Advanced Characterization of Asphalt and Concrete Materials

A rational rehabilitation design should be based on the understanding and knowledge of the existing pavement distress or condition. The purpose of this research was to investigate the effects of reclaimed asphalt pavement (RAP) content and cement content on the strength of full-depth reclamation (FDR) base. FDR for asphalt pavement with cement as the stabilizer was used as the base course. The full-factorial experimental design included five RAP contents and five cement contents. To ensure the reproducibility, there were three replicates for each specimen. The 7 days; unconfined compressive strength (UCS) was used as the control parameters. The five RAP contents consisted of 0%, 25%, 50%, 75%, and 100%. The five cement blending content included 0.5%, 1.0%, 1.5%, 2.0%, and 2.5%. The test results indicate that the optimum design was 50% RAP and 2% cement.

This study evaluates the effects of asphalt binder's performance grade (PG) on the dynamic modulus (|E*|) mastercurves of Superpave (SP) mixes typically found in the state of New Mexico. A total of three hot-mix asphalt (HMA) mixes were collected. They were produced from three different binder grades and one with aggregate gradation containing 35% of reclaimed asphalt pavement (RAP). Field collected HMA mixes were compacted and cored to cylindrical specimens. The specimens were then tested for dynamic modulus at five different temperatures and six different frequencies of loading. Master curves for all the HMA mixes were then developed and compared. A noticeable amount of divergence was found while comparing these mastercurves among each other. It was observed that stiffer binder produces HMA concrete with high dynamic modulus value. However, this trend is not always true. In the case of HMA mixes with RAP, the dynamic modulus of the HMA increases considerably, although the mix has a softer binder. The dynamic modulus of these RAP-included HMA materials could be as high as twice the dynamic modulus of HMA without RAP.

For cost savings and environmental benefits, recycled materials known as recycled asphalt pavement (RAP) and recycled asphalt shingles (RAS) have been widely used by the asphalt paving industry in recent years. To maximize the benefit of using RAS, the properties of the recycled materials, especially the asphalt binder properties, should be characterized before the mix design. In most cases, the solvent-based asphalt binder extraction and recovery is unavoidable for binder characterization. However, most of the RAS binder is very stiff, which raises concerns about the asphalt binder recovery method, for example, whether or not the solvent is left in the recovered asphalt binder and if the recovered asphalt binder is stiffened due to over-cooking for removing the solvent. In this paper, the authors compared both rheological properties and chemical components of the original binder before recovery with the same binder after recovery. The rheological properties of the asphalt binder were evaluated using DSR and BBR, and its chemical property was measured with Fourier transform infrared spectroscopy (FTIR). The results indicate that the extraction and recovery process did not change properties of the RAS binder. Therefore, the asphalt extraction and recovery process are valid for the RAS asphalt binder evaluation.

The quality of cold recycled asphalt mixes in most European countries is currently characterized primarily by indirect tensile strength or stiffness assessed after the defined curing period. These characteristics are usually supplemented by residual values of both parameters after immersion in water. This way of assessing quality empirically is very simple, fast, and well-established. Conversely, it also has some unnoticed weaknesses. A major disadvantage is probably the strong dependency on various factors like e.g. the method of test specimen compaction. Technical specifications in different European countries prescribe the preparation of test specimens by using different equipment that is based on static, dynamic, or slow rotational compaction (gyratory compactor). The laboratory compaction method applied naturally affects bulk density and voids content, thus directly influencing the values of indirect strength or stiffness modulus as well. This paper focuses on the assessment of cylindrical test specimen preparation and its effect on quality determination for cold recycled asphalt mixes. The specimens were prepared by a static pressure compacting machine, Marshall hammer and gyratory compactor. Two mixes were used, one of them containing bituminous emulsion and the other one with bituminous foam, whereas the cement content was identical.

In this study, cement mortar and concrete were used to investigate some accelerated curing on the strength and chloride electrical penetration of concrete. To evaluate some rapid testing procedures that could run a series of tests within one day to attain an estimate of the 28-day strength of the concrete, specimens with microwave heating in different hydration stages were tested on compressive strength and chloride electrical penetration. The initial result was that the accelerated curing on fresh mortar or concrete samples that combines steam curing and microwave heating could increase strength successfully within one day. Some accelerated curing samples could reach 7-day compressive strength, and the others could reach 28-day compressive strength. It was found that the 28-day chloride electrical penetrability of the accelerated curing samples reduce greatly when curing them in water after the accelerated curing. This contributes to the denseness of microstructure and reduces the chloride electrical penetrability. The steam and microwave techniques could provide the advantage of quick and uniform heating for curing of cement mortar and concrete.

