Journal of Materials in Civil Engineering

Eastern hemlock (Tsuga canadensis) is an abundant yet underutilized low-value tree species native to the northeast region of the United States. Developing value-added markets for these trees would improve local forest management and bolster local forest economies. This paper presents an analytical and experimental investigation into the structural capabilities of double vertical glue-laminated eastern hemlock beams that are reinforced with a tensile layer of laminated veneer bamboo (LVB). LVB is a sustainable engineered bamboo product with appreciable and reliable tensile strength. This study examines the effect of LVB reinforcement on failure modes, bending strength, stiffness, ductility, and design values of eastern hemlock beams. Analytical methods are presented for modeling nonlinear structural behavior of beams in bending and inspecting failure modes for different wood strengths, followed by finite-element modeling of both reinforced and unreinforced beams. Four-point bending tests were conducted and the results confirmed the analytical predictions. Tests indicated a 16% increase in beam stiffness and an 81% increase in characteristic (fifth percentile) modulus of rupture (MOR). A methodology is proposed for determining optimum rate of reinforcement for structural performance.

Water damage is a major obstacle to the development of warm mix asphalt (WMA) technology. The addition of antistripping agents (ASAs) increases the difficulty of construction, and it may interact with warm mix additives, resulting in the uncertainty of long-term performance of asphalt mixture. In this paper, a silicone-based warm mix additive with adhesion promoting properties with the proprietary name TEGO, was studied. The warm mixing mechanism of the additive and the effect on asphalt-aggregate interface adhesion was mainly studied. The rotational viscosity (RV) of the asphalt binder and asphalt mortar with different dosages of TEGO at different temperatures was investigated based on the RV test to evaluate the warm mixing efficiency of each component in TEGO from two levels, the binder and the mortar. The infrared (IR) spectrum of asphalt binder before and after modification with TEGO and the two aggregates before and after treatment with TEGO was tested to evaluate the microcosmic mechanism of the additive in the asphalt mixture system. The concept of surface free energy (SFE) and the corresponding indexes [work of cohesion of asphalt, work of adhesion between asphalt and aggregate, and spreading coefficient (${\mathrm{S}}_{\mathrm{a}/\mathrm{b}}$)] was tested to evaluate the workability and water damage resistance of the mixture comprehensively. The results showed that the warm mixing mechanism of TEGO mainly includes viscosity reduction, interfacial lubrication, and improvement of wettability of asphalt to aggregate. TEGO can form a good physical combination with aggregates and it enhances the bonding potential of asphalt with aggregates.

The dynamic shear rheometer was used to investigate the effect of polyphosphoric acid (PPA) and styrene-butadiene-styrene (SBS) modification on the rheological and mechanical behavior of asphalt binder and asphalt mastic. In this research, three SBS contents (2%, 4%, and 6%) and three PPA contents (0.5%, 1%, and 2% by weight of neat asphalt binder) were used. Also, two volume fractions (18% and 35%) of silica filler were selected to fabricate asphalt mastic samples. In total, 1 neat asphalt binder, 6 modified asphalt samples, and 12 modified asphalt mastics were investigated. By using storage and loss moduli data of all samples in a frequency range between 0.1 and 100 Hz at various temperatures between −25°C and 22°C, the Cole-Cole and black space diagrams were plotted and analyzed. The results clearly show that the linear viscoelastic behavior of asphalt mastic is directly related to asphalt binder because of the identical forms of the Cole-Cole curve. An optical microscope was also used to see filler particle distribution in the bitumen structure. The stiffening phenomenon for a volume fraction of 35% was observed in comparison with a volume fraction of 18%, consistent with other previous research work. Adding PPA causes extra stiffening related to formation of the strong structure of PPA between filler particles.

