Journal of Materials in Civil Engineering

This research investigates the effect of pulse shaper, lateral inertia and friction on the strain-rate sensitivity of ultra-high-performance fiber-reinforced concrete (UHP-FRC) using a split Hopkinson pressure bar (SHPB) by finite-element analysis. Assigned material parameters of UHP-FRC are provided by calibrating concrete material characteristics given in commercially available software. Following the material model calibration, a parametric study on the design of pulse shaper is carried out to satisfy the requirements of SHPB testing. Material confinement effects, including inertia effect and friction effect, are isolated from the strain-rate sensitivity of UHP-FRC under compressive impact loading. Numerical simulation results show that (1) the calibrated KCC model can well-predict the experimentally behavior of UHP-FRC; (2) an aluminum 6061-T6 disc with 1.8-mm thickness and 8-mm diameter is an ideal pulse shaper for SHPB testing of UHP-FRC at $20\mathrm{m}/\mathrm{s}$ impact velocity; (3) at an impact velocity of $20\mathrm{m}/\mathrm{s}$, the dynamic impact factor (DIF) due to lateral inertia confinement reaches 1.06, and the DIF due to combined lateral inertia and friction increases from 1.06 to 1.18 with the friction coefficient increasing from 0 to 0.2.

Concrete has inherent low tensile strength and fails at low tensile strains. These drawbacks have been bypassed by the introduction of discontinuous randomly distributed fibers to the concrete. The fiber-matrix interfacial behavior is of critical importance to the properties of fiber-reinforced concrete (FRC), which is usually assessed by fiber pullout tests. In this paper, a rigorous pullout test setup was developed with 50-mm-diameter × 100-mm-height cylindrical concrete specimens and utilized to investigate fiber-matrix interfacial behavior of hooked-end steel FRC with two fiber sizes and various embedment depths. The relation of fiber pullout load-end slip displacement and its average curves established the efficiency of the utilized fiber pullout test setup concerning the repeatability and reliability. Four components of the fiber matrix interactions were observed for hooked-end steel fibers. These include the elastic fiber-matrix bond, partial fiber-matrix debonding, full fiber-matrix debonding, and fiber (softening, hardening, and frictional) pullout components. Results showed that the ultimate pullout load of the fiber increases with an increase in size of fiber and embedment depth. Moreover, the hook of the fiber that has a 45-degree bending angle and a 2.5- or 3.0-mm length governs the overall pullout characteristics of hooked-end steel fibers.

Self-healing microencapsulation in asphalt concrete is an emerging technology that would allow this particular material to resist cracking damage caused by vehicular and environmental loading. The objectives of this study were to evaluate the effects of asphalt rejuvenators on asphalt binder, to select a suitable healing agent for asphaltic materials, and to develop a synthesis procedure for the production of microencapsulation of asphalt rejuvenators. Produced microcapsules were characterized using scanning electron microscopy (SEM) to assess the effects of preparation parameters on the size and morphology of the microcapsules. Based on the results of the experimental program, it was concluded that the use of sunflower oil as a rejuvenator was effective in reversing the aging of asphalt binder and to positively affect both the high-temperature and low-temperature grades of the binder. In contrast, the use of PennzSuppress as a rejuvenator was not effective in reversing the aging of asphalt binder and only marginally influenced the grades of the aged and extracted binders at both low and high temperatures. Based on these results, microencapsulation of sunflower oil was selected given its effectiveness in reversing the aging of asphalt binder. A synthesis procedure was developed for the preparation of microencapsulation of sunflower oil and to characterize microcapsule properties such as diameter and morphology.

The indirect Brazilian test is widely used in engineering practice to indirectly determine the tensile strength of concrete. The Brazilian test (splitting tension test) is performed by applying a concentrated compressive load across the diameter of a disc-specimen. A series of dynamic Brazilian disc tests for concrete specimens were conducted using the split Hopkinson pressure bar (SHPB) technique. The objective of this paper is to investigate the standard Brazilian test by comparing the results obtained using the test with those obtained using a loaded arc, together with a comparison of the experimental results and the statistical analysis. The effect of loading angle on the dynamic splitting tensile strength was studied by one-way analysis of variance. By using linear regression method, the Weibull statistical model was introduced to obtain the relationship between the loading angle and dynamic splitting tensile strength of concrete. It was concluded that dynamic tensile strength of concrete is strongly dependent on the type of jaws. A general increase in failure load was obtained with an increasing angle of loading arc for all specimens tested. With an increase of loading angle, the Weibull parameters increase. The Weibull statistical model can describe the distribution law of the dynamic tensile strength of concrete.

