Journal of Materials in Civil Engineering

This study examines the role of alkali hydroxide and its concentration on the microstructure and compression strength of fly ash–based geopolymer concrete. Geopolymer is an innovative ceramic material, composed of long chains and networks of inorganic molecules, that is used as an alternative to conventional portland cement for civil infrastructure applications. Some of the advantages of geopolymer concrete are its fast setting time, rapid strength development, and its significantly reduced carbon footprint. In this study, aluminosilicate geopolymers with different alkaline solutions [NaOH, KOH, Ba $(\mathrm{OH}{)}_2$, and LiOH] were prepared by mixing Class C (9.42% CaO) and Class F-fly ash (1.29% CaO). The samples were cured under different experimental conditions and then tested for compressive strength. X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) have been used to identify the new phases formed in the geopolymeric matrix. The results revealed that microstructural properties of fly ash particles and calcium content have a significant effect on the setting time and the compressive strength of geopolymer concrete, and the structure of the formed geopolymer is typically glasslike. The early polymerization of geopolymer concrete is dependent on the concentration of the sodium hydroxide solution (NaOH). The exclusive use of NaOH showed the highest compressive strength when compared with other combinations of alkali hydroxides.

In Thailand, the skid resistance in road pavements requires considerable improvement in order to increase road network safety. However, skid-resistance values can only be measured in situ, that is on the road itself, and prior to post-construction stages. So, skid-resistance values have not been accounted for during the aggregate selection and mixing processes. In this study, a skid-resistance predictive model at the construction stage was developed based on the essential aggregate and mixture characteristics that are the influential factors. Three main types of Thai aggregates (limestone, granite, and basalt) were mixed in asphalt concrete to make the pavement for the construction sites, which were sourced and collected to make test asphalt concrete. These aggregates were obtained from Thailand’s main regions and covered 14 provinces, with 90 projects for mean texture depth test and 110 projects for skid-resistance test, to provide accurate representation. Aggregates and their standard densely-graded asphalt concrete mixtures of 9.5 and 12.5 mm maximum aggregate sizes were used to perform in the construction site. The skid-resistance value (SRV) was measured by a pendulum tester. In addition, the textural characteristics of asphalt concrete pavement, based on different aggregate mixtures, were also analyzed with respect to a sand patch method. The results of the study demonstrated that the developed predictive model in terms of aggregates and mixture characteristics (polished stone value, gradation, and mixture surface texture) provided acceptable SRV prediction with high statistic levels [$R$-square $(R^2)>0.78$, mean square error (MSE) $<0.00089$ and F-significance $<0.05$]. The model will be put forward for inclusion in the preventive scheme for road safety management by the Department of Rural Roads, Thailand.

This paper proposes the use of the maturity method and a two-phase composite model for the prediction of dam concrete modulus of elasticity. The methodology was validated with test results obtained from experimental in situ setup using creep cells placed in the dam’s body, subjected to variable environmental conditions. It is shown that composite models can be used to predict the modulus of elasticity of in situ dam concrete based on the modulus of elasticity of the wet-screened concrete.

Departments of transportation (DOTs) currently use the conventional three-coat system as the predominant choice for the corrosion protection of steel bridge structures. Eliminating one step in the coating process could potentially save time and cost associated with lane closures and traffic control costs. This research paper evaluates several two-coat systems based on the zinc-rich primer and polysiloxane topcoat technology. All samples were conditioned and coated in a state-of-the-art, climate-controlled paint booth, simulating common field ENvironmental CONditions (ENCON) (ENCON 1: 25 °C/50% RH, ENCON 2: 10 °C/40%RH, and ENCON 3: 32°C/80% RH). Accelerated weathering tests were performed on 435 coated samples (scribed and unscribed). Regardless of the ENCON considered, the performance of the two-coat system is very comparable to the three-coat system. This coating technology offers much improved performance with quicker set time and better adhesion pull-off strength. Considering its durability and ease of application, this two-coat system can be attractive to other public and private agencies to enhance and extend the service life of steel structures.

