Journal of Materials in Civil Engineering

The self-healing mechanism of asphalt has always been a challenging issue for pavement engineers; up to now there is no general agreement on the fundamental mechanism. In this paper, combined with atomic force microscopy (AFM) technology, the self-healing mechanism of asphalt is simulated by using the phase-field model in two ways: thermodynamic approach and mechanical approach. In the thermodynamic approach, self-healing is considered as a material-phase-rearrangement process. Microcracks will form and disappear in the stress concentration zone near the phase interfaces because of phase separation, which is demonstrated by AFM results. In the mechanical approach, the microstructure is described using a phase-field variable that assumes a positive field in the intact solid and negative one in the existing crack void. Allen-Cahn dynamics are adopted to evolve the phase-field variable that the surface energy will result in the wetting of two surfaces and finally leads to self-healing. By using both approaches, one can better understand the asphalt self-healing mechanism.

The feasibility of making slag-bonded construction wallboard through carbon dioxide activation of steel slag was investigated. The steel slag used in the study is a by-product of the Klockner Oxygen Blown Maxhutte (KOBM) steel-making process. The ${\mathrm{CO}}_2$-activated steel slag can potentially be used as a cementing material in place of ordinary portland cement (OPC). The 2-h carbonation strength of the activated steel slag reached 46 MPa and the 28-day strength after carbonation and hydration was more than 60 MPa. Carbonation of steel slag enabled ${\mathrm{CO}}_2$ utilization up to 6.8% on a dry-slag-mass basis. The high early strength obtained in ${\mathrm{CO}}_2$-activated slag is attributed to the rapid formation of calcium-silicate-hydrates and calcium carbonates. The precipitation of rhombohedral ${\mathrm{CaCO}}_3$ nanoparticles significantly enhances packing density and reduces the porosity of the carbonate matrix. A slag-bonded wallboard using sawdust as lightweight filler was successfully fabricated and its mechanical performance was comparable to cement-based commercial products.

Glass fiber-reinforced polymer (GFRP) composites have been increasingly used in the construction of civil structures because of their light weight and high strength, tailored flexibility, and corrosion resistance. Such structural materials also present potential for a multifunctional design where functions other than load-carrying capacity, such as thermal insulation, energy supply, and intelligent inspection can be incorporated into one GFRP structural component. This paper further extends this concept by the development of the self-luminous function. In this application, a translucent resin modified with self-luminous powders, together with the nature of glass fibers, is able to illuminate the resulting GFRP composite in darkness and therefore provide the structural members with new architectural and aesthetic features or other service signatures. Mechanical experiments, luminance measurements, and scanning electron microscopy (SEM) imaging have been conducted to examine the self-luminous GFRP composites, and the results are reported in this paper.

Chip seals constructed in areas with a combination of high truck traffic volume and high climatic temperatures are susceptible bleeding in the wheel paths and raveling in nonwheel path areas. These failures arise from inherent differences in traffic loading in the two areas. Addressing this problem calls for the binder application rate for the two regions to be varied and using asphalt binders with a high stiffness at high temperatures to prevent bleeding. No well-established design methods that yield a different binder application rate exists. Although equipment for applying variable binder rates exists, there is limited performance data, and no guidelines for calibrating the equipment in the field exist. This paper presents the findings of field studies in which both uniform and variable application rates were used to construct asphalt-rubber chip seals in California. The results show that using different binder application rates in and out of wheel paths can mitigate bleeding and raveling. The paper also presents a new field calibration test method for both conventional and variable rate distributor spray bars.

Steel corrosion is a major problem with concrete structures. For cracked concrete structures exposed to chloride environment, chloride diffusivity through the crack ($D_{cr}$) is higher than that through the concrete matrix ($D_o$), and therefore, the corrosion will occur at an earlier time. In this study, finite-element analysis is performed to study the process of chloride diffusion through cracks. For various values of $D_o$, $D_{cr}$, and crack width, the chloride-concentration distribution is determined. Based on the simulation results, the empirical equation for an equivalent diffusion coefficient ($D_{eq}$) will be derived, which can be used directly in the solution of the one-dimensional diffusion equation to calculate the predicted chloride profile, the corrosion-initiation time, and penetration of corrosion front. The study will provide a convenient but accurate approach for predicting the chloride diffusion, including the corrosion initiation, under real-world situations where cracks are present in a concrete structure.

