Voids In Mineral Aggregate Research Articles

Optimal Bitumen-Aggregate Ratio Selection Method of Hot Mix Asphalt Based on Closest Compaction Condition

Abstract An optimal bitumen-aggregate ratio selection method for hot mix asphalt, based on aggregate closest compact condition, was introduced. According to research, high correlation within dry density, voids in mineral aggregate (VMA) and voids in coarse aggregate (VCA) versus bitumen-aggregate ratio was discovered. Dry density increases with increase of bitumen-aggregate ratio until it reaches a peak, and then decreases. VMA and VCA have the inverse trend. The advantage of the unique extreme point rule of the conic is the relationship of bitumen-aggregate ratio versus dry density and that the VMA and VCA can be indicated by conic regression analysis, and the corresponding bitumen-aggregate ratio can be achieved as well. In this paper, the new design method was adopted for hot mix asphalt in various gradations and the differences from the previous design method were also illustrated. The inaccurate bitumen-aggregate ratio due to previous design criterion can be avoided through setting the closest compact condition. This can also be recommended as the design criterion.

Is Normal Distribution the Most Appropriate Statistical Distribution for Volumetric Properties in Asphalt Mixtures?

Abstract Volumetric properties are essential for a better understanding of how to design the mixtures. Due to the irregularity of aggregate shape, these properties vary randomly with the same gradation. In this paper, the volumetric properties [bulk specific gravity (γf), air voids (VV), voids in mineral aggregate (VMA), and voids filled with asphalt (VFA)] were determined on two mixtures types, namely, A and B. These mixtures were statistically analyzed using different distribution methods. Seventy-two samples of Mixture A and 52 of Mixture B were fabricated using the Marshall design method. Results of the study showed that the Weibull distribution could reflect the probability distribution law of the volumetric properties of the mixtures. The two-parameter Weibull distribution function appears to be more appropriate or use with γf and VFA, whereas the three-parameter Weibull distribution function was most appropriate for VV and VMA. The analysis of test results also revealed that there are significant differences in the volumetric properties of the two mixtures tested at the same confidence level. The confidence interval decreases with a decrease in reliability.

Field Evaluation of Asphalt Film Thickness as a Design Parameter in Superpave Mix Design

Research shows that asphalt film thickness (AFT) is related to mix performance. The use of AFT as a mix design parameter has always been a challenge because of the complexity of estimating AFT based on mix parameters. The aggregate surface area and the effective volume of asphalt are important components in the calculation of AFT. This study compares the voids in mineral aggregate (VMA) and AFT as mix design parameters against the field performance of Superpave mixes. Film thickness was estimated by different formulas using calculated aggregate surface area. Data on early flushing sections of Superpave mixes was used to correlate film thickness to distress development and other mix design parameters. The pavement sections considered for the study were observed to have undergone flushing and rutting problems. Field cores from flushed and non-flushed sections were obtained and verified for compliance with Superpave specifications. The results of this research related AFr to mix design parameters but showed that depending on the method of calculation, AFT, as a mix design parameter, mayor may not be helpful in explaining specific field performance distresses such as rutting or bleeding.

Effect of Specifications Type on the Quality of Paving Contracts in New Brunswick

Construction specifications are used by transportation agencies to define the client's requirements of the final product. The primary motivation of adopting the newer end result specification (ERS) or performance related specification over method-based specification (MBS) is to reduce clients' costs, encourage contractors' innovation, and improve overall quality. However, some transportation agencies have been reluctant to fully implement ERS due to lack of demonstrated evidence on whether they achieve comparable level of quality or performance. This paper investigates whether the specification type has any effect on quality. The case study presented is based on data from New Brunswick Department of Transportation (NBDOT) from years 2003–2007. NBDOT generally uses ERSs to call paving contracts equal to or larger than 8,000 t. MBSs are used for all other smaller paving contracts. The most prevalent indicator variables for accepting asphalt paving jobs in North America [that is, percent theoretical maximum relative density, asphalt binder content, air voids, voids in mineral aggregates, percent passing 4.75 mm (No. 4), and 75 µm (No. 200) sieves] were investigated. Statistical analysis was performed to compare the deviation of the quality indicator variables from their respective job mix formula values for paving projects that used MBS or ERS. ANOVA results revealed that there were no significant differences between the qualities achieved from the 2 specification types. Also, no significant differences were found from within-specification comparisons over the time frame examined. Given the possible cost advantages from agency's point of view, the flexibility of the contractors to innovate and the fact that this study demonstrates quality is not compromised, there is an opportunity for agencies to expand or fully adopt the use of ERS specifications.

