Journal of Materials in Civil Engineering

Many concrete water-distribution systems are past their service life and need repair due to leaks associated with cracks. Autogenous healing of concrete cracks and leaks can sometimes occur if the chemistry of distributed water is favorable, whereas small leaks eventually cause pipe failures if water chemistry is unfavorable. This study evaluates autogenous healing of simulated potable-water concrete distribution pipe leaks. Cement mortar pipe sections with leaks created by controlled cracking, extremes of decalcification, and water chemistry are studied, with the trajectory of leaks (and autogenous repair) monitored by permeability. Cracked specimens show significantly high permeability compared with decalcified specimens. The healing solutions reduce the permeability of the damaged specimens by as much as a factor of 12.5 for cracked specimens and by a factor of 3.5 for decalcified specimens. The healing process essentially requires solutions with supersaturated amounts of calcium carbonate to significantly reduce permeability of the cracked or leached specimens.

Fly ash, a supplementary cementitious material, is normally used in conjunction with portland cement to improve the durability properties of concrete in the field, such as sea-crossing bridges, high-speed railways, and mass concrete in dams. Currently, these concrete structures are frequently exposed to sulfate environments. The object of this paper is to investigate the relationship among content of calcium hydroxide (CH), formation of gypsum, and compressive strength, as well as the relationship among the formation of ettringite, pore structure, and expansion properties in blend cement paste at long-term sulfate attack, up to 1,110 days. Mercury intrusion porosimetry (MIP) and thermo gravimetric (TG) analysis were used to evaluate the pore structure and content of CH, respectively. The results show that there is a significant negative relationship between CH content and the coefficient of compressive strength during sulfate attack as more gypsum formation is contributed for the loss of strength. Compared to the reference sample, the addition of 20% and 40% fly ash decreased the CH content by 16.7% and 25.1% through the pozzolanic reaction, which reduced the formation of gypsum and prevented the decalcification of calcium silicate hydrate (C-S-H). Crystallization pressure, due to the formation of ettringite in a limited space, is discussed to explain the cracking of cement-based materials. Several harmful pores ($>0.1\mathrm{\mu m}$) were formed in the reference sample due to crystal pressure with the formation of ettringite, which caused the expansion and exacerbated the diffusion of sulfate ions. The pozzolanic reaction of fly ash also improved the pore structures and reduced the degree of supersaturation of ettringite by preventing the ingress of external sulfate ions.

This study examines the merits of applying a biomodifier (Bio-binder, Sustainable Infrastructure Material Lab, NC A&T State University, Greensboro, North Carolina) as a fog sealant on the surface of bituminous materials to delay aging specifically caused by ultraviolet (UV) radiation during pavement service life. This study uses four types of bituminous-based materials: an asphalt binder [Performance Grade (PG 64-22) and three types of crack sealants with varying polymer content and different viscosities. Materials were prepared in small samples on aluminum plates and aged under continuous UV and UV/moisture/condensation conditioning. Changes in the chemical characteristics of the materials were then analyzed using Fourier-transform infrared spectroscopy and energy-dispersive X-ray spectroscopy. The results show that the oxygen uptake of bituminous materials after exposure to UV aging are significantly lower in specimens covered with Bio-binder compared with uncoated ones. The complex modulus and creep compliance were measured using a dynamic shear rheometer. The complex modulus for asphalt binder samples showed an increase that could be due to partial diffusion of the biomodifier in the specimens. However, in sealant samples in which the Bio-binder was removed prior to performing the experiments, the shear modulus showed a significant decrease, indicating that the sealants covered with Bio-binder remained softer compared with the uncovered samples. The results also showed a higher nonrecoverable creep compliance and a lower percent recovery at 3.2 kPa strain rate for specimens coated by Bio-binder compared with the samples with no coating, showing that the fog sealant can effectively improve properties of the sealant samples. Overall, the findings demonstrate that Bio-binder can be a promising candidate to be used as a fog sealant for bituminous binder and crack sealants to delay UV aging.