This study evaluated the performance of geopolymer concretes based on a binary mixture of fly ash (FA) with blast furnace slag (GBFS) in an $80/20$ ratio and activated with a mixture of sodium silicate and sodium hydroxide. FA/GBFS and portland cement (OPC) concretes were immersed in 5% by weight sodium sulfate and magnesium sulfate solutions. Volumetric expansion and mechanical resistance loss were measured, and the reaction products were characterized by X-ray diffraction and scanning electron microscopy. The highest levels of deterioration were found in the probes exposed to ${\mathrm{MgSO}}_4$, indicating the higher aggressiveness of this solution. After aging for 360 days in ${\mathrm{MgSO}}_4$, the FA/GBFS concrete expanded by 0.04% and decreased its mechanical resistance by 33%, compared to 0.08 and 48%, respectively, for similarly treated OPC concretes. However, the same exposure to ${\mathrm{Na}}_2{\mathrm{SO}}_4$ increased the observed FA/GBFS resistance while reducing the mechanical resistance of OPC by 30%. This relates to their respective expansion percentages of 0.0068 and 0.412% and the presence of expansive ettringite in the OPC concretes.

Cement asphalt emulsion (CA) mortar is a key material in the nonballast slab track. Its properties are largely dependent on the compatibility between asphalt emulsion and cement. The mixing stability of asphalt emulsion with cement is investigated by analyzing the viscosity of CA paste. Viscosity and the critical particle volume fraction of CA paste are proposed as indexes in evaluating the mixing stability of asphalt emulsion with cement, and factors influencing the mixing stability of asphalt emulsion are studied. Mixing stability is dependent on mixing method, superplasticizer, and emulsion type. The premixing cement method, superplasticizer, and good asphalt emulsion can increase the critical particle volume fraction of CA paste, which is helpful in achieving a low water–to–cement mass ratio (W/C). Anionic emulsion has much better mixing stability with cement than does cationic emulsion. The critical particle volume fraction of CA pastes with anionic emulsion increases stably with the mass ratio of asphalt emulsion to cement (AE/C), but the critical particle volume fraction of CA pastes with cationic emulsion increases little with AE/C. This work proposes a method for choosing an asphalt emulsion with good mixing stability, and provides methods to improve the mixing stability of asphalt emulsion with cement.

During their lifecycle, a building and its components should fulfill a set of performance requirements. However, in reality, from the moment in which a building is placed in use, its deterioration process begins. Buildings and especially their façades, more exposed to the external environmental agents, suffer throughout their service life several types of depreciation, becoming obsolete, economically destitute, or physically deteriorated, leading to the end of their service life. This paper intends to establish a correlation between functional criteria (FBSL) and physical degradation ($S_w$) in the definition of service-life prediction models. In this study, these models are applied to 203 natural stone claddings (directly adhered to the substrate), located in the Lisbon area, Portugal. The functionality and degradation condition of the façades analyzed are evaluated through visual inspections. Vulnerability and risks (intrinsic and extrinsic variables) are considered in the evaluation of both methods, as the factors that affect the physical and functional service life of buildings. These models are implemented based on a survey of expert opinion. This study allows establishment of a hierarchical scale concerning the priority of intervention in the stone claddings, based on physical and functional criteria. This information is extremely important in the implementation of maintenance programs in large building stocks.

Bacteria-induced mineral precipitation is an environmentally friendly technology to enhance the self-healing ability of concrete cracks. However, the self-healing capacity of concrete was improved at the expense of extra bacteria-based additives incorporated into a concrete matrix, and the influence of bacteria-based additives on a concrete matrix has not been fully understood. The objective of this work was to investigate the effects of bacteria-based additives on the properties of a cement paste matrix. Two types of bacteria-based additives (Type 1 and Type 2) were developed to improve the concrete self-healing capacity mainly achieved by bacteria-induced mineral precipitations. The mineral precipitations induced by two types of bacteria-based additives in the liquid medium were analyzed with a scanning electron microscope (SEM) and X-ray diffraction (XRD). Then, the crack-healing capacity of cement paste specimens with both bacteria-based additives was evaluated on the basis of area repairing rate. Moreover, the mechanical and carbonate resistance properties of cement paste specimens were investigated in detail. Experimental results showed that both bacteria-based additives could be utilized to design a self-healing cementitious material system. Incorporation of the Type 1 additive into cement paste resulted in a decrease of about 14.7%, 6.8%, and 0.1% in compressive strength after 3, 7, and 28 days of curing, respectively. However, incorporation of the Type 2 additive into cement paste resulted in a decrease of about 1.6% and 2.2% in compressive strength after 3 and 7 days of curing, respectively, and an 8.1% increase after 28 days of curing. The carbonation depths of control specimens, specimens with Type 1 and specimens with Type 2 were 6.6 mm, 7.0 mm, and 6.5 mm, respectively, after 3 days of accelerated carbonation. These results suggested that the two types of bacteria-based additives could be used to design a self-healing concrete system, though a slight compressive strength loss in early curing age was found.