After a comprehensive experimental program on asphalt mastic modified with styrene-butadiene-styrene (SBS) and polyphosphoric acid (PPA) with two filling ratios of 18% and 35%, in this paper, a biphasic finite-element method was implemented to simulate asphalt mastic as a heterogeneous medium consisting of aggregate particles as inclusions within the asphalt binder as the matrix. For this purpose, linear viscoelastic properties of neat and modified asphalt binders including complex shear modulus ($G^{*}$) and phase angle ($\delta$) were obtained from the results of dynamic shear rheometer tests in frequency sweep mode, and the generalized Maxwell model was used to prepare material properties for inputting in ABAQUS, which was used to solve the problem numerically. In this research, the structure of aggregate particles was randomly generated, thanks to the custom software MOA (French acronym for random object modeler), based on the aggregate’s grading curve. Comparing the results of numerical modeling with experimental test results showed that, for a filling ratio of 18% by volume, random generation of inclusions can successfully simulate linear viscoelastic behavior of original and modified asphalt mastic. However, with respect to the higher difference between numerical results and experimental observation of asphalt mastic samples with a filling ratio of 35%, a phenomenon known as stiffening effect was captured by using optical microscope pictures and simulated in a numerical model, which positively eliminated the error of numerical modeling.

Mud pumping has been known to cause severe track degradation and compromise the safety of train operations. Mud pumping is normally the result of simultaneous upward intrusion of fine-grained soils into the ballast voids and downward penetration of ballast particles into the subgrade. Understanding ballast particle movement in clean versus muddy track and under dry versus wet conditions is critical for railroad engineers to make timely and effective maintenance decisions. SmartRock, a battery-powered wireless device that is produced using 3D printing technology and resembles a piece of ballast, can sense, record, and transmit its movement in real time. SmartRocks were recently used in a field test to investigate ballast particle movement in two sections of Norfolk Southern track: a control section with clean ballast and a section with an established mud-pumping problem. SmartRocks were installed in the ballast cribs in each section to investigate particle movement under both freight and passenger trains. The results show the differences of tie and ballast particle movement in clean and mud-spot sections under different freight trains. Tie acceleration was decaying from the previous wheel load under the middle of car in the mud-spot section; ballast particle acceleration appeared to be identical in both sections when the ballast condition was dry but severer in the mud-spot section when the ballast condition was wet. Two characteristics of ballast movement were used to assess ballast condition: peak acceleration range and Arias intensity. These results can be used to identify potential problematic locations on the track to prevent major repair in the future.

Sulfoaluminate cement (SAC)–asphalt emulsion (AE) mortar is a promising repair mortar for cement and asphalt emulsion (CA) mortar (CAM) used in high-speed railways. This paper deals with the rheological performance of SAC-AE pastes. The effects of AE charge type (cationic and anionic emulsions) and AE/SAC mass ratios ($A/C$) on rheological performance are investigated. Results show that the rheological performance of SAC-AE pastes are affected both by interactions between SAC particles and AE particles and by the cement volume fraction. Compared with SAC–anionic asphalt emulsion (AAE) pastes, SAC–cationic asphalt emulsion (CAE) pastes have a higher shear stress with $A/C$ ratios of 0.1–0.7, but slightly lower shear stress with $A/C$ ratios of 1.3–1.6. SAC-AAE with an $A/C$ ratio of 0.3 demonstrates premium rheological performance. Both the Herschel-Bulkley model and the Bingham model fit well with the rheological curves for pastes with $A/C$ ratios of 0–0.7. The non-Newtonian fluidity indicator also confirms this. However, the Bingham model is not fit for SAC-AE paste with $A/C$ ratios of 1.0–1.7. With similar water content, SAC-AE paste with high $A/C$ ratios demonstrates less shear stress than that with low $A/C$ ratios. The rheological performances of portland cement–AE pastes ($\mathit{A}/\mathit{C}$ 0–0.7) are also briefly studied for comparison.

