Journal of Materials in Civil Engineering

This study investigates the combined actions of flexural fatigue loading and chloride exposure by an experimental examination of the initial fatigue loading cycles (0.2, 0.4, 0.8, and 1.2 million), chloride exposure duration (0, 3, and 6 months), and modeling estimating service life. The results show the following: (1) at the initial fatigue loading cycles of 0.4, 0.8, and 1.2 million, (a) the chloride diffusivity of tensile concrete is similar, which are greater than the specimens initially fatigue loaded with 0.2 million cycles; (b) the chloride diffusivity of compressive concrete increases as the initial fatigue loading cycles increase; and (c) specimens present similar values of fatigue life and service life, which are shorter than the specimens initially fatigue loaded with 0.2 million cycles. (2) As the chloride exposure duration increases from 3 to 6 months, (a) chloride contents of tensile concrete increases more than that of compressive concrete, but both diffusion coefficients decrease; and (b) the fatigue life decreases by ~25%–75% and service life decreases by ~28%–55%. (3) There is an exponential correlation between the fatigue life and service life of beams.

The present study demonstrates the influence of integrating phase change materials (PCMs) on hydration and microstructure properties of nanosilica admixed cementitious mortar. First, the optimized dosage of nanosilica in correspondence to compressive strength was determined. Subsequently, the desired proportion of PCMs was identified pertaining to a designated compressive strength of 35 MPa at the curing age of 28 days. The hydration and microstructure studies were carried out through thermo gravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM), respectively. Further, thermal properties were determined by means of differential scanning calorimetry (DSC). Incorporation of nanosilica into the cementitious mortar was found to have a positive influence on early strength development and durability, however, there was found to be an increase in chemical shrinkage as compared to the control mixture. PCMs integrated cementitious mortar improved the thermal efficiency as well as reduced the chemical shrinkage, but adversely affected the mechanical, hydration, and durability properties. With respect to development of compressive strength of the cementitious mortar, it is found that n-octadecane PCMs performed better amidst other PCMs, such as paraffin and sodium carbonate hydrates. Further, studies were carried out on cementitious mortar having both nanosilica (optimized proportion) and PCMs (the best performing). From the results, it is found that cementitious mortar comprising of both nanosilica and PCMs have compensated the drawbacks of one another. Blended mortar (having both nanosilica and PCMs) showed superior strength gain at early age, better durability resistance, low chemical shrinkage, and superior thermal performance.

Pervious concrete can be utilized simultaneously as a pavement surface and part of a stormwater management system. In cold climates, it may be exposed to deicers, many of which have been shown to deteriorate the strength and durability of pavements. Pervious concrete specimens made with limestone, ordinary portland cement, and tap water were subjected to a 3% ${\mathrm{MgCl}}_2$ deicing solution weekly for 17 weeks and allowed to air dry between applications, simulating a severe season of deicer applications. Tap water was used as a control. The compressive strengths of the specimens were measured and were slightly less after the deicer application for one batch, but the average compressive strength for the 20 control specimens from different batches was 15.2 MPa with an average porosity of 24.6%. The 22 specimens from different batches with deicer applications averaged 15.6 MPa with an average porosity of 24.3%. Statistical analyses indicate that the strength varied more with porosity than with the deicer applications. The remaining strength of the deicer-exposed specimens is indicative of the resilience of pervious concrete.

Current gradation design in Superpave mix design method is an empirical-based trial-and-error method, which is costly and time-consuming. Moreover, few mechanical properties have been evaluated during the mix design to assist the mix optimization. This paper describes a novel aggregate gradation and asphalt mixture design concept that estimates the target gradation and optimum asphalt content at an early stage. Voids in mineral aggregate (VMA) is used as a media to link the properties of aggregates and asphalt binder to their engineering properties based on an analysis of aggregate packing. A design example is provided to describe the new design method step by step. As a fast and simple design method, it helps to evaluate the quality of an existing gradation and mix design, and adjust the gradation to satisfy both volumetrics and mechanical properties. With local material calibration to take into account the variation in aggregate shape and angularity, and validated in seven different projects of Washington State, this method can be integrated together with the balanced mix design concept as a convenient practical and research tool to achieve better designs that not only satisfy the performance test but also meet the volumetrics criteria.

Connections in mass timber structural systems are critical for transferring lateral forces from mass timber elements such as shear walls and diaphragms. Cross-laminated timber (CLT) is a prominent mass timber material used to manufacture these wall and floor assemblies. Although research exists that investigated the fire performance of CLT walls and floors, very little investigation has been devoted to the thermal performance of the connection systems themselves. This void in the data and knowledge surrounding CLT connections is an impediment for modeling the elevated temperature performance of CLT structures. Therefore, a series of shear tests were conducted on a CLT L-bracket connection assembly to characterize the thermal degradation of peak loads and initial stiffness as a function of exposure duration at a given temperature. A total of 116 specimens, including four control specimens, were tested according to a matrix of 28 exposure duration-temperature combinations. Two analytical models are developed to explain the thermal degradation—one assuming a mechanism based on first-order kinetics and the second using a statistical regression. The results of this work indicate that the degradation of peak load and initial stiffness with respect to exposure duration occurred at a linear rate and depended on temperature, according to the Arrhenius activation energy theory. This research is a step toward a holistic evaluation of elevated temperature modeling of CLT structures.

Exterior old glazed tiled facades have been a very important heritage testimony of Portuguese culture and traditions throughout the years. The adhesion of the mortars to the old tiles is a very important factor in the behavior of the tiled facades. This study performs a mechanical and water behavioral characterization of compatible air lime (AL) mortars with old substrates and tiles and a microstructural characterization of tile/mortar interface to evaluate the bond between the materials. Formulated lime mortars present mechanical strength values that provide compatibility. Compressive strength varies between 0.42 and 0.61 MPa in AL-based mortars and between 1.09 and 1.60 MPa in lime metakaolin (MK) mortars. $\mathrm{Ca}/\mathrm{Si}$ evolution by EDS analysis provides indications on penetration of lime paste into ceramic biscuit. Higher $\mathrm{Ca}/\mathrm{Si}$ values result in higher bond strength values.

