Journal of Materials in Civil Engineering

To repair microcracks in cast-in-place concrete bridge decks and improve the quality of bridge deck pavement, low-viscosity epoxy grouting material was prepared. The effects of different diluent types and dosages on the viscosity, operable time, and mechanical properties of the epoxy grouting materials were compared. The variation of the bond strength, tensile strength, and engineering strain of the grouting material with the dosage of the active diluent (AD-I, AD-II, and AD-III) was explored. Based on the reconstruction data envelopment analysis (DEA) method, a model for optimizing the composition of the grouting material was established. The results show that the initial viscosity and 30-min average viscosity of the epoxy grouting material initially decreased rapidly, then declined more slowly. When the dosage of active diluent was 15%, the operable time increased more than 150% compared with the epoxy grouting material without active diluent. The tensile strength and engineering strain of the epoxy grouting material at low temperature first increased slightly and then decreased rapidly. The tensile strength at room temperature and high temperature was basically the same as that at low temperature, while the engineering strain increased overall. The bonding strength of the epoxy grouting material increased slightly first and then decreased rapidly with the addition of AD-I and AD-II active diluent and decreased rapidly with the increase of AD-III active diluent. Through reconstruction and optimization of the DEA method, the final optimal epoxy grouting material formulations were found to be AD-I-15, AD-II-15, AD-III-10, and the dosage of AD-I, AD-II, and AD-III active diluent accounts for 15%, 15%, and 10% of the epoxy resin, respectively. The low-viscosity epoxy grouting material prepared in this study had excellent groutability and mechanical properties, which can provide an effective guarantee for the repair of microcracks in cast-in-place concrete.

This paper describes the results of a study on the influence of mesoporous silica of the Mobil composition of matter No. 41 (MCM-41) structure type on the early-age properties of the cement matrix (CM) and the microstructure development. To date, no studies related to the use of MCM-41 to modify the CM structure have been reported in the literature. The MCM-41 used in this study was produced from a waste material created during the conversion process of fly ash into synthetic zeolites. A number of physicomechanical, and compositional properties were tested. MCM-41 was applied in amounts of 0.25%–2% by weight of cement in a manner that allowed its uniform dispersion, and tests were performed as a function of maturation time, i.e., after 1, 3, 7, 14, and 28 days. The MCM-41 was found to accelerate the cement hydration process and its use promotes the formation of a more compact, gel-like CSH phase with greater cohesion.

Roller-compacted concrete (RCC) structures are often destroyed by coupling damage of freeze–thaw and complex loads in cold conditions, resulting in degradation of the mechanical properties of the RCC. In this study, the failure process of freeze–thaw RCC in the triaxial compression test and the law of crack development were studied through a combination of tests and the discrete-element method (DEM). The results showed that the freeze–thaw damage degree of the RCC presents three different stages: (1) growth, (2) slow growth, and (3) rapid growth phases. It was found that 125 cycles can be regarded as a critical point of RCC freeze–thaw damage, beyond which the damage degree increases sharply. With the increasing number of freezing–thawing cycles, the brittle failure weakened and the failure patterns became increasingly severe. The cracks on the failure surface mainly passed through the cement mortar and interfacial transition zone, whereas the coarse aggregate was rarely damaged. The peak strain was regarded as the critical point for the damage of freezing–thawing cycles coupled with triaxial compression. Before the peak strain, microcrack growth of the RCC was not obvious, and the coupling damage was relatively weak. As the microcrack approached the peak strain, it grew rapidly and the coupling damage increased remarkably.

In order to achieve better efficiency of dispersed fiber reinforcement in cementitious composites, manufacturers need to be able to directly control the fiber orientation. The magnetic orientation of fibers is an effective way to align fibers in the desired direction of the main tensile stresses and significantly improve the load-bearing capacity of the composite material. In this study, cementitious composites with different percentages of fiber reinforcement were subjected to the magnetic fiber-orienting process and their resulting mechanical parameters were examined. Also, a nondestructive method was used to evaluate the fiber orientation and volume. The flexural strengths and the capacity to dissipate mechanical energy were improved considerably compared to the reference nonoriented specimens. The nondestructive method was also reasonably accurate to predict these results.

Sand-bentonite mixtures (SBM) are usually compacted as clay covers and liners of the landfill. However, unavoidable factors such as heterogeneity in compaction result in variable densities that causes low strength, high volumetric shrinkage, and increased hydraulic conductivity of SBM; hence, additives are often required for enhancement. This article focuses on the applicability of Polythene terephthalate (PET)–based chemically recycled polymer, i.e., Bis (2-hydroxyl) terephthalate (BHET) to enhance SBM for covers and liners. The required BHET polymer content in SBM specimens prepared at three molding densities (1.55, 1.65, and $1.75\mathrm{g}/{\mathrm{cm}}^3$) was evaluated based on three criteria: low hydraulic conductivity ($k<{10}^{-7}\mathrm{cm}/\mathrm{s}$), high unconfined compressive strength ($q_u>200\mathrm{kPa}$), higher split tensile strength ($q_t$), and low volumetric shrinkage, $VS<4\%$. One-dimension (1D) consolidation, $q_u$, $q_t$ and $VS$ tests were performed by mixing 0%, 1%, 2%, and 3% of BHET with sand-bentonite ($75:25$ in weight ratio). BHET addition to SBM molded even at lowest density offered resistance to both compression ($C_c$) and swelling ($C_s$), thereby reducing the coefficient of consolidation ($C_v$) and the hydraulic conductivity ($k$). With an increase in molding density, the polymer addition showed an increment in $q_u$, $q_t$, and reduction in $VS$ values. A BHET content of 3% of the SBM was enough to meet all three criteria for covers and liners at all three molding densities. Scanning Electron Microscopy (SEM) revealed polymer links and films formation at the interparticle contact points of bentonites and SBM. Energy-dispersive X-ray spectroscopy (EDX) analysis confirms the elemental interaction of BHET and montmorillonite. Both SEM and EDX tests support the proposed binding mechanism and conceptual model for the BHET enhanced SBM.