The response of concrete under uniaxial loading is dependent on its density and the height-to-diameter ($\mathrm{H}:\mathrm{D}$) ratio of the specimen, and this phenomenon has received wide attention in research on normal concrete. However, few studies have paid attention to foamed concrete. The objective of this study is to investigate the effects of height-to-diameter ($\mathrm{H}:\mathrm{D}$) ratios on the failure forms and mechanical characteristics of foamed concrete at different densities. For the purposes of this study, four different densities (300, 450, 600, and $800\mathrm{kg}/{\mathrm{m}}^3$) of foamed concrete were prepared. The specimens were all cut to the same diameter (50 mm) but had different $\mathrm{H}:\mathrm{D}$ ratios (0.5, 1.0, 1.5, and 2.0). A series of uniaxial compressive tests were carried out, and the effects of $\mathrm{H}:\mathrm{D}$ ratios on failure forms, compressive strength, and elastic modulus were determined. The results showed that the failure forms of foamed concrete mainly correlated with its density; it was less influenced by $\mathrm{H}:\mathrm{D}$ ratio. The failure forms can be divided into three categories: local crushing failure, splitting failure, and shear failure. The compressive strength ratio decreased with the increase of $\mathrm{H}:\mathrm{D}$ ratio for foamed concrete with densities of 450, 600, and $800\mathrm{kg}/{\mathrm{m}}^3$, while the elastic modulus followed an opposite trend. The variation of the effects of $\mathrm{H}:\mathrm{D}$ ratio on compressive strength ratio and elastic modulus was similar: the higher the density was, the greater the effect. However, it is interesting to note that the $\mathrm{H}:\mathrm{D}$ ratio seemed to have little influence on either of them for the foamed concrete with a low density of $300\mathrm{kg}/{\mathrm{m}}^3$. A prediction model that reflects the variation of compressive strength ratio with the densities and $\mathrm{H}:\mathrm{D}$ ratios was deduced. Two other prediction results were prepared for comparison. Furthermore, a prediction model to reflect the variation of the elastic modulus ratio with the densities and $\mathrm{H}:\mathrm{D}$ ratios is proposed.

The behavior of soil–geogrid interaction is a dominant factor in the long-term performance of geogrid-reinforced earth structures. This study investigates the interaction of sandy soil and the embedded geogrid by pullout tests with the application of a novel testing method using fiber Bragg grating (FBG) sensors. Three influencing parameters are considered: dry density of soil, initial normal stress, and fixing condition of the pullout back end. A displacement-controlled mode is used for the normal stress, and the pullout load is applied at a constant loading rate. The results indicate that for the case with a free back end, the peak shear stress mobilizes from the front face toward the back end with the elongation of the geogrid during the pullout process, before the entire slippage of the geogrid. With higher dry density or higher initial normal stress, the mobilization of the peak shear stress transmits more slowly and the distribution area of shear stress along the geogrid is accordingly narrower due to the corresponding higher resistance by the soil particles. However, the values of the peak shear stress in these two cases are still higher than in cases with lower dry density or lower initial normal stress. By contrast, a different distribution mode of shear stress along the soil–geogrid interface is identified for geogrid with a fixed back end, with maximum shear stress developing near the front face for all pullout displacements.

The mechanical behavior of asphalt binder is highly sensitive to temperature. The manner in which mechanical characteristics change with temperature can also vary significantly from one asphalt to another. With such variations, grading the rutting resistance of the binder by measuring a mechanical parameter of the binder at a single temperature will not be accurate, nor will ranking by determining the temperature at which a mechanical property reduces to a certain value. For precise characterization of rutting resistance of asphalt binders, a high-temperature binder specification should take into account both the sensitivity of mechanical behavior to changes in temperature and the variations in such temperature sensitivity from one binder to another. This study conducts an experimental investigation and an analysis of existing data in the literature to examine the nature of the temperature dependence of the various material parameters used to characterize rutting resistance of binders. Particularly, the nature of the temperature dependence of the nonrecoverable creep compliance from multiple stress creep recovery (MSCR) tests is investigated. The Arrhenius relationship is found to fit the relationship between mechanical properties and temperature in the high-temperature range reasonably accurately. The activation energy corresponding to the Arrhenius equation, however, is found to vary significantly between the binders. Taking these issues into consideration, a new approach to grading the rutting resistance of asphalt binders is developed that uses the Arrhenius-like temperature dependence exhibited by asphalt binders.

This paper studies the influence of curing regimes on the performance and microstructure of polymer-modified mortar. Mortars with five different ratios (0%, 5%, 10%, 15%, and 20%) of styrene-butadiene copolymer (SB) dispersion to calcium sulfoaluminate (CSA) cement at a constant flowability were investigated. Four temperatures (0°C, 5°C, 20°C, and 40°C) and three relative humidities (RH) varying from low ($32\pm 2\%$), middle ($63\pm 10\%$), to high ($96\pm 3\%$) were considered for mortar specimens curing. The experimental results show that the addition of SB improves the flexural and tensile bond strength development but not the compressive strength. The best performance of CSA cement mortar is achieved with 20% of SB. However, the mechanical properties of CSA cement mortar are significantly degraded when the addition of SB is 5%. High temperature and HRH often lead to the formation of ettringite. The larger size ettringite and polymer film intertwine, which makes the CSA cement mortar denser and thus stronger. Accordingly, the properties of CSA cement mortar including flexural and tensile bond strength are significantly improved. Also, it was found that the CSA cement mortar had very low water capillary adsorption rate even when cured at 0°C, and the addition of SB dispersion provides CSA cement mortar better water resistance.