An experimental test is proposed to investigate the interface shear strength between carbonated concrete substrate and self-compacting concrete (SCC) overlay. Thirty-nine Z-type specimens consisting of two L-type concrete members were designed and subjected to direct shear test. One L-type concrete member was cast as substrate and carbonated. Then the SCC was cast as overlay. The effects of carbonation of substrate, strength of SCC overlay, and interfacial treatment on shear strength were discussed and clarified. A coefficient was developed to consider the influence of carbonation on the shear strength prediction between old concrete substrate and new SCC overlay. Results showed that carbonation of substrate affects both the interface shear strength and cracking. The shear strength increased by 30% when the carbonation depth of substrate was deeper than 20 mm. The location of shear crack was changed from the bonding interface to the interface between the carbonated and uncarbonated layers within the substrate. The strength of new self-compacting concrete and the interface treatment also affected the interface shear strength. For specimens without interfacial planted bars, the shear strength increased with the strength of SCC overlay until it was more than 5 MPa greater than that of the substrate. The strength of SCC overlay, however, had negligible effect on the shear strength of specimens reinforced with interfacial planted bars.

This paper proposes a conceptual framework for describing the small-strain shear modulus ($G_{\max }$) of cement-treated clay based on the results of parametric studies covering the influence of mix ratio, curing time, void ratio, stress state, overconsolidation, and yielding on the small-strain shear modulus of cement-treated soft clay. The small-strain shear modulus under the unconfined condition ($G_{\max 0}$) is first examined and the results are correlated to the unconfined compressive strength ($q_u$). The influence of effective confining stress ($p^{\prime }$) is then included and shown to be well-described by a superposition relation. Finally, the small-strain shear modulus of overconsolidated specimens is discussed. The results show that the modulus of these specimens can also be characterized as a sum of two components, one reflecting the effects of cementation and stress history and the other reflecting the effects of the current mean effective stress, overconsolidation, and destructuration history. Of these three factors, the mean effective stress was found to have the most significant effect, whereas the effects of overconsolidation and history of loss of cementation are generally much less significant.

This paper investigated the corrosion fatigue crack propagation mechanism of high-strength steel bar HRB400 in various corrosive environments. Fatigue crack growth (FCG) tests were conducted under different fatigue loading types, environments, and stress ratios. The fatigue loading type included the constant and stepwise decreasing load amplitude. The environments were air, distilled water, 3.5% NaCl solution, and an artificially accelerated corrosive environment. The stress ratio ranged from 0.1 to 0.7. The threshold stress-intensity factor range and FCG rate under various test conditions were obtained. The FCG path and fracture morphology were examined by optical microscopy and scanning electron microscopy, respectively. The threshold stress-intensity factor ranges, FCG rates, FCG paths, and fracture features under different conditions were compared. The corrosion fatigue mechanism of the steel bar under the test environments were quantitatively analyzed. The results showed that hydrogen embrittlement played a predominant role in the corrosion fatigue process of the HRB400 steel bar. The contribution of anodic dissolution to the FCG rate increased as the aggressiveness level increased. The contribution of hydrogen embrittlement to the FCG rate increased with the increase of stress ratio and stress-intensity factor range.

This research aims at producing high-strength, water-resistant, gypsum-based materials (from used plaster moulds) with the additions of glass cullet and cements and investigating the influence of glass cullet contents on their properties. Block-shaped specimens of gypsum mortars containing 70–90 wt% $\beta$-hemihydrate with up to 20 wt% cullet waste powder and a small amount of Portland and calcium aluminate cements, as early strength enhancer and setting time modifier, were cured under damp, ambient air for 7–90 days. Properties including setting times, water absorption, compressive strength, water resistance, volume change, and microstructure were observed. The results exhibited that all specimens could retain their original strength after $10\mathrm{wet}/\mathrm{dry}$ cycles, while the volume shrinkage difference between 7 and 90 days was small (3%–7%), which is consistent with the minimal change of bulk densities at various curing times (densities $1.1–1.20\mathrm{g}/{\mathrm{cm}}^3$). Prolonged curing times led to lower water resistance due to a combination of hydration and pozzolanic reaction products. The mixture with 10 wt% cullet provided optimum characteristics and retained strength of 5.5 MPa with the smallest volume shrinkage of 7% at 90-day curing, suggesting possible applications for indoor and nonstructural outdoor applications.

In the study, the effect of 4% sodium sulfate (${\mathrm{Na}}_2{\mathrm{SO}}_4$) as an activator on cement pastes with 0%, 20%, and 40% fly-ash replacements and a low water-to-cementitious materials ratio of 0.30 was investigated. The investigation was conducted to evaluate the effectiveness of the technique for the utilization of fly ash in developing sustainable concrete. The use of ${\mathrm{Na}}_2{\mathrm{SO}}_4$ decreased setting times of the fresh pastes and increased compressive strength of the hardened pastes up to 28 days irrespective of fly-ash replacement. The use decreased ${\mathrm{Ca}(\mathrm{OH})}_2$ content in the hardened pastes irrespective of fly-ash replacement. Meanwhile, it increased ${\mathrm{Ca}(\mathrm{OH})}_2$ consumption by the pozzolanic reaction of fly ash and content of calcium silicate and aluminate hydrates in the hardened fly-ash–cement pastes. Consequently, the use of ${\mathrm{Na}}_2{\mathrm{SO}}_4$ negatively affected cement hydration in the hardened cement pastes without fly ash, while it accelerated ettringite formation and pozzolanic reaction of fly ash in the hardened pastes.

The research presented in this paper is aimed at developing novel alternative sustainable stabilized earth materials for use in load-bearing affordable housing construction. Prototype-stabilized earth materials have been produced in the laboratory, incorporating a range of solid wastes, including aggregates derived from construction and demolition waste as well as industrial processes. The earth construction materials were stabilized with either portland cement, Portland cement and lime, or through alkali activation. Experimental results for compressive strength are reported, together with findings from a comparative life cycle inventory analysis. Construction and demolition waste shows promise as a potential aggregate for stabilized earth construction. The use of processed ground blast furnace slag together with fly ash is also promising for the development of alkali-activated stabilization.