Cold in-place recycling (CIR) is a pavement rehabilitation technique that has been used for decades. During this time, single-component binder (SCB) systems have governed the market. Single-component binders are defined as those with one binder or two if the secondary binder dosage is 1% or less (e.g., 3% asphalt emulsion with 1% hydrated lime). In contrast, this paper investigates multiple-component binder (MCB) systems (e.g., 2.5% emulsion with 2% portland cement). This paper’s objective is threefold: (1) present a universal CIR design framework applicable to any cementitious and/or bituminous material; (2) demonstrate MCB sustainability advantages; and (3) conduct an extensive SCB and MCB characterization. Universal design framework components include specimen preparation, curing, and testing protocols. Nine binder combinations were tested for wheel tracking, permeability, modulus, strength, and cracking response. Cement SCBs yielded low cracking resistance, high rutting resistance, and favorable economics; emulsion SCBs yielded the opposite. Multiple-component binders balanced cracking, rutting, and economics. The work presented in this paper could benefit agencies in many ways, for example, by promoting informed decisions regarding CIR performance and economics.

Based on the microstructure-based discrete-element method (DEM), this study aims to investigate the effect of vertical aggregate homogeneity, i.e., aggregate homogeneity in vertical cross sections, on the uniaxial penetration test of asphalt mixtures. An aggregate homogeneity index, which can be used to evaluate aggregate homogeneity in a two-dimensional (2D) cross section, was briefly introduced. The vertical aggregate distribution was evaluated by the index. Microstructure-based discrete-element modeling of a uniaxial penetration test was accomplished by a discrete-element program called particle flow code in two dimensions. The effect of vertical aggregate homogeneity on penetration strengths regarding a uniaxial penetration test was simulated by the DEM. The obtained results were verified by uniaxial penetration testing. Results show that the effect of vertical aggregate homogeneity on penetration strengths can be numerically simulated by the microstructure-based DEM. The penetration strengths in the uniaxial penetration test are anisotropic. Vertical aggregate homogeneity also dominates the variation of penetration strengths in the uniaxial penetration test. A good correlation between vertical aggregate homogeneity and the variation of penetration strengths is also observed.

The values of key parameters, asphalt aggregate ratio, mixing/compacting temperature, striking/compacting times, and fiber content are usually determined according to bulk properties or empirical values when molding asphalt mixture, which is inefficient and subjective. In this study, a modified response surface methodology (RSM) method was introduced to comprehensively optimize design of asphalt mixture molding process with the optimal value of pavement performance as a response variable. The single-factor tests were first conducted to find the specific ranges of key factors in the response surface models. Then the response surface models between effect factors and three different pavement performance parameters were established based on the Box-Behnken design (BBD) theory. Lastly, the analytic hierarchy process (AHP) was applied to determine weights distribution of the effect factors, and the optimal values of effect factors and pavement performances were obtained. Results indicate that fitting errors of this modified RSM method is lower than 1.2%, and that the average prediction error is 0.87%. This modified model was proven to possess favorable fitting accuracy, predictive capability, and stability. Meanwhile, the method can ensure volumetric parameters are in compliance with regulatory requirements under the premise of improving the overall asphalt pavement performance.

The objective of the study is to investigate the suitability of some concrete components for producing high-performance heavy-density concrete that could afford radiation shielding during service in Egyptian nuclear power plants. The author surveyed the Egyptian deserts for ensuring the existence and defining the locations of the special types of natural ores for the coarse aggregates that are known to be used for radiation-shielding concrete. The study introduces industrial air-cooled slag as an innovative substitute for such types of natural concrete aggregates. In addition, new chemical additives are presented for enhancing the attenuation properties of concrete against the affecting radiation in a nuclear power plant.