To study the reason why the evaluation result of fracture energy is sometimes inconsistent with in situ cracking, the accuracy of fracture energy in evaluating low-temperature cracking resistance of asphalt mixture was investigated. Firstly, the composition of fracture energy in the thermal stress restrained specimen test (TSRST), semicircular bending test (SCB), disk-shaped compact tension test (DCT), indirect tensile test (IDT), and three-point bending beam test (3PBB) was analyzed and the accuracy of fracture energy was discussed. Then, based on the defect of fracture energy, the evaluation index and test method in evaluating the low-temperature cracking resistance of asphalt mixture were proposed. Finally, some test results were used to verify the rationality of the proposed evaluation index. The results show that the fracture energy determined from TSRST, SCB, DCT, 3PBB, and IDT may be inaccurate to evaluate the low-temperature cracking resistance of asphalt mixture, as the fracture energy in these test methods is mainly the surface energy. If fracture energy was used to evaluate the low-temperature cracking resistance of asphalt mixture, it may choose a mixture with high modulus, poor relaxation performance, or fabricated by high surface energy materials. The dissipative energy caused by the stress relaxation should not be ignored when using energy as the evaluation index. The viscous dissipative energy obtained from DCT, SCB, or IDT at two different test temperatures was recommended to evaluate the low-temperature cracking resistance.

Concrete structures are exposed to water throughout their service life. Nowadays, fiber-reinforced concrete is the most preferred concrete due to its superior mechanical properties. However, good mechanical properties alone cannot protect concrete against the environmental conditions it may encounter during its service life. In particular, water is an inevitable factor faced by concrete elements. In this study, the permeability properties of concrete produced with different combinations of four different fibers were investigated. Hybrid fiber concrete (HFC) was made using the central composite design method. Steel, glass fiber, synthetic, and polypropylene fibers were hybridized among themselves, and the aggregate and paste phases of concrete were hybridized with electric arc furnace slag aggregate (EAFS) and fly ash (FA), respectively. Ultrasonic pulse rate, rapid chloride permeability (RCP), capillary water absorption capacity, and carbonation depth (CD) of HFC were determined. Statistically significant and nonsignificant parameters for each response were determined. Simultaneous substitution of EAFS and FA reduced the capillarity coefficient and CD of HFC. The RCP of HFC depends mainly on two factors: binder dosage and steel fiber ratio. The most suitable fiber for reducing CD was glass fiber. The estimated RCP, ultrasonic pulse velocity (UPV), and capillary water absorption capacity (CWAC) results were compared with the control sample, and the results were 81%, 114%, and 86% of the control sample.

The storage stability of polyethylene (PE)-modified asphalt was investigated. The experimental results of this paper show that the storage stability of PE-modified asphalt is poor, and it is difficult to solve the compatibility problem between PE and base asphalt by adding stabilizer. In this paper, the study and application of the rubber plastic composite method to improve the compatibility of PE and base asphalt was investigated. The experimental result shows that styrene-butadiene-styrene block copolymer (SBS) could be melted with waste PE with a twin-screw extruder to prepare PE-SBS modifier. The PE-SBS modified asphalt prepared is stable in storage. The compatibility of PE and base asphalt is improved effectively by rubber plastic composite method. Infrared spectra show that PE-SBS is mainly formed by physical action.

The present study aims to develop a two-yoke magnetic sensor system, measuring the mass loss of steel in concrete subjected to nonuniform corrosion. The impressed current method was employed to induce the nonuniform corrosion of steel in concrete specimens. Experiments and theoretical calculations based on the finite-element method were performed to verify the effectiveness of the two-yoke magnetic sensor. Parametric analyses were carried out to investigate the effects of distribution of rust layer, the geometry of steel bar, as well as the depth of concrete cover on the results of magnetic flux density sensed by the sensor. Results showed a good accuracy in estimating the mass loss of nonuniformly corroding steel by the change of magnetic flux density. Little influence was exhibited by varying the amount of corrosion products including the distribution of rust layer and the volume expansion ratio. It revealed the effectiveness and accuracy of the two-yoke magnetic sensor in quantitatively evaluating the corrosion degree of nonuniformly corroding steel irrespective of different distributions of rust layer. With respect to the sensitivity in structures with large concrete cover, the two-yoke magnetic sensor demonstrated a better performance than the external magnetic sensor.

The synthesis parameters, such as alkali activator type and content and water/binder (w/b) ratio, directly affect the dissolution and geopolymerization kinetics in geopolymers, playing a major role in its flow performance over time. However, the isolated effect of each parameter on the rheology of fresh metakaolin-based geopolymer is still not completely understood. This work assessed the effect of the alkali type (Na or K), concentration (15% or 20% by weight of the activating solution), and $w/b$ ratio (from 0.70 to 0.80) on the fresh properties of metakaolin-based geopolymers. Minislump and Marsh cone tests with the use of image analysis and dynamic strain sweep rheometry were conducted at different testing times. The results showed that a high $w/b$ ratio increased the initial flowability of paste (reduced the yield stress and Marsh cone time, and increased the minislump) as expected, whereas the flowability was reduced over time. Increasing the alkali concentration also increased the flowability of pastes regardless of the alkali type used. The most important finding is the corroboration that the type of alkali (${\mathrm{Na}}^{+}$ or ${\mathrm{K}}^{+}$) was the parameter that had the greatest impact on the rheological behavior of pastes: mixes produced with potassium-based activator had higher flowability compared with those produced with sodium-based activator for the same concentration, $w/b$ ratio, and testing time. The increased yield stress reduced workability, which might negatively affect its applicability and consequently the hardened performance of the material. Therefore, if high flowability is required, the use of potassium must be considered, either through its partial or complete presence in the alkali activator.