Synthesis of geopolymer using metakaolin (MK) usually requires a relatively high curing temperature, which limits the application of MK-based geopolymers in the practice of civil engineering. With the goal of developing a cementitious composite that can be cured at room temperature, in the present study, ground granulated blast furnace slag powder was incorporated into MK for the synthesis of a geopolymer. With the aid of compressive strength tests, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM), the influence of slag’s impact on the consistency, gelling time, and mechanical properties of the gelling system, as well as the reaction mechanism of the composite system, were investigated. The results showed that the incorporation of slag into MK improved the consistency of the slurry and shortened the setting time. A high-strength paste was synthesized successfully using the MK-slag composite system under ambient temperature curing. Results of XRD and FTIR analyses indicated that MK geopolymerization and slag hydration occurred simultaneously in the MK-slag composite system via alkali activation. The structure of hardened paste consists of both C-S-H-type and N-A-S-H-type gels. The activator module and the MK/slag mass ratio were the main factors affecting the strength of the synthesized products: when the slag replacement ratio was no more than 40%, the strength of the reaction products decreased with an increase of the activator module; when the slag replacement ratio reached or exceeded 60%, the strength of the reaction products increased with the increasing activator module.

This paper uses mixture tests on cores from a full-scale and untrafficked test section to evaluate mixture conditioning protocols intended to simulate asphalt mixture damage experienced from non–load-associated environmental factors. Seven protocols were evaluated against up to 5 years of aging in a hot climate. After matching conditioning protocols to field aging with multiple mixture tests, this paper places secondary emphasis on selecting a suitable mixture test to detect mixture damage caused by non–load-associated environmental factors or laboratory damage mechanisms (i.e., oxidation, moisture, and volume change by freeze-thaw cycles). The data suggest that Cantabro mass loss was appropriate for pairing conditioning protocols to field aging and that 5 days of oven oxidation at 85°C in compacted mixtures was the least severe conditioning protocol considered (simulating 0–2 years of field aging). The protocol that conditioned field cores for 5 days of oven oxidation at 85°C followed by 14 days in 64°C water and one freeze-thaw cycle simulated 4–5 years of field aging in Columbus, Mississippi.

Geopolymers are an environmentally friendly cementitious materials, which have the advantages of high strength, good durability, and stability; however, geopolymers also have some limitations, such as strong brittleness and low toughness. In this experiment, polyacrylamide (PAM) was used to improve the toughness of granulated blast furnace slag (GBFS)–based geopolymers. The water/binder (W/B) ratio was fixed at 0.5; the content of alkaline activator (${\mathrm{Na}}_2\mathrm{O}\mathrm{wt}\%$) was fixed at 6.0 wt%; and the alkaline activator modulus was fixed at 0.8. The effect of PAM (0, 0.25, 0.5, 0.75, 1.0, 3.0, and 5.0 wt%) was investigated with respect to compressive strength, flexural strength, and bending toughness of GBFS-based geopolymers. To determine the reason the bending toughness of GBFS-based geopolymers can be improved with PAM, microscopic test methods such as Fourier transform infrared (FTIR), ${}^{29}\mathrm{Si}$ nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) were also performed. With an increase in PAM content, the compressive strength, flexural strength, and bending toughness of GBFS-based geopolymers increased initially and then decreased. The compressive strength, flexural strength, and bending toughness of GBFS-based geopolymers reached their maximum value when PAM content was 0.5 wt%. Compared to the control specimen, flexural strength/compressive strength ratio of PAM-modified samples showed an increase of 28.3%. The bending toughness of PAM-modified samples increased by 70.4%. Results of microscopic tests proved that PAM elicited a multiscale modification effect on GBFS-based geopolymers at molecular and submicroscopic levels.