Fluidized bed combustion fly ash (FBCFA) is a promising industrial side stream to be used as a partial cement replacement material. Untreated and milled FBCFAs from cocombustion of peat and wood were used to replace 20% of portland cement in air-entrained and non-air-entrained mortars. Additionally, equivalent mortars containing fly ash from pulverized coal combustion (CFA) were prepared to compare FBCFAs with more conventional standardized cement replacement material. The study found that both FBCFAs produced mortars with similar compressive strengths compared to a reference, indicating that milling did not affect reactivity of ashes. Air-entrained FBCFA-containing mortars had about the same amount of entrained air compared to the reference mortar. FBCFAs outperformed CFA as a cement replacement material, which produced lower compressive strengths and reduced the amount of entrained air. Non-air-entrained mortar containing CFA suffered severe damage during the freeze–thaw (FT) experiment, unlike non-air-entrained mortars containing untreated or milled FBCFA. The addition of an air-entrainment agent improved FT resistance of all mortars, except those that contained milled FBCFA, which nevertheless had good FT resistance. This first-of-its-kind investigation of the suitability of peat-wood FBCFAs as a supplementary cementitious material in air-entrained mortars suggests a potential use of FBCFAs in cold-region concreting.

When tire derived aggregate (TDA) is used as a lightweight monolithic fill in civil engineering applications, such as embankments and retaining walls, the shearing behavior of TDA-interfaces with different materials should be carefully considered. This paper presents results from large-scale direct shear tests performed on interfaces between Type B TDA and layers of sand, aggregate, and clay for initial normal stress ranging from 19.0 to 76.7 kPa. To match field conditions, a separation nonwoven geotextile was used at the TDA-sand and TDA-clay interfaces, and a separation woven geotextile was used at the TDA-aggregate interface. Large shear displacements, typically between 200 and 350 mm, were required to fully mobilize the secant friction angle. Peak secant interface friction angles range from 26° to 32°, and peak strength envelopes are linear for the sand interface and nonlinear for the aggregate and clay interfaces. Failure envelopes for the TDA-soil interfaces are bounded above by the Type B TDA internal failure envelope and below by the Type B TDA-concrete interface failure envelope. A pair of replicate tests using woven and nonwoven geotextiles for the TDA-aggregate interface indicated that geotextile type had little effect on measured shear behavior as they only provide separation.

Adequate load transfer in concrete-filled steel tubes (CFSTs) requires a close interaction between the steel walls and the concrete core. The present work analyzes the adhesion and confinement effects in steel tubes promoted by three types of lightweight concrete: without any admixture (reference), with an expansive agent (EA), and with an air-entraining admixture (AEA). The following tests were performed: expanding the potential of the admixtures, characterization of the hardened concretes, shear tests, axial compression with load applied to the concrete core, and axial compression applied to the mixed section. The results indicated that the dimensional variation generated by the EA induces a confinement prestress, which improves interface adhesion and, thus, the performance of the CFST. The concrete with AEA presented a lower modulus of elasticity and superficial irregularities that contributed to the manifestation of mechanic adhesion, adhesion by friction, and a high degree of confinement. Although the AEA-CFSTs presented compressive strength 2% lower than the reference, they were 10% lighter. On the other hand, the EA-CFST presented a similar density and an 8% increase in the compressive strength. In conclusion, the use of both admixtures contributed to a suitable performance of the filling cores.

This study compared the effect of seven common curing conditions on the compressive strength, pore alkalinity, efflorescence, and shrinkage of five alkali-activated fly ash and slag (AAFS) mortars and one cement mix. The fly ash to slag ratio and the activator content were altered in the AAFS mortars, which were then placed in the fog room, the carbonation chamber, the outside environment, bottom contact with water, and surface contact with 0%, 3.5%, and 10% sodium chloride solutions. It was found that the shrinkage was primarily a function of the dryness of the environment. The submerged curing conditions increased the extent of leaching but reduced shrinkage. For mixes with a high activator content, the effect of leaching was small. Therefore the compressive strength improved as a result of the reduced shrinkage, with the highest achieving 129.5 MPa at 56 days. The alkalinity of the curing solutions decreased as their salinity increased after 56 days of submergence. The rate of diffusion decreased as the concentration difference of the sodium cations decreased; therefore, the extent of leaching was lowered. This could incentivize the use of AAFS instead of cement, especially in highly saline underground environments.

The paper attempts to understand the macroresponse of fiber-reinforced polymer (FRP) confined concrete in terms of mesolevel interactions. Cylindrical specimens are modeled using a three-dimensional (3D) discrete-element formulation that uses polyhedrons of required geometry to closely approximate the actual shape and size of coarse aggregates. A coupled discrete-continuum approach is adopted to account for damage at length scales smaller than the smallest particle modeled. Constitutive models that capture aspects of mesobehavior crucial to confined concrete are developed, and mesoscale features affecting interface cracking, slip, and mortar damage are investigated. Increased confinement is seen to lead to some reduction in Mode I cracking and a marginal increase in Mode II cracking at the interfaces. However, the principal mechanism for strength gain is seen to be the prevention of localization and dispersal of slip. Increase in confining stiffness also results in increased mortar damage, which limits strength gain due to confinement, as well as a remarkable reversal of the platen effect.

The present study investigates the possibility of introducing zinc oxide nanoparticles into the cement raw mix so as to reduce the energy consumption and ${\mathrm{CO}}_2$ emissions during processing. Zinc oxide nanoparticles are prepared via a hydrothermal growth method using zinc acetate dihydrate and sodium hydroxide as precursors. The percentages of zinc oxide nanopowder added to the cement raw material was varied between 1% and 3%. The resulted clinker and cement samples were characterized using X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), and compressive strength tests. It is concluded that the addition of 1% synthesized zinc oxide nanopowder into portland cement production improves the burnability of the cement raw mixture. A reduction of clinker temperature up to 1,300°C, instead of the 1,450°C–1,500°C usually required, was achieved, thereby enabling a reduction in both energy consumption and greenhouse gas emissions. The 28-day strength is within the target design compressive strength of $42.5\mathrm{N}/{\mathrm{mm}}^2$.