In order to improve the fresh properties and freeze-thaw resistance of cementitious systems, water-reducing and air-entraining admixtures are actively used in concrete mixtures. Generally, these mentioned admixtures are added to concrete mixtures as two separate admixtures. In this case, when the properties/compositions of one of the admixtures change, compatibility problems of admixtures may occur with each other or with the cement, and the fresh/hardened properties of the concrete may be adversely affected. In this study, a modified water-reducing admixture with both fluidity and air-entraining properties was produced. The utilization effect of high-range water-reducing admixtures (HRWR) having different ethylene oxide/propylene oxide (EO/PO)–based air-entraining surfactants (AES) on some properties of concrete mixtures was investigated. For this purpose, firstly, hybrid silicone AESs with a silicon content of 20%, 33%, and 38.5% were supplied. Then, HRWRs containing seven different AES were produced by using substitution and synthesis methods. In HRWRs produced by the substitution method, 3 and 5 wt. % of HRWR were substituted with EO/PO-based hybrid silicon AES. In the other method, EO/PO-based hybrid silicon air-entraining macromonomers were bonded to the HRWR at ratios of 1, 3, and 5 wt. % during its synthesis process. Replacing HRWR with hybrid silicone AESs increased admixture demand to provide the target slump value in concrete mixtures. Utilization of AESs containing 20% and 33% silicon in HRWR by the substitution method positively affected the permeability and compressive strength of concrete mixtures, while the rise of this ratio to 38.5% by using the synthesis method did not affect them significantly. The presence of surfactant with 20% silicon in 3% and 5% of the admixture and with 33% silicon in 5% of the admixture positively affected frost resistance of concrete mixtures. However, the use of surfactants with 33% silicon content in 3% of the admixture and 38.5% silicon in 1%, 3%, and 5% of the admixture showed a negative effect on the frost resistance of the mixtures.

High-quality coarse aggregates are routinely used for the surface, base, and subbase layers in paved roads or the surface course in unpaved low-volume roads. Unfortunately, high-quality aggregates meeting stringent material specifications are becoming increasingly costly and difficult to find within reasonable distances of road construction projects. Various stabilization technologies can be employed to improve the mechanical properties of available aggregate materials, providing environmental and economic benefits. This investigation used three laboratory test methods to evaluate and compare all the existing kinds of additive technologies suitable to stabilize a coarse-graded road unbound layer. Two traditional solutions (cement and bitumen) and eleven nontraditional solutions (categorized as either brine salts, clay binders, organic nonpetroleum products, organic petroleum products, or synthetic polymers) were included. Repeated load triaxial tests were performed to evaluate the dynamic behavior of the untreated and treated aggregates in terms of their resilient modulus and the resistance against permanent deformation. A modified version of the rolling bottle test was used to appraise the stripping resistance offered by each additive. A microscopic analysis was conducted to visually evaluate the propensity of the additives to adequately coat the surface of the aggregates. All the stabilization technologies improved the material stiffness, with the most significant improvements produced by calcium chloride salt, bentonite, lignosulfonate, and cement mixed with a mineral mixture. The stabilization additives effectively reduced permanent deformations, except for the specimens stabilized with polyurethane and bitumen. Finally, the polymer-based additives and bitumen demonstrated very good resistance to stripping, with polyurethane providing the smallest mass loss. This study documents that nontraditional stabilization technologies can provide effective alternatives to the traditional stabilizers and documents that a “one-size-fits-all” additive agent is unlikely to be developed.

The incorporation of fiber into cementitious composites is considered a reassuring way to enhance its mechanical properties. However, high-temperature exposure can severely affect it. This investigation aims to study the high-temperature behavior of cementitious composite containing steel and glass fibers from microstructure to mechanical properties. To examine the compressive and tensile strength, the specimens were heated to the target temperature (200°C, 300°C, 400°C, 650°C, and 800°C) and tested in the hot state. The volume fraction for steel fiber was 0.25% and 0.5%, and for glass fiber, it was 0.25%. Moreover, to examine the microstructural transformation, scanning electron microscope, X-ray diffraction, and thermogravimetric analyses were conducted on the samples extracted from the heated specimens. Based on the results, the mortar containing steel fiber enjoyed better mechanical strength at high temperatures. The inclusion of steel fibers could improve the compressive and tensile strength of the normal mortar, on average, by 9% and 14% at 400°C. However, the excessive inclusion of those adversely affected the compressive strength, particularly at temperatures above 650°C. Moreover, all types of mortars experienced a fluctuation phase in their mechanical strength at the range of 28°C–400°C resulting from rehydration of portlandite and evaporation of free water. The main reduction branch commenced at temperatures above 400°C, where decomposition of portlandite and microcrack development were noticeable.

The addition of virgin polymers to asphalt binders is a technique widely used in the asphalt paving industry, because this approach helps improve the performance and extends the longevity of asphalt pavements. In recent years, modification of asphalt binders with polymeric waste has received a lot of attention from asphalt industry experts, due to economic and environmental benefits. This paper aims at evaluating the rheological characteristics at low and intermediate temperatures of a performance grade (PG) 64-22 asphalt binder modified with crumb rubber (CR) from discarded tires and recycled low-density polyethylene (RPE) from post-industrial sources, with the following component proportions by percentage of mass: $86\le \mathrm{binder}\le 100$, $0\le \mathrm{RPE}\le 4$, and $0\le \mathrm{CR}\le 10$. To achieve this objective, a series of rheological tests were performed, namely: linear amplitude sweep, Superpave performance grading, and frequency sweep. The results indicated that the modifiers increased the fatigue resistance of the asphalt binders. The addition of 4% RPE had a worsening effect on the low-temperature performance of the asphalt binder. Nevertheless, with the hybrid modification with CR, the binder’s low-temperature performance was restored. Furthermore, the modifiers improved the asphalt binder’s temperature susceptibility, based on $|{\mathrm{G}}^{*}|$ data from master curves.