Characterizing crack propagation of asphalt mixtures is helpful for optimizing mixture design and predicting cracking performance of asphalt pavements. This paper explores a new method based on the cyclic semicircular bending (SCB) test to characterize crack growth rate and evaluate fatigue cracking resistance of asphalt mixtures. For characterizing crack growth rate, the difficulty is the measurement of crack length during testing. A digital image correlation (DIC) was used to track the crack propagation during the test, which was used to establish a correlation curve with the corresponding crack mouth opening displacement (CMOD) measurements. Four sulfur-extended asphalt (SEA) mixtures with different dosages of sulfur were evaluated with the proposed cyclic SCB test. The results of the test fitted well to the Paris law function, and the Paris law coefficients of SEA mixtures were identified. They were also consistent with the test results from the monotonic SCB test and horizontal strain field of the crack tip characterized using the DIC. The cyclic SCB test showed substantially lower coefficients of variance in terms of the number of cycles to failure compared with other traditional fatigue tests such as the bending beam fatigue test and the Texas overlay test. Regarding the effects of sulfur, test results showed that a low level of sulfur addition, such as 15%, softens asphalt binder to the stage where more damage can be induced in a controlled-stress mode of loading, while extra sulfur would act as fillers to stiffen the asphalt binder when the dosage was greater, such as 30%–45%.

Thermal cracking is a perennial concern for large-volume concrete projects; for instance, dams and foundations. The concrete coefficient of thermal expansion (CTE) is well recognized as a key parameter influencing thermal cracking of concrete. Aggregates are volumetrically the predominant constituent of concrete. Aggregate shape varies due to rock type and manufacturing methods. However, its effect on concrete CTE has rarely been studied. This study develops an analytical approach based on effective self-consistent theory to predict concrete CTE considering coarse aggregate shape. The analytical model is validated with laboratory tests. It is found that coarse aggregate shape has little effect on concrete CTE. The influences of other factors on concrete CTE are also studied, including coarse aggregate gradation and type, coarse aggregate, and cement mortar CTEs.

This paper studies the effectiveness of calcium sulfoaluminate (CSA), which has a much lower carbon footprint than conventional ordinary portland cement (OPC), in geotechnical applications which use high water:cement ratios. Unconfined compressive strength is used to compare OPC and CSA treated sand. Apart from its ecofriendly characteristics, CSA-treated sand has significantly high initial strength development due to the fast hydration of ye’elimite. Two curing methods are used to simulate wet field and dry field conditions. For both OPC-treated and CSA-treated sand, the samples cured underwater have lower strength than the dry-cured samples. However, the strength reduction due to wet curing is less for CSA than for OPC. In addition, recoverable strength loss is observed in CSA-treated sand subjected to wet curing between 7 and 14 days, which is not observed in dry curing. The effect of water content on the strength of cemented sand is presented. The use of CSA would help move toward a sustainable approach to reduce the carbon footprint in geotechnical applications.

Cement-stabilized rammed earth (CSRE) is used for load-bearing walls. CSRE is a monolithic construction that is constructed by compaction of processed soil in a rigid formwork. The compacted layer thickness varies between 100 and 150 mm. Generally, a dry density in excess of $\mathrm{1,800}\mathrm{kg}/{\mathrm{m}}^3$ is achieved for CSRE through compaction. Apart from the need for very rigid/stiff formwork, a considerable amount of compaction energy is expended in achieving such high dry densities. The paper (1) examines the influence of layer thickness on characteristics of CSRE; and (2) explores use of superplasticizers for reducing the compaction energy. Considering four different layer thicknesses, the strength and stress–strain characteristics of CSRE were experimentally determined. The compaction energy and characteristics of CSRE were monitored by using different dosages of superplasticizer additive. The major findings of the investigations are (1) optimum compacted layer thickness giving maximum compressive strength for CSRE is 90–100 mm; and (2) the compaction energy reduces by half with the use of 0.65% of superplasticizer with enhanced strength and modulus for CSRE.