Soil reinforcement using synthetic fibers is a proven technique for enhancing engineering properties to meet the requirements of subgrade materials for pavement projects. The safe and economical design of fiber-reinforced pavement layers requires better insights into their unsaturated behavior. The soil–water characteristic curve (SWCC) is a measure of the water content inside soil pores at a given suction and is considered an essential property to better understand or predict the behavior of unsaturated fiber-reinforced soils. This paper centers on investigating the soil–water characteristic curves for typical expansive clay reinforced with two different types of polypropylene fibers having different surface morphological properties. The effect of an increase in the fiber dosage (0.2% and 0.6% by dry weight of soil) and fiber lengths (6 and 12 mm) on the resultant SWCC patterns is investigated. The addition of lime is considered to enhance the bonding between clay particles and fiber elements to ensure better friction mobilization levels. SWCCs were determined for all experimental mixtures using a combination of axis translation and filter paper techniques that cover the entire matric suction range during measurements. Volume changes undergone during suction measurements have been duly highlighted and discussed. Furthermore, the one-dimensional deformation (swelling/consolidation) characteristics of these lime-blended fiber-reinforced mixtures at different levels of initial matric suction are studied, and the correlations between initial matric suction with both compression index (${\mathrm{C}}_{\mathrm{c}}$) and swell index (${\mathrm{C}}_{\mathrm{s}}$) are established. The results indicate a significant change in the shape of the SWCC for lime-blended fiber-reinforced mixtures compared with the shape of the SWCC for natural clay. The contribution of fiber inclination to altering the shape of the SWCC curve is observed as slight regardless of the type, length, and dosage of fiber. Compression and swell indices for tested mixtures increased proportionately with an increase in initial matric suction levels. Doubling the length of the fiber also induced an increase in the compression index. Under no stress conditions did both fiber type and fiber length have a marginal effect on the swell potential and SWCCs.

The fatigue resistance of two conventional and two polymer modified binders using a new definition of failure in the linear amplitude sweep (LAS) test was assessed in this study. Viscoelastic continuum damage (VECD) theory was used to determine the relationship between number of cycles to failure ($N_f$) and strain level ($\gamma$). Experimental investigation at 10°C, 20°C, and 30°C was conducted on the asphalt binders to validate the proposed theory and compare it with the analysis used in the conventional LAS test. The ratio ($R$) of difference in pseudo stress–strain and true stress–strain area to the area of pseudo stress–strain curve is proposed as a quantifiable parameter of damage. The new definition of failure was found to offer better correlation between damage and the stored potential energy compared with the LAS test. The results evidently justify the applicability of the new damage parameter, which can be used easily with the conventional LAS test protocol.

Efflorescence is a staining salt deposit that usually forms on or near the surface of portland concrete products. It is not an indication of internal damage, but rather an aesthetic blemish that affects a product’s appearance, leading to higher replacement and rejection rates. The primary goal of this work was to investigate whether early-age carbonation curing helps reduce or eliminate efflorescence formation in concrete paver blocks. The devised carbonation technique involved curing concrete pavers in a chamber filled with either pure-gas (99.5% carbon dioxide concentration) or flue-gas (20% carbon dioxide concentration) under a pressure of 5 bar. Efflorescence formation in hydrated and carbonated pavers was evaluated using a modified wicking test. A MATLAB-assisted image-analysis technique was used to quantify efflorescence severity. Results clearly show that pure-gas carbonation successfully eliminated surface efflorescence compared to paver batches that underwent flue-gas carbonation and conventional hydration curing. This improved performance was attributed mainly to a reduction in permeability, which in turn was a result of the densifying precipitation of calcium carbonate crystals during pure-gas carbonation. Results from X-ray diffraction (XRD) and scanning electron microscope (SEM)—coupled with energy-dispersive X-ray spectroscopy (EDX)—identified efflorescence as crystalline potassium-sulfate-based salt deposits.

Two types of polymer latexes and one expansive agent were employed to investigate their effects on the resistance of cement asphalt (CA) pastes to sulfuric acid. Mercury intrusion porosimetry, a thermogravimetric analysis, and scanning electron microscopy were performed to analyze the microstructure of the CA pastes. Anticorrosion coefficients were calculated by comparing the compressive strength before and after corrosion. Results show that the chemical attack by sulfuric acid on the CA pastes begins from the neutralization reaction, accompanied by the crystalline expansion of calcium sulfate in pores and the decompositions of C-S-H gel and asphalt. At a mass ratio of asphalt to cement (A/C) of 0.2, Latex I enhances the anticorrosion coefficients of the CA pastes at low dosages but reduces them at high dosages. In contrast, Latex II results in a completely inverted effect on the anticorrosion coefficients. At an A/C of 0.6, the addition of both Latex I and II visibly increases the anticorrosion coefficients, owing to the binding effect of latex on hydrates. Compared to Latex I, Latex II results in a more obvious increase in the anticorrosion coefficients. With the inclusion of the expansive agent, the anticorrosion coefficients of the CA pastes at the A/C of 0.2 sharply decrease, while the ones at the A/C of 0.6 significantly increase. It is concluded that the precipitation of calcium sulfate crystals in a compact structure produces expansion stress and microcracks, thereby decreasing the strength and anticorrosion coefficients of CA pastes at low A/C values. In the case of high A/C values, the paste structure is difficult to be damaged, owing to the binding effects of asphalt membranes. Hence, the anticorrosion coefficients are increased by adding the expansive agent.

Rutting and fatigue of asphalt pavements, as two important distresses, are significantly influenced by the properties of binders. This study aimed to improve the resistance of asphalt mixtures to permanent deformation and fatigue using two recycled waste-polymer components in recycled crumb rubber (CR) and polyethylene (PE). The assessed pavement properties of the modified asphalt mixtures were characterized by wheel tracking, uniaxial penetration, and four-point bending (4PB) tests. The wheel tracking test indicated that the integrated modification technique, by functionally incorporating PE and CR, enhanced the dynamic stability of the asphalt mixtures and that PE dosage was a key variable. From the uniaxial penetration test, it was revealed that the shear strength of the asphalt mixtures at high temperature could be improved by the integrated modification method, indicating the method’s potential to reduce the flow rutting of asphalt pavements. Meanwhile, both the CR and PE were shown to increase the cohesive behavior of the asphalt mixtures, with the friction angle value sensitive to PE dosage. The addition of PE reduced the fatigue life of the asphalt mixtures; the CR improved the PE-modified mixtures’ fatigue resistance. The findings from this study will be beneficial in developing sustainable and durable asphalt pavements, tailoring the reuse of different types of polymer wastes in asphalt pavements, and minimizing waste disposal at landfills.