Processed tire wastes mixed with soils are applicable as lightweight fillers for slopes, subbases of pavements and retaining walls that may be subjected to seismic loads, e.g., earthquake or traffic loads. The dynamic response of granulated rubber-soil mixtures, such as the dynamic shear modulus, damping factors and liquefaction resistance, is essential in the design of such a system. This report presents the results of the dynamic behavior of granulated rubber-sand mixtures using resonant column tests and cyclic triaxial tests to assess the potential use of recycled rubber crumb in improving the performance of granular materials by mixing with different tire crumb sizes and fractions. Two contact types are identified that could explain the evolutionary behavior of the shear modulus and the damping ratio. The results of the rubber-sand mixtures are compared with the results from the literature. The mix ratio is shown to significantly influence the dynamic shear modulus and the liquefaction susceptibility. The results serve as a supplement to enrich the database of the dynamic behavior of soil-rubber mixtures as lightweight filler materials in dry and saturated conditions.

The influence of initial water-curing time on the mechanical properties of engineered cementitious composites (ECCs) was investigated by employing a four-point bending test, compressive strength, and flexural strength. Five different curing regimes were applied to the specimens, which were in continuous room-air storage, curing in the laboratory room air after submersion in water for 3, 7, 14, and 28 days, respectively. The experimental results show that the deflection and the toughness index of ECC under water-curing conditions decrease gradually as water-curing time is prolonged. First cracking load, peak load, compressive strength, and flexural strength increase as water-curing time increases and total curing age is extended. The higher volume of fly ash is beneficial in lowering the adverse effect of water-curing time on the mechanical properties of ECCs. The cement of ECCs replaced by 80% fly ash by weight exhibited good ductility and mechanical properties whenwater curing time was 7 days. Otherwise, it was found that moisture content of had a certain influence on the ECC specimen’s deflection-load curve. Therefore, water-curing regimes are key factors for achieving robust strain hardening and multiple cracking behaviors in ECCs.

Dispersive clays undergo deflocculation in the presence of relatively pure still water to form colloidal suspensions and as such are highly susceptible to erosion and piping. Lime treatment is one of the most practical methods to improve such undesirable characteristics of dispersive clays, as well as improve their mechanical properties. The present research aims to quantify the influence of amounts of hydrated lime, compacted dry unit weight, and curing time in the assessment of transformation to a nondispersive state by the lime treatment, as well as improving durability, strength, and stiffness properties of clay–lime mixtures. This manuscript advances understanding of the parameters controlling strength and stiffness of compacted lime-treated dispersive clay soil by quantifying the influence of porosity/lime index initial shear modulus ($G_o$) and unconfined compressive ($q_u$) and split tensile ($q_t$) strengths. A single $q_t/q_u$ relationship equal to 0.136 was found, being independent of the porosity/lime index and curing time. Unique relationships between $G_o/q_u$ and adjusted porosity/lime index of the dispersive clay soil–lime mixtures is shown for each curing time studied, linking initial stiffness and strength. Finally, while 2% of lime is enough to turn the dispersive clay studied herein into a nondispersive soil, it is quite clear that the minimum amount of lime for clay stabilization is 3%, at any dry unit weight, and this amount of lime definitely enhances both strength and stiffness. However, regarding durability, 5% is the amount of lime needed for guaranteeing endurance of the stabilized dispersive clay–lime blends.

In this study, cyclic behavior and dynamic properties of Renusagar pond ash samples reinforced with geotextiles have been studied. Pond ash samples were collected from the upstream side of the pond ash embankment. Laboratory tests have been carried out to obtain the material properties of the pond ash. Strain-controlled cyclic triaxial tests have been carried out on reconstituted pond ash samples with and without geotextiles, at varying confining pressures (70, 100, and 150 kPa), loading frequencies (1 and 0.5 Hz), and cyclic shear-strain amplitudes (0.5, 0.8, and 1.05%). The woven geotextiles were used as reinforcing materials, which were placed in the pond ash samples in one and three layers. Results show that the pond ash samples reinforced with geotextiles exhibit better friction angle, drainage properties, and liquefaction resistance. It may be concluded that pond ash reinforced with geotextiles can be used effectively as embankment construction material.

