Air Void Ratio Research Articles

아스팔트 포장의 시공 포설두께에 따른 투수계수 변화특성

The permeability of HMA(hot mixed asphalt) is a major influencing factor for long-term performance of the pavement. Especially, the lift thickness of the pavement during construction causes a wide range of physical properties of HMA. This study investigates the correlationship between the lift thickness and the physical properties of HMA through a series of laboratory experiments. The specimens were cored from a construction site of the dense graded asphalt pavement. The cored samples have various lift thickness and the number of compaction for the study. The results of the study show that the permeability of the sample decreases with the apperant density and t/NMAS, and the air void ratio. Therefore, the commonly used construction method as a constant lift thickness regardless of conditions needs to be reconsidered.

Proposed Compaction Procedure for Dry Process Crumb Rubber Modified Asphalt Mixtures Using Air Void Content and Expansion Ratio

The dry process for crumb rubber modified (CRM) asphalt mixtures is characterized by a simple construction process that results in greater environmental benefits than the wet process does. However, the difficulties of compaction in the dry process often lead to unstable pavement performance; therefore, its application is highly restricted. This research aims to investigate the compaction procedure for dry process CRM asphalt mixtures using air void content and expansion ratio as the principal indices for evaluation. To evaluate the key factors affecting compaction, a series of CRM mixtures were prepared and compacted at four different crumb rubber contents by total aggregate volume of 3.0 %, 5.5 %, 8.0 %, and 10 %. First, with the air void ratio as the target indicator, the crumb rubber content, compaction temperature, and compaction method were evaluated to determine the appropriate compaction procedure. Second, the variations in height and expansion ratio of the CRM asphalt mixture specimens with different crumb rubber contents were analyzed in order to calculate the expansion ratio. The results indicated that generally the height and expansion ratio increase as the crumb rubber content of the CRM asphalt mixtures increases. Furthermore, it was found that when the crumb rubber addition was 5.5 % of the bulk volume of minerals, the volume stability of the mixture was improved, and this value is recommended for dry process CRM asphalt mixtures.

Study on Volume Performance of Conductive Asphalt Concrete Based on Freeze-Thaw Cycle

Conductive asphalt concrete, a kind of intelligent materials, can serve as asphalt solar collector, asphalt heater and self monitor. And moisture damage is one of the most common performance degradation of asphalt concrete. This paper investigates the volume properties of conductive asphalt concrete based on Freeze-thaw cycles. Marshall specimen was frozen and thawed repeatedly and a cycle consists 16h at -18oC and 8h at 60oC. The change of air void and weight loss ratio were chosen to evaluate the moisture resistance of conductive asphalt concrete. Three types of asphalt mixture (control, CAC 1 and CAC 2) were used to study the effect of initial void and material composition on moisture resistance. The results show that both the framework structures and the material composition have a great effect on antifreeze-thaw property of asphalt concrete, which provides an efficient guidance for application of this technology in pavement.

Estimation of Optimum Compaction Temperature for PMA and WMA Mixtures by Volumetric Property Evaluation

Abstract The optimum compaction temperature (OCT) is defined as the temperature at which asphalt provides proper viscosity in an asphalt mixture. For normal asphalt, the proper viscosity level has been suggested as 280 ± 30 mm2/s by the American Association of State Highway and Transportation Officials (AASHTO). This suggestion has been effectively utilized in selecting the OCT of normal hot-mix asphalt (HMA). However, because polymer-modified asphalt (PMA) and warm-mix asphalt (WMA) have been used recently, it is difficult to apply this method in general. This study evaluates important volumetric properties (air void ratio and void filled with asphalt) of HMA and WMA mixes. The three binders evaluated included 64-22 and 76-22 for HMA and 70-22 for WMA for dense-graded asphalt mixtures compacted using a Superpave gyratory compactor. The OCT at which the optimum asphalt content could be obtained was determined for the three binders. The OCTs obtained via volumetric property evaluation were 20 °C and 38 °C lower than the values determined via the AASHTO method for PMA and WMA. In mechanical performance comparisons, the mixture compacted at the lower OCT was not inferior to the mixture compacted at a higher OCT. It is therefore concluded that the OCT should be determined based on the volumetric property of mixtures, because compaction is not solely a function of viscosity, especially for PMA and WMA mixtures.

Evaluation of Air Void Distributions of Cement Asphalt Emulsion Mixes Using an X-Ray Computed Tomography Scanner

Abstract Air void distributions of cement asphalt emulsion mixes are different from those of ordinary asphalt mixes. In order to evaluate a relationship between air voids and aggregate gradations, or binders of the mixes, an x-ray computed tomography (CT) scanner was used to quantify air void ratio, air void area, and air void size in the mixes. A rheometer and scanning electron microscope (SEM) were adopted to analyze viscosity and microstructures of the asphalt emulsion composites. The results indicate that larger air voids are concentrated on the top and the bottom of the mixes. The middle part of the mixes, which constitutes about 60–70 % of its thickness, has a nearly uniform size of air voids. The demarcation of air void ratio between suspended dense structure and framework dense structure is 6.0 %; and that between framework dense structure and framework void structure is 9.0 %. Adoption of ordinary Portland cement and appropriate increase of asphalt emulsion dosages are beneficial to the decrease of the air void ratio. The binders exert little effect on the increase of the air void sizes than the aggregate gradation types do. Benefits of cement addition are to generate hydrates which are helpful to decrease the air void ratios of the mixes.