The pore size distributions of hardened cement pastes were studied in the research reported in this paper in order to investigate whether there was a relationship with the risk of freeze thaw related distress. Mercury intrusion porosimetry (MIP) and cyclic freezing and thawing tests were used to assess cement pastes with different water-to-cement (w/c) ratios and supplementary cementitious materials. Typical pavement mixtures contain a range of pore sizes similar to those in aggregate prone to D-cracking. Such pore sizes are reported to resist drying, thus they may increase saturation and so the risk of damage under freezing and thawing.

The CL90 mortar (i.e., the nonhydraulic lime mortar) is dramatically more water retaining than any of the hydraulic mortars. This paper investigates the possible role of simple ionic solutions used as mix water on the water transport kinetics and mechanical properties of hydrated lime mortars. The results show that the addition of sulphate solutions as mix water does not only improve the transfer sorptivity and time to dewater, but also consistency and setting time of hydrated lime mortars. Compressive strength of hydrated lime mortars is significantly increased when potassium sulphate is used as mix water solution, and this is supported with microstructural analysis. The parameters studied in this paper form the main barriers to the use of hydrated lime mortars in construction practice; therefore, the use of hydrated lime mortars may be encouraged if the simple ionic solutions as mix water can improve the fresh and hardened properties of these mortars.

This paper presents a new equation for estimating the permanent strain of different combinations of recycled clay masonry and recycled concrete aggregate using the concept of matric suction. The aim of this paper was to develop a new equation with a single set of constants for all the materials. The unbound granular material (UGM) was prepared at moisture contents ranging between 70 and 90% of optimum moisture content (OMC) and tested in a repeated-load triaxial test (RLTT) apparatus under a single-stress state. Soil water characteristic curves (SWCC) were established for each material by preparing samples at various moisture contents and measuring matric suction with filter papers. In order to obtain the wet end of the SWCC, further samples were conditioned on a tension plate at suctions controlled by the hanging water column method. Permanent strain was influenced by moisture content or suction and was found to provide a better correlation with suction than with moisture content. Permanent deformation under a single-stress state was able to be estimated successfully using an equation developed on the basis of number of load repetitions, initial matric suction, dry density ratio, weighted plasticity index, and masonry content in the blend. Sets of material constants were found for all UGMs. It is shown that the equation can be used with a single set of constants to provide satisfactory predictions of permanent strain ($R^2=0.87$) for all UGMs, over a wide range of moisture states.

Epoxy resins, which are currently used as floor-finishing materials in underground parking lots, have many disadvantages, such as peeling, decreased bond strength under wet conditions, low impact resistance, poor film rigidity, susceptibility to corrosion, and environmental unfriendliness. Hence, in this study, an attempt is made to determine the optimal mixing ratios of silica with a silane coupling agent for use as cover materials for concrete floors. Accordingly, experiments were carried out to determine the viability of hybrid finishing materials for use on floors, with 3-glycidoxypropyltrimethoxysilane as the silane coupling agent. Based on the results of adhesion strength, impact resistance, flexural strength, compressive strength, and length change tests, the optimal silica/silane mixing ratio (mass ratio) was found to be $1:1.75$.