Over the years, coal fly ash has been used as a backfill material in embankments, mines, roads and around pipelines. Recently, there has been a growing interest in its alkali activation for synthesis of both geopolymers and highly porous minerals known as zeolites. These end products find applications as cement admixtures, molecular sieves, and for contaminant depuration in aqueous media. In this regard, the textural characteristics, viz, particle size, pore size, and pore structure distribution characteristics of alkali activated fly ashes elucidate their potential as porous additives to cement and concrete, reactive media in permeable reactive barriers, and sorbents for contaminant removal. With this in view, this study investigates the particle size and pore structure modifications occurring in calcium hydroxide–based activation of coal fly ash. Furthermore, the morphological features also show the effect of alkali interaction on the reduction in larger sized particles and on the steady growth in smaller-sized crystals.

The feasibility of carbonation curing of precast fly ash concrete is studied. If fly ash concrete can be produced by carbonation curing, the carbon footprint of the products can be significantly reduced. In this paper, the relationship between carbonation reaction and pozzolanic reaction was examined. After carbonation curing with different duration and fly ash content, the cement reaction degree was estimated through the equivalent nonevaporable water content, and the fly ash reaction degree was analyzed through a selective acid dissolution test. It was found that the pozzolanic reaction of fly ash in a fly ash–ordinary portland cement (OPC) system was hindered by early carbonation reaction. The higher the early carbonation degree, the lower the pozzolanic reaction of fly ash. In addition, fly ash–OPC paste was more reactive with carbon dioxide than plain cement paste. Therefore, controlled carbonation at an early age is necessary to trade off the carbon emission reduction with performance gain. The study shows that if fly ash content is limited to 20% of cementitious material and carbonation curing duration is not to exceed 12 h, fly ash concrete can be produced with higher early strength, comparable late strength, better durability performance, and a carbon emission reduction of 36%. After subsequent hydration, carbonated fly ash concrete can have a pH value comparable with the hydration reference and can be used in precast concretes with steel reinforcement.

This study evaluated the aging characteristics of foamed warm mix asphalt (WMA) produced by water injection in comparison to traditional hot mix asphalt (HMA). Two asphalt binders (PG 70-22 and PG 64-22) and one aggregate (12.5-mm NMAS limestone aggregate) were used in this study. The short-term and long-term aging of the two asphalt binders were simulated using the rolling thin film oven (RTFO) and pressure aging vessel (PAV), respectively, while AASHTO’s standard practice for mixture conditioning for hot mix asphalt was used to simulate the short-term and long-term aging of the laboratory-prepared asphalt mixtures. The dynamic shear rheometer (DSR) was used to characterize the viscoelastic behavior of the original (unaged, RTFO-aged, and PAV-aged) and recovered asphalt binders; Fourier-transform infrared (FTIR) spectroscopy was used to identify and quantify the amount of functional groups present in the asphalt binders; and gel permeation chromatography (GPC) was used to determine the molecular size distribution within the asphalt binders. In addition, this study investigated the effect of the extraction and recovery procedures on the recovered binder properties. It was observed that the extraction and recovery procedures had little effect on the rheological properties of PG 70-22, but a significant effect on PG 64-22. In addition, $G^{*}/\sin \delta$ and $G^{*}\sin \delta$ values were obtained for the asphalt binders recovered from short-term and long-term oven-aged HMA mixtures that were comparable to or slightly higher than those recovered from foamed WMA mixtures. This indicates that foamed WMA mixtures undergo comparable or lower levels of aging than traditional HMA mixtures. The DSR test results were confirmed by the FTIR and GPC test results.

Plasterboard components are widely used in current buildings worldwide. Despite their extensive use, the lack of a comprehensive test campaign on plasterboards in current literature is noted. An extensive test campaign consisting of 302 tests on plasterboards is performed both in tension and compression. A set of five plasterboard typologies is selected. The tests are performed in two different load directions: parallel or transversal to the direction of production. Tensile strength of the boards was systematically smaller than compressive strength, whereas elastic modulus values in compression and in tension are similar. Two different regression laws are defined for compression and tension behavior. An orthotropic behavior was exhibited in cases where the boards are loaded in tension. The significant influence of board thickness on their mechanical properties was also highlighted. Finally, the most appropriate probability distribution function was estimated for several mechanical parameters, and the corresponding data dispersion is evaluated. The performed activities can be used as reference for future numerical studies involving plasterboards.