While the monitoring of longitudinal (P) waves has been widely investigated to estimate the initial setting time of concrete mixtures based on the variation in P-wave velocities, it is difficult to accurately estimate the setting time owing to the sensitivity of P-waves to air voids and the difficulties in identifying the final setting time from smooth velocity variations. Furthermore, shear-horizontal (SH) waves are advantageous over P waves for monitoring the setting time owing to their high signal-to-noise ratio and sensitivity of the shear-wave velocity ($V_s$) to solid structure development. This study proposes an SH-wave-based method to identify the abrupt increase in the $V_s$ values at the initial and final setting times. The proposed method was verified against traditional penetration resistance tests and P-wave tests with two sets of concrete specimens having different water-to-cement ratios. Although the initial setting times from the P-wave and SH-wave tests are close with the differences of 9% and 21% for the two sets of specimens, however, the smooth velocity variations from the P-wave tests cannot identify the final setting time that can be clearly captured with the abrupt increase of $V_s$ from the SH-wave tests. Both setting times from the SH-wave tests and the penetration resistance tests have a high correlation with a coefficient of determination (${\mathrm{R}}^2$) of 0.9875. The results demonstrated the high sensitivity of $V_s$ to the setting time and the potential applications of SH waves for monitoring the setting time of concrete mixtures.

Magnesium oxychloride cement (MOC), a type of special construction material, has drawn much research attention in solid waste utilization and environment protection thanks to its eco-friendly production process. The potential consumption of limestone powder (LSP) in MOC products would further mitigate the environmental pollution. This study investigates the feasibility of using LSP in optimized MOC pastes. By adding 10%–40% by weight LSP, the flowability, mechanical, and microstructure properties of LSP-MOC pastes (MOC pastes mixed with LSP) were experimentally evaluated. Results showed that LSP had an adverse effect on the flowability and retarded the setting process. In terms of mechanical properties, decreases in flexural and compressive strength became significant in the presence of LSP. However, it is noteworthy that expansion was mitigated via free deformation tests, which was also reflected by microstructures. By defining normalized expansion strain, the overall strength-expansion performance was analyzed, resulting in a maximum consumption of 30% by weight LSP at a slight improvement in MOC pastes.

Large amounts of waste products have been and most probably will continue to be produced with urbanization, industrialization, and technological developments. The study presented herein is devoted to using blast furnace slag in cement-based composites as much as possible. For this purpose, the mechanical properties and microstructural differences of alkaline (sodium hydroxide and sodium silicate solutions)-absorbed mortars that contain 25%, 50%, and 75% (by mass) ground granulated blast furnace slag were investigated. According to the test results, it was found that a positive effect of sodium hydroxide curing on strength development started to be seen as the slag content in the mortar specimens increased. In addition, in order to see the effect of the curing time, 3-day and 7-day cured mortar samples were kept in air for 25 and 21 days, and then strength tests were conducted. Twenty-eight-day–cured samples had a compressive strength value close to that of samples with 7 days of curing plus 21 days of resting period. In addition, in the case of substitution of ground granulated blast furnace slag (GBFS) in mortar, curing mortar samples in sodium silicate is the most effective way to alter compressive strengths compared with the other curing conditions.

This research was developed for the evaluation of the mechanical response of a mixture of soil and reclaimed-asphalt pavement (RAP) stabilized with cement. Mixtures were made containing 70% Osorio sand and 30% reclaimed-asphalt pavement (RAP), and portland cement. Tests of unconfined strength, pulse-velocity, durability, and simple shear were performed. The unconfined strength tests showed that the porosity/cement index controls the unconfined compressive, splitting tensile, and flexural tensile strength of the mixtures. The replacement of part of the Osorio sand by RAP did not present an expressive drop of strength in these tests. The pulse-velocity test presented that the initial shear modulus and the porosity/cement index, unconfined compressive strength, and tensile strength could be related. Wetting–drying durability tests displayed that the accumulated loss of mass increased when the cement content and the dry unit weight decreased. The monotonic shear response showed that the inclusion of RAP positively influenced the internal friction angle of the material and the cohesive intercept presented higher values for samples with lower porosity/cement index. The cyclic shear response presented that the shear modulus degradation was lower when the stress variation was lower. For higher variations, the degradation was greater.

This work investigates the influence of calcium leaching on mechanical and physical properties of limestone powder (LS)–cement pastes cured under different temperatures. In order to achieve this goal, three different mass percentages of LS (10%, 30%, and 50%) were selected to replace cement, and the LS–cement pastes were cured under three different temperatures (5°C, 20°C, and 50°C). The LS–cement pastes were soaked in ${\mathrm{NH}}_4\mathrm{Cl}$ solution to accelerate the calcium leaching and simulate the leaching influence from water. The mechanical and physical properties including the compressive strength, flexural strength, Vickers hardness (VH), leaching depth, and electrochemical impendence spectroscopy (EIS) were conducted. The prediction model of VH and the relationship between equivalent VH and mechanical strength were built. The microstructure of LS–cement pastes is characterized by X-ray diffraction (XRD), thermogravimetric (TG), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) tests. Experimental results demonstrate that with the increase of LS, the decrease degree of mechanical and physical properties of LS–cement pastes increases gradually; Furthermore, the leaching damage degree of LS–cement pastes is the largest under curing temperature of 5°C, followed by 50°C and 20°C. The microstructure results reveal that the $\mathrm{Ca}{(\mathrm{OH})}_2$ in the leached zone of LS–cement pastes is completely dissolved, and the calcium leaching makes the LS–cement pastes cured under 5°C obtain the loosest structure and the most serious leaching damage, followed by 50°C and 20°C.