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.

Lower nappe aeration in smooth channels: experimental data and numerical simulation

Bed aerators designed to increase air void ratio are used to prevent cavitation and related damages in spillways. Air entrained in spillway discharges also increases the dissolved oxygen concentration of the water, which can be important for the downstream fishery. This study considers results from a systematic series of measurements along the jet formed by a bed aerator, involving concentration profiles, pressure profiles, velocity fields and corresponding air discharges. The experimental results are, then, compared, with results of computational fluid dynamics (CFD) simulations with the aim of predicting the air discharge numerically. Comparisons with jet lengths and the air entrainment coefficients from the literature are also made. It is shown that numerical predictive tools furnish air discharges comparable to measured values. However, if more detailed predictions are desired, verification experiments are still necessary.

On the swelling potential of compacted high plasticity clays

In earthworks engineering, predicting the influence of the water content and the dry density on compacted soils deformation is a fundamental issue, which is particularly important for the use of clays in embankments. This paper presents the experimental results and a microstructural interpretation of swelling tests performed on four clays, compacted at different water contents and dry densities. The influences of dry density and water content on the swelling potential are described, showing the coupled effect of these two parameters. In order to quantify this coupling, the initial air void ratio is defined and it is observed that this air void ratio has an apparent linear relationship with the void ratio after swelling. This observation enables analysing all the tests in a synthetic manner, by plotting the origin ordinate and the slope of the linear relationships versus the initial hydrous state. Moreover, one of the clays microstructure was analysed using mercury intrusion porosimetry (MIP). The results show that swelling leads to a micropores increase and a macropores decrease. In addition, micropores volume increase does not depend on the initial dry densities, whereas the macropores volume increase does. For further discussion, a simplified microstructural model is proposed allowing the interpretation of the soil swelling using MIP results. The comparison between the model prediction and the microstructure observation supports the interpretation of the swelling tests and shows that the origin ordinate and the slope of the relationship between the initial air void ratio and the final void ratio can be linked to micropores and macropores volume variations. However, the comparison also shows that the simplified microstructural model presents some limitations when applied to very dry or wet soils.

Advances in modelling hysteretic water retention curve in deformable soils

Experimental findings on the hysteretic nature of the soil water retention curve, relating the degree of saturation to the matric suction, have generally to be superimposed with the aspects due to the deformability of the soil matrix. Indeed, most state-of-the-art models for retention curves only feature one of these two essential features, that is either capillary hysteresis or void ratio dependency. In an effort to set an advanced comprehensive model for the retention curves, it is proposed to review some recent results of the capillary hysteresis and focus on the elasto-plastic analogy in the degree of saturation versus suction relationship. The paper also contributes to quantifying the effects of mechanical straining on the retention curve on the basis of experimental data from the literature besides those obtained by the authors. The intrinsic shape of the soil water retention curve is first defined, followed by the empiric relationship between air entry value and void ratio. The retention sub-model of a complete constitutive model for unsaturated soils is described, the mathematical formulation being based on kinematic hardening and featuring direct coupling with the mechanical stress-strain module. Model capabilities are assessed on complex retention outlines, displaying the added value of the proposed framework for prediction issues.

MEASURING METHOD FOR VOID RATIO OF POROUS CONCRETE APPLYING PRESSURE METHOD

Accurate measurement of void ratio is essential for porous concrete, since its attractive performances are mainly determined by the continuous void. Measurement methods of air void ratio of porous concrete are prepared in the technical committee report of Japan Concrete Institute i.e. volumetric method and weighing method. In order to measure the void ratio of various types of porous concrete with wide range of aggregate size, however, it is sometimes difficult to apply them when a high accuracy is required. Especially, when small size aggregates are used for porous concrete, the error of measurement is not negligible because the amount of retained water in the pore during a measurement procedure is not expected to be very small. In the present study, in order to solve this problem, the authors have proposed a new method using an air meter, which realizes a clear separation of the sort of voids i.e. continuous, semicontinuous, and independent voids. Also, rather high accuracy can be expected and the required time for the measurement can be reasonably shortened.

Triaxial constant stress and constant strain rate tests on ice-rich permafrost samples

A range of mechanical compression tests were conducted on frozen soil samples at temperatures close to the melting point of ice to determine both the creep and the strength properties under triaxial stress conditions. The samples were obtained from two rock glaciers in the Swiss Alps. For comparison, additional samples were prepared artificially for testing. The results showed that the minimum creep strain rate increases exponentially with increasing temperature and applied deviatoric stress. The applied strain rate is the main parameter influencing resistance. However, test results show that the micromechanical behaviour is similar for all tests and independent of the applied loading condition. Measurements of the volumetric strain showed that the sample composition has a major influence, so samples with high air void ratios resulted in continuous contraction (i.e., reduction of the sample volume), whereas samples with low volumetric air and ice contents demonstrated dilatant behaviour.Key words: permafrost, frozen soil, creep, strength, triaxial testing, self-healing.