Sustainability is becoming a major concern for geotechnical engineering as this industry consumes considerable amounts of resources. Efforts have been made to reduce such impacts by incorporating industrial wastes in new materials and identifying materials that have a low burden on the environment. Nonetheless, there is still limited guidance on how to develop resource-efficient dosages for geotechnical materials. On the other hand, equations in which strength is formulated as a function of experimentally controlled variables (e.g., lime content or dry unit weight) have been devised for such materials. This means that distinct combinations of values can be assigned to these variables to attain a target strength. These equations allow the rate of gains in strength provided by each variable to be jointly assessed with the resources required to produce such gains. This manuscript proposes a method to rank such variables when jointly considering mechanical and environmental performances. This ranking allows a number of strategies to develop resource efficient dosages to be elicited. The proposed method is used to devise guidelines for a lime-treated soil. Results show that the main strategy is to increase dry unit weight rather than lime content as the former is more efficient when jointly considering gains in strength and resource consumption. The method presented herein is an initial effort towards the formulation of a comprehensive framework for optimizing the dosages of geotechnical materials, integrating environmental and mechanical considerations.

There has been a significant increase in axle loads, speed, and traffic volumes in railway transport systems in recent years. This has stimulated improvements of track component characteristics from the aspects of stability, durability, and energy absorption. This research has focused on concrete sleepers as the main element of the track superstructure. It investigates the efficiency and practicability of using steel fibers in improvements of sleeper characteristics, including load-carrying capacity, energy absorption, and dynamic properties. This is done through a comprehensive experimental work. Extensive static and dynamic tests were carried out on the prestressed concrete sleepers designed and manufactured with various amounts of hybrid steel fibers (a mixture of short and long fibers) and different numbers of prestressing steel wires. The research results have indicated that the use of hybrid steel fibers in the sleepers leads to an increase in load-carrying capacity, energy absorption, and consequently improvements in the service life of the sleepers. The results have also indicated that the new sleepers have the same dynamic characteristics (natural frequency, damping ratio, and mode shapes) as the conventional ones. Considering the improvements made in the mechanical properties of the new sleepers and the resulting construction costs, it has been shown that the new sleepers are more effective and cost efficient for high-speed tracks when compared with the conventional ones.

This study investigates the effect of high temperature on microstructure and mechanical properties of high-toughness fiber-reinforced cementitious composites. Pore size distribution, microstructure, and mechanical properties are tested after exposure to 20, 200, 400, 600, and 800°C. The variation of chemical compositions after elevated temperatures leads to color changes of fibers and matrix, which can be clearly verified from energy dispersive X-ray analysis (EDAX). Furthermore, pore size of the composites decreases gradually at 200 and 400°C. Compressive strength varies consistently with the microstructure, showing that fire damage does not inevitably lead to the deterioration of mechanical properties. However, residual flexural properties decrease significantly because of the melting of PVA fiber. As a covering layer of the structures, the composites exhibits excellent fire protection to reinforced concrete columns.

Fiber-matrix bond properties of alkali-activated slag cements (AASC)–based composites have not been studied comprehensively in literature. Within the scope of this study, the effects of AASC matrix phase composition and the silicate modulus of activator solution on the pullout behavior of steel fiber were investigated under water- and steam-curing conditions. Test results showed that AASC have a superior bond strength compared to portland cement (PC). Bond strength of AASC mortars with a compressive strength greater than 18 MPa were found higher than that of PC mortar with a compressive strength of 55 MPa. When the compressive strength of AASCs is higher than 40 MPa, the bond strength of AASC exceeds the bond strength of PC mortars that have compressive strength of 120 MPa. Microstructural analysis revealed that the map cracking in the fiber-matrix transition zone, which was induced by high drying shrinkage of AASC, can be eliminated by incorporating pozzolans. Consequently, it is possible to produce much higher-performance fiber-reinforced composites by using AASC owing to its superior adherence to steel fiber.