Repetitive loads result in increased irrecoverable strain and, consequently, fatigue cracking failure. Fatigue resistance is the prime factor controlling the service life of the concrete pavements. This research study utilized natural rubber latex (NRL) to enhance the mechanical strength and flexural fatigue resistance of normal concrete. The effect of influence factors, such as water to cement ($\mathrm{w}/\mathrm{c}$) and dry rubber to cement ($\mathrm{r}/\mathrm{c}$) ratios, on the compressive and flexural strengths and flexural fatigue behavior was studied. Normal and NRL concretes were subjected to compressive, flexural, and flexural fatigue tests. At all $\mathrm{w}/\mathrm{c}$ ratios, a higher $\mathrm{r}/\mathrm{c}$ ratio resulted in a lower compressive strength but higher flexural strength. The highest flexural strength was found at the optimum $\mathrm{r}/\mathrm{c}$ ratios of 0.58, 1.16, and 1.73 for $\mathrm{w}/\mathrm{c}=0.3$, 0.4, and 0.5, respectively. Concrete modified by NRL at the $\mathrm{r}/\mathrm{c}$ ≤ optimum ratio had lower plastic deformation than normal concrete at the same applied flexural stress, hence, higher fatigue life ($N_f$). As a result, the NRL-concrete pavement at the optimum $\mathrm{r}/\mathrm{c}$ ratio was found to have a thinner thickness than the normal concrete pavement for the same traffic load conditions at the same service life, which can reduce the operational cost. A cost-effective mix design method of NRL-concrete pavement with the optimized construction (operation and material) cost was also recommended. The outcomes of this research will facilitate the utilization of the NRL additive alternative to synthetic polymer for sustainable NRL-concrete pavement in Thailand and other Southeast Asian and South American countries, which are major global producers of natural rubber.

In this study, the effects of ultrahigh-performance concrete (UHPC) and normal-strength concrete (NSC) as repair materials on the bond strength and overlay transition zone (OTZ) microstructure were investigated. The single-side shear test was performed to obtain the shear bond strength at the interfaces between the repair materials and concrete substrates, and three types of substrate strength grades were adopted. OTZ crack width was measured and characterized using kernel density estimation, and the OTZ porosity was quantitatively characterized based on the gray-level value, for which $10\text{-}\mathrm{\mu m}$-wide strips successively extending from the substrate surface to the repair material were selected. The porosity of each strip was calculated as the percentage of the area of this component to the total area of the strip. The micromechanical properties were determined using a nanoindenter. The results show that the UHPC-combined substrate had a higher bond strength than the NSC-combined substrate for the three substrate strength grades. The UHPC decreased the OTZ crack width. Moreover, the fraction of pores in the OTZ of the UHPC was lower than that of the NSC. The modulus and hardness values of the OTZ for the UHPC exceeded those for the NSC. These superior OTZ microstructure properties of the UHPC repair materials explain the high bond strength of the UHPC-combined substrate. Therefore, UHPC combined with a concrete substrate featuring a rough surface represents a useful repair material.

Considering the defects of insufficient low-temperature flexibility and high cost of epoxy asphalt binder, low-cost polypropylene glycol (PPG) and toluene diisocyanate (TDI) were used to synthesize two polyurethane (PU) prepolymers (PTPU) with different isocyanate group (─ NCO) contents, and the properties of PTPU-modified asphalt binders and mixtures were studied. First, the mixing parameters of the PTPU-modified asphalt binders were determined through tests, and its storage stability, high- and low-temperature creep characteristics were studied. Then the microscopic modification mechanism of PTPU-modified asphalt binders was explored. Finally, the PTPU-modified asphalt binders were used to prepare mixtures, and the application performance in bridge deck pavement was evaluated. The results showed that PTPU-modified asphalt binder has satisfactory storage stability and high- and low-temperature performance. Chemical reactions occur during the modification process which change the micromorphology of the asphalt binder, and its high-and low-temperature performance and the adhesion to the aggregates are improved. The increase of -NCO content improves the high-temperature stability and mechanical strength of the PTPU-modified asphalt binder but reduces the flexibility. Hence, the ─ NCO content in PTPU can be adjusted according to actual needs during application. The PTPU-modified asphalt mixture has a good comprehensive performance, its low-temperature anticracking performance is improved greatly compared with that of epoxy asphalt mixture, and the lower price gives it good promotion and application prospects in engineering applications.

The rheological behavior of recycled asphalt binders is important in the design of the optimum content of reclaimed asphalt pavement (RAP) material to be used in highway recycling projects. In this study, oscillatory tests were performed on recycled binders of varying RAP concentrations. The complex modulus master curves were constructed using the time–temperature superposition principle. The zero shear viscosities (ZSVs) were estimated using the Carreau–Yasuda model on the complex viscosity master curves for all the recycled binder combinations. It was found that the activation energy of flow changed linearly from 115.1 to $185.8\mathrm{kJ}/\mathrm{mol}$ with an increase in the RAP content, whereas ZSV varied exponentially with an increase in the RAP content. A good correlation was found between the ZSV and the Superpave rutting parameter ($G^{*}/\sin \delta$). An equation was derived to predict the $G^{*}/\sin \delta$ at any RAP concentration and temperature. For practical use, a $G^{*}/\sin \delta$ contour plot approach is introduced to calculate directly the maximum and minimum RAP content for any target binder grade suitable for the construction site. cA noticeable change in rheological behavior of recycled binders was observed on either side of the 40% RAP incorporation level.

According to the physical causality principle, the two components of complex modulus are not independent yet interrelated to each other via Kramers-Kronig relationships. Using two mathematical functions to predict simultaneously the dynamic modulus (DM) and phase angle (PA) generally leads to the violation of the causality principle. Therefore, the calculation of one component based on the other one is a vital task for using mathematical models to predict the linear viscoelastic (LVE) behavior of asphaltic materials. In addition, the relaxation modulus (RM) or the creep compliance (CC) in the form of sums of exponential functions (SEFs) is necessary for the efficient resolution of the stress–strain relationship in the time domain. This paper presented a novel method for calculating with high accuracy the RM and CC in the form of SEFs based on the input DM master curve. First, the midpoint integration scheme was used to calculate the PA based on the exact relationship between the PA and DM. After that, the storage modulus and compliance were computed and decomposed with high accuracy into SEFs using a special technique. Then, the closed-form formula of the RM and CC were derived thanks to the special form function of the storage modulus and compliance. Finally, the special technique was used once again to decompose with high accuracy the RM and CC into SEFs for possible uses in finite-element method (FEM) analysis in the time domain. The results showed that the relative errors of all LVE properties computed were lower than 0.1 percent at all calculating points.