In this study, three types of viscoelastic laminated composite dampers (VLCDs) were fabricated and experimentally analyzed. The dampers were fabricated by adding mesh skeleton materials to acrylic rubber to increase its stiffness; this can provide greater restoring force to passive control structures under the same strain conditions. The mechanical properties of the VLCDs were studied by measuring the maximum shear stress, storage shear modulus, loss factor, and equivalent viscous damping ratio under the same ambient temperature and different loading schemes. The experimental results showed that: (1) the addition of aramid mesh skeleton material to the damper can improve its stiffness without changing the matrix of the damping material; (2) the strain amplitude significantly affects the mechanical properties of VLCDs; (3) the excitation frequency has a slight impact on these mechanical properties; and (4) the influence of large-strain low-cycle fatigue on these mechanical properties is significant during the first 15 cycles and less significant during the next 15 cycles. Furthermore, hysteresis curves were calculated and simulated using the Bouc-Wen-Baber-Noori model. The simulation and experimental results agreed well with each other.

This paper presents the results of an experimental investigation carried out to determine the consolidating effect of ureolytic and nonureolytic Bacillus sp. on desert sand. Bacteria-infused desert-sand bricks were prepared using various binders (cement, lime, fly ash), and their engineering properties were evaluated. The results showed an increase of ~19% in compressive strength and water absorption value of 17% in bacteria treated desert sand-cement bricks relative to the same properties in control. In treated bricks field emission scanning electron microscopy (FESEM) analysis revealed thick biodepositions at points of particle to particle contact of desert sand, creating a densified microstructure compared to untreated bricks. X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) analysis of bacteria-treated desert sand–cement bricks indicated the enhanced formation of other hydration products in addition to calcite, and thermogravimetric (TG) analysis validated the formation of additional C─ S─ H (approximately 12%) and calcium hydroxide (approximately 40%). This study shows that nonureolytic bacteria–infused desert sand–cement bricks can achieve an unfired compressive strength ≥ 5 MPa and, therefore, may serve as a sustainable alternative to other conventionally available bricks.

Past seismic events have led to severe damage and even collapse of unreinforced masonry (URM) structure in a brittle manner. The present study is focused on improving the in-plane strength and ductility of masonry wallets (made using both clay bricks and fly-ash bricks) by strengthening with the following two cost-effective materials: polypropylene (PP) band and steel wire mesh. Further, half-scale bricks of both types were also used to check the suitability of these bricks for the scale-down model. Diagonal compression tests were carried out for 36 wallets (four URM and 32 reinforced) as per ASTM standard recommendations. Two linear variable displacement transducers (LVDT) were placed on the specimen to measure the compression and tension during testing. The shear strength of each wallet was evaluated using a set of equations. Further, shear modulus and pseudoductility were computed by analyzing the experimental results of unreinforced and strengthened wallets. Close agreement of the analytical and experimental results validate the use of the analytical model for predicting the shear capacity of the in-plane loaded wallet. The improvement in ductility presented in this study is meant to compare the enhanced deformation ability of the strengthened wallets to its URM counterparts. The conclusion reached is that both strengthening materials are effective in enhancing the load-carrying capacity, shear strength, and deformation ability of the unreinforced masonry wallet.

The objectives of this study are (1) to investigate the microstructural changes in structural steels that are exposed to fire accidents; and (2) to understand their influence on post-fire mechanical properties. Specifically, three structural steels—ASTM A36, ASTM A572, and ASTM A992—are employed, and three post-fire mechanical properties—yield strength, ultimate tensile strength, and ductility—are determined. Structural steel specimens are subjected to high temperatures ranging from 500°C to 1,000°C for 1 h and are subsequently air-cooled. Post-fire mechanical properties of air-cooled specimens are determined using uniaxial tension tests. Metallographic specimens are prepared, and microstructural analysis is carried out. Changes in metallurgical phases are tracked, and the grain sizes of the corresponding metallurgical phases are evaluated as a function of exposed temperature. By observing the post-fire mechanical properties of steels along with the microstructural analysis, an increase in ferrite volume fraction and ferrite grain size clearly leads to a reduction in both the post-fire yield strength and ultimate tensile strength of ASTM A36 steels. The increase in ferrite grain size alone resulted in an increase in the ductility of ASTM A36 steels. Based on the results obtained in this study, multivariate linear regression equations are proposed to evaluate the post-fire yield strength of all three structural steels as a function of ferrite grain size and pearlite colony size. The results of this study will be useful to forensic engineers when evaluating the residual strength of fire-affected steel structures based on microstructures, especially when elevated temperature values are not available.

This paper presents investigations on the effects of edge-oxidized graphene oxide (EOGO) on the rheological performance of cement composites. EOGO is produced by a mechanochemical process that can be large production with significantly reduced cost, which enables practical use in infrastructure construction. The work scope is limited to the use of EOGO as an additive in cement paste and cement mortar. This study explored two mix design methods, a dry-mix design and wet-mix design. The dry-mix design method involves the use of EOGO as a dry powder in cement composites, whereas the wet-mix design method means its use as a water-dispersed solution through a sonication process in those cement composites. Varied contents of EOGO ranging from 0.01% through 1.0% were used in both mix design methods. The experimental results show that EOGO-cement composites show higher viscosity than control specimens, which is supported by a microstructure assessment with scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). In addition, it is found that the fluidity of cement composites slightly decreased and apparent viscosity slightly increased with the wet-mix design when compared with the dry-mix design. These results indicate that using the dry-mix design method for EOGO-cement composites is feasible and more practical for field applications.

To evaluate the feasibility of using basalt and pumice as pozzolanic materials in a cement-based material, this paper is focused on the pozzolanic activity component (PAC) of basalt and pumice. PAC was explored as a characteristic index of potential pozzolanicity to express the intrinsic capacity of pozzolans regardless of particle size and other external factors. PAC was calculated as the product of chemical composition (${\mathrm{SiO}}_2{+\mathrm{Al}}_2{\mathrm{O}}_3{+\mathrm{Fe}}_2{\mathrm{O}}_3$) content and amorphous phase content in rock; the former was analyzed using a wet chemical analysis, and the latter was determined by X-ray diffraction (XRD). Using chemical composition data, petrographic characteristics, powder XRD, and pozzolanic activity index data, it was summarized that both basalt and pumice had significant pozzolanicity and were suitable for use as supplementary cementitious materials. The relationship between the PAC and the pozzolanic activity index was evaluated through the ratio of mortar strengths achieved therewith. The results could be used to select basalt and pumice for use as pozzolans.