Accumulated strain prediction of polypropylene modified marshall specimens in repeated creep test using artificial neural networks

This study presents an application of artificial neural networks (ANN) for the prediction of repeated creep test results for polypropylene (PP) modified asphalt mixtures. Polypropylene fibers are used to modify the bituminous binder in order to improve the physical and mechanical properties of the resulting asphaltic mixture. Marshall specimens, fabricated with M-03 type polypropylene fibers at optimum bitumen content were tested using universal testing machine (UTM-5P) in order to determine their rheological/creep behavior under repeated loading. Different load values and loading patterns have been applied to the previously prepared specimens at a predetermined temperature. It has been shown that the addition of polypropylene fibers results in improved Marshall stabilities and decrease in the flow values, providing the increase of the service life of samples under repeated creep testing. The proposed ANN model uses the physical properties of standard Marshall specimens such as polypropylene type, specimen height, unit weight, voids in mineral aggregate, voids filled with asphalt, air voids and repeated creep test properties such as rest period and pulse counts in order to predict the accumulated strain values obtained at the end of mechanical tests. Moreover parametric analyses have been carried out. The results of parametric analyses were used to evaluate the accumulated strain of the Marshall specimens subjected to repeated load creep tests in a quite well manner.

Utilization of white cement bypass dust as filler in asphalt concrete mixtures

This research was carried out to investigate potential reuses of white cement bypass dust (WCBPD) in the Hashemite Kingdom of Jordan. For this purpose, five different asphalt concrete mixtures were prepared using lime mineral filler (control), 2%, 4%, 6%, and 8% WCBPD substitution for lime mineral filler (LMF). The mixtures were subjected to Marshall testing. Results indicated that the substitution of 2% WCBPD for LMF essentially produced almost the same optimum bitumen content (OBC) as the control mixtures (5.5% by weight of aggregate). The substitution of 4% WCBPD slightly increased the OBC to 5.7% by weight of aggregate without any significant negative effect on asphalt concrete properties (stability, flow, voids in mineral aggregates (VMA), and percent of air voids (Pav)). However, further increase in the substitution ratios (6% and 8%) WCBPD was associated with an increase in the OBC to 6.1% and 6.2%, respectively, which makes them uneconomical mixtures. Thus, 4% WCBPD substitution for LMF would be the optimum used in asphalt paving mixtures.

Evaluation and design of fiber-reinforced asphalt mixtures

This paper investigated the volumetric and mechanical properties, and design method of fiber-reinforced asphalt mixtures. Four different fiber were used: polyester, polyacrylonitrile, lignin, and asbestos fibers. Marshall tests were performed to measure the volumetric and mechanical properties of asphalt mixtures. Performance tests were also conducted to examine moisture susceptibility and dynamic stability. Results show that the optimum asphalt content, air void, void in mineral aggregate and Marshall stability increase, while bulk specific gravity decreases after adding fibers into asphalt mixtures. Optimum asphalt content, Marshall stability, and dynamic stability increase initially and then decrease with increasing fiber content. It also shows that the polyester and polyacrylonitrile fibers have higher stability due to their higher networking effect, while the lignin and asbestos fibers result in higher optimum asphalt content and VFA (asphalt filled in the voids of mineral aggregates) due to their higher absorption of asphalts. A design procedure for fiber-reinforced asphalt mixture is proposed, which elects the fiber type based on the characteristics of both fiber and asphalt mixture, designs the optimum asphalt content following the Marshall method, and then determines the optimum fiber content in terms of performance test results. Based on the test results, a fiber content of 0.35% by mass of mixture is recommended for the polyester fiber used in this study.