The dynamic modulus ($|E^{*}|$) of asphalt mixtures is an important parameter in pavement design and analysis. Although the $|E^{*}|$ values of freshly prepared hot-mix asphalt (HMA) mixtures can be conveniently determined through laboratory tests, the $|E^{*}|$ values of field pavements continuously evolve as asphalt binder ages, and hence are difficult to determine. To examine the effects of asphalt binder aging on the $|E^{*}|$ of asphalt mixtures, a new piece of equipment is developed for the accelerated aging treatment of compacted asphalt mixture specimens. A set of small-size sampling, binder extraction, and recovery methods are used to determine the aging state of asphalt binder in asphalt mixtures. Three types of asphalt mixtures with different aging states are used to study the effects of aging on the $|E^{*}|$ changes. In addition, based on the $|E^{*}|$ test results, mixtures’ volumetric properties, and binders’ rheological properties at different aging states, the accuracy and robustness of six commonly used $|E^{*}|$ prediction models are compared. The developed equipment and method are anticipated to assist with the characterization of aged asphalt mixtures and the further improvement of $|E^{*}|$ prediction models.

Mild steel is one of the most commonly used materials in the construction industry throughout the world, but it is also very vulnerable to corrosion in aggressive environments. There is little research on how corrosion and the hydrogen released from the corrosion process affect the mechanical properties of the corroded steel. The intention of this paper is to present results produced from a comprehensive experimental program designed to investigate the effects of corrosion and corresponding hydrogen on the degradation of mechanical properties of mild steel in corrosive soil environments. Both microstructural analysis and mechanical tests on corroded steel are undertaken at different exposure times and conditions of corrosion. The effects of corrosion and the released hydrogen on steel are examined phenomenologically and analyzed quantitatively at the microstructural level in terms of constituent elements and phase changes, and at the macrostructural level in terms of mechanical properties of strength and ductility. From the analysis of test results, a relationship of cause and effect of corrosion, hydrogen release, and strength reduction is established. The results and their analysis presented in the paper can contribute to the body of knowledge related to the degradation of mild steel, which helps in determining its service life prediction under corrosive environments.

An indentation test was developed to indirectly determine the effective tensile strength of lightly cemented sand by iterative method. The description of the test is followed by a discussion and comparison of the determination of the effective tensile strength of soil under a framework proposed in previous research. Test results reveal that, in general, tensile strength is proportional to indenter diameter ($a$) to specimen diameter ratio ($b$), $a/b$, and has no apparent relationship with the specimen height ($H$) to diameter ratio, $H/2b$. The iterative method provides a more realistic approach to compute the tensile stress beyond the traditional method. In addition, the iterated parameter, $K$, was found to be linearly related to the $a/b$ ratio, for a given specimen, regardless of $H/2b$ value. Finally, the effective tensile strength was verified by an indentation test in conjunction with the pressure plate test and consolidated undrained triaxial test under an unsaturated soil framework.

This paper investigates the feasibility of converting municipal sewage sludge and municipal solid waste incineration (MSWI) bottom ash to a construction material for the dikes of a sludge-only containment. The sewage sludge and MSWI bottom ash were solidified and stabilized by various binders including portland cement, lime, gypsum, and a combination of some of these binders. The solidified/stabilized products, referred to as solidified sludge, would possess higher strength and lower leachability of toxicity, and thus may be beneficially used as the dike construction material. To assess the feasibility of the beneficial use, a series of laboratory tests including strength test, leaching test, wetting-drying test, and biodegradation test was performed to determine the most suitable binder, the optimum mixing ratio, and both short-term and long-term properties of the solidified sludge. It was found that the use of combined cement and gypsum as a binder was most effective in increasing strength of the solidified sludge and decreasing leaching potential. Wetting-drying cycles reduced both short-term and long-term strengths of the solidified sludge. After four cycles (over eight months), the unconfined compression strength (UCS) was decreased by 78% while the cohesion intercept was decreased by 71% and the friction angle by 17%. Biodegradation also reduced the UCS of the solidified sludge, and after the 12-month test, the reduction in UCS was approximately 73%. The findings of the laboratory tests indicated that both short-term and long-term properties of the solidified sludge should be considered in the design and construction of the containment dikes.