Cold recycled mixtures with bitumen emulsion and cement (CRMEC) are an environment-friendly and economic recycling technology in pavement rehabilitation. The low tensile strength and relative low pavement properties of CRMEC greatly limit its application scope. Wetting agent and superplasticizer, which can greatly change the fresh properties of cement bitumen emulsion (CBE) paste and adjust the interaction between bitumen emulsion and cement, were employed to increase the pavement properties of CRMEC. The bulk specific gravity (BSG), indirect tensile strength (ITS), moisture susceptibility, and low-temperature performance of CRMEC were investigated. Results indicate that superplasticizer can greatly improve the BSG, ITS, and low-temperature performance of CRMEC. Besides, CRMEC with superplasticizer has an equal moisture susceptibility as the reference CRMEC. A wetting agent can increase the ITS of CRMEC but decreases its frost resistance and low-temperature deformability. Besides, CRMEC with both surfactants features lower ITS and worse frost resistance and low-temperature performance than CRMEC with only superplasticizer. The corresponding mechanisms were studied. Results indicate that both surfactants can reduce the viscosity of CBE paste. Superplasticizer is beneficial to form a uniform bitumen membrane structure in CBE paste. The wetting agent can greatly decrease the contact angle of bitumen emulsion, but it is harmful to the formation of bitumen membrane in CBE paste. Therefore, superplasticizer is recommended to improve the pavement properties of CRMEC.

The performance of conventional or reclaimed asphalt pavement (RAP) mixes depends on the properties of the virgin and RAP binders. The fundamental characteristics of different materials often are used to explain the mechanical performance. Surface free energy (SFE) is one such property that can be considered to explain the fracture and rutting performance and moisture damage resistance of bituminous binders and mixes. The correlation between different rheological properties of binders (virgin as well as RAP blends) and the SFE, determined by the sessile drop technique, was explored in this study. Two commonly used virgin binders and different virgin–RAP binder blends (prepared by varying the RAP content in the blend) were evaluated. Penetration, softening point, viscosity, Superpave rutting and fatigue parameters, multiple stress creep and recovery (MSCR), and linear amplitude sweep (LAS) test parameters of the binders were measured and correlated with SFE. Total cohesive surface free energy of the binders was found to correlate well with (1) cohesive/stiffness properties of the virgin and RAP binders represented by penetration, softening point, and $G^{*}$ (complex shear modulus); (2) the viscoelastic response indicated by phase angle and percentage strain recovered; (3) rutting resistance, represented by the Superpave rutting parameter ($G^{*}/\sin \delta$) (where $\delta$ is phase angle) and non-recoverable compliance measured in the MSCR test; and (4) fatigue performance indicators such as the Superpave fatigue parameter ($G^{*}\sin \delta$) and the fatigue life estimated from LAS test. The study clearly established the correlation between SFE and the mechanical parameters evaluated in the study and indicates the need to conduct a more-detailed and exhaustive experimental program to develop generalized relationships applicable to a wider range of binders than considered in this study. The fact that a single binder parameter measured by a simple method can explain multiple aspects of performance is a promising prospect.

A laboratory study was conducted to develop a thin-lift overlay (Thinlay) mix design containing a polymer-modified PG58-34E+ binder with a 3.5% add to the mix, and 40% fine reclaimed asphalt pavement (RAP) that would meet the criteria for the State of Iowa using a bioderived rejuvenator called sub-epoxidized soybean oil (SESO). Two groups of binder and mix specimens were created for this investigation: (1) a control with no SESO, and (2) a rejuvenated group with 0.28% SESO by total mix weight (4.88% by total binder content-RAP binder + PG58-34E+), where the binder groups were evaluated using the multiple stress creep recovery (MSCR) test and bending beam rheometer (BBR), while the mix groups were evaluated using rutting, low-temperature, and fatigue performance tests. Binder results showed that the optimal dosage of SESO must be higher than 8% to achieve a PG46-46E+ to account for RAP inclusion in the mix design. Binder performance had a significant effect on low-temperature mix and fatigue performance, while rutting performance was found to be acceptable for the rejuvenated group.

Steel manufacturing factories usually dump byproduct recycled steel randomly in open areas, creating environmental hazards. Using such materials in highway construction could be a solution to the environmental hazards generated from their disposal. A combined method of physical and chemical stabilization was used in this study to investigate the value of using mill scale (MS) and cementitious materials in improving the strength and deformation properties of subgrade soil. The results showed that MS additives effectively reduced plasticity and increased maximum dry unit weight, unconfined compression strength (UCS), and California bearing ratio (CBR). Subgrade soil with 20% MS was treated with cement and lime to obtain a strength value of 1.7 MPa (after 7 days of curing) for subbase application. A repeated load triaxial (RLT) device was used to perform resilient modulus ($M_R$) and permanent deformation tests in order to evaluate the response of laboratory-molded stabilized specimens under cyclic loading in accordance with a standard testing procedure. Study findings are explained through a microstructural analysis that used scanning electron microscopy (SEM) supplied with energy-dispersive X-ray spectroscopy (SEM/EDX). The test results showed that, in addition to solving the MS disposal problem, the use of MS as an additive had a favorable influence on the geotechnical properties of the soil.

The angularity of coarse aggregates significantly influences the performance of asphalt pavement. However, the research remains in the qualitative stage, and no universal evaluation standard has been proposed. This research proposes image-based methods to quantitatively analyze the angularity of coarse aggregates, thereby providing corresponding evaluation standards. First, aggregate levels of 4.75–9.5, 9.5–13.2, and 13.2–16 mm were obtained by sieving experiments, which were then abraded 0, 400, 800, and 1,200 times using a Los Angeles abrasion machine. Subsequently, the aggregate particle angularity parameters, including circumference, area, convex hull circumference, convex hull area, and total number of corner points, were calculated. Meanwhile, the aggregate imaging system (AIMS) gradient, skeleton extraction, convex hull, and uncompacted void content (UVC) methods were used to evaluate the angularities of the aggregates. Thereafter, the AC-13C-type mixture test specimens were formed using different angularity aggregates. On this basis, the angularity-related pavement skid resistance and rut resistance tests were conducted. The results show that the skeleton extraction method performs excellently for evaluating all aggregate levels, while the convex hull method is suitable for 9.5- and 13.2-mm aggregates, the AIMS gradient method is suitable for assessing 4.75- and 9.5-mm aggregates, and the UVC method is suitable for assessing 9.5- and 13.2-mm aggregates.