The feasibility of the preparation of strain-hardening cementitious composites (SHCC) relies to a great extent on the properties of one of its main constituents, quartz sand. The particle size distribution (PSD) of such sand should satisfy certain criteria specifically for SHCC to deliver quasi-static responses under tensile stress. The successful use of naturally available sand helps preparation of a cost-effective SHCC. The aim of the current paper was to evaluate the potential use of white quartz sand that is naturally available in the Arabian Gulf with different PSDs to produce different mixtures of SHCC. These mixtures were prepared with different ranges of workability to obtain optimized fresh and hardened properties with improved strain-hardening response. The effect of workability on the compressive, flexural and tensile properties has shown that there is an optimal workability range among the defined ranges that provided improved strain-hardening responses under tensile stress. The mode of cracking propagation and fiber failure in tested SHCC mixtures was investigated using stereo-optical microscopy and SEM analyses to reveal different failure mechanisms of the mixtures.

Owing to its importance to the assessment and design of reinforced concrete structures, it is essential to determine the chloride diffusivity of concrete. This paper develops a random walk algorithm for the chloride diffusivity of concrete with the aggregate shape effect. In this algorithm, an equivalent aggregate model is established by coating each aggregate particle with an interfacial transition zone (ITZ) layer and the equivalent ITZ thickness is estimated through stereological analysis. The chloride diffusivity of each equivalent aggregate is then formulated by an effective medium approximation. Finally, the random walk algorithm is adopted to compute the chloride diffusivity of concrete. After the validity of the simulation algorithm is verified with two sets of experimental data, the effects of the aggregate content, the aggregate aspect ratio, and the ITZ thickness on the chloride diffusivity of concrete are evaluated in a quantitative manner. The paper concludes that the random walk algorithm can estimate the chloride diffusivity of concrete with reasonable accuracy.

Thermal cutting is a common engineering practice that is used to obtain the final shape of structural components. The characteristics of the cut surface and the material transformations caused by the cutting method determine the corresponding fatigue behavior. However, design codes, including the AASHTO LRFD bridge-design specifications, provide fatigue design curves for a limited number of situations. In the case of cut edges, only flame cutting is covered, whereas plasma and laser cutting are not associated to any category. In the case of cut holes, AASHTO specifications only consider the fatigue performance of drilled and punched holes, limiting the use of thermal cutting processes to, for example, produce bolt holes. All this restricts the use of thermal cut technologies in many applications. This paper analyzes the effects of flame, plasma and laser cutting on the fatigue behavior of cut edges and cut holes performed on structural steels. With this aim, an experimental program composed of 300 fatigue specimens has been completed. The obtained $S\text{-}N$ results have been used to estimate the corresponding proposal of AASHTO detail categories.

In the present work, the effect of different percentages of nano-montmorillonite (NM) powder on the mechanical and microstructural properties of hardened cement paste and mortar were studied. The portland cement was replaced with montmorillonite nanoparticles with 0.5, 1, 1.5, 2, 2.5, and 3 weight percentages of cement. The mechanical properties of cement mortar including compressive strength, tensile strength, and flexural strength according to the ASTM standard and the microstructure of cement paste were investigated using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-powder, field emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDX) techniques. The obtained results revealed that adding cement with replaced montmorillonite nanoparticles up to 1.5% will enhance the compressive strength, tensile strength, flexural strength, and improve the microstructure of cement because of filler effect and acceleration of cement hydration through the nucleation effect. Therefore, 1.5% addition of montmorillonite nanoparticles can be considered as an optimum value.

Bitumen as a main and efficient material in the behavior of hot mix asphalt (HMA) already has attracted the attention of various researchers. Bitumen modification with polymeric and nonpolymeric materials was considered one of the main research subjects relevant to increasing road life cycles. Crumb rubber is one of the appropriate bitumen modifiers due to its desired properties, and it also helps to reduce environmental pollution. In the current research, two types of mesh, crumb rubber (mesh of Nos. 14 and 50), with three different percentages (10, 15, and 20%), have been mixed with three types of bitumen, and the obtained results have been investigated on high-temperature (HT), intermediate-temperature (IT), low-temperature (LT), and viscosity properties. Also, in order to investigate the impact of aging on stated parameters, test results on bitumen samples modified by crumb rubber, before and after aging, have been studied.