This paper aims to use ${}^{29}\mathrm{Si}$ nuclear magnetic resonance (NMR) for investigating the effect of nanofillers on the C-S-H gel structure of hardened cement paste, analyze the modification mechanism of nanofillers from a microscopic perspective, and then provide fundamentals for controlling the macroscopic properties of cement-based materials. Different curing temperatures (25°C and 90°C) and nanofiller types [including $\mathrm{nano}\text{-}{\mathrm{SiO}}_2$, $\mathrm{nano}\text{-}{\mathrm{ZrO}}_2$, $\mathrm{nano}\text{-}{\mathrm{TiO}}_2$, carbon nanotubes (CNTs), nano-boron nitride (nano-BN), and multilayer graphenes (MLGs)] are considered as the influencing factors. Three characterization parameters [polymerization degree, mean molecular chain length (MCL), and hydration degree] are calculated and used as the evaluation indexes. Experimental results show that the incorporation of most types of nanofillers can cause increases in all of these three parameters. With the increase of curing temperature, the polymerization degree of C-S-H gel is further enhanced, because the layered or even spatial network structures of silicate tetrahedron occur in the C-S-H gel. The composites with MLGs present the maximum increase values of polymerization degree, MCL, and hydration degree, by 786.2%, 166.5%, and 27.4% compared with control cement paste, respectively, which is mainly attributed to the nanofiller morphology (unique two-dimensional stacked flake structure) and the functional group (carboxyl-functionalized) on the surface of nanofillers. Fluctuations of polymerization degree and MCL appear in composites with $\mathrm{nano}\text{-}{\mathrm{TiO}}_2$ and with CNTs, relative to the particle sizes, crystal phases, and surface modification of nanofillers. The effect mechanisms of nanofillers on C-S-H gel can be attributed to two main aspects: (1) the nucleation effect and pozzolanic effect (just for $\mathrm{nano}\text{-}{\mathrm{SiO}}_2$) of nanofillers facilitate the cement hydration; (2) the high water absorption capability of nanofillers reduces the proton water inside C-S-H gel, and shortens the distance between the structural groups of Ca, O, and Si atoms. The chemical bonds (ionic bonds and covalent bonds) between these groups are enhanced and the values of polymerization degree and MCL are therefore increased.

This study numerically investigates the failure processes of recycled aggregate concrete (RAC) and natural aggregate concrete (NAC). A two-dimensional simulation based on a discrete-element method (DEM) is conducted with a universal distinct-element code (UDEC) program. RAC is modeled by a combination of rigid Voronoi blocks cemented to each other using contacts for interfaces. The determination procedure of contact microparameters is analyzed, and a series of microscopic contact parameters in different components of modeled recycled aggregate concrete (MRAC) is calibrated using nanoindentation results. The complete stress-strain curves, fracture process, and failure pattern of numerical model are verified by experimental results, proving its accuracy and validation. The initiation, propagation, and coalescence of microcracks and subsequent nonlinear deformation behaviors of cement mortar, modeled natural aggregate, and recycled aggregate concrete are captured through DEM numerical simulations and compared with digital image correlation (DIC) results. It is found that both the new interfacial transition zone and the old interfacial transition zone are the weak links in RAC, where most microcracks initiate and propagate into the cement mortar region. The failure behaviors of MRAC revealed by both experimental and numerical results can effectively provide insights into the failure mechanism and enhancement of RAC.

Increasing the percentage of reclaimed styrene-butadiene-styrene (SBS)–modified asphalt pavement (RAP-SBS) is a promising way to promote the development of sustainable roadway systems. The excellent properties of RAP-SBS are the key to its application in high percentages. This study evaluates the properties of hot mix asphalt (HMA) mixtures with 0%, 30%, 50%, and 70% RAP-SBS replacement in terms of rutting, low-temperature anticracking, and moisture susceptibility. The dynamic modulus test evaluates the stiffness. Both unaged and long-term aged (LOTA) samples are evaluated. Moreover, the effect of freeze-thaw (F-T) cycles on the splitting strength is also investigated. The results show that the RAP-SBS is feasible to recycle, and HMAs mixture with higher percentages of RAP-SBS exhibit better rutting resistance, and lower anti-cracking properties and moisture susceptibility. When the RAP-SBS percentage is less than 30%, the anticracking property of the recycled mixture is basically close to that of HMA mixture between $-20$ to $-10°\mathrm{C}$, and the moisture susceptibility of the two types of mixture is similar when the percentage is less than 50%, but the durability of both recycled mixtures is poor. In addition, no continuous increase in dynamic modulus is demonstrated as the RAP-SBS percentage increases. When subjected to F-T cycles, the strength of mixtures with RAP-SBS is more sensitive than that of HMA mixtures, especially for mixtures with high RAP-SBS percentages.