This paper evaluated alternative test methods to determine the crushing potential of aggregates and documented the influence of aggregate characteristics on the engineering properties of asphalt mixes. Six aggregates sampled from different sources were subjected to various aggregate tests, including the Los Angeles abrasion, micro-Deval, soundness magnesium, and acid insoluble tests. A Superpave mix with a 12.5-mm (1/2-in.) nominal maximum aggregate size gradation was produced with each aggregate source using the same PG 64-22 asphalt binder. The mixtures were produced to investigate the impact of aggregate properties on their volumetric properties as well as the tensile strength from the indirect tension tests and rutting potential from the Hamburg wheel tracking tests. Correlation analyses among the measured parameters identified the aggregate crushing value as a promising alternative test method to quantify the crushing potential of aggregates and to adjust the gradation accordingly to produce mixtures with optimized volumetric properties.

The effect of ethylene vinyl acetate (EVA) on the aging properties and rheological properties of rubberized asphalt was measured in this paper to identify the optimum proportion of EVA combined with waste tire rubber (WTR) modified asphalt. Aging methods of thin-film oven test (TFOT) and pressure aging vessel test (PAV) were conducted to imitate the different degrees of the aging process. At first, frequency sweep at different temperatures was carried out to construct the construction of $G^{*}$ master curves, following the time-temperature superposition principle, to evaluate the aging sensitivity. The black diagram was depicted to compare the rheological behavior of different asphalt binders. The calculation of the WLF equation based on the shift factor of master curves was conducted to calculate the values and aging index of 15°C DSRFn to assess the resistance to fatigue cracking at the intermediate temperature. Then, zero shear viscosity (ZSV) and rutting factor ($G^{*}/\sin \delta$) at 60°C were also used to calculate the aging index, because these both are measurements of resistance to rutting deformation at high temperature. Finally, the microstructure of unaged and aged asphalt binder was studied by Fourier transform infrared spectroscopy (FTIR). The relationship between rheological and chemical indexes was studied. The results show that 15%WTR+4%EVA has the best antiaging performance, and EVA can reduce the aging sensitivity of different parameters, especially in the high-temperature area.

The chemical composition of a bitumen dictates its rheological properties as well as its performance in an asphalt mixture. Any bitumen comprises a wide variety of complex hydrocarbons, and its chemical composition can be characterized by many different parameters. Similarly, the mechanical properties of any given bitumen are typically characterized based on its time-temperature dependent rheological properties at different stress levels. This study characterizes the chemical makeup of a set of bitumens from several different producers based on their polarity and compares these characteristics to mechanical properties associated with the Superpave performance grading (PG) of bitumen and its tensile strength. To do this, a novel fractionation technique was used to separate the bitumens into chemical fractions, while performance testing was performed on the original bitumens. The results were compared using a statistical analysis software to examine relationships between the chemical fractions and physical properties. The results show that high temperature stiffness is strongly dictated by the asphaltene content and that the low temperature stiffness is strongly dictated by the aromatic and resin content. The useful temperature interval showed a good correlation with asphaltenes and resins. Finally, the tensile strength of the bitumens also showed a strong correlation with SARA parameters. Bitumens that deviated from some of these correlations also showed an uncharacteristic response in some other mechanical or elemental property measurements. The relationship between time-dependent characteristics and polar fractions was not strong and requires further understanding.

The aim of present investigation is to evaluate the carbonation resistance of self-compacting concrete (SCC) containing copper slag (CS) as fine aggregates. A total of 18 mixes were prepared, which were divided in to three series, namely CS-based mixes (Series 1), CS-based mixes with silica fume (Series 2), and CS-based mixes with metakaolin (Series 3). Compressive strength was assessed at the curing age of 7, 28, 56, 90, and 120 days, whereas accelerated carbonation was carried out for ${\mathrm{CO}}_2$ attack duration of 4, 8, 12, and 16 weeks after curing period of 28 and 120 days. The results of compressive strength revealed that Series 3 performed better among three series. Carbonation depth decreased with increase in the content of CS substitution for each series. Among three series, minimum carbonation depth was noticed for Series 3 followed by Series 2 and Series 1. This study evinces that CS can be utilized as fine aggregate with supplementary cementitious materials (SCMs) in the construction sector to bestow better resistance to the carbonation.

The details of experimental testing of thermomechanically treated reinforcing bars at elevated temperatures are presented in this paper. Rebars of 10-, 12-, 16-, 20-, and 25-mm diameter were used in the testing program. An electrical furnace was used to heat the bars to 100°C–900°C in increments of 100°C. The chemical composition of the rebars complied with bar manufacturing standards. The effect of bar diameter on the mechanical properties was random at ambient temperature, which also followed for the testing at elevated temperatures. These differences were due to the differences in the bar chemical composition. The yield plateau of the 25-mm-diameter bar disappeared on heating at 100°C, whereas this phenomenon occurred at 300°C for the rest of the bars. The rebar ultimate strength up to 300°C was higher compared with the strength at ambient temperature owing to blue-brittleness effects. The reduction coefficients for the proportional and yield strengths and the elastic moduli for all bars were similar at all heating temperatures. Brittle behavior of the bars tested at high temperatures was observed relative to the ambient temperature up to 500°C, which changed to ductile behavior thereafter. The suggested models to predict stress–strain curves for the strain-hardening region provided a reasonable match with the average observed curves for the bars tested at both ambient and elevated temperatures.

Highfriction surface treatment (HFST) has been widely utilized by state departments of transportation (DOTs) to reduce friction related vehicle crashes. However, although many studies have been conducted to enhance the durability of HFST, limited information is available on the properties of the HFST epoxy–bauxite mortar. Although an HFST may contribute little to the pavement structural capacity, its epoxy–bauxite mortars have several distinguishing properties that may result in incompatibilities between the HFST and underlying pavement. Consequently, knowledge of the HFST epoxy–bauxite mortar properties is critical to ensuring its durability. This paper determined the physical and mechanical properties of epoxy–bauxite mortar for HFSTs. An empirical method was developed to estimate an approximate binder content. Comprehensive laboratory testing determined the properties, including density, Poisson’s ratio, coefficient of thermal expansion (CTE), dynamic modulus, and crack resistance. It was found that the HFST epoxy–bauxite mortar has a CTE significantly higher than that of hot-mix asphalt (HMA) mixtures and portland cement concrete (PCC). The HFST epoxy–bauxite mortar basically is a viscoelastic material with very low water-absorption ability and a dynamic modulus greater than that of a HMA mixture. The test results of fracture energy, tensile strength, and crack progression rate (CPR) consistently indicated that the HFST epoxy–bauxite mortar has very good cracking resistance.

