Air Void Content Research Articles

Predictive Artificial Neural Network Laboratory Fatigue Endurance Limit Model for Asphalt Concrete Pavements Based on the Volumetric Properties and Loading Conditions

Asphalt concrete healing is one of the important concepts related to flexible pavement structures. Fatigue endurance limit (FEL) is defined as the strain limit under which no damage will be accumulated in the pavement and is directly related to asphalt healing. Pavement section designed to handle a strain value equivalent to the endurance limit (EL) strain will be considered as a perpetual pavement. All four-point bending beam fatigue testing results from the NCHRP 944-A project were extracted and utilized in the development of artificial neural network (ANN) EL strain predictive model based on mixture volumetric properties and loading conditions. ANN model architecture, as well as the prediction process of the EL strain utilizing the generated model, were presented and explained. Furthermore, a stand-alone equation that predicts the EL strain value was extracted from the developed ANN model utilizing the eclectic approach. Moreover, the EL strain value was predicted utilizing the new equation and compared with the EL strain value predicted by other prediction models available in literature. A total of 705 beam fatigue lab test data points were utilized in model training and evaluation at ratios of 70%, 15%, and 15% for training, testing, and validation, respectively. The developed model is capable of predicting the EL strain value as a function of binder grade, temperature, air void content, asphalt content, SR, failure cycles number, and rest period. The reliability of the developed stand-alone equation and the ANN model was presented by reasonable coefficient of determination (R2) value and significance value (F).

Determining Optimum Number of Gyrations for Porous Asphalt Mixtures Using Superpave Gyratory Compactor

The compaction characteristics of porous asphalt (PA) mixtures are significantly different from those of traditional dense-graded asphalt mixtures. Compaction efforts are critical for PA mixtures to exhibit good performance in terms of strength, functionality, and durability. The objective of this study was to determine the optimum number of gyrations for typical PA mixtures compacted using a Superpave gyratory compactor. The compaction characteristics and the influence of seven gyration levels on the indicators of air voids (AV) content, Marshall Stability (MS), multi-directional permeability, stone-on-stone contact, and durability of PA mixture were investigated through laboratory experiments. A multi-directional permeameter was designed to evaluate the multi-directional permeability of PA mixtures, including vertical, horizontal, and combined horizontal-vertical permeability. The AV content, multi-directional permeability decreases with the increasing gyrations. Based on the requirements of each indicator, the minimum and maximum gyrations for each indicator were determined. Balancing the performance of strength, functionality, and durability, the optimum number of gyrations for the PA mixtures was determined to be between 45 and 75 gyrations, which allows for different gyrations depending on the application of the PA mixture. Finally, the requirements of MS, horizontal permeability, and combined horizontal-vertical permeability are recommended for improving the performance of PA mixture.

Generation of virtual asphalt concrete in a physics engine

The precise, quick and efficient simulation of asphalt concrete is an important step to select asphalt mixtures for a range of applications. A method to create virtual aggregates based on aggregates' topological properties and aggregate skeletons like those of asphalt concrete using a physics engine is proposed. It can produce hundreds of virtual aggregates with shape properties equivalent to these of real ones in a matter of seconds, pack them to a level of compaction like that of the Marshall compactor, and measure properties such as the expected air voids content and number of contacts between the aggregates. In the paper, only aggregates bigger than 2 mm have been considered due to computing efficiency. Besides, it was found that the main factors influencing asphalt compaction are the number of aggregates in the mixture and the amount of dust, or aggregates smaller than 2 mm, which correspond to the parts of the solid skeleton that have not been simulated.