Asphalt pavement rutting is caused primarily by shear stresses induced by heavy truckloads. Many tests have been developed to determine asphalt mix rutting potential. However, due to limited correlation with field rutting performance, long testing hours, and difficulties of sample fabricating, no test can be used as a fast and straightforward assessment tool for quality control or quality assurance/acceptance (QC/QA) purpose. In this study, a shearing fixture was developed to investigate the shear rutting potentials of the asphalt mixture more easily and rapidly. An analytical solution was derived from the mechanical analysis. With this solution, the stress distributions of the specimen under the shear loading were analyzed and plotted. These stress distribution plots are also compared with those under the other loading fixtures, such as the indirect tension (IDT) fixture and Marshall fixture. The comparison indicates that the developed shearing fixture is good at inducing shear stress to the specimen and manifesting the shear rutting mechanism. Several scenarios were evaluated by varying the loading fixture configurations, such as the bottom support arc length and angle. The impacts of these configuration elements on the stress distribution were investigated. Laboratory-mixed and laboratory-molded specimens were tested using the shearing fixture, and the test results show high repeatability. The mechanical analysis and experiments indicate that the new shear rutting test is very promising for evaluating the asphalt mix rutting potential quickly and straightforwardly.

Bituminous mixtures recover from fracture damage during rest periods and at high service temperatures due to their self-healing ability. Steric hardening of binders is a time-dependent phenomenon whose effect on the mechanical properties is similar to that of healing. Most of the healing evaluation methods used by different researchers do not consider the effect of steric hardening while explaining the effect of healing in the mixes. Hence, an attempt was made in the present study to quantify the contribution of steric hardening to the healing of bitumen. A multistage procedure was employed to separate the effect of steric hardening from the healing effect. In the steric hardening test, the bitumen sample was given a prolonged rest to evaluate the increase in the modulus value due to steric hardening. A storage recuperation test was carried out to quantify the combined effect of self-healing and steric hardening. The true healing potential of the binders was estimated by eliminating the effect of steric hardening from total recovery occurring during the rest period. Steric hardening was observed to be more in stiffer binders and at lower test temperature. Softer binders had more self-healing potential than stiffer binders. It was observed that the effect of steric hardening dictated the trends of total recovery, indicating that its contribution is significant. Thus, neglecting the effect of steric hardening while estimating the true healing potential of bitumen leads to inaccurate estimation and interpretation of healing results.

Plastic waste (PW) generation continuously increases every year due to the growing population and demand for plastic materials. This situation poses a challenge to many countries, including developed ones, on how to dispose of PW. Accordingly, PW was utilized in this study to replace coarse aggregates partially in high-volume fly-ash (HVFA) concrete. However, PW decreased the strength and durability of concrete. To address this issue, graphene nanoplatelets (GNPs) were added to mitigate the negative consequences of PW and HVFA on concrete’s properties. The objective of this study is to investigate the influences of PW and GNP contents on the durability and deformation of HVFA concrete. Response-surface methodology (RSM) was used to design and optimize a series of cement mixes to achieve the most desirable properties. Independent variables included PW content as partial replacement for coarse aggregates (0%, 15%, 30%, 45%, and 60% by volume), fly ash as partial substitute for cement (0%, 20%, 40%, 60%, and 80% by volume), and GNPs as additives (0%, 0.075%, 0.15%, 0.225%, and 0.3%). The considered responses were concrete unit weight, modulus of elasticity (MoE), and Cantabro abrasion loss at 300 revolutions. Results showed that PW and HVFA decreased concrete unit weight and MoE but increased Cantabro abrasion loss. By contrast, GNPs increased concrete unit weight and MoE but decreased Cantabro abrasion loss. PW and HVFA also increased the compressive toughness and porosity of concrete, while GNPs increased its stiffness but decreased its compressive toughness and porosity. The mathematical models developed to predict the unit weight, MoE, and abrasion resistance of concrete were significant, with errors of less than 6%. An optimized mix was achieved by partially replacing 12.44% of coarse aggregates with PW and 24.57% of cement with fly ash and adding 0.279% GNPs with a desirability of 100%.

High-strength concrete (HSC) with a low water-to-cement (w/c) ratio always exhibits high shrinkage at an early age. Concrete with shrinkage that is subjected to restraint is prone to trigger harmful cracking, which facilitates the application of fibers. Although mechanical properties of cementitious materials with various fibers have been extensively investigated, little research has characterized the stress relaxation and cracking potential of HSC with polyvinyl alcohol (PVA) fibers. This paper aimed to expand the limitation by means of the experiment campaign, including free shrinkage measurements and restrained ring tests on HSC with PVA fibers. The proportion of PVA fibers was 0.0%, 0.2%, 0.4%, and 0.6% by volume of HSC. Experimental study and the corresponding analysis indicated the following: free shrinkage of HSC diminished as the PVA fiber proportion increased; residual stress induced from the restrained shrinkage of the concrete ring diminished with an increase of the PVA fiber proportion; the reduction in the stress rate correlated with an increase in the PVA fiber proportion. Relaxed stress increased as PVA fiber proportion increased; the age of cracking of the HSC was postponed due to the incorporation of PVA fibers; and a low cracking potential of HSC was revealed as the PVA fiber proportion increased.

Four high-workability (pumpable and self-compacting) concrete mix designs are presented that incorporate steelmaking slags with additions of both metallic and polymeric fibers. Electric arc furnace slag (EAFS) as aggregate, and ladle furnace slag (LFS) and ground granulated blast furnace slag (GGBFS) as supplementary cementitious material (SCM) are applied to optimize the sustainability of the mix design. The main variables in the microstructural analysis, the porosity and the pore structure of the hardened mixes, were assessed with mercury intrusion porosimetry (MIP), X-ray computed tomography (XCT) and water capillary penetration analysis. Moreover, shrinkage was observed to decrease when adding metallic fibers and LFS. In general, scanning electron microscopy (SEM) observations revealed good quality concrete microstructures. Accelerated aging tests at a moderate temperature (72°C) produced a slight lengthening, which affected the dimensional stability of all the mixtures, which was also conditioned by their micro-porosity. The internal damage induced by this test decreased the brittle fracture strength of the concrete mixes, although the use of GGBFS and LFS moderated that damage, due to the increased compliance of the cementitious matrix.

