm3. For 200-mm-tall specimens, only the double-plunger compression method was able to produce specimens with density distribution of similar uniformity.
Wed, 01 Sep 1993 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/845431993-09-01T00:00:00Z