In an attempt to improve the sustainability of construction and reduce portland cement (PC) consumption, the use of supplementary cementitious materials (SCMs), such as ground granulated blast-furnace slag (GGBS), has become a common practice. On the other hand, to increase the durability of cementitious composites, various internal curing agents, including superabsorbent polymers (SAPs), are often used. Owing to their high capacity to absorb, retain, and release water, SAPs can provide additional water for continuous hydration and lead to more homogeneous microstructures. They are usually neutralized by alkali metals (sodium and potassium) to increase their absorption capacities and keep them stable in PC cementitious matrices. This article discusses the applicability of SAPs in blended systems. It aims to evaluate the effect of GGBS on the water absorption capacity and stability of three partially neutralized SAPs. SAP swelling capacity and kinetics of absorption, pH of binder solutions over time, and the mechanical properties of PC-GGBS matrices are analyzed. The results show that alkali content of up to 4% by weight leads to a GGBS system that is comparable to a stable PC system. Above this limit, SAP degradation starts to take place due to ion exchange with GGBS solution components, resulting in lower compressive strength compared to PC matrices. Thus, the excess of alkalis in SAP networks plays an important role in GGBS aqueous solutions.

The implementation of roller-integrated continuous compaction control (CCC) technology on three types of granite residual subgrade (GRS) was evaluated in this work; the three types of GRS are cement-treated GRS, GRS with aggregate, and natural GRS. Four common roller measurement values were calculated and analyzed: compaction meter value (CMV), compaction control value (CCV), machine drive power (MDP), and acceleration amplitude (AA). Both the sand cone test and the geodetic leveling test were conducted to evaluate the soil compaction efficiency during construction. Results revealed that cement-treated GRS could be compacted more easily than untreated materials with the same compaction effort. The correlation analyses between point measurements and roller measurement values indicate that the optimum roller measurement values for the cement-treated GRS, the GRS with aggregate, and natural GRS are CMV, AA, and CMV, respectively. Meanwhile, roller measurement values strongly rely on roller operation parameters and lift thickness, especially for the cement-treated GRS.

This study investigates the creep behaviors of basalt fiber–einforced polymer (BFRP) tendons as a prestressing material in salt solution. Static tensile tests and creep tests were conducted on the BFRP tendons after aging subjected to salt solution. Experimental variables included the aging temperature and aging duration. The tensile strength, elastic modulus, creep strain, and creep rupture stress of the degraded BFRP tendons are analyzed and discussed. Furthermore, a scanning electron microscopy analysis was conducted to clarify the degradation mechanism of the creep behavior. The results show that the aging temperature and duration in salt solution have a negligible effect on the creep strain increase of BFRP. The ratio of the creep rupture stress to the original tensile strength of BFRP tendons aged in salt solution decreases considerably. However, the ratio of the creep rupture stress to the degraded tensile strength exhibits no degradation, which indicates that the impact of the sustained load is independent of the impact of the salt solution on the mechanical behaviors of BFRP tendons. The appearance of corrosion channels in BFRP tendons, which accelerate successive fiber-matrix debonding under a sustained load, is determined to be the main cause for the degradation of its creep behavior in salt solution. These results provide a reference for the determination of the long-term stress of BFRP tendons used in offshore structures.

Aeration of cement and cement mortars is a critical step in the manufacture of aerated concrete. Presently, metallic powders and foams are used for air entrainment. This paper explores a new method of air entrainment. Aerated concrete has been prepared in the laboratory with separate systems of cement-sand, cement-fly ash, and cement-GBFS (granulated blast furnace slag). Each system has been aerated with different volumes of colloidal gas aphrons (CGAs). CGAs are used as an aerating medium, and a kinetic generation model is studied using anionic, cationic, and nonionic surfactants. The paste density and air content have been measured for the green mass of mortar produced. The resulting aerated concrete after curing has been evaluated for its properties, e.g., porosity, dry density and, compressive strength. The microstructure of aerated concrete produced by the CGAs method of aeration has been studied using scanning electron microscope, which confirmed that the CGAs can create stable air voids in the cement mortar leading to its successful aeration. The method of manufacture of aerated concrete by the CGAs route of air entrainment has the potential for utilization of higher percentages of industrial wastes like fly ash and GBFS.