Self-compacting concrete (SCC) is widely used in the China Rail Track System (CRTS) III slab ballastless track filling-layer structure for high-speed railways (HSRs). In cold regions, the thin filling-layer SCC is subjected to the coupling effects of freeze–thaw cycles and load, shortening the service life of the track structure. This study focused on the performance evolution and damage constitutive model of thin flat plate SCC under the coupling effects of freeze–thaw cycles and load using a self-designed preloading device. Results showed that the increase of freeze–thaw cycles reduced the performance of SCC gradually. When SCC was exposed to 300 freeze–thaw cycles, the mass loss rate was 2.41%, peak stress (${\sigma }_p$) decreased by 23.1%, peak strain (${\epsilon }_p$) increased by 67.9%, and relative elastic modulus ($E_i/E_0$) decreased to 47.9%. However, when SCC was subjected to the coupled effect of 300 freeze–thaw cycles and $1/3$ peak stress, the mass loss rate was 2.95%, ${\sigma }_p$ decreased by 35.5%, ${\epsilon }_p$ increased by 79.9%, and $E_i/E_0$ decreased to 42.9%. Compared with freeze–thaw cycles alone, the coupled effect of freeze–thaw cycles and load accelerated deterioration of SCC. A damage constitutive model of SCC derived from the hypothesis of Lemaitre strain equivalent and Weibull statistical distribution could well describe the constitutive relation of SCC under the coupling of freeze–thaw cycles and load. As the number of freeze–thaw cycles increased, shape parameter $m$ exponentially decreased and scale parameter $a$ changed according to the cubic equation of one variable. Shape parameter $m$ decreased with the increase of the number of freeze–thaw cycles, and scale parameter $a$ in the Weibull statistical distribution was related to freeze–thaw cycles and load.

In this study, the residual of hemp products as biomass wastes has been ground into powders to be used in cement-based materials. The effect of untreated and alkaline-treated hemp powders on the hydration of portland cement paste was studied by isothermal calorimetry analysis, thermogravimetric analysis, Fourier transform infrared spectroscopy analysis, and scanning electron microscopy analysis. The results show that partially replacing cement with untreated and alkaline-treated hemp powders can delay cement hydration and reduce the degree of hydration. Compared with untreated hemp powders, alkaline-treated (washed or nonwashed) hemp powders show a lower set delay effect on cement hydration; moreover, distilled-water-washed treated hemp powders delay less than nonwashed treated hemp powders. The study also shows that coarse hemp powders exert a lower set delay effect on cement hydration than fine hemp powders. Generally, the distilled-water-washed treated coarse hemp powders exert the minimum delay effect on cement hydration.

Self-healing properties of concrete mean that concrete can repair cracks and effectively slow down the penetration of chloride ions. This work develops a chloride ion transport mesoscale model to study how chloride ions diffuse into concrete with crack self-healing properties. This model consists of aggregate, mortar, interfacial transition zone (ITZ), crack, and damage zone (DZ) phases. It was validated by experimental data. Based on this mesoscale model, the dynamic crack self-healing process was simulated by moving mesh technology using finite-element software. Crack and DZ sizes varied as a function of time. Distribution of the chloride concentration in cracks and DZs during self-healing and the influence of self-healing rate on chloride concentration distribution, as well as that of the ITZ and DZ on chloride concentration distribution, are analyzed and discussed.

Performance evaluation of cementitious mortar reinforced with natural fibers (jute) and synthetic (polypropylene) fibers is carried out in this article with respect to mechanical response and life cycle cost estimation. The individual mechanical properties of the two fibers were observed to have significantly influenced the mechanical properties of composites. Uniaxial direct tensile and flexural strength of the composites made with jute fibers were higher than those of the polypropylene fibers, whereas the tensile strain and flexural displacement were higher for the polypropylene-based composites, which is in accordance with the response behavior of individual fibers. A combination of these fibers also demonstrated an improvement in strength as well as ductility characteristics, especially with regard to tension and flexure. Life cycle cost estimates and sensitivity analysis demonstrate that polypropylene fiber–reinforced cementitious composites perform better compared to jute fiber reinforcement followed by cementitious samples with no fiber reinforcement.

In this paper, an analytical stress–strain model is proposed that emphasizes the influence of steel fibers of different geometry and volume content on the behavior of the confined reactive powder concrete (RPC) columns. The proposed model takes into account the influence of the geometry and volume content of steel fiber on the behavior of the confined RPC column in terms of peak load, corresponding deformation, and post peak behavior. The behavior of the confined RPC columns reinforced with different types of steel fiber subjected to concentric loading is represented analytically. The analytical behavior of the fibrous RPC columns is verified with the results obtained experimentally from the literature. The outcomes show that the proposed analytical model to present the behavior of confined fibrous RPC columns is in very good agreement with the results obtained experimentally.

This article addresses the performance of structural lightweight aggregate concretes and the relation of their performance to density class. Natural expanded silicate materials treated with a hydrophobic agent were used and their effects were systematically investigated. Three lightweight concretes with densities of about 1,000, 1,150, and $\mathrm{1,400}\mathrm{kg}/{\mathrm{m}}^3$ (classes D1.0, D1.2, and D1.4) were designed by applying an optimized particle packing theory. The microstructure, mechanical properties, and durability of the developed concretes were determined and the relations of these properties with density were evaluated. The lightweight concretes showed excellent structural efficiency, with 28-day compressive strengths of about 23, 28, and 42 MPa, respectively. Microstructural analyses showed that the developed concretes had a rather compact microstructure, contributing to enhanced strength. Existing codes for calculating concrete $E$-modulus were compared, and the best predicting formula is proposed. Mix D1.4 showed relatively low drying shrinkage, which can be attributed to relatively low initial water use and the internal curing effect brought about by the applied lightweight aggregate. The developed mixes showed excellent durability, as indicated by very low water penetration after 72 h of exposure under a pressure of 0.5 MPa (5 bars) and very small mass loss after 56 cycles of a freeze–thaw test under both deionized water and NaCl conditions.