Cooling asphalt pavement by increasing thermal conductivity of steel fiber asphalt mixture

High-temperature asphalt pavements will intensify urban heat island effect and cause many pavement distresses. In order to cool asphalt pavement, two types of steel fiber, curved hook steel fiber (CH-SF) and long sawtooth steel fiber (LS-SF), were used to increase the thermal conductivity of asphalt mixture. The results show that the addition of steel fiber increased the air voids content of asphalt mixture, of which CH-SF had a stronger influence. Six compaction levels were used to investigate the compaction characteristic of steel fiber asphalt mixture. It is found that greater compaction work would induce the mixtures to be further compacted. When the steel fiber asphalt mixtures were compacted to have an air voids content of about 4.0%, CH-SF was more effective to increase the thermal conductivity and splitting strength of asphalt mixture than LS-SF. The indoor irradiation test shows that using 1.0% CH-SF asphalt mixture below the top asphalt layer could reduce the temperature at the depth of 4 cm by 1.8 ℃. The findings in this study indicate that using CH-SF can increase the thermal conductivity of asphalt mixture, on the condition that the CH-SF asphalt mixture is compacted to have an appropriate air voids content.

Using steel fibers to accelerate the heat conduction in asphalt mixture and its performance evaluation

In order to accelerate the heat flow in asphalt pavement, two types of steel fiber, curved hook steel fiber and long sawtooth steel fiber, were used to prepare steel fiber asphalt mixture (SFAM). The results show that all the SFAM specimens presented higher air voids contents at the two ends, compared with control asphalt mixture. From the results of dynamic modulus and creep test it is found that the deformation resistance of SFAMs gradually reduced with the increase of steel fiber content, which could be explained by the air voids distribution characteristics of SFAM specimens. On the contrary, SFAM showed excellent low-temperature cracking resistance and fatigue performance. Combining the above results, it is recommended to use 1.0% curved hook steel fiber to reinforce asphalt mixture for improving the thermal conductivity and road performances of asphalt mixture. Because of the reduced deformation resistance of SFAM, the cooling performance of SFAM asphalt pavement needs to be investigated in future studies, based on which the rutting depth can be simulated by means of finite element analysis to determine the actual influence of steel fiber on the rutting resistance of asphalt pavement.

Uncertainty analysis of in-situ pavement compaction considering microstructural characteristics of asphalt mixtures

The compaction process of pavement during construction critically influences the mechanical performance of the pavement. However, this sophisticated procedure, including asphalt mixing, pre-paving, and multi-step compactions, could induce significant compaction variation, which, to some extent, might cause unwanted distresses in the early service of pavement. An insight into the in-situ compaction variation would benefit the estimation of compaction quality and further optimize the compaction procedure. For this reason, this study estimated the in-situ compaction quality incorporated with an uncertainty analysis. A total of 45 samples were cored from a newly constructed test track. The volumetric and microstructural parameters (air void content, degree of compaction, fractal dimensions of aggregate and air voids) were calculated through digital image processing for each sample. Additionally, the mechanical property (indirect tensile strength) of the asphalt samples was measured by indirect tensile test. Subsequently, two uncertainty approaches, namely the non-probability convex model and decision tree, were employed to feature the data distribution and figure out the priority factor that influences the mechanical performance of asphalt mixtures. The results indicated that the microstructure of asphalt mixtures remarkably affected the distribution of the degree of compaction. Additionally, asphalt mixtures' indirect tensile strength was associated with compaction indicators differently depending on the measuring temperatures.

Performance study and application of porous ultra-thin wearing course for asphalt pavement maintenance

An ultra-thin layer wearing course with thickness between 15mm and 30mm are developed and applied for maintenance of asphalt pavement. The maximum size of the coarse aggregate is 10 mm. In this study, the high viscosity modified bitumen is used as binder for improving the anti-rutting and raveling performance of a porous mixture. Mixture designed study is carried out by combing the functional and structural performance measurements. The target air voids contents for those ultra-thin surfaces are between 15% and 20%. Important factors presenting the high temperature property, moisture feature, low temperature feature and anti-raveling performance are investigated in lab. Meanwhile, surface characteristic which reflect the sound absorption is also observed. A feasibility of using the ultra-thin wearing course mixture in China is proved. Trial sections are constructed in southeast part of China for studying the performance of ultra-thin waring course in maintenance engineering. The achievements from the study will provide technical support for the maintenance of asphalt pavement with moderate surface damage. It will also improve the skid resistance and the noise reducing function of the old pavement, which presents superior social and environmental benefits.