Rejuvenators are primarily added to aged binders to restore their properties by lowering their stiffness and improving their stress relaxation. The type of interaction that takes place between the rejuvenator and the binder is still under extensive study. This research aims at investigating the extent by which the performance grade (PG) and source of the original binder affect the performance of a soybean-derived rejuvenator. The rejuvenator was added at a dosage of 6% and 12% by weight of the binder to three distinctly different binders, namely a PG58-28 binder, an extracted reclaimed asphalt pavement (RAP) binder, and a residuum oil super critical extraction (ROSE) unit bottom binder. The binders were selected so that they varied significantly in terms of their properties, performance grade, and source. The rheological properties of the rejuvenated binders were studied using a dynamic shear rheometer (DSR) and bending beam rheometer (BBR) at different stages of aging. Using the DSR, temperature-frequency sweeps were conducted and the complex shear modulus master curves as well as the phase angle master curves were constructed. The data from the master curves were used to assess changes in fatigue and rutting parameters with rejuvenation. The fatigue behavior was further investigated using linear amplitude sweep testing. The results indicate that the rejuvenator had a similar effect on the binders; however, the extent of rejuvenation was more pronounced for the stiffer binders.

The performance of reactive MgO cement (RMC)-based concrete formulations is determined by the carbonation process, which is hindered by the inadequate ${\mathrm{CO}}_2$ dissolution in the pore solution. This study addresses the improvement of carbonation and associated performance of carbonated RMC-based concrete samples via the introduction of sodium bicarbonate (SBC) and sodium chloride (SC). The use of these additives increases the initial pH, which accelerates the dissolution of ${\mathrm{CO}}_2$ within the pore solution. The influence of SBC and SC on the progress of hydration is evaluated by isothermal calorimetry and pH measurements. Mechanical performance results are supported by X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), which identify the formation and morphology of final phases. The presence of SBC and SC enhances the dissolution of ${\mathrm{CO}}_2$ and improves the content and morphology of carbonate phases, leading to the formation of a strong carbonate network that increases sample performance by $>100\%$ at 28 days.

The facture failure of asphalt concrete at low temperature is one of the main deterioration modes for asphalt pavement. This study combines experimental tests and heterogeneous simulations to analyze the fracture properties, the internal tensile force, and the crack propagation of asphalt concrete in three fracture loading modes (mode I fracturing, mode II fracturing, and mixed mode I and II fracturing) and at four temperatures ($-15°\mathrm{C}$, $-6°\mathrm{C}$, 0°C, and 10°C). The fracture loading mode and temperature have significant effect on the fracture properties, the internal tensile force, and the crack propagation. Results show that (1) the fracture toughness in mixed mode I and II fracturing is the lowest, whereas the crack velocity in mode I fracturing is the fastest; (2) the crack path of asphalt concrete subjected to shear loading condition is more complex; (3) the propagation trend of the main cracks at $-15°\mathrm{C}$ and $-6°\mathrm{C}$ is similar, and passes through aggregates and mastics directly; (4) although the main crack at 0°C still passes through aggregate, it tends to cross the aggregate edge and passes through the aggregate/mastic interface; (5) deflection of the main crack occurs when the path of least resistance is around a relatively strong aggregate and passes along the aggregate/mastic interface at 10°C; and (6) the maximum internal tensile force and the number of failed contacts are consistent with the fracture toughness and the crack morphology, respectively.