Multigrade asphalt cement (MAC) is a liquefied binder material by chemical method and is widely applied in heavy traffic pavement environments. Its high construction temperature restricts its application in low temperature. The latest Evotherm product (Evotherm warm-mixed asphalt, EWMA) was added into MAC to produce a composite binder. Dense graded hot-mixed mixture AC-20 was selected as the studied aim, and Marshall method was used when the mixture was designed. MAC added in different dosages of EWMA (EWMA-MAC) and was mixed with aggregate at 180¢C and compacted attemperatures of 155¢C, 140¢C, and 125¢C. The air voids of EWMA-MAC mixture with 0.7% EWMA compacted at 155¢C and 140¢C were very close to those of MAC mixture compacted at 170¢C. Water stability, high and low temperature properties of EWMA-MAC mixture with 0.7% EWMA compacted at 155¢C, 140¢C, and 125¢C were measured and discussed. The field tested results showed that EWMA technology can improve the workability of MAC mixture at low temperature and obtain good early pavement performances.

The goal of this research was to develop an experimental method for evaluating the physical and chemical CO₂ sorption capacity of solid waste from the coal energy and cement industries with a new material called ash carbonated concrete (ACC). The proposed ACC material is a highly porous cementitious material intended to rapidly sequester CO₂ and reduce other coal energy waste. ACC relies on the bonding of ash with cement to physically stabilize ash material, and calcium carbonation to chemically fixate CO₂. To accurately quantify the CO₂ absorption process, a new testing technique was proposed. The constant temperature pressurized reaction chamber (CTPRC) isolates temperature effects and measures gas absorption volumes through pressure change measurements. Results from different blends of ash, aluminum, water, and cement indicate that the CTPRC can accurately differentiate chemical and physical sorption and quantify the amount of consumed CO₂.

The main objective of the research was to modify Colombian asphalts with natural waxes to produce warm mix asphalt and determine their mechanical and dynamic properties. The mixtures evaluated correspond to the md-10 and md-12 gradation curves, as defined in the specifications of the Urban Development Institute (IDU) of Bogota. The first step of the research comprised materials characterization (i.e., granular aggregate, asphalt, and natural waxes) and the determination of the wax and asphalt optimal percentages to be added to the mixes. Afterward, the warm-mixed asphalt mixtures were prepared and compacted at different temperature levels (i.e., 110, 130, and 150 °C) to evaluate the effect of modified asphalt in their mechanical and dynamic response. The resilient moduli (RM), preserved strength, and indirect tensile strength (ITS) tests were used to determine the asphalt mixture properties. The results showed that the use of natural waxes reduces the asphalt viscosity and, therefore, decreases the mixtures' production and compaction temperatures, which significantly reduces the energy consumption during the production process. Finally, based on the test results, the mechanical and dynamic properties of the modified asphalt mixtures with waxes are similar to those of conventional mixtures, which allows for establishing their feasibility for implementation and practical use.

Because a small amount of water is incorporated during the foaming process, water sensitivity of warm-mixed asphalt has become a research interest. The asphalt layer may fail prematurely in the presence of water, especially when it is poorly designed and constructed. The cohesive bond of the mastic (asphalt binder plus mineral filler) and adhesive bond between aggregates and the asphalt binder weakens in the presence of water. Therefore, the chemical thermodynamics theory help a great deal on characterizing the adhesive properties of the warm-mixed asphalt using foaming process. Moisture damage models of asphalt mixtures are presented based on surface and interface theory. Using the capillary rise method and the Sessile drop method, surface energy parameters of aggregate and asphalt are determined, respectively. This paper presented comparative results for two types of aggregates (limestone and sandstone) and two asphalt binders (control hot-mix asphalt and foamed asphalt) for a total of four different mixtures. The water sensitivity of four mixtures are ranked. The results indicate that surface energy of foamed asphalt is almost equivalent to that of control hot-mix asphalt, and limestone has a higher surface energy and a better water resistance compared to sandstone. It is found that foamed asphalt using limestone has good water resistance.

This paper presents testing of fatigue life of asphalt concrete that has been subjected to action of water and frost. Simulation of water and frost action was based on the original AASHTO T283 method and its modification. The original method was modified in such a way that instead of a single freeze-thaw cycle, 50 and 150 cycles were applied. Fatigue life was measured in the indirect tensile fatigue test in the Nottingham asphalt tester (NAT) apparatus. The asphalt concrete specimens were prepared in the laboratory. Some specimens contained liquid adhesive agent (namely fatty amine), and others did not. The detrimental effect of water and frost was clearly identified. The testing procedure results and practical conclusions are presented.

The annual road building objects-load increase causes a strengthening requirement for used materials and construction. Therefore, it is necessary to find new compositions satisfying all modern requirements that are nonpolluting and cost effective. One of the main tasks is creating new types of sealing materials; this task can be implemented by using raw materials changing the product damp proof ability. So currently the state-of-the-art sealing materials of the new generation: polymer-bitumen mastics have the lead. The presentational work is focused on developing efficient hydraulic insulating mastic based on a nanomodified polymer-bitumen binder with fine-dispersion filler. Such mastic can be used in constructional engineering in automobile and airport road surface building, in expansion joints making, as a water seal for water supply pipes, and for other artificial structures and is an efficient compound for road composites.