Using Crumb of Tires in Hot Asphalt Mixture as a Part of Aggregate

Scrap tires are a major part of the global solid waste management problem. In recent years, the problem of waste tires has become very acute that there is an urgent need to find an optimal and efficient way to use scrap tires in asphalt mixtures. The previous studies showed that the utilization of crumb of tires has more effect on asphalt mixture performance, which is represented increasing in the Marshall Stability and increasing crumb of tires causes increasing in Marshall Flow and increasing in air voids content additionally more than original mixes. This paper used crumb of tires in asphalt mixture as a part of aggregate. Three sizes of the grade of crumb tires were used in asphalt mixture No. 4 (4.75 mm), No. 8 (2.36) mm and No. 50 (300µmm). Three percentages of asphalt binder (4, 5 and 6) by weight with three percentages of crumb tires (2, 4 and 8) % by weight also were used with aggregates for preparing asphalt mixture specimens. Asphalt mixture specimens were conducted according to Marshall Methods. Thirty-six specimens were equipped for evaluating Marshall Properties (Marshall Stability and flow, air voids percentage, bulk density, maximum bulk density, and Marshall Stiffness). Indirect Tensile Strength test (ITS) has been applied to obtain the cracking resistance of asphalt mixture using twenty-four specimens, which contains crumb tires. The results showed that the applying of the crumb tires has a significant performance of asphalt mixture by increasing the Marshall stability, flow, air voids, and decreasing bulk density and indirect tensile strength compared to the original mixtures.

Predication of nano-silica modified porous asphalt under dynamic creep by using finite element analysis

In areas with heavy rainfall, the conventional pavement may not be suitable due to low drainage capability. This will cause to a storm failure. To solve this, Porous asphalt (PA) is one of the innovative asphalts that can significantly overcome the issue of storm-water problem. The high air voids content characteristic of PA compares with conventional pavement in Malaysia is very suitable in managing the storm-water. However, PA suffers a few problems such as decrement of strength and tensile strength due to high air voids content which lead to permanent deformation. In order to enhance the performance of PA against the permanent deformation an additive material used to increase the strength of the PA called Nano-silica particles. Therefore, the purpose of this study is to evaluate the dynamic creep of Nano-silica modified PA by developing a finite element analysis (FEA) model. Moreover, this study the dynamic creep performance of porous asphalt with different proportion of Nano-silica particles 0%, 2% and 4% was predicted. A finite element model will be simulated by using ABAQUS 6.14 software for the PA sample in order to achieve the objectives of the study. From this study it was concluded that, the develop model was reliable use to predict the performance of PA in terms of dynamic creep and the utilizing of Nano-silica in PA mixture result changes in the rheological properties of the asphalt binder which lead to an enhancement of its performance against the permanent deformation.

Newly Developed Aggregate Gradation for Five Asean Countries

This paper presents the new aggregate gradation of the porous asphalt (PA) mixture in five Asean countries including Malaysia, Indonesia, Vietnam, Thailand and Singapore. The PA aggregate gradation need to be developed as it may suit all of the countries and the air voids content for Asean countries can be standardized. This study was carried out to investigate the air voids properties. Several aggregate testing should be conducted in order to get the new porous asphalt aggregate gradation that suits all Asean countries. Sieve analysis test was conducted to see the patterns of the aggregate gradation curve. Sieve analysis test were tested three times for each of the countries to get the best average. The results were then plotted in one graph for all countries to be evaluated. From the analysis, Singapore specification started with 0.075mm, followed by 0.15mm, 0.3mm, o.6mm and 2.36mm are seems to have all the criteria in terms of aggregate gradations for fine aggregate and the rest are from Thailand aggregate specification for lower line while for upper line, Vietnam specifications were proved to have all the criteria within all five countries gradations.