Soft and semisolid states of fine-grained soils and clay minerals (FGS-CMs) are frequently dealt with during execution of infrastructure projects located in the coastal areas, analysis of natural hazards, and mineral processing. In most of these cases, the FGS-CMs flow like a slurry, and hence determination of their rheological characteristics becomes essential. However, test methods and approaches available for determining the rheological behavior of the FGS-CMs when they transform from the solid to the liquid state are yet to evolve. This study uses a parallel-plate rheometer, which is widely used for rheological characterization of complex fluids (i.e., fluids which exhibit yield stress), to determine the rheological parameters (i.e., yield stress, ${\tau }_y$, and strains) of the FGS-CMs with a consistency near the liquid limit. A critical analysis of the existing protocols that are used to determine ${\tau }_y$ and their applicability to FGS-CMs is conducted. The constant shear-rate (CSR) test, when conducted at low shear-rate, yields the most accurate ${\tau }_y$ of FGS-CMs. Subsequently, the results are used to develop a generalized relationship which explains the variation of the ${\tau }_y$ of the FGS-CM with the consistency represented as water content normalized with respect to the liquid limit. Furthermore, to understand the nature of strains that develop during the preyielding regime of FGS-CMs, creep-relaxation (CR) tests are conducted by imposing stress equivalent to different fractions of ${\tau }_y$. The results from CR tests were utilized in the development of a novel methodology to determine the elastic component of the shear modulus, $G_E$, of FGS-CMs. This study reveals that FGS-CMs behave as a linear elastoplastic material in the preyield stage, contrary to the much expected purely elastic response, providing a new insight in the realm of contemporary geomechanics.

The present study investigated effect of fiber type and hybrid modes on flexural toughness and fracture mechanics behavior of ultrahigh-performance concrete (UHPC) with coarse aggregates was investigated. Results showed that with inclusion of coarse aggregate, UHPC had a higher compressive strength and elastic modulus, and that different fiber types and hybrid modes act similarly. Coarse aggregate brought a disadvantage to bonding strength, dispersion coefficient, and orientation factor of steel fiber. For UHPC mixtures with coarse aggregates, the effect of fiber type and hybridization was slight on the first cracking strengths, but it was significant on the ultimate flexural strengths. In addition, compared with UHPC beams with smooth fiber, those with hooked-end fiber blended with smooth fibers had a better flexural performance, i.e., flexural toughness values, fracture energy, and characteristics length. Therefore, fiber hybridization was one of most effective alternatives to improve the flexural toughness and fracture mechanics behavior of the UHPC incorporating coarse aggregates.

The need to reduce the world’s ecological footprint has encouraged the construction sector to look for more innovative solutions to reuse its waste production. Since concrete waste is one of the biggest waste streams in the sector and in the world, reusing it would largely contribute to solve this problem. Various strategies have been followed and this kind of waste has been mostly used in road pavements activities. However, it has been proved that it is possible to use this waste for current concrete structural elements. This investigation proved that it is also possible to produce high-performance concrete made of both fine and coarse recycled concrete aggregates. It was even possible to produce a type of high-performance concrete made with total replacement of natural aggregates. However, present legislation, in the world in general and in Portugal in particular, does not allow this level of replacement ratio, particularly for fine recycled aggregates. In fact, most of the legislation around the world do not allow to use fine recycled aggregates in high-performance concrete. In this work, a simple specification proposal is presented to incorporate both fine and coarse aggregates to produce high-performance concrete. It was the result of a wide experimental campaign constituted of 3,049 laboratory tests. This specification defines the types of cement mix and the maximum replacement ratios that should be respected to produce five classes of high-performance concrete.

Geopolymer is a cementitious material known for its environmental benefits and characteristics comparable to those of conventional ordinary portland cement. Geopolymer concrete (GPC) is a relatively new construction material that is yet to be regulated by standards due to the high variability in the mix design. This paper thoroughly investigates the mechanical, chemical, and durability properties of three types of GPC in an attempt to improve mix designs. In Type I, four concrete mixes were synthesized with high binder content (43%) and 3%–6% microsilica. In Type II, four concrete mixes were made with moderate binder content (20%) and 0%–6% calcium carbonate. In Type III, one mix was designed with low binder content (15%). High compressive strength (71.6 MPa) was achieved by the M1 mix of Type I. Type II and III mixes showed strengths superior to those of comparable mixes from previous studies. It was found that Type I mixes were more prone to microcracking than mixes with a lower binder content, resulting in poor durability performances. Type II and III mixes performed similarly in the durability tests, which was mainly due to their similar binder contents. It was shown that microsilica and calcium carbonate could be added to GPC mixes without a significant impact on durability performance.