Proper understanding of the field performance of lime-treated expansive soils requires the evaluation of their unsaturated properties under stress conditions similar to that in the field. This paper studied the influence of net vertical stress on the soil-water characteristic curves (SWCC) of lime-treated expansive clay. The first phase of this study investigated the influence of lime content and curing period under low net vertical stress (7 kPa) using axis translation and filter paper techniques with simultaneous measurements of sample volume change. The second phase evaluated the SWCCs of untreated and lime-treated clays under vertical stresses of 100 and 600 kPa. Different representations of SWCCs were considered in the interpretation of test results. Test results indicated that lime content had a significant effect on the shape and air entry value of SWCCs because of changes in soil microstructure, whereas curing period had a far less significant effect. Furthermore, the application of net vertical stress delayed the desaturation of samples causing increase in air entry value. On the basis of plots for the variation of void ratio versus suction, the increase in air entry value was attributed to considerable reduction in volume (void ratio) associated with the application of the net vertical stress causing samples to remain saturated up to high suctions levels.

Recently, dynamic modulus ($|E^{*}|$) test has gained substantial acceptance for Superpave mix performance evaluation and in designing asphalt pavements for rutting and fatigue cracking. Mechanistic empirical pavement design guide (MEPDG currently branded as AASHTOW are ME pavement design) is currently the state-of-the-art method of designing asphalt pavements and it utilizes $|E^{*}|$ data. Unfortunately, neither Superpave mix design method nor ME pavement design has used $|E^{*}|$ to evaluate asphalt concrete (AC) moisture damage. Though $|E^{*}|$ based rut and fatigue models are available in ME pavement design, there has not been any model for moisture damage of AC. To this end, this study attempts to correlate $|E^{*}|$ with moisture damage as a first step to moving toward mechanistic understanding. Moisture-induced sensitivity tester (MIST) is used for moisture conditioning of asphalt samples. Moisture damage resulting from MIST conditioning is evaluated using the dynamic modulus ratio (DMR) of wet to dry samples. MIST conditioning is found to decrease the $|E^{*}|$ value of asphalt concrete (AC) indicating the presence of moisture damage. Moreover, moisture damage shows an increasing trend with increasing MIST-conditioning number of cycles, temperatures, and pressures. To capture the correlation between DMR with MIST-conditioning cycles and pressures, two different models are developed. The coefficient of determination $R^2=0.969$ and $R^2=0.839$ are obtained for the MIST-cycle and MIST-pressure models. It is hoped that these models are incorporated in the ME pavement design in future.

One common concern limiting the proliferation of high-volume fly ash (HVFA) concrete mixtures is the significant delay in setting that is sometimes encountered in field concrete mixtures. While several methods to mitigate the delayed setting times of HVFA mixtures have been demonstrated, a related issue is the prediction of setting times in field mixtures, so that construction operations including finishing and curing can be anticipated and properly scheduled. This paper presents a feasibility study evaluating the employment of simple electrical measurements to predict the setting time of paste mixtures on which concurrent Vicat needle penetration testing was performed. Electrical, setting, and accompanying calorimetry tests are conducted at three different temperatures, each under quasi-isothermal conditions to minimize the confounding influence of temperature variation on the obtained results. Electrical resistance (or heat flow) measurements can be used to adequately predict a mixture’s initial setting time for a wide variety of binary and ternary powder blends, prepared at a constant water volume fraction. However, a simple parametric study in 100% ordinary portland cement pastes in which water content (water-to-cement ratio) is varied indicates that the relation between resistance trends and subsequent setting times is strongly dependent on the water content, as is also the case for the thermal measurements. This suggests that employment of this approach for field mixtures may require predetermination of the resistance-setting time relationship for each mixture of interest (e.g., calibration) or at least that the on-site water content of the concrete mixture be assessed and verified by a separate measurement.

Asphalt mixture compaction is an important procedure of asphalt pavement construction and can significantly affect the performance of pavement. In recent years, the finite element method (FEM) has been utilized by researchers to study asphalt mixture compaction. However, FEM is a continuum approach and unable to take into account the slippage and interlock of aggregates during the compaction process. With its inherent advantages, the discrete element method (DEM) is a more suitable tool than FEM to simulate asphalt mixture compaction. In this study, an open source DEM code was applied to simulate three types of hot-mix asphalt (HMA) compaction for the first time: superpave gyratory compaction, vibration compaction, and kneading compaction. A viscoelastic contact law was used for the simulation and the parameters were obtained through nonlinear regression analysis of dynamic modulus test results. The DEM simulation results show good agreement with lab compaction test results, which indicates that DEM is a reasonable tool to simulate asphalt mixture compaction and has tremendous potential to help guide asphalt mixture compaction.