EXPERIMENTAL STUDY ON THE LARGE-STONE ASPHALT MIXTURE DURABILITY FOR AIRPORT ASPHALT SURFACE-BASE LAYER

A series of laboratory tests were conducted on the large stone asphalt mixture. The tests were also carried out on the conventional type asphalt mixture. Based on the test results, this paper focuses the effects of air void ratio of the large asphalt mixture on the bending strength/deformation, the raveling and the asphalt deterioration characteristics. Then the characteristics are compared with those of conventional type asphalt mixture to be applicable for airport asphalt surface-base layer.

Effective Thermal Conductivity of Solid Material in Bread.

The effective thermal conductivity of solid material in white bread was investigated. First, the effective thermal conductivities of baked bread were measured as a function of air void ratio after compressing the bread to varying degrees. Second, this compressed bread was freeze dried to remove the effects of water, after which thermal conductivities were again measured. Measurements of thermal conductivity for each type of sample were made using both the hot wire and the steady state parallel plate methods at 276K, 297K, and 308K. By extrapolating these results, thermal conductivities of bread with equivalent solid contents were obtained. The thermal conductivity values for the two phase samples (solid-liquid and solid-gas) were analyzed using a simple series-parallel model, and the conductivity of the solid component can be expressed by the following empirical formula, using the temperature T as a parameter : λs = 0.3585(1+0.00226(T-273)) W·m-1·K-1.

Controlling Collapse Settlement of Stiff Clay Compacted fill based on In-Situ Compression Tests

Severe collapse settlements in fill of stiff clays or weak rocks can occur several times due to inundation. This paper shows a method used for controlling the placement of stiff clays to reduce collapse settlement in a residential development. An in-situ compression test developed by the authors was used to observe the settlement of trial fills compacted by three types of rollers. The results of the in-situ tests were compared with those of the laboratory compression tests conducted on undisturbed samples taken from the test site, and it was shown that the vertical strains in the both cases coincided. Guide indices for the control of the placement of fill previously presented, such as the density, air void ratio or strength of the fill, have been re-evaluated following the results of the in-situ compression tests according to a current code for the maximum incremental inclination of houses by Architectural Institute of Japan. It was found that the following procedures should be adopted at the site as guidelines for placement of the stiff clays: ① The soil should be spread in layers less than 30 cm thick and compacted by two passes of a vibrating roller of 9.8 tons at least, ② The relative density of the fill should be greater than 98%, ③ The strength as measured by a dynamic cone test should be greater than 5 blows per 30 cm, ④ The air void ratio should be less than 12%, and ⑤ Water should be spread before compaction when fill-materials lose more than 1.5% of water content due to drying.

A STUDY ON COMPACTION CONTROL BY FWD IN RAILWAY EMBANKMENT WORK

The intensity of compaction in railway embankment is controlled by K30-value in the plate loading test for road. However, the plate loading test takes much time and needs a large reaction equipment. Thus, it is necessary to work out a simple and easy method for compaction control in railway embankment work. The present paper gives an outline of the rolling compaction test to applying FWD to compaction control in railway embankment work. The result from rolling compaction test shows that K-value by FWD correlates with several values indicating the compaction level (degree of compaction, air void ratio, K30-value), leading to the conclusion that it is possible to apply FWD to compaction control in railway embankment work.

The electrical resistivity characteristics of compacted clays

This technical note describes work carried out on the electrical resistivity characteristics of a clay-water electrolyte system. The samples were tested over a range of consistency indices and at varying degrees of compaction. Resistivity/fractional volume of water relationships have been established for two different clays, a Cheshire clay and a London clay, over a practical range of moisture contents. A unique relationship exists between these parameters for each clay. The resistivity of a clay is a function of moisture content and degree of saturation. At a particular moisure content, an increase in the degree of saturation (or a decrease in the air-void ratio) will mean a decrease in resistivity. (TRRL)

Nonlinear Viscoelastic Properties of Bituminous Concretes

Abstract Viscoelastic properties of bituminous concretes have been studied by observing creep behavior under a large range of compressive stress levels and temperatures. Effect of air void content on the creep properties has been observed. Results indicate that the test materials display linear viscoelastic properties only at low stress levels and temperatures. Master creep compliance curves corresponding to the linear range were obtained using the time-temperature shift hypothesis. The nonlinear creep behavior that is found to occur at higher stress levels and temperature has been characterized by the nonlinear viscoelasticity theory and the creep compliance functions based upon this theory were evaluated for the test materials. It is found that an increase in air void ratio leads to higher creep strains for a given stress level.