Behaviours of incorporating ceramsite into epoxy asphalt mixture as thermal resistance aggregates

ABSTRACT Ceramsite epoxy asphalt mixture (CEAM) was prepared by adding ceramsite (CS) to replace aggregate with 0%, 16%, 41%, and 63%. The thermal stability of epoxy asphalt (EA) and CS, and their adhesion were analysed. Laboratory tests were performed to assess the mechanical properties and thermal resistance of CEAM compared with styrene–butadiene-styrene (SBS) copolymer modified asphalt. Results indicate that EA has good stability and adhesion to CS under high-temperature conditions. The air-void content of CEAM gradually increases, and the density gradually decreases with an increase in CS content. The strength, high-temperature stability, moisture resistance, and low-temperature performance of CEAM are slightly affected by the CS content, significantly different from those of the SBS-modified asphalt mixture. Adding CS can significantly improve the thermal resistance of CEAM. In addition, through the performance analysis of CEAM under two laboratory compaction levels, it is found that compared with high compaction level, CEAM under light compaction level has higher strength, better high-temperature stability, and thermal resistance due to more stable aggregate gradation and higher air-void content. Therefore, the light compaction level is the recommended compaction method for the CEAM.

Characterization of Air Void in Porous Asphalt Mixture Using Image Techniques and Permeability Test

In this study, air void contents and distributions of porous asphalt mixtures along the vertical and horizontal directions were quantitatively measured on planar images. Air void contents were determined using some image techniques; while the permeability was measured by the falling head test. Two aggregate gradations (G1 and G2) and three blow numbers (30, 40, and 50) were chosen to explore the effects of gradation and compaction effort on the porosity and permeability. Results showed that porosities and permeabilities are symmetrically distributed along the middle of the specimens; the porosities and permeabilities got the minimum values around the middle zone. A finer gradation or a significant compaction effort generally led to a lower porosity and permeability coefficient. In the horizontal direction, the air void content showed an increasing trend from the outside layer to the inner layer, indicating the nonuniformity of porosity distribution.

Pavement wear process and abrasive wear resistance of asphalt concrete

The aim of the article is an improvement of abrasion resistance of materials of road pavements and giving practical recommendations during the pavement designing to the construction organizations. The Prall Test method was used to identify the factors influencing the wear resistance of asphalt concrete. Studied mixtures and materials are typical for the highway construction in the Russian Federation and the Republic of Tatarstan. The influence of such factors as the type of mix, the size of the aggregate, the type of binder and the quality of the aggregate was studied. The study shows that the increase of the wear resistance and coarseness of the aggregate when using a polymer-modified binder and the reduction of the content of air voids increase the wear resistance of asphalt concrete mixtures.

Effect of aging and moisture damage on the cracking resistance of rubberized asphalt mixture

Abstract The use of crumb rubber to modify asphalt mixtures has astounding economic and environmental benefits. However, the use of asphalt mixture modified by crumb rubber is uncertain specifically when it is added by the dry method due to the low stability and cracking performance of the produced mixtures. Moreover, the high air void content of the produced mixture results in its low resistance to moisture damage and aging effect. This study attempts to investigate the effect of moisture damage and aging on the cracking performance of rubberized asphalt mixtures. Indirect tensile strength test was used to investigate the CT index, fracture energy, and tensile strength. The IDEAL-CT characterization correlated well with field performance in terms of thermal cracking and reflective cracking. The test was conducted before and after exposure of the asphalt samples to two levels of aging and one level of moisture damage. Results show that the total fracture energy of rubberized asphalt is higher than that of the control mixtures. However, the rubberized mixture shows low tensile strength particularly for the moisture conditioning. Meanwhile, the rubberized mixture has a higher CT index value than the control mixtures.