AM2, an airfield matting system made from extruded 6061-T6 aluminum alloy, is used to construct temporary aircraft operating surfaces. This matting system can support heavy aircraft loads even when placed directly over graded in situ soils. This paper presents the development of a test protocol and corresponding relationships that can be used to predict fatigue failure of AM2’s mechanical joints over any subgrade California bearing ratio (CBR) when subjected to high tire pressure single-wheel aircraft loading. First, full-scale simulated aircraft traffic experiments were conducted over sections of AM2 installed on subgrades with CBRs of 6, 10, 15, 25, and 100% to monitor subgrade deformation and fatigue failure. An increasing amplitude displacement function developed from a subgrade deformation model was then used to create a new laboratory procedure to simulate fatigue experienced by the matting system’s complex mechanical connectors under moving aircraft loads. Laboratory test results had strong correlations with field data and, therefore, have promise for predicting fatigue performance without the expense of full-scale experiments.

The dynamic deformation behavior of ultrasoft soil foundations is one of the major concerns in the field of geotechnical engineering. In this study, a series of cyclic triaxial tests with different vibration frequencies, $f$, and cyclic stress ratios, CSRs, has been conducted to investigate the dynamic deformation and cyclic degradation of ultrasoft soil from Binhai, China. The results reveal that the vibration frequencies have a substantial influence on the dynamic deformation of the ultrasoft soil. The inflection frequency is 3 Hz. The value of the strain at failure of ultrasoft soil is between 0.99 and 1.6%, lower than that of general soft soils. The effect of $f$ on the degradation index, $\delta$, of ultrasoft soil is different from that of general clay soils. In addition, CSRs have a significant influence on the axial strain development mode. Compared with general soft soil, the effect of CSRs on the degradation index of ultrasoft soil is discussed.

Difficulties presented by the direct tensile test of nonhomogeneous, brittle materials were circumvented by the proposal of an indirect tensile test for concrete, known in the literature as the Brazilian test, which found applications in the technology of concrete, rocks, ceramics and other materials. Relationships between the predictions of the Brazilian test and the results of both the direct tensile test and the unconfined compression test have been proposed on the basis of experimental evidence. On the other hand, developments in numerical fracture analysis allowed for the examination of the fracture process in the test, including the consideration of scale and rate effects. The discrete element method was used to determine the nonlinear response of brittle solids and to predict the response of simulated concrete samples subjected to indirect tensile tests. This paper extends this approach to more precisely quantify the role of factors such as the width and stiffness of the strips inserted between the press platens and the sample cylinders. The flexibility of the strip exerts a marginal influence on the result of the test. The predictions of the indirect splitting tensile test would significantly improve by replacing the wood strip (with $\beta =0.1$) by a metallic strip with curved lower surface and larger width. A thorough experimental program should be carried out to establish the optimum width for normal concrete and/or other materials or sample sizes.

Two forms of microstructures in different types of asphaltenes and asphalt binder samples were discovered by using transmission electron microscopy (TEM). The first type of the microstructures is needle-shaped with a crystalline structure, while the second type is plate-shaped without a regular pattern. The size of the microstructures ranges from a few nanometers to several micrometers. The microstructures are more prevalent in field-aged asphalt binder and asphaltenes samples than those in nonaged ones. Experimental results indicate that both forms of microstructures are not made of wax, but asphaltenes molecules. The two forms of asphaltenes microstructures differ in morphology, microscopic structure, chemical composition, and resistance to electron radiation damage, indicating that they are formed by different mechanisms and have different physicochemical properties. Both types of microstructures also show thermal stability at elevated temperatures. The prevalence, size, and shape of the microstructures in field-aged asphalt binder may impart significant impacts on binder engineering properties in pavement use as well as its behaviors in recycling or rejuvenation. Hence, the microstructures are believed to be the key to understanding asphalt binder aging, aging control/reversal methods. More studies are needed to investigate the newly found microstructures.

The present study describes the reuse of mineral-cement emulsion (MCE) mixtures from old and damaged pavements. Different recycling and compaction methods are presented and evaluated using strength tests to find the optimal composition. Marshall, gyratory, and static compaction methods were used and the results were analyzed. The methodology included measurements of Marshall stability and flow, compressive strength, frost resistance, and air void content. Analysis of the results showed a strong correlation between the compaction method used and the final result. The data show that a comparison of compaction methods is possible only when the methods are modified appropriately and the corresponding adjustments of MCE mixtures were proposed. The modifications included variations in compaction conditions. The optimal number of gyrations and the minimal height of the specimen were determined as a recommendation for future comparison with the Marshall method. Tests of the MCE mixtures showed that by implementing the suggested laboratory compaction methods, it is possible to obtain satisfactory correlation rates between the laboratory and in situ MCE features.