Most available tests of asphalt mixture performance against moisture damage or the effect of additives examined the asphalt mixture’s overall performance. Considering the different mechanisms of moisture damage, studying antistripping additives’ effect on failure mechanisms might provide a better view of the asphalt mixture’s performance against moisture. Accordingly, herein, the effects of various antistripping additives, including a liquid antistripping additive (dodecylamine) and a nano-magnesium hydroxide additive, each at two bitumen weight percentages, with two types of aggregates with different mineralogical properties and a PG 64-16 bitumen on moisture damage mechanism were investigated. The cohesion and adhesion mechanisms of moisture damage were examined using the pull off test, and the asphalt mixture’s overall performance was assessed using the indirect tensile strength (ITS) test in multiple dry and wet conditions (1, 2, and 3 freeze-thaw cycles) according to the modified Lottman test. The results revealed that the use of 0.4% dodecylamine and 1% nano-magnesium hydroxide in the mixtures made with lime aggregates increases the tensile strength ratio (TSR) from 62.67% to 85.4% and 84.8%, respectively. In mixtures made with granite aggregates, TSR increased from 54.45% to 72.49% and 71.35%, respectively. The failure mechanisms’ assessment showed that the use of 1% nano-magnesium hydroxide in mixtures made with granite aggregate elevated the pull off in the adhesion failure mechanism by 80%, and the pull off increased by 70% in the cohesion failure mechanism. Moreover, the pull off increased by 63% for limestone mixtures in the cohesion failure mechanism and by 56% in the adhesion failure mechanism. The dodecylamine additive with the highest pull off and ITS ratio in all freeze-thaw cycles was more suitable than nano-magnesium hydroxide to promote the asphalt mixtures’ overall performance against moisture. The statistical analysis also indicated the significant effect of dodecylamine and nano-magnesium hydroxide additives on asphalt mixtures’ moisture sensitivity reduction at a 95% confidence level. The findings show that some additives have a stronger effect on adhesion strength and some effect on cohesion strength, but the additive that better improves the overall asphalt mix performance depends on mix design characteristics and aggregate and bitumen type.

In chemically treated soils, producing binding gels changes the soil structure and pore-size distribution, consequently affecting the treated soil-water-retention characteristics. Alkali-activated materials have recently gained popularity to be used as a sustainable chemical binder for soil stabilization. This study was aimed at investing how alkaline activation changes the water-retention characteristics of a treated clay using a small-scale centrifuge at low suction level by drying process in experimental conditions. Alkali-activated clay-fly ash was fabricated by mixing 60% fly ash and 40% clay then the mixture was activated by 10 M NaOH solutions. A small geotechnical centrifuging setup was utilized so as to estimate the variation of water content due to the suction-induced drying process. It was observed that the saturation degree fell in the ranges of 62.9%–78.3% and 71.8%–87.8% for the untreated and treated clay, respectively. The centrifuging results were verified against some distinguished available models. The water-retention characteristics of alkali-activated clay-fly ash were found to be substantially different from that of the untreated clay. Indeed, for the treated clay, the lower air-entry value suction and higher water-retention tendency for higher suction levels are controlled by its larger mean pore diameter and higher specific surface, respectively. Additionally, flocculated fabric produced due to alkaline activation contains small clusters with water entrapment potential needing tremendous suction pressures to be drained.

In this paper, the effect of metakaolin on the performance of magnesium potassium phosphate cement (MKPC) with a high water-to-solid (w/s) ratio of 0.375 was studied. MKPC was prepared by substituting metakaolin for varying amounts of magnesia. The results showed that the increase of metakaolin led to a decrease in the fluidity of the fresh MKPC slurry. Additionally, the presence of metakaolin reduced the maximum temperature of the second peak in the MKPC hydration reaction and delayed its appearance. This is because of the amount of magnesia as an effective alkaline component decreased. Metakaolin improved the compressive strength of MKPC by reducing the porosity and forming new hydration products. Moreover, it was found that the compressive strength of MKPC with 30% metakaolin exhibited the highest at 20.36 MPa at 28 days and showed a downward trend when metakaolin exceeded 30%. Metakaolin owns the pozzolanic effect as well as the filling effect in the MKPC system of a high w/s ratio, which is the reason for the improvement in compressive strength and reduction of chloride diffusion. This work provides some fundamental information for understanding the high w/s ratio MKPC modified by metakaolin, which helps to promote its application in the field of anticorrosion coatings and waste stabilization/solidification binders.

The purpose of this study was to conduct a performance evaluation to investigate the effect of a newer type of asphalt binder modification system and to demonstrate the importance of performance prediction modeling over use of only mix stiffness or a single performance index property to compare asphalt binder modification systems. Four asphalt mixtures with different amount of modifiers were evaluated in this study. Laboratory characterization included complex modulus, direct tension cyclic fatigue, cracking tolerance index, disk-shaped compact tension, indirect tensile creep and strength, and Hamburg wheel tracking tests. In addition, advanced performance prediction programs including AASHTOWare Pavement ME, FlexPAVE, and IlliTC were utilized to predict mixture performance. Based on the results of laboratory testing and performance simulations, the reactive isocyanate-based modifier (RIB) and styrene-butadiene-styrene (SBS) modifiers improved the properties and performance of the control mixture with respect to rutting and fatigue cracking but may have a negative effect with respect to thermal cracking. Modification of the control mixture with the combination of RIB and SBS balanced good rutting and fatigue cracking performance while maintaining thermal cracking resistance, indicating that the RIB + SBS modification may be a good candidate for further evaluation and field trial consideration.