Influences of crumb rubber size and type on reclaimed asphalt pavement (RAP) mixtures

Over the years, recycling has become one of the most attractive pavement rehabilitation alternatives, and different recycling methods are now available to address specific pavement distresses and structural needs. The objective of this study was to investigate and evaluate the engineering properties of crumb rubber size and type influences on reclaimed asphalt pavement (RAP) mixtures. The experimental design for this study included the use of three rubber sizes and two rubber types (ambient or cryogenic) in the mixture containing 25% RAP mixtures. In this study, the results of the experiments indicated that the addition of crumb rubber was helpful in increasing the voids in mineral aggregate (VMA) in Superpave mix design and improving rutting resistance of mixture regardless of rubber size and type. On the other hand, indirect tensile strength (ITS) values show no significant difference for mixtures made with three type rubber sizes. However, the increase of rubber size, regardless of rubber type, reduced the resilient modulus values but extended the fatigue life of the modified mixtures.

Methodology of Assessing Testing Variation for Volumetric Quantities in Hot Mix Asphalt Production

Abstract Increasingly, in road construction, pay incentives and disincentives are being related to both the average test results that are obtained during quality assurance testing as well as the variability associated with these values. As a result, state highway agencies must be fully aware of the expected variability that can be associated with each acceptance test since the results will not only be used for acceptance but may be used for pay adjustment also. In this study, a methodology was developed to assess the testing variability in hot-mix asphalt production. The study focused on determining allowable testing variations for the calculated volumetric quantities, including the air voids content and voids in mineral aggregate (VMA) determined from gyratory compacted specimens. A new standard of determining an allowable testing variation for VMA was developed. Furthermore, a test data analysis plan to extract the testing variation from the total measured variation for the hot-mix asphalt quality parameters was developed.

Use of Tank Bottom Sludge to Construct and Upgrade Unpaved Roads

Tank bottoms are the liquids and residue, such as heavy hydrocarbons, solids, sands, and emulsions, that collect at the bottom of the treating vessel or that remain at the bottom of storage tanks after a period of service. Sludge composition is 50% to 65% crude oil, 20% to 35% water, and 5% to 20% solids. Disposal of tank sludge is a significant item of tank maintenance costs. Results are presented on the use of tank bottoms as a binder to construct and upgrade unpaved roads. Various sludge samples were initially characterized for chemical and physical composition, then three mixtures were prepared by using blends of aggregates and tank bottoms. No bitumen was used in the mixes. The mixtures include hot mix (aggregate and sludge were both heated), heated sludge and cold aggregate mix, and cold mix (no heat was applied). The Marshall mix design (ASTM D1559) was followed in the preparation and testing of the specimens. Results indicate that tank bottoms act as a binder to the aggregate and can provide significant strength. Heating both the sludge and the aggregate resulted in the highest stability value of 11.9 kN. An optimum sludge content of 6.5% by total weight of the mixture satisfied the requirements for low (3.3 kN) or medium (5.3 kN) trafficked surfaces or base layers according to Asphalt Institute specifications. Other mix properties, such as flow, air voids, voids in mineral aggregate, and voids filled with asphalt, were acceptable.

Minimum voids in mineral aggregate in hot-mix asphalt based on asphalt film thickness

This study is aimed at determining the relationship between asphalt film thickness and aging characteristics of various hot-mix asphalt (HMA) mixtures. Resilient modulus and indirect tensile strength tests were conducted on the Superpave Gyratory-compacted specimens with five different asphalt film thicknesses in order to determine an optimum asphalt film thickness. From the relationships between the asphalt film thickness and resilient modulus and indirect tensile strength test values of the short and long-term aged samples, optimum asphalt film thickness has been determined about 9–10 μm. The minimum void content of mineral aggregate (VMA) to obtain this optimum asphalt film thickness can be calculated as 15.2%.

EFFECT OF USING WASTE CEMENT DUST AS A MINERAL FILLER ON THE MECHANICAL PROPERTIES OF HOT MIX ASPHALT تأثير استخدام بودرة تراب الأسمنت على الخواص الميکانيکية للخلطات الأسفلتية

By pass cement dust is proposed within this research as an alternative to traditional limestone mineral filler in hot mix asphalt (HMA). The effect of using waste cement dust as a mineral filler on the mechanical properties of hot mix asphalt was investigated. The optimum cement dust content was determined. The studied mechanical properties include Marshall properties, indirect tensile strength, and unconfined compressive strength. Five asphalt concrete mixtures with various cement dust contents, namely; 0%, 25%, 50%, 75% and 100% by weight of the limestone mineral filler were studied. Laboratory testing has revealed an enhancement in Marshall and mechanical properties of asphalt concrete mixtures when cement dust was used. Marshall testing results have indicated an increase in the stability, unit weight and a decrease in the flow, voids ratio and voids in mineral aggregates when the percentage of cement dust content increases. The indirect tensile strength and unconfined compressive strength have also increased as the ratio of cement dust increased. The optimum cement dust ratio was found to be 100% of the used mineral filler. Hence, cement dust can totally replace lime stone mineral filler in asphalt paving mixtures.