Thermal cracking is the predominant flexible pavement distress in northern climates, causing transverse cracks perpendicular to the direction of traffic. The indirect tensile (IDT) strength test is currently the most widely used method to characterize thermal cracking susceptibility and is required in mechanistic empirical pavement design. When laboratory IDT strength testing data are not available, it is predicted by pavement design software using mixture volumetrics and Superpave performance grade (PG) of the binder. The primary purpose of this study was to examine the IDT strength characteristics of asphalt mixtures commonly used by the Michigan Department of Transportation (MDOT) and to develop improved prediction methods for IDT strength. Laboratory testing of 62 unique MDOT mixtures (a total of 201 samples with replicates) showed that the pavement design software predicted the IDT strength very poorly. Three models were developed to improve the accuracy of IDT strength prediction. First, the current software’s predictive equation for IDT strength was locally calibrated. Then, an improved statistical model was developed to predict low-temperature IDT strength, based on the information typically available in job mix formulas. Finally, an artificial neural network (ANN)–based model was developed to further improve the accuracy of the low-temperature strength predictions using information from job mix formulas. All three models showed increased prediction performance when compared with the software’s IDT strength prediction.

Cement asphalt emulsion paste (CA paste) is known to be a low-yield stress suspension suitable for many applications in which high flowability is desired. The factors that lead to the low yield stress of CA paste are still unknown, however. The effect of the components in CA paste on the rheology of fresh CA paste is studied to reveal the primary factors that lead to the low yield stress. The effect of emulsifier and superplasticizer on cement paste, the effect of asphalt emulsion, and viscosity modifying agents on CA paste are studied. Results indicate that emulsifier can reduce the yield stress and apparent viscosity of cement paste, but the effect of emulsifier is small compared to the effect of the superplasticizer. The low yield stress of CA pastes is primarily because of the combined effect of superplasticizer and asphalt emulsion. Both CA paste without superplasticizer and cement paste have high yield stress. Viscosity modifying agents can significantly increase yield stress of CA paste without changing minimum apparent viscosity, which is an efficient way to change the rheological behavior of CA paste with low yield stress.

The reuse of recycled construction and demolition (C&D) aggregates in civil engineering infrastructure applications has been considered a low-carbon solution to replace conventional pavement aggregates. Evaluating the strength development mechanism and interparticle flow of forces in geopolymer stabilized C&D aggregates will provide fundamental understanding of the behavior of stabilized C&D aggregates. The C&D aggregates studied are reclaimed asphalt pavement (RAP), recycled concrete aggregate (RCA), and crushed brick (CB). The performance of alkali-activated fly ash (geopolymer) on the stabilization of C&D aggregates, under different curing conditions and sample preparation methods were studied. Fly ash was used as the precursor for the alkali-activated binder that was used to stabilize the C&D aggregates. The effect of low and high content of fly ash–based geopolymers on strength development of recycled materials is investigated for the first time. Sodium silicate and sodium hydroxide were used, with different ratios, to intensify the alkaline environment for fly ash to accelerate the strength development of the mixture. The effect of static and dynamic compaction on the density and strength development was investigated for both low-content fly ash and high-content fly ash. Temperature treatment of geopolymer stabilized C&D aggregates up to 40°C and humidity curing in the moisture chamber for 7 days indicated improvement of the strength development of the mixture. The results of unconfined compressive strength (UCS) and resilient modulus testing of geopolymer-stabilized C&D aggregates indicate that alkali-activated fly ash is a viable binder for the stabilization of C&D aggregates.

Wheel track rutting is one of the most important issues associated with asphalt pavements. The considerable increase in highway traffic loads, notably in developing countries, has accelerated the appearance of this type of deformation. This defect leads to the accelerated degradation of the pavement and considerably reduces the level of road safety provided to the users. This paper presents the results of a study on the effects of organophilic nanoclay on the rheological behavior and performance to permanent deformation of asphalt mixtures. Two asphalt mixtures designed according to a standard methodology were investigated. A reference mixture was produced with a conventional asphalt binder and the other mixture with an asphalt nanocomposite prepared with nanoclay. The rheological evaluations were carried out on four-point fatigue test equipment under different load frequencies and test temperatures. For each test condition, the complex modulus ($|E^{*}|$) and phase angle ($\varphi$) were determined, along with the $|E^{*}|/\sin \varphi$ parameter associated with the permanent deformation behavior of the asphalt mixture. The resistance to permanent deformation was tested in a traffic simulator. The results obtained demonstrated an improvement in the rheological properties and resistance to permanent deformation of the asphalt mixture with the addition of organophilic nanoclay.