The thermal and strength properties and microstructural characteristics of lightweight composites composed of cement matrices aerated by various methods are evaluated. The influence of methods that increase the overall porosity of the cement composites and their overall effect on the thermal and strength properties of the composites are discussed. The porosity of the composites was increased using either an air-entraining admixture, reactive aluminum powder, or aerogel particles. The porosity distribution graphs determined by using mercury and optical porosimetry are presented. A discussion on the technical difficulties that arise during porosity evaluation of the composites with aerogel additive is reviewed. The increased porosity of individual composites results in a significant reduction of the thermal conductivity coefficients, $\lambda$. Relatively low values of $\lambda$ were observed in concretes aerated with the air-entraining admixture and with aerogel particles. Simultaneously, none of the composites showed any significant decrease of the volumetric specific heat, $c_v$. However, aeration of the composites brought about a strong reduction of the compressive strength. The biggest drops were observed for the concretes with air-entraining admixture.

Asphalt pavements are commonly used for highways and airport runways. In pavement design and analysis, environmental factors such as temperature need to be taken into account to accurately predict the service life of asphalt pavements. The effect of temperature variations on the mechanical performance of asphalt mixtures was investigated at the microscale in this study. X-ray computed tomography (X-ray CT) scanning and digital image processing (DIP) techniques were applied to detect, analyze, and reconstruct the microstructure of asphalt specimens. Based on DIP, indicators related to air voids before and after fatigue testing were obtained and are discussed in this study. The results show that higher test temperatures resulted in larger air voids and promote crack initiation. Asphalt specimens measured at higher temperatures exhibited more prominent cracking characteristics because of decreased bonding capability between asphalt mastic and aggregates and because of decreased strength of the asphalt mastic. Finite-element simulations were conducted to simulate uniaxial compression tests. With increasing temperature, the proportion of larger compressive maximum principal stresses at the interface between the asphalt mortar and the aggregates decreased. Energy dissipation decreased with increasing temperature. The results reveal the significant influence of temperature on the fatigue damage and mechanical responses of asphalt; further investigations should be carried out to facilitate the improvement of the pavement design process.

Lightweight self-compacting concrete (LWSCC) is an advanced concrete that combines the advantages of both lightweight concrete (LWC) and self-compacting concrete (SCC). This concrete provides an excellent solution to decreasing the self-weight of a structure while making pouring easier and removing the construction challenges and complications. This study examined the impact of elevated temperatures on normal-strength lightweight self-compacting concrete (NSLWSCC) and high-strength lightweight self-compacting concrete (HSLWSCC) through its residual properties vis-à-vis compressive and tensile strengths, modulus of elasticity, mass loss, and spalling intensity. LWSCCs were designed using lightweight aggregate (LWA), which replaced coarse and fine aggregates at certain percentages. Three types of LWA used in this study are scoria, perlite, and polystyrene. Mixes consisted of six NSLWSCCs (50% and 100% scoria, 50% and 100% perlite, 20% and 30% polystyrene) and two HSLWSCCs (50% scoria). The residual properties were measured by heating $100\times 200\mathrm{mm}$ cylinder specimens to 100°C, 300°C, 600°C, and 900°C. The result shows that the NSLWSCCs tend to achieve maximum strength at 100°C and then gradually decrease as the temperature increases. But in the case of HSLWSCCs, maximum strength was achieved at 300°C. Minor spalling with bubbles, holes, and cracking was observed at only 900°C in the NSLWSCC, while a major explosion occurred at 300°C in the HSLWSCC. The overall result indicates that the magnitude of loss of strength, mass loss, and intensity of spalling is proportional to temperature after a certain point. This study shows how the strength and thermal stability of LWSCC made from scoria, perlite, and polystyrene changes after exposure to high temperatures.