Evaluation of Healing Property of Asphalt Mixtures

Although repeated traffic loading causes damage to accumulate in asphalt pavements, the damage heals during rest periods (time between traffic loadings). Consequently, this healing enhances the fatigue life of the pavement. A method was developed to determine the healing rate of asphalt mixtures in terms of recovered dissipated creep strain energy (DCSE) per unit time. The healing properties of four different asphalt mixtures were evaluated with this approach. The test procedure consists of a repeated loading test and periodic resilient modulus tests. A normalized healing rate in terms of DCSE/DCSEapplied was defined to evaluate the healing properties independent of the amount of damage incurred in the mixture. From the test results, it was determined that the healing rates of the asphalt mixtures tested increased dramatically above 10°C and were more affected by the aggregate structural characteristics (i.e., aggregate interlock, film thickness, voids in mineral aggregate) of the mixtures than by polymer...

Evaluating Specification Limits

The results of a study to evaluate the existing South Carolina Department of Transportation (SCDOT) hot-mix asphalt quality assurance specification are presented. When the existing specification was developed, assumed values were used for the standard deviations needed to establish the specification limits. Acceptance test results from 39 different projects were analyzed to determine standard deviation values that were being obtained for asphalt content, air voids, voids in mineral aggregate, and density. For each project, standard deviation values were calculated for each lot, and these were then pooled to obtain a typical value for the project. The target miss variability, that is, the ability of contractors to center their processes on the target, was also determined for each acceptance characteristic. The project and target miss values were then used to establish a typical process standard deviation value for each of the four acceptance characteristics. All these standard deviation values proved to be...

Evaluating Specification Limits

The results of a study to evaluate the existing South Carolina Department of Transportation (SCDOT) hot-mix asphalt quality assurance specification are presented. When the existing specification was developed, assumed values were used for the standard deviations needed to establish the specification limits. Acceptance test results from 39 different projects were analyzed to determine standard deviation values that were being obtained for asphalt content, air voids, voids in mineral aggregate, and density. For each project, standard deviation values were calculated for each lot, and these were then pooled to obtain a typical value for the project. The target miss variability, that is, the ability of contractors to center their processes on the target, was also determined for each acceptance characteristic. The project and target miss values were then used to establish a typical process standard deviation value for each of the four acceptance characteristics. All these standard deviation values proved to be smaller than those initially assumed and resulted in the SCDOT narrowing the specification limits for each of the acceptance characteristics. The project standard deviation values justified that these changes were made to reflect the actual variability that was present and not simply to tighten the specifications.

Evaluation of Healing Property of Asphalt Mixtures

Although repeated traffic loading causes damage to accumulate in asphalt pavements, the damage heals during rest periods (time between traffic loadings). Consequently, this healing enhances the fatigue life of the pavement. A method was developed to determine the healing rate of asphalt mixtures in terms of recovered dissipated creep strain energy (DCSE) per unit time. The healing properties of four different asphalt mixtures were evaluated with this approach. The test procedure consists of a repeated loading test and periodic resilient modulus tests. A normalized healing rate in terms of DCSE/DCSEapplied was defined to evaluate the healing properties independent of the amount of damage incurred in the mixture. From the test results, it was determined that the healing rates of the asphalt mixtures tested increased dramatically above 10°C and were more affected by the aggregate structural characteristics (i.e., aggregate interlock, film thickness, voids in mineral aggregate) of the mixtures than by polymer modification. Although styrene-butadiene-styrene polymer modification reduced the rate of damage accumulation, it had no effect on the healing rate of the mixtures tested.