The sigmoidal equation is usually used to make predictions for dynamic modulus ($|E^{*}|$), but equations to predict phase angle are still unavailable. In this study, equations to predict both the $|E^{*}|$ and phase angle for asphalt mixtures were proposed. The expression for the $|E^{*}|$ prediction in the proposed model is the same as the sigmoidal equation, while the predictive equation for the phase angle was derived based on the Kramers-Kronig equation, which reveals the relation between the $|E^{*}|$ and phase angle. The new predictive equation set is called the initial proposed (IP) model, as differentiated from the modified proposed (MP) model, in which an additional coefficient was given to the equation. To validate the IP and MP models, the equations were used to fit the $|E^{*}|$ and phase angle data at a wide range of temperatures and frequencies from 14 different asphalt mixtures. The coefficients and shift factors in the equations were obtained from a nonlinear least-squares optimization using optimization software. The predicted results using the sigmoidal equation and the IP and MP models were compared through the measured $|E^{*}|$ and phase angle values, $|E^{*}|$ and phase angle master curves, shift factors, Cole-Cole plots, and black space diagrams. The results showed that both the IP and MP models predicted the $|E^{*}|$ and phase angle well, and the MP model made more precise predictions for both the $|E^{*}|$ and phase angle as compared to the IP model. The MP model and the sigmoidal equation obtained close $|E^{*}|$ master curves and shift factors but slightly differed from the IP model. In addition, the IP and MP models successfully predicted the existence of the maximum and minimum values of the $|E^{*}|$ and phase angle through the construction of master curves. The proposed models developed in this study can be an effective approach to predict the $|E^{*}|$ and phase angle in a wide range of temperatures and frequencies for asphalt mixtures.

Two types of steel, 20MnCr5 and S275JR, are compared in this paper based on numerical prediction of their fracture behavior. The comparison was made using the numerically determined $J$-integral, an important fracture mechanics parameter. For that reason, a numerical algorithm that calculates the $J$-integral as a measure of crack driving force was developed. As an input, the algorithm uses results from the finite element analysis conducted on numerical models of two types of specimens usually used in experimental fracture investigations, single-edge notched bend (SENB) and disc compact type (DCT). The $J$-integral results obtained are plotted versus specimen crack growth size ($\mathrm{\Delta }a$) for a range of specimens’ initial crack sizes ($a/W=0.25$, 0.5, 0.75).

In this study, a precision study for dynamic modulus ($E^{*}$) testing is performed through independent assurance (IA) testing. The University of New Mexico (UNM) and AMEC Environment and Infrastructure, Inc. (AMEC) laboratories participated in this study. The precision and accuracy of the $E^{*}$ data are evaluated using $E^{*}$-trend plots, coefficient of variation (COV), within-laboratory consistency ($k$-statistic) plots, between-laboratory consistency ($h$-statistic) plots, one-way analysis of variance (ANOVA), and repeatability and reproducibility studies. The $E^{*}$-trend and mastercurve plots showed overlapping $E^{*}$ data at each temperature and loading frequency, suggesting no significant difference between the samples tested. Average COV values for UNM and AMEC laboratories were found to be 10 and 14%, respectively, which are acceptable for properly conducted testing. Average $k$-statistic values of $-0.3$ and 0.3 and average $h$-statistic values of 0.8 and 1.0 were found for UNM and AMEC laboratories, respectively, which indicated very good precision and accuracy. One-way ANOVA showed no significant difference between the means of UNM and AMEC test results. The average $E^{*}$ ranges for UNM and AMEC laboratories were determined to be 12 and 15, which are well below the repeatability and reproducibility limits. Based on the statistical analysis of the independent assurance test data, it can be concluded that $E^{*}$ testing is precise and accurate.