Influence of the addition of carbon fibers on the properties of hydraulic lime mortars: comparison with glass and basalt fibers

In recent years, the use of hydraulic lime in conservation and restoration of historic buildings has increased due to the pathological processes involved in the use of Portland cement. This investigation deter­mines the properties of hydraulic lime mortars with added carbon fibers for their possible use in restoration of architectural heritage. The results obtained are compared with mortars to which glass and basalt fibers have been added. The results show that the fibers affect significantly the behaviour of the mortar. Although the fibers have a negative impact in the workability and increase the air void content, they improve significantly the mechanical strengths. Although no relevant differences have been found in the pre-cracking behaviour, it has been proven that the fibers avoid a fragile behaviour of the mortar, showing a better post-cracking behaviour. Mortars with carbon fibers are the ones that show the best performance, increasing the toughness up to 12080% over the reference mortars.

3D-Reconstruction and characterization of the pore microstructure within the asphalt FAM using the X-ray micro-computed tomography

Fine aggregate matrix (FAM) is considered as a key component affecting the performance of asphalt mixtures, but there is a lack of systematic research on the sample fabrication methods and the measurement of the air void. This study aims to investigate the internal pore structure of the FAM samples with different nominal maximum aggregate sizes (NMAS) fabricated by three different compaction methods, including Marshall compaction, Superpave gyratory compaction (SGC) and a popular direct compaction method. The three-dimensional microstructures of FAM specimens were reconstructed by the micro-computed tomography (mCT) scanning test. Air void quantity, volume, and spatial distribution of each FAM sample were obtained by analyzing the microstructure. Volumetric method and surface-dry method were also used to measure the air void content. The results show that the surface-dry method shows a better consistence with the mCT method. When comparing the void distribution of FAMs fabricated by different methods, it was found that the specimens prepared by the direct compaction method show different distributions of air voids with that cored from SGC samples, while the Marshall compaction method performed with more instability with respect to the total air voids. Spatial distribution indicated that FAMs fabricated by direct compaction method would have a concentration of void on the top or bottom due to the edge effects of the compacting process. The specimens cored from the SGC samples showed a better uniformity at large particle size. In general, the direct compaction method is recommended in the study of mortar with NMAS no more than 1.18 mm, while, it is better to fabricate FAM specimens cored from SGC samples when the NMAS is larger.

The Effect of Steel and Polypropylene Fibers on the Properties of Horizontally Formed Concrete.

The article presents a comparative analysis of the impact of the addition of steel and polypropylene fibers on the properties of the concrete mixes and hardened concrete used in the concrete floor industry. The behavior of concrete intended for floors is different from conventional structural concrete because it is formed horizontally; until now, the effect of steel and polypropylene fibers on the properties of concrete formed horizontally has not yet been fully understood. Therefore, the aim of this article is to examine this issue and compare the behavior of concrete modified with steel and polypropylene fibers in concrete that is formed horizontally. The following properties of fresh concrete mixes were analyzed: consistency, the content of air-voids, and bulk density. Consequently, the following properties of hardened concrete were analyzed: compressive strength, bending tensile strength, and brittleness. It was confirmed that steel and polypropylene fibers have a different type of effect on the properties of fresh concrete mixes and hardened concrete. Finally, a combined economic and mechanical analysis was performed.

Evaluation of Asphalt Mixtures Containing Metallic Fibers from Recycled Tires to Promote Crack-Healing.