There is very limited literature regarding asphalt mixture aging evaluation using asphaltene as a parametric assessor. However, a few studies have recommended that aging characteristics of asphalt mixtures be evaluated by utilizing the potentiality of asphaltene as a rational aging indicator and formulate a methodology to assess long-term flexible pavement performance. The main objective of this research was to investigate the aging behavior of asphalt binders and mixtures, and develop aging indices and parametric models with asphaltene as a rational performance indicator based on fundamental asphalt material characteristics. Asphaltene content increased from short- to long-term aged condition with rubber- and polymer-modified binders depicting higher magnitudes than the virgin binders. During aging, because of absorption of oils, asphaltene contents do not increment superfluously, furthering modified binder particularly rubber modified bitumen to age at a slower rate. The effect of asphalt mixtures’ aging using $E^{*}$ parameter as the performance indicator helped develop mixture aging indices ($A_{M}I$) at different temperatures and frequencies. To further understand the applications of $A_{M}I$ on aging phenomenon of asphalt mixtures, $A_{M}I$ parametric predictive model was developed encompassing asphaltene aging indices and mixture properties, which was mathematically fair and robust. $A_{M}I$ was capable of explaining the influence of binder and mixture properties along with asphaltene as a performance indicator. Although a limited number of mixtures was utilized in this research, a rational algorithm/methodology was devised and proposed to relate physical, rheological, and chemical parameters of asphalt binders with that of the parametric performance of asphalt mixtures.

Premature deterioration and reduction in the life of reinforced concrete (RC) structures due to corrosion of the embedded reinforcing steel bars is a major concern across the world, and the time for formation of longitudinal cracks has been largely accepted as the “service life” of the structure. It is also widely known that the formation and deposition of expansive corrosion products (of iron) on the bars exert radial pressure on the cover concrete, which finally cracks. In this case, it is reasonable to assume that the composition of the corrosion products, in terms of the different phases of the oxides and hydroxides, and their relative percentages, play a vital role in determining the loss of weight (of iron) that causes sufficient pressure for the onset of such longitudinal cracks. It is interesting that virtually no quantitative information is available in the literature on this subject. The main thrust of the present work is to understand the effect of composition and relative amount of different rust phases with longitudinal crack initiation in RC structures. A laboratory study was carried out where corrosion in the reinforcement embedded in concrete specimens was accelerated by impressing a direct current. The amount and composition of the corrosion products were determined using sophisticated spectroscopic and microscopic methods. This composition was compared with that of the corrosion products taken from the embedded reinforcement in a 50-year-old concrete building; it was found to be very similar. Carrying the work further, this composition was used to estimate the critical amount of corrosion ($w_{cr}$) required for the onset of longitudinal cracks using an axisymmetric plane strain formulation of corrosion pressure in RC structures. An effort was made to study the effect of concrete compressive strength and the cover-to-diameter ratio on $w_{cr}$. The typical values found were in the range of 38.5 to $53\mathrm{mg}/{\mathrm{cm}}^2$.

Standard concrete creep prediction models are essential for structural design; however, it would be unrealistic to expect accurate prediction results without calibration and validations through experimental studies involving local materials and conditions. This paper reports on the long-term creep of high-strength concrete based on experimental work of six independent concrete mixtures involving three types of aggregate, where three mixtures of them incorporated 10% silica fume. Creep testing was conducted with consideration of standard guidelines for loading and strain measurements for up to 2.5 years. Creep coefficients computed from measured strains indicated a substantial influence of the silica fume and aggregate types. The study found that two of the examined models were capable of producing reasonable predictions of the creep for concretes without silica fume. On the other hand, the a current industry model showed reasonable prediction of the creep of concretes with silica fume while underestimating creep for concretes without silica fume. Finally, a mixed formulation model with features from two of the models is proposed and calibrated for concretes with or without silica fume.