This article studies the possibility of using market available glued-laminated timber (GLT) based on melamine-urea-formaldehyde (MUF) adhesives as an alternative to traditional solid timber sleepers. The study comprised an examination of the effect of creosote treatment on the short-term and durability after accelerated aging of the glue lines (delamination and shear strength) and the potential for full sapwood penetration by the creosote. Creosote treatment showed a negative effect on shear strength and delamination, more severe in the nonstructural than the structural GLT specimens tested. Full penetration of creosote into the sapwood was not achieved. GLT elements based on MUF adhesives can be considered an alternative to solid wood sleepers if specific grading of lamellas, proper treatment schedule, and highly controlled factory production are implemented.

In this study, the rheological properties and activation energy (AE) of unaged and aged asphalts blended with different percentages of binder, recovered from three reclaimed asphalt pavement (RAP) sources, were investigated. Superpave asphalt binder tests were used to evaluate the effects of the recovered asphalt binder source and content. The results indicated that the addition of recovered binder from each source increased the viscosity, $G^{*}/\sin \delta$, and $G^{*}\sin \delta$. The increase in viscosity per 1% recovered binder was evaluated using non-dimensional viscosity index ($\nabla {\eta }_{\mathrm{RAP}}$). In addition, the increase in $G^{*}/\sin \delta$ and $G^{*}\sin \delta$ per 1% recovered binder were investigated using relative Superpave rutting gradient (RSRG) and relative $G^{*}\sin \delta$ gradient (RG) factors, respectively. The results indicated that the $\nabla {\eta }_{\mathrm{RAP}}$, RSRG, and RG depended on recovered binder source, content, aging, and test temperature. The interpretation of the AE results depended on the physical phase of the asphalt blends, irrespective of the recovered binder source and content. The AE increased when the physical phases of the asphalt blends were in liquid and semiliquid (high phase angle) states over the range of temperatures tested compared with the control asphalt binder. However, the AE decreased when the physical phase of the asphalt blend samples was solid (low phase angle).

The behavior and properties of rendering mortars, in the fresh state, are influenced primarily by particle grading, amount of water employed, and the shape and surface texture of particles. Production processes and application of rendering mortars demand an appropriate adjustment in their materials so that the plasticity and consistency need to be optimized allowing an appropriate execution of rendering. The friction between particles of sand is decisive in the rheological behavior of mortars. In this context, the present study evaluates the mortar flow behavior focusing on the influence of microfine content and grading of sands on friction angle of mortars. For experimental development, mortars that differ according to binder/aggregate ratios and aggregate grading distributions were used, in addition to using sands with different microfine contents. The mortar consistencies were established based on the cone penetration test. The mortars were tested to determine the internal friction angle using the direct shear test. The yield stress was obtained from the Vane test. The results indicate a relationship between the microfine content and the internal friction angle of the mortars, identifying a strong influences of friction under the behavior of flow of the rendering mortars.

Several prediction criteria have been proposed to rank asphalt binders based on their rutting performance, and each one has been shown to be able to predict rutting behavior observed in either accelerated loading field tests or under highway traffic with some level of success. In this study, an analysis of these rutting prediction criteria was conducted in order to identify the virtues and shortcomings of each. Asphalt binders that were used in the accelerated loading facility (ALF) study conducted by the Federal Highway Administration (FHWA) were obtained and studied. The experimental data obtained on these binders were fit with a nonlinear viscoelastic model so that it can be used to predict their response under different loading conditions. By comparing predicted behavior based on the nonlinear viscoelastic model and the various rutting prediction criteria, the part of the complex nonlinear mechanical behavior of these binders that each criterion addresses was determined. Results show that each criterion represents the resistance offered by asphalt binders to permanent strain over a specific range of stresses. Results also show that a simple viscosity test might be sufficient to characterize the rutting performance of asphalt binders accurately.