Using recycled materials in construction of asphalt pavements yields both economic and technical advantages. Recycled asphalt shingles (RAS) and reclaimed asphalt pavement (RAP) are two major sources to serve this purpose for which proper design and characterization are key elements. In this study, engineering properties of asphalt concrete containing RAP and RAS under dynamic loading were investigated. Three asphalt mixes were designed and included in this research: a conventional mix with no RAP/RAS as a control, a mix with 35% RAP, and finally a mix with 35% RAP and 5% RAS. A conventional resonant column (RC) apparatus was retrofitted and used for testing the specimens in torsional mode. Testing was conducted at five temperatures ranging from 10 to 45°C. Damping ratios and moduli of the mixes were analyzed and compared to assess the effect of the recycled materials on dynamic properties of asphalt concrete. Results clearly show the impact of RAP and RAS in increasing the mix stiffness. The study also included uniaxial dynamic modulus (DM) testing of the control mix to compare the moduli measured at high frequencies through RC testing to those estimated by the DM master curve through extrapolation. Results show that the modulus obtained from RC testing correlates well with that extrapolated from DM tests. Results also indicate that the accuracy of such correlation is significantly increased once dependency of Poisson’s ratio on modulus is incorporated.

This paper reports a systematic study conducted during application of pumping concrete for distances up to 2.432 km at an actual construction site. Admixture design for maintaining flowable concretes through 12 h, while setting within 20 h and developing stripping strength in 30 h was critical. Full-scale field trials for checking field behavior of concrete, pump, their interactions and manpower training are synergistic; weather plays a critical role. The mixes are to be adjusted in response to change in ambient temperatures and differences between production and placement temperatures. A distance-dependent mixture design approach was used for optimizations that lead to the development of a distance-paste-binder curve.

As a long-life road surfacing material, epoxy asphalt has many benefits such as high strength, excellent bonding properties, high temperature stability, and high resistance to low temperature cracking. With the increasing use of epoxy asphalt in orthotropic steel bridge deck pavements, there has been an urgent need for a fast, easy, and reliable maintenance method. Microwave heating provides a promising method for epoxy asphalt curing. This study explored the possibility of using microwave heating for epoxy asphalt curing and investigated the effects of microwave heating on chemical and physical properties of epoxy asphalt. An epoxy asphalt suitable for microwave heating was prepared, tested for its tensile properties, and characterized using thermal analysis, infrared analysis, and microscopy tests. The results showed that the epoxy asphalt cured by microwave heating had a better ductility than that cured by conventional heating. The fluorescence and scanning electronic microscopy (SEM) observations showed that microwave curing could reduce the size of asphalt particles dispersed in the continuous phase of epoxy, thus improving the compatibility between epoxy resin and asphalt.

Compressed stabilized earth blocks (CSEBs) are typically produced with laterites because of their abundance in the tropics. However, the formation of laterites is governed by the nature of the parent rock, the age of the land surface, climate, and topography and drainage conditions resulting in laterites with varying mineral compositions. Because the geotechnical composition of tropical residual soils appears to be largely controlled by their mineral composition, the first level of any classification system should take into account the factors giving rise to their development. This paper summarizes the results of an analysis of the effect of mineralogical composition on the performance characteristics of CSEBs. The results from the X-ray diffraction analysis show that the soil samples consist of varying proportions of quartz and kaolinite alongside other minerals. The results obtained from this investigation show that soils with higher quartz and kaolinite content produced blocks with better performance characteristics and consequently required lower levels of stabilization. The statistical models developed show a significant correlation between quartz content and some performance characteristics of the CSEBs (e.g., compressive strength and water absorption). Kaolinite, on the other hand, did not show any significant correlation. This may suggest that mineralogy of samples may also be a significant criterion for the selection of suitable soils for the production of CSEBs.