This paper presents the results of an extensive experimental study carried out to characterize the mechanical behavior of plastic concrete materials in consolidated undrained triaxial compression tests. The effect of various parameters such as confining pressure, mix design, age, and curing condition on the mechanical behavior including total and effective shear strength parameters, pore water pressure development, and the failure modes of the corresponding specimens was investigated. The geotechnical parameters of plastic concrete required for drained and undrained numerical analyses of embankment dams containing plastic concrete cutoff walls were presented as well. It was shown that the variation of confining pressure and plastic concrete mix design including cement and bentonite content and coarseness of aggregates obviously affects the contractive-dilative behavior and resultant excess pore pressure during undrained tests. The effects of specific curing condition of the plastic concrete samples under high water head as well as their failure mode at the completion of the tests were also investigated. The results revealed that the mode of failure varies from bulge-shaped sides to completely distinct shear bond in the various samples based on the mix design and confining pressure acting on the specimens.

The bond between fabric reinforced cementitious matrix (FRCM) and masonry substrates is investigated in this paper. An experimental investigation was performed on eighteen clay brick specimens strengthened with a single layer of carbon FRCM (CFRCM). Direct shear tests (single lap) were conducted at an ambient temperature of 20°C varying the bond length of the CFRCM reinforcement [$L_b=150(6)$, 200 (8), 250 (10), and 300 (12) mm (in.)]. Experimental bond strength values, bond-slip law, and failure modes described and analyzed in this paper allow for evidencing of the bond performances of the CFRCM-masonry substrates. Finally, an analytical local bond-slip law was defined and used to compare theoretical predictions and experimental results.

Cracks are ubiquitous in concrete materials and can destabilize a concrete structure, regardless of size or type. This study focuses on the cracking behavior of main and branching cracks in concrete. Compression tests and an ultrahigh-speed camera are utilized to capture the crack formation. Crack length and cracking speed under a compressive load are measured and calculated. An accurate method for measuring crack characteristics is presented. Results show that the length–time and developing speed–time curves of the branching crack exhibit an evident fluctuation compared with that of the main crack. The main crack maintained a relatively stable crack development speed during the entire loading process. This relatively stable speed may result from the development of the branching crack. If the concrete is damaged, then the branching crack can delay the cracking speed of the main crack and minimize damage.

Air-entrained high performance concrete (HPC) crossties or ties (alternatively called sleepers outside of North America) have been observed to suffer structural and material degradation at the rail seat area (RSA), including freeze-thaw damage. The manifestation of any damage at the RSA is hazardous because future high-speed railroad lines utilizing HPC crossties will be installed in regions across the United States with extensive freeze-thaw temperature cycling. To better understand the extent of cyclic freezing temperatures at the RSA, an environmental study was undertaken to measure the internal temperature at various locations of instrumented HPC crossties that were installed in a track for 1 year. The experimentally measured internal temperature values are compared against the results of a pair of models (a solar radiation model and a one-dimensional, multilayered heat transfer model) that utilize only public weather data as model inputs. The pair of models is found to satisfactorily predict the freezing internal temperatures of concrete crossties, specifically during winter months. The validation of this temperature modeling expands the HPC crosstie practitioner’s set of tools necessary to better understand environmental design criteria of this critical piece of infrastructure with regard to freeze-thaw damage.