Evaluation of Two Compaction Levels for Designing Stone Matrix Asphalt

Current stone matrix asphalt (SMA) design guidelines list two compaction options to design SMA, 50 blows Marshall or 100 gyrations with the Superpave® gyratory compactor (SGC). However, some states have found that 100 gyrations with the SGC is excessive for their materials. In this study a lower compaction level of 65 gyrations was used to compare with the standard 100 gyrations to design SMA mixtures. Results showed that mixtures designed by 65 gyrations had an average of 0.7% higher optimum asphalt content and 1.5% higher voids in mineral aggregate (VMA) than those designed by 100 gyrations. All mixtures designed by 65 gyrations met the minimum asphalt content and VMA requirements for SMA, whereas only eight of 15 mixtures designed by 100 gyrations met those two requirements. Compaction at 100 gyrations resulted in an additional 0.62% average aggregate breakdown at the critical sieve as compared with 65 gyrations. SMA mixtures designed by 65 gyrations and 100 gyrations had an average asphalt pavement an...

Evaluation of Two Compaction Levels for Designing Stone Matrix Asphalt

Current stone matrix asphalt (SMA) design guidelines list two compaction options to design SMA, 50 blows Marshall or 100 gyrations with the Superpave® gyratory compactor (SGC). However, some states have found that 100 gyrations with the SGC is excessive for their materials. In this study a lower compaction level of 65 gyrations was used to compare with the standard 100 gyrations to design SMA mixtures. Results showed that mixtures designed by 65 gyrations had an average of 0.7% higher optimum asphalt content and 1.5% higher voids in mineral aggregate (VMA) than those designed by 100 gyrations. All mixtures designed by 65 gyrations met the minimum asphalt content and VMA requirements for SMA, whereas only eight of 15 mixtures designed by 100 gyrations met those two requirements. Compaction at 100 gyrations resulted in an additional 0.62% average aggregate breakdown at the critical sieve as compared with 65 gyrations. SMA mixtures designed by 65 gyrations and 100 gyrations had an average asphalt pavement analyzer rut depth of 3.9 mm and 3.1 mm, respectively. Thirteen of 15 mixtures designed by 65 gyrations performed well if 5.0 mm was set as the maximum allowed rut depth. On the basis of this study, 65 gyrations can be used to design a more durable SMA mixture, while still maintaining the good rutting resistance that SMA mixtures are noted for. The successful design by 65 gyrations for all five aggregates in this study indicates that a lower design compaction level may allow the use of more aggregate sources for SMA mixtures.

Mechanistic and Volumetric Properties of Asphalt Mixtures with Recycled Asphalt Pavement

This research examines how the addition of recycled asphalt pavement (RAP) changes the volumetric and mechanistic properties of asphalt mixtures. A Superpave® 19-mm mixture containing 0% RAP was the control for evaluating properties of mixes containing 15%, 25%, and 40% RAP. Two types of RAP were evaluated: a processed RAP and an unprocessed RAP (grindings). Testing included dynamic modulus in tension and compression, creep compliance in compression, and creep flow in compression. Dynamic modulus and creep compliance master curves were constructed with the use of the time–temperature superposition principle to describe the behavior of each mix over a range of temperatures. The voids in mineral aggregate (VMA) and voids filled with asphalt (VFA) of the RAP mixtures increased at the 25% and 40% levels, and there was also an influence of preheating time on the volumetric properties. The dynamic modulus of the processed RAP mixtures increased from the control to 15% RAP level, but the 25% and 40% RAP mixtures had dynamic modulus curves similar to that of the control mixture in both tension and compression. The creep compliance curves showed similar trends. A combination of gradation, asphalt content, and volumetric properties is likely the cause of these trends.

Mechanistic and Volumetric Properties of Asphalt Mixtures with Recycled Asphalt Pavement

This research examines how the addition of recycled asphalt pavement (RAP) changes the volumetric and mechanistic properties of asphalt mixtures. A Superpave® 19-mm mixture containing 0% RAP was the control for evaluating properties of mixes containing 15%, 25%, and 40% RAP. Two types of RAP were evaluated: a processed RAP and an unprocessed RAP (grindings). Testing included dynamic modulus in tension and compression, creep compliance in compression, and creep flow in compression. Dynamic modulus and creep compliance master curves were constructed with the use of the time-temperature superposition principle to describe the behavior of each mix over a range of temperatures. The voids in mineral aggregate (VMA) and voids filled with asphalt (VFA) of the RAP mixtures increased at the 25% and 40% levels, and there was also an influence of preheating time on the volumetric properties. The dynamic modulus of the processed RAP mixtures increased from the control to 15% RAP level, but the 25% and 40% RAP mixtures...