In the conservation of ancient masonry structures, due to the scarcity of traditional slaked lime putty, an hydrated lime putty could possibly be used as an alternative binder. The hydrated lime putty can be obtained by soaking the dry hydrated lime powders in water for a certain time. In this article, two approaches to increase the specific surface area of the hydrated lime putty are evaluated. One approach reduces the particle/agglomerate size and the other one mainly aims to promote the formation of $\mathrm{Ca}{(\mathrm{OH})}_2$ hexagonal platelets. Several ways were found to be effective in reducing the particle/agglomerate size, including preselection of high-purity dry hydrated lime with finer particles, by conducation 1-h-long ultrasonication and the addition of 0.5% by weight polycarboxylate-based plasticizer. Meanwhile, a cold-and-hot cycling treatment were found to be effective in promoting the formation of hexagonal platelets of $\mathrm{Ca}{(\mathrm{OH})}_2$. Three cycles, each consisting of 12 h of stirring at room temperature and 36 h stirring at 80°C, were performed on the supersaturated aqueous $\mathrm{Ca}{(\mathrm{OH})}_2$ solutions. After three cycles, well-developed $\mathrm{Ca}{(\mathrm{OH})}_2$ hexagonal platelets were found throughout the microstructure.

This work focuses on modeling fatigue for aged asphalt mixtures. This is accomplished by combining existing models and adapting asphalt mixture aging laboratory procedures. The aging model used is based on the evolution of an internal state variable, and it is capable of taking into account the effect of aging temperature. The simplified viscoelastic continuum damage (S-VECD) model was selected for representing the fatigue damage behavior. Results at four aging states were analyzed, including the unaged mixture. Aged mixtures were obtained by heating loose asphalt mixture in an oven for two periods (2 and 45 days) and two temperatures (85 and 135°C). Based on the results from linear viscoelastic and S-VECD characterization, it was concluded that aging produces less damage tolerant materials; i.e., fatigue failure is observed for less evolved damage states. However, depending on the pavement conditions and on the pavement cross section geometry, because of the increase in material stiffness, aging may not be responsible for a decrease in fatigue life.

In this paper, the performance and structural changes in cement-treated soils under influence of freeze/thaw ($\mathrm{f}/\mathrm{t}$) exposure are investigated. Specimens from plastic and compacted soil-cement mix designs were exposed to different $\mathrm{f}/\mathrm{t}$ scenarios to study the influence of $\mathrm{f}/\mathrm{t}$ dimensionality (i.e., one-dimensional versus three-dimensional exposure) and specimens’ age at the time of $\mathrm{f}/\mathrm{t}$ exposure on changes in their performance. Changes in hydraulic conductivity, unconfined compressive strength, and longitudinal resonant frequency of the specimens were studied under each exposure scenario. An examination of the microstructure of the $\mathrm{f}/\mathrm{t}$ exposed and control specimens using transmitted light optical microscopy was also performed to evaluate how the soil-cement matrix was disrupted after exposure to $\mathrm{f}/\mathrm{t}$ cycling. Observations showed increases in water content of the mix design (when wet of optimum water content), as well as increased specimen age at the time of exposure may increase $\mathrm{f}/\mathrm{t}$ susceptibility. On the other hand, comparison of the performance of the specimens exposed to 1D and 3D $\mathrm{f}/\mathrm{t}$ exposure did not show any significant variation. Microstructural analysis of petrographic thin section samples from control and $\mathrm{f}/\mathrm{t}$ exposed specimens showed that while optical microscopy can detect matrix disintegration for highly damaged specimens, it is not able to identify structural degradation at early stages of damage development.

Ensuring proper compaction of asphalt concrete in the field is necessary for high performance of pavements, and understanding how different asphalt concrete technologies compact can lead to better compaction in the field. This research examines a chemically modified warm-mix asphalt material that was (1) plant mixed, lab compacted; (2) reheated, plant mixed, lab compacted; and (3) lab mixed, lab compacted, and explores how changing the compaction temperatures and compaction pressures influences the compaction characteristics in the lab. In addition, the chemically modified warm-mix asphalt was compared to foamed material and traditional hot-mix asphalt in the lab-mixed lab-compacted state. Overall, workability energy index (WEI), compactability energy index (CEI), compaction densification index (CDI), and number of gyrations required to reach 92% maximum specific gravity ($G_{\mathrm{mm}}$) (N92) followed expected trends of increasing compaction effort required with decreasing temperature or pressure, while locking point and gyratory compactibility index (GCI) did not. For the chemically modified warm-mix asphalt, WEI provided the most-consistent results across sample preparation methods, compaction temperatures, and compaction pressures. However, trends were not as clear when comparing chemically modified warm-mix asphalt, foamed warm-mix asphalt, and hot-mix asphalt.