The strength properties of concrete strengthened with a polymer including phosphazene after exposure to high temperatures is investigated in this study. The Taguchi ${\mathrm{L}}_{25}$ ($5^5$) method was used to reduce the number of experiments and to find the parameters affecting the experimental results. Percentage of phosphazene in the monomer (0%, 1%, 2%, 3%, and 4%), curing period (28, 60, 90, 180, and 365 days), cement content (300, 350, 400, 450, and $500\mathrm{kg}/{\mathrm{m}}^3$), and high temperature (20°C, 200°C, 400°C, 600°C, and 800°C) were chosen as experimental parameters. For the experiments, $100\times 100\times 100\mathrm{mm}$ cubes were prepared. The specimens were removed from water after the end of predetermined curing times and dried at $105\pm 5°\mathrm{C}$. Then, they were exposed to temperatures of 200°C, 400°C, 600°C, and 800°C. The next step was impregnation of the samples with a vinyl acetate monomer containing phosphazene for a 24-h period under atmospheric conditions. The polymerization of specimens was conducted at 60°C for 4 h. The compressive strength, ultrasonic pulse velocity, and changes in weight were determined for the specimens. Furthermore, X-ray powder diffraction (XRD), energy dispersive X-ray (EDX), and scanning electron microscope (SEM) image analyses of specimens were carried out. The findings showed that the best results were found from specimens with low cement content and 3% polymer containing phosphazene. Therefore, this study has found that polymer containing phosphazene can strengthen buildings exposed to high temperatures.

Stabilization methods have been widely used to enhance the strength properties of sand to meet the demands of geotechnical engineering. In this paper, a mixture of organic polymer stabilizer (OPS) and polypropylene fiber (PF) was used as the soil stabilizer to reinforce sand. Laboratory tests were used to study the strength properties of the reinforced sand. Mixtures with different proportions of 1%, 2%, 3%, and 4% OPS and 0.2%, 0.4%, 0.6%, and 0.8% PF were designed for these tests. The mechanism of incorporating reinforcement was studied by images from a scanning electron microscope (SEM). The test results revealed that the strength properties of sand specimens reinforced with a mixture of OPS and PF improved strongly. The addition of OPS-PF provided great enwrapping and bonding ability to keep the sand structure stable. The reinforcements imparted by a mixture of organic polymer and fiber can be chosen as an effective technique to enhance the strength of sand for its efficient engineering application.

Nanoindentation is a powerful tool used to study localized material behavior. However, it is not possible to directly obtain the indentation stress strain from the experimental data. In this study, an axisymmetric finite-element (FE) model was developed to study the nanoscale stress-strain distribution of the nonaggregate phase of asphalt concrete (AC) under aged and unaged conditions. To represent the field condition, the nanolevel response of the nonaggregate phase of AC was studied under fixed and increasing amplitudes of cyclic loads. The developed FE model was also used to study effects of stress variation, frictional coefficient, and bonding between the different AC lifts. From the results, it was observed that creep phenomenon at the nanolevel due to cyclic loading was much faster in the unaged condition. It was also observed that during nanoindentation, material not only undergoes a massive compressive stress, but it also generates a large tensile stress. Although the frictional coefficient was found to have no effect on the nanoindentation response, it was found that bonding between the AC lifts affects the nanolevel response of the nonaggregate phase of AC.