This paper reports part of an international research project with the long-term aim of developing more sustainable asphalt mixture with crack-healing properties by the addition of recycled metallic waste from industrial sources. Specifically, this article presents an evaluation of the physical, thermophysical, and mechanical properties of asphalt mixtures with metallic fiber obtained from recycled tires for crack-healing purposes. Detailed results on the crack-healing of asphalt mixtures will be reported in a second article. Results showed a small reduction on the bulk density and increase in the air voids content was quantified with increasing fiber contents. The experimental results showed that mixing and compaction was more difficult for higher fiber contents due to less space for the bitumen to freely flow and fill the voids of the mixtures. Computed tomography (CT) results allowed to identify clustering and orientation of the fibers. The samples were electrically conductive, and the electrical resistivity decreased with the increase of the fiber content. Fiber content had a direct effect on the indirect tensile stiffness modulus (ITSM) and strength (ITS) that decreased with increasing temperature for mixtures and with increase in fiber content. However, the indirect tensile strength ratio (ITSR) was within acceptable limits. In short, results indicate that fibers from recycled tires have a potential for use within asphalt mixtures to promote crack-healing.

High-viscosity modified asphalt mixtures for double-layer porous asphalt pavement: Design optimization and evaluation metrics

Porous asphalt mixture has been extensively exploited as a surfacing layer on highways because it contributes to controlling pavement runoff, enhancing driving safety, mitigating urban-heat island, and reducing tire-pavement noise. This study proposes a methodology to design two types of high-viscosity modified porous asphalt mixtures with target air voids of 20% and 22% (PAC-10 and PAC-16) for the double-layer porous asphalt pavement, involving in fabricating high-viscosity asphalt, formulating aggregate gradations, and optimizing asphalt-aggregate ratio. Firstly, high-viscosity asphalt was manufactured by incorporating high-viscosity modifier into the base asphalt by 12% and 15% (Base-12, Base-15) and crumb rubber-modified asphalt by 8% (CR-8). The physical properties, 60 °C dynamic viscosity, rotational viscosity and viscoelastic properties of high-viscosity asphalt were characterized. Next, based on orthogonal design method, two aggregate gradations were optimized for PAC-10 and PAC-16 mixtures. Furthermore, the Draindown and Cantabro tests were carried to determine the optimum asphalt-aggregate ratios. Finally, the performance metrics of air void content, permeability coefficient, high-temperature and low-temperature performance, and moisture susceptibility was evaluated on PAC-10 and PAC-16 mixtures. The results show that with the addition of high-viscosity modifier into asphalt binder, the softening point, ductility, 60 °C dynamic viscosity, rotational viscosity, complex shear modulus, phase angle, and rutting factor of the binder are increased while the penetration is decreased. The formula of voids volume of the mixture as a function of aggregate gradation is developed, which facilitates the determination of aggregate gradation. Furthermore, the optimum asphalt-aggregate ratio is found to be 4.7% for PAC-10 mixture and 4.1–4.4% for PAC-16 mixture. Both PAC-16 and PAC-10 mixtures with CR-8 are recommended to construct the double-layer porous asphalt pavement.

Design and evaluation of mechanical properties of cement grouted bituminous mixes (CGBM)

Cement Grouted Bituminous Mix (CGBM) is a composite paving mix comprising of a high voids bituminous mix impregnated with a cementitious grout. This type of mix is suitable for wearing course. The high void mix is prepared by selecting a suitable aggregate gradation, binder content and compaction effort to result in sufficiently optimized air void content. Six different cement grouted bituminous mixes prepared with varying aggregate gradations, compaction effort and grout composition are evaluated in this study. To design an acceptable bituminous mixture skeleton for CGBM, the effects of aggregate gradation on resulting grouting in the mixture are analysed. Results showed that the extent of grouting in bituminous mixture skeleton is affected by its internal void interconnectivity, structure and size of pores rather than the initial void volume. A mix design approach is developed to prepare the bituminous mix skeleton for CGBM. The study also examines the issues related to the design of aggregate gradation and cementitious grout and evaluates the properties of cement grouted bituminous mixes. For laboratory samples, X-ray Micro Computed Tomography (XRμCT) test was used to analyse the air voids content and their interconnectivity. Test sections were laid in field and monitored for their performance. Field core samples extracted showed effective full depth grouting. Falling Weight Deflectometer test was also conducted to check the in-situ moduli of CGBM mix.