Concrete spalling results primarily from a thermo-mechanical process because of high thermal gradients, and a moisture-clog process because of the build-up of pore-water pressure. This paper attempted to isolate these mechanisms and quantify their magnitude. Twelve reinforced concrete panels were tested under hydrocarbon fire conditions. The test conditions included different thicknesses, concrete strengths, and specimen sizes. The panels were tested with no additional loading except self weight, and instrumented with in situ thermocouples and pore-pressure gauges. Spalling was quantified according to mass loss and visually represented by three-dimensional (3D) contour surface plots. The research presented for the first time a method to quantify spalling as mass loss in terms of water mass and solid mass. The continuous moisture transport during heating produces a saturated drying front, causing strength degradation and cracking that allows water pooling on the nonexposed fire side. The moisture transport plays an important role in all the mechanisms that contribute to concrete spalling.

Throughout concrete structures’ service life span, deterioration inevitably occurs. A typical phenomenon of deterioration in concrete structures is cracking, which affects durability and integrity of these structures. Repair and maintenance of concrete structures are labor and capital intensive; it can also be difficult to access the degree of damage after the construction is completed. Self-healing is a possible solution. An encapsulation strategy is widely considered as a versatile and effective strategy for self-healing. In this review, attention is focused one valuation of different healing agents and encapsulation techniques. Eight key factors that affect the effectiveness of self-healing by encapsulation are discussed; these are (1) robustness during mixing, (2) probability of cracks encountering the capsules, (3) curing time and condition, (4) effect of empty capsules on concrete strength, (5) controllability of release of healing agent, (6) stability of healing agent, (7) sealing ability and recovery of durability and strength of concrete matrix (as a result of self-healing), and (8) repeatability of self-healing action. Finally, gaps in current research and important areas for future research are identified.

Expansive soils undergo a considerable amount of volume change because of moisture fluctuations and cause severe damage to lightweight structures. In this study, an attempt is made to stabilize the expansive soils to improve their swelling, stiffness, and damping properties with class C fly ash. The percentage of fly ash was varied between 5 and 20% by dry weight of the soil. A series of fixed-free type resonant column tests were performed to determine the dynamic properties, including shear modulus (G) and damping ratio (D); and Poisson’s ratio ($\nu$) of untreated and fly ash treated expansive soils. Prior to the testing, the specimens were cured for 1, 7, and 28 days in a humidity chamber. It is observed that the shear modulus of expansive clay has increased and corresponding damping ratio has decreased with increase in the fly ash content. The curing time has practically negligible influence on the normalized shear modulus and damping ratio of the treated specimens. A generalized equation is proposed for the upper and lower bound normalized shear modulus degradation curves for stabilized clays. An economical design alternative for a vertically vibrating machine is suggested based on the improved dynamic soil properties of the clay.

Splitting resistance of mortise members loaded perpendicular to grain in pegged mortise and tenon joints is an important property in the design of timber frame joints. This paper investigated the effect of loaded edge distance and wood species upon the strength of mortise members loaded perpendicular to grain. To prevent failure of the tenon or pegs, a steel tenon and Grade 8 bolts were substituted. Load and stiffness values from experimental results were significantly different for the factors of loaded edge distance and specific gravity. Perpendicular-to-grain splitting resistance from CSA 086 predicted values were equivalent to the lower specific gravity wood values tested. The Canadian design literature did not account for differences in specific gravity due to different wood species, particularly white oak which is commonly used in timber framing. Comparison of the mortise testing to previous mortise and tenon joint testing showed similar maximum load and stiffness performance.

This study reports an enhanced soundproof performance of polyvinyl acetate (PVA)-based coating by adding high-aspect-ratio calcium sulfate whiskers. One efficient microwave-assisted (MA) method is adopted to synthesize ${\mathrm{CaSO}}_4$ whiskers with a high aspect ratio of 40–80. The two-step MA method is capable of forming highly crystalline ${\mathrm{CaSO}}_4·2{\mathrm{H}}_2\mathrm{O}$ crystals at 85°C, demonstrated by X-ray diffraction analysis. This work uses an anechoic termination method to analyze the sound transmission loss (TL) of PVA-based coatings. The TL of ${\mathrm{CaSO}}_4/\mathrm{PVA}$ composite coating shows an increased trend with the amount of ${\mathrm{CaSO}}_4$ whiskers within the frequency region of 400–3,600 Hz. The improved TL can be attributed to the fact that an air pocket is contained in the ${\mathrm{CaSO}}_4$ stacking layer, imparting the reflection and refraction during the sound wave transmission in the composite coating. The energy of incident sound waves is weakened by consecutive reflection, scattering, refraction, and diffraction of sound waves in the ${\mathrm{CaSO}}_4/\mathrm{PVA}$ composite coating. Since the ${\mathrm{CaSO}}_4$ whiskers are synthesized from industrial wastewater by the MA method, the ${\mathrm{CaSO}}_4/\mathrm{PVA}$ composite coating can serve as eco-environmental decoration materials due to its excellent soundproof performance.