Limited research exists on the benefits of using geogrids to reinforce portland cement concrete structural and nonstructural members. Concrete pavement overlay is one application in which the use of geogrids can potentially enhance performance and in which the use of reinforcing steel bars is subject to various constraints and limitations. Preliminary research findings have shown that the inclusion of geogrids in portland cement concrete leads to a definitive improvement in postcracking behavior in terms of ductility, load capacity, and crack propagation control. Through a rigorous experimental program, this study aimed to verify and further enhance the current knowledge regarding the behavior of geogrid-reinforced concrete (GRC) elements compared to that of plain concrete and steel-reinforced elements. The findings were used in characterizing the behavior of GRC and applying it to a finite-element model developed using ADINA software. The model was then used to predict the behavior of a geogrid-reinforced concrete overlay and compare it to that of a conventional plain concrete overlay over a given flexible pavement structure.

This study used a large-scale cyclic shear test to investigate the interaction mechanisms between a geogrid and its surrounding aggregate in a cyclic loading mode to simulate traffic loads. Interactions at the geogrid–aggregate interface were quantified in terms of a parameter called resilient interface shear modulus $G_i$. The test protocol was derived from the triaxial test to apply cyclic shear loading under different normal stresses. Four interfaces were used in the study, including two types of base-course materials reinforced by a biaxial and triaxial geogrid. Results showed that the cyclic shear test had good repeatability, and the $G_i$ of each interface was a function of both normal stress and cyclic shear stress: $G_i$ decreased with an increasing cyclic shear stress but increased with an increasing normal stress. A modified three-parameter model was used to predict $G_i$, and the model parameters were determined for the three different interfaces. It was found that the three-parameter model could characterize the resilient interface shear modulus very well. The presented cyclic shear test along the resilient interface shear modulus shows enormous potential for characterizing geogrid-reinforced base materials.

This paper summarizes the results of laboratory tests that were performed to characterize the blending of recycled asphalt binders [recycled asphalt shingles (RAS) and reclaimed asphalt pavement (RAP) binders] and virgin asphalt binders and to examine the effects of RAP and RAS on the fatigue cracking resistance of asphalt mixtures. Atomic force microscopy (AFM) was used to characterize the interfacial zone that develops between RAP and a virgin asphalt binder and compare it to the interfacial zone that develops between tear-off RAS and the same virgin asphalt binder. Several asphalt mixtures with RAS, RAP, and combinations of the two were also evaluated, including a control mixture (with no RAP or RAS), a mixture containing 30% RAP, a mixture containing 5% tear-off RAS, and a mixture containing 20% RAP and 3% tear-off RAS. A semicircular bend (SCB) test was used to examine the resistance of the asphalt mixtures to fatigue cracking. The AFM test results indicated that blending occurred between the considered RAP and virgin asphalt binders. A reduction in adhesive bonding energy was observed in the blending zone due to the presence of RAP. However, the adhesive bonding energy of the blending zone was significantly higher than the adhesive bonding energy in the RAP binder. The AFM imaging and force spectroscopy experiments revealed no blending between the considered tear-off RAS material and the virgin asphalt binder. The SCB test results showed that the inclusion of the tear-off RAS in the asphalt mixtures considered in this study significantly reduced their fatigue cracking resistance.

In this study, a dynamic shear rheometer (DSR) and bending beam rheometer (BBR) were employed to characterize the rheological properties of asphalt modified with polyphosphoric acid (PPA) and containing different mineral fillers, forming a material referred to as asphalt mastic. Pulverized limestone filler (PLF), portland cement (PC), and hydrated lime (HL) were selected as mineral fillers. Filler-to-binder (F/A) ratios of 0.6, 0.9, 1.2, and 1.5 were chosen, which are defined as the weight ratio of filler and asphalt binder. The effects of F/A ratio and filler type on the complex shear modulus, phase angle, rutting parameter, fatigue parameter, m-value, and creep stiffness of various PPA-modified asphalt mastics were studied. Regression functions were built to express the relations between rutting parameter, fatigue parameter, creep stiffness, and F/A. The results indicated that the F/A significantly affected the stiffness of the modified asphalt mastic regardless of testing temperature, but had little effect on m-value at low temperatures. The modified asphalt mastics with different fillers showed different stiffness values but almost the same phase angle at the identical testing temperature.