To evaluate the self-healing capability of asphalt mixtures, this paper puts forward a fuzzy evaluation method for self-healing of asphalt mixtures on the basis of a comprehensive study on the influence factors of self-healing capability. First, the authors selected 18 judgment indicators and established a numerical method to describe these indicators. Four types of subordinate functions with 16 mathematical expressions were set up to describe the continuous indicators, and empirical methods were used to deal with dispersion indicators. Then, the authors adopted an expert-giving-marks method to define the weight coefficients of these judgment indicators. A fuzzy evaluation model was set up, and two types of evaluation principles—successive evaluation and common evaluation principles—were proposed. The analysis results of an engineering example using the proposed method verify the feasibility and effectiveness of the fuzzy evaluation method for self-healing capability of asphalt mixtures.

Earth pressure cell (EPC) is used to measure vertical stresses at different depths of pavement due to traffic loading. Typically, it is considered that this sensor is not affected by arching phenomenon. As the sensor is made up of steel, its stiffness is greater than the surrounding soil materials. Therefore, the sensor may report greater stress for arching action compared to the actual value. This study investigated the arching effect by finite element model (FEM) and validates the results by field data from installed EPCs due to traffic and falling weight deflectometer (FWD) loads on an instrumented pavement section in New Mexico, USA. Results show that vertical stress response measured on the top of sub-base (445 mm depth) and top of subgrade (645 mm depth) increases up to 2.72 and 2.21%, respectively, for arching action. The vertical stress on top of base decreases with increase in EPC stiffness. Field measured vertical stresses under traffic and FWD loads at different depths agree with these FEM outputs.

This study focuses on how the voids in mineral aggregate (VMA) and performance of dense grade asphalt concrete (DGAC) are influenced by the 100% replacement of coarse natural aggregates with basic oxygen furnace (BOF) slag. By using different mixture designs to obtain the optimal asphalt content, and then conducting performance tests and analysis of variance (ANOVA) between the test set and the comparison set, this study explores whether the replacement of coarse natural aggregate with BOF slag would reduce the durability and strength of DGAC. The mixture design results show that the BOF aggregates decreased the VMA of hot-mix asphalt; however, laboratory performance tests, especially moisture sensitivity and creep tests, showed that the lack of VMA did not adversely affect the durability of DGAC. Based on these results, 100% replacement of coarse natural aggregates with BOF slag is considered feasible and worthy of further study.

Application of high modulus asphalt (HiMA) concrete can improve not only rutting resistance but also the bearing capacity of pavement structure. In this paper, a new type of HiMA is developed, The mixture is coarse aggregate gap-graded, large nominal maximum particle size (NMAS) and uses hard asphalt binder to evaluate the performance of this HiMA. Their volumetric characteristics, high-temperature stability, mechanics characteristics, and fatigue resistant are evaluated. The mechanics characteristics include compressive and flexural strength, compressive resilient modulus, and dynamic complex modulus, among others. The results illustrate that HiMA with a hard asphalt binder has better rutting resistant, bearing capacity, and durability.

The purpose of this paper is to estimate the effect of asphalt content on dynamic characterization of hot-mix asphalt (HMA). For this objective, five varying asphalt contents were selected, mixtures with the same coarse aggregate gap gradation (CAGG). The dynamic modulus test method recommended by NCHRP 9-29 was adopted to evaluate the dynamic characterization of these materials. The dynamic modulus |E*|, phase angle and their master curve characteristic parameters were achieved to evaluate the performance of HMA. Finally, the rationality of the Hirsch prediction model to predict maximum value of dynamic modulus for this gradation is discussed. The results indicate that asphalt content has influences on viscous and elastic properties of mixture.

It is important to understand the mechanism of dilation for asphalt pavement design. In this paper dilatancy theories are discussed including Rowe's and Roscoe's stress-dilatancy, and so on. The uniaxial compressive test is employed to measure dilation of asphalt mixtures under various test temperatures. Radial and volume changes of asphalt mixture specimens are obtained by UTM-25 multifunctional material system and special radial displacement transducers. The tested result is illustrated through Reynolds' dilatancy theory. The experimental result shows that the test temperature and time were found to play an important role on the dilation behavior of asphalt mixtures. The dilation characteristics are affected by the aggregate properties such as density, friction coefficient, shape, and size angular. Thus, the constitutive of dilation of asphalt mixture should be considered the aforementioned points. Analysis using Reynolds' dilatancy theory suggests that the dilation is governed by the kinematic constraints imposed by the aggregate skeleton.

Using recycled asphalt pavement (RAP) in asphalt concrete has been practiced for decades. Recent attention has been mostly placed on increasing the amount of RAP, as well as using recycled asphalt shingles (RAS) in asphalt concrete. Use of RAS in asphalt concrete poses special challenges as it includes very stiff binder and mastic. There are two types of RAS used in asphalt concrete: one is scrap asphalt shingles coming from manufacturing waste and other is the post-consumer waste. In either case, it is important to understand the properties of the RAS binder and consider those properties in an engineering design for incorporation into asphalt concrete. Recovering and laboratory testing of the RAS binder does not follow conventional techniques due to high stiffness. Research was conducted to find suitable techniques for determination of RAS binder characteristics at both high and low temperatures, and a guide was developed on the best approach for recovery and testing of the RAS binder.