Caltrans is currently implementing a California version of the superior performing asphalt pavements (Superpave) mix design procedure for hot-mix asphalt (HMA) to replace the long been used Hveem mix design process, and is interested in including performance-related tests for mix design and quality assurance. The objective of this study was to compare the repeated load triaxial (RLT) rutting test using the asphalt mixture performance tester (AMPT) and the repeated shear test at constant height (RSCH) using repeated simple shear tester (RSST) for characterization for Caltrans mechanistic-empirical (ME) pavement design in terms of usefulness of the results, difficulty, and time required to obtain results. The results indicated that there is potential to use the unconfined RLT test as a substitute for the RSCH test for mix design and quality assurance, and to use the confined or unconfined RLT for ME characterization. However, the preliminary results regarding shift factors to convert results from RLT to RSCH to make use of previously calibrated models need more comprehensive evaluation.

Soils are natural and environmentally friendly materials that are widely used for constructing earth structures such as pavement. In these structures, soils are often unsaturated and subjected to cyclic loads and daily variations in suction and temperature. Up to now, suction and thermal effects on plastic-strain accumulation under cyclic loads have not been fully understood. In this study, cyclic triaxial tests were carried out on unsaturated compacted silt using a temperature and suction-controlled triaxial system. Suctions from 0 to 60 kilopascals (kPa) and temperatures from 20 to 60°C were considered. It is found that there is a threshold cyclic deviator stress below which the soil specimen reaches an essentially reversible response (plastic shakedown) within 100 cycles. The threshold value increases with an increase in suction, but it seems to be insensitive to temperature changes. Conversely, at a given cyclic deviator stress, measured soil-plastic strain at zero suction is about four times of that at suction of 60 kPa. Similarly, soil plastic strain induced by a given cyclic deviator stress almost doubles when soil temperature increases from 20 to 60°C. The observed thermal effects imply that conventional design methods in geotechnical and pavement engineering may underestimate soil-plastic strain when the ground temperature is significantly higher than the design temperature. Furthermore, the observed suction and thermal effects on strain accumulations are mainly because yield stress of unsaturated soil increases with increasing suction (suction hardening), but decreases with increasing temperature (thermal softening). With a higher-yield stress, smaller plastic strain would be induced by cyclic loads.

Dilatancy measurements of double-layer specimens were recorded during cyclic shear tests to derive information on the interface fatigue behavior. Two direct shear testing devices, representing the two most common types of guillotine and inclined configurations, were used. The results clearly highlight a dilatancy variability from the random aggregates distribution at the contact plane, even for specimens prepared in the same way, A saw-chain model is introduced for useful schematization of volumetric expansion during the shear test. Moreover, a new interpretation of the interface fatigue event is presented, based on the trend of dilatancy speed, which shows three stages: (1) important movement perpendicular to the sliding plane; (2) insignificant increase in dilatancy; and (3) crisis and detachment. The number of loading cycles at the beginning ($N_{\text{override}}$) and end ($N_{\text{crisis}}$) of the dilatancy is introduced as significant moments of the interface fatigue evolution.

The transport and inhibition behaviors of a migrating corrosion inhibitor (MCI, marked PCI-2015) in reinforced concrete (in this paper, only mortar specimens were used for testing) contained different contents of NaCl (0.25, 0.5, 0.75, and 1% by weight of cement) with three water-cement ratios (0.45, 0.55, and 0.65) were investigated by using absorption tests and electrochemical measurements. The results indicated that the measured absorption weight of PCI-2015 basically agrees with the numerical value calculated by the modified MCI transport model, and the representative absorbed weight of PCI-2015 in W/C 0.65 concrete with 1% NaCl was $16.23\mathrm{g}/\mathrm{kg}$ at 1 day, while the corrosion current ($I_{\text{corr}}$) of steel bars in the concrete was reduced to $\mathrm{0.02}\mathrm{\mu A}\mathrm{/}{\mathrm{cm}}^{\mathrm{2}}$ from the initial data $\mathrm{1.38}\mathrm{\mu A}\mathrm{/}{\mathrm{cm}}^{\mathrm{2}}$. The visual observation of surface condition for steel bars in concrete mixed with 1% NaCl by broken specimens showed that the surfaces of steel bars in concrete treated with PCI-2015 were bright. X-ray photoelectron spectroscopy (XPS) analysis of steel bar removed from concrete specimens demonstrated the chloride ion on the steel surface was replaced by atoms or molecules of the inhibitor. By using multivariate nonlinear regression analysis, the relationship among the corrosion current density ($I_{\text{corr}}$) of steel bar in concrete, water-soluble chloride contents ($C_{\mathrm{Cl}}$), and the calculated mass concentration of PCI-2015 at steel-concrete interfacial zone ($C_{\text{in}}$) were established. So a quantitative assessment method for MCI repairing steel bars in chloride contaminated concrete based on MCI inhibition and transport performance was suggested.