The purpose of this study was to determine the relationship between the coefficient of permeability, porosity, and voids in total mixture (VTM) of fine-graded hot-mix asphalt (HMA). Two fine-graded HMA mixtures used in Michigan were prepared with the same binder contents (5.5%) and nominal maximum aggregate sizes (NMAS) of 9.5 mm and 12.5 mm, respectively. For each mixture, laboratory specimens were fabricated using a superpave gyratory compactor (SGC) with 25, 50, and 75 gyrations, respectively. The coefficient of permeability increased as the air void and porosity values increased. After the first moisture conditioning, the porosity and coefficient of permeability increased for most of the specimens. After the second moisture conditioning, it was observed that specimens had a reduced porosity and coefficient of permeability. There were significant differences for porosity and permeability before and after the first moisture conditioning. However, there were no significant differences for porosity and permeability before and after the second moisture conditioning. Regarding moisture conditioning, the 12.5-mm gradation tended to have a more stable structure than the 9.5-mm gradation. This tendency was indirectly observed from the rutting performance test. This study is helpful in the design of asphalt mixtures that can resist pore pressure damage.

The phenomena involved in portland cement hydration and interactions with nanosilica are very complex and not yet fully understood. In addition, few papers have currently proposed to investigate the microstructure and mechanical properties of ternary mixtures using portland cement, colloidal nanosilica, and highly reactive mineral additions. This article investigates, for the first time, the behavior of different highly reactive mineral additions (silica fume and metakaolin) when partially replaced by colloidal nanosilica in the microstructure and hydration of cementitious materials. For the study of the cementitious material microstructures, a Langavant calorimeter, compressive strength, X-ray diffraction, thermogravimetry, infrared spectroscopy, and mercury intrusion porosimetry were used. The pastes with a 1% substitution of highly reactive mineral additions by nanosilica showed higher compressive strength and more refined porosity than the pastes with only silica fume or metakaolin. The results show that nanosilica appears to have better synergism with metakaolin than with silica fume.

Natural weak cohesive subgrade soils are considered low quality foundations for pavement structures that may lead to significant pavement distresses. Several solutions can be proposed to enhance pavement behavior under cyclic loads such as stabilizing clays with cement or lime, removing and replacing weak material, or increasing the base thickness to reduce the stresses on subgrade. Despite the effectiveness of using additives like lime and cement for subgrade stabilization, cement and lime are considered environmentally unfriendly owing to the generated emission during their production. Recently, several researchers have shown the potential of using biopolymers as alternative for traditional additives. This study investigates the feasibility of using sodium alginate biopolymer for treating weak cohesive subgrades particularly under repeated traffic loads for pavement construction applications. Two different soils (clay and silt), representing a typical range of cohesive soils in the delta region in Egypt, were investigated. The sodium alginate was added to the cohesive soils in the range of 0% to 6% using two different mixing methods (wet and dry). The experimental program included basic engineering tests, resilient modulus, and unconfined compressive strength tests, along with other chemical tests such as Fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA). In addition, scanning electronic microscope (SEM) images were performed for both untreated and treated soils at different alginate contents. Results showed that the resilient modulus of the treated subgrade soils generally increased with the increase in sodium alginate content up to an optimum value of 2% and 4% for clayey and silty soils, respectively. This significant improvement was reached in the first 4 days of curing with continuous gain of strength up to 28 days. This increase in resilient modulus was found to be dependent on the soil type, alginate concentration, curing time, and treatment method. The microlevel tests, TGA, SEM, and FTIR, confirmed the presence of the cementation polymer due to sodium alginate that increased the bond and cross-linking between particles, and consequently an increase in the soil stiffness and strength occurred.

Rocklike specimens with a grout-infilled flaw having different inclination angles were prepared for uniaxial compressive tests to study the effect of types of grouting materials and flaw inclination angle on the compressive strength and crack behavior of specimens. Epoxy resin and cement paste were chosen as grouting materials; the mechanical properties of these two grouting materials are totally different. The experimental results showed that types of grouting materials play a significant role in improving the uniaxial compressive strength of specimens with a grout-infilled flaw. The grouting effect for epoxy resin is better than that of cement paste. The grouting effect has a close relation to the flaw inclination angle; whether the specimen is grouted with cement paste or epoxy resin, the grouting effect is significant when the flaw inclination angle is 60° and not good when the flaw inclination angle is 90°. Cracking behaviors and failure patterns were found to be affected by grouting materials and flaw inclination angle. The present study is helpful to understand the mechanical properties of rock masses with grout-infilled fractures.