This research focused on the strength characteristics of superfine cement–grouted sand with various gradations and relative densities. At first, grout properties of superfine cement suspensions were studied. The sedimentation and the setting time increased but the viscosity decreased as the water–cement (W/C) ratio increased. Additionally, the groutability of superfine cement suspensions with different W/C ratios into various graded sand specimens having different relative densities was tried. The groutability of suspensions especially into the fine sand specimens was successful with certain W/C ratios and increased as the W/C ratio increased but decreased as the relative density increased. Grouted sand samples remained in tanks filled with water at a temperature of 20°C until testing time and subjected to unconfined compressive strength (UCS) tests at different time intervals. The UCS of grouted sand specimens decreased as the W/C ratio increased, but it increased as the relative density increased. The UCS of grouted fine sand was greater than that of medium sand. Furthermore, the UCS of grouted samples increased with time.

Among the numerous advantages of stone mastic asphalt (SMA) is its ability to provide durable surfacing, as well as its high resistance to rutting due to heavy axle loads. The level of research on the utilization of waste and by-products in the construction of SMA is still low, especially in developing countries. To address this gap, this study evaluated the performance characteristics of SMA incorporating electric arc furnace (EAF) steel slag and copper mine tailings (CMT). Mix 1 consisted of 100% granite; Mix 2 was 80% granite, 20% CMT; Mix 3 consisted of 80% EAF steel slag and 20% CMT; and Mix 4 was 40% EAF steel slag, 40% granite, and 20% CMT. The moisture susceptibility of the mixes was within the allowable limits and the mixture prepared with PG 76-22 is more susceptible to water damage. The resilient modulus of ethylene-vinyl acetate (EVA)–modified $80/100$ mixes is also greater than PG 76-22 mixtures at both temperatures of 25°C and 40°C for the unaged and aged samples. The obtained results show that the mix containing EAF steel slag and CMT exhibited superior performance to the control mix sample. In conclusion, incorporating EAF steel slag and CMT into the SMA mixture has significantly improved the SMA performance characteristics and simultaneously increased the rutting susceptibility of the mixture.

This study investigated the effects of hybrid steel fiber of different sizes (6 and 13 mm) on the uniaxial compression performance of ultra-high performance concrete (UHPC). The failure pattern, stress–strain relationship, and toughness under the uniaxial compression of a reference UHPC mixture with no fiber and five UHPC mixtures with mono or hybrid fiber content of 2%, by volume of concrete, were studied. The results indicated that the incorporation of hybrid fiber significantly improved compression properties, with increased strength and toughness. An UHPC mixture with 1.5% long and 0.5% short fiber showed the best compressive behavior, whereas those with 2% short fiber showed the worst properties. Based on the obtained peak stress, strain at peak stress, elastic modulus, and compression toughness index, an analytical model was proposed to generate the complete stress–strain relationship. The proposed model agreed well with the experimental results.

The static bending tests and the split Hopkinson pressure bar (SHPB) dynamic bending tests of concrete are investigated in this paper, and the effects of different initial static loading history on the dynamic tensile strength of concrete are explored. The initial static loadings are divided into five grades, 0, 25, 50, 75, and 90% of static tensile strength, respectively. A large number of mesostructure images of specimens have been obtained by the means of a scanning electron microscope (SEM) and used to analyze the influence of the microstructure and microcrack propagation on the dynamic performance of concrete. In addition, the Weibull distribution model is introduced to analyze the test results, which show that the dynamic tensile strength of concrete increases significantly with an increase in strain rate. When the initial static loading level does not exceed 50%, dynamic tensile strength is basically stable; but when the initial static loading level is more than 75%, dynamic strength begins to decrease.