As ultra-high-performance concrete (UHPC) becomes more widely used, the need for good concrete tensile tests for fiber-reinforced concrete has become apparent. However, there is not yet one universally used test method. This research compares the results between standard direct tension, four-point flexure, and double-punch tests. Each test method was run on batches of UHPC made with two fiber types each at five different doses by percent volume, resulting in a testing matrix of 10 different mixes. The results of each test method were plotted to see how well different outcomes, such as peak strength and toughness, would reflect differences in fiber content. The results of the two indirect tension tests were then compared to the results of the direct tension test to see how well they correlated. Results showed that the average maximum stresses of each test method did not have good correlation but that measures of toughness or postcracking strength did have reliable correlation between the direct tension test and both of the simpler test methods.

Ultraviolet (UV) aging can cause serious degradation of asphalt performance and shorten the service life of asphalt pavement. In this research, a kind of layered ultraviolet reflective material Ca/Mg/Al layered dihydroxyl metal hydroxides (Ca/Mg/Al-LDHs) was prepared from phosphorus tailings by the acid hydrolysis, purification, coprecipitation, and hydrothermal method (APCH) and used to enhance the anti-UV aging performance of asphalt binder. The synthesis condition of Ca/Mg/Al-LDHs was optimized according to the UV reflectivity of the hydrotalcite prepared and their effects on the physical and antiaging properties of asphalt binder were investigated. Organic surface modifier (KH560) was used to modify the Ca/Mg/Al-LDHs to improve their compatibility with asphalt. The results show that Ca/Mg/Al-LDHs can be prepared from phosphorus tailings by the APCH method. The optimal molar ratio of divalent ions to trivalent ions to produce Ca/Mg/Al-LDHs was 2, and the optimal pH was 10. The Ca/Mg/Al-LDHs achieves 94.1% of the UV light reflectance of commercial LDHs. The Ca/Mg/Al-LDHs could reflect 65%–83% of UV light from 280 to 400 nm. The surface modification can improve the compatibility of LDHs with asphalt and the anti-UV aging performance of LDHs-modified asphalt. The Ca/Mg/Al-LDHs prepared from phosphate tailings improved the anti-UV aging performance of asphalt; they have a similar anti-UV aging effect on asphalt binder as commercial LDHs.

This work addressed the issues of poor bonding and low forming strength of emulsified type cold-mix asphalt (CMA). The aim of this study was to improve the pothole repair effect. Accordingly, waterborne epoxy resin (WER) was adopted as an emulsifier, and samples of WER-emulsified CMA reinforced with polypropylene fiber were prepared in the laboratory. First, the mixing ratio of WER and curing agent was optimized through three indexes and storage stability tests. Second, fluorescence microscopy, dynamic shear rheology (DSR), and bending beam rheometer (BBR) tests were conducted to determine the ratio between WER and curing agent, called WERC, in emulsified asphalt binder. After that, pavement performance and bonding characteristics of asphalt mixes produced by this binder were evaluated to analyze the feasibility of using WER-emulsified type CMA in pothole repair and to determine the optimal WERC content. The results show that the best mixing ratio of E-44 and EH-05 is 1.5:1, and WER-emulsified type CMA mixes have shown improved strength, high-temperature rutting resistance, water stability, low-temperature crack resistance, and interfacial bonding characteristics. With the increase of WERC, the performance influence range gradually slows down. Considering overall performance improvement and cost, best WERC content is finally determined as 6.5%. The newly developed emulsified type CMA can be applied to the rapid repair of pavement potholes.

When soil is subjected to freeze–thaw cycles, its macro morphology and overall strength experience certain changes that often are caused by microscopic modifications of its internal structure in geological hazards. To clarify the relationship between the microstructure characteristics and the macro deformation of silt under cyclic freeze–thaws, eight silt samples with different compactions and moisture contents were set up to conduct five cycles and computed tomography (CT). The displacement and CT images of the soil were obtained. The displacement monitoring results show that there was a relationship between compaction and moisture content, which determined whether the silt experienced a settlement or an expansion. To capture the quantitative microstructural characteristics from the CT images, the two-dimensional threshold histogram method was improved, and the threshold values between fracture and soil units in the freezing and thawing states were found. Furthermore, six microstructural parameters of fractures were obtained. Through correlation analyses, the relationship between the microstructural parameters and soil displacement was verified to be similar to that between the physical parameters and the displacement. In addition, an exponential statistical model of micro and macro parameters was established, showing that the soil microstructure can be improved, and the displacement is constrained within a relatively tight bound after cyclic freeze–thaws.

Environmental temperature is usually variable in the field and can significantly affect the mechanical behavior of cemented soil. However, how the initially low-temperature curing affects the strength behavior of cemented lean clay is still pending. To identify the influence of changing temperature on the strength behavior of cemented lean clay, a series of unconfined compression strength (UCS) tests were carried out in this research. Based on test results, an overall detrimental influence on the unconfined compressive strength ($q_u$) was found due to low-temperature curing. Compared with cemented lean clay cured at a constant low temperature, an increase in $q_u$ was observed when the curing temperature rose again to 20°C, and the recovery in $q_u$ depends mainly upon the initial low-temperature curing time. The improvement in cement hydration was the main source in strength gain for cemented lean clay cured initially at 5°C/10°C. However, for cemented lean clay once cured at 0°C, the formation and thawing of pore ice damaged the soil structure and resulted in permanent damage to the development of strength. Moreover, the failure strain ${\epsilon }_f$ and secant modulus $E_{50}$ were consistent well with $q_u$ when the temperature was not less than 5°C. For cemented lean clay used in this study, a curing temperature range of 5°C–20°C would guarantee adequate $q_u$.

This study deals with the recovery of deinking sludge (DS) generated during waste paper recycling. The aim is to integrate this sludge in the fired-bricks formulation with different percentages. These mixtures are fired, and the study of the general aspect, loss on fire, and water absorption enables characterization of this material. Different compression tests are carried out on studied samples to characterize the strength and compare its performance to the standard. The mixtures’ optimization and the elaboration conditions are the main objectives to obtain a new construction material with competitive performances conforming to the standards.

In-depth exploration of the performance evolution process of hot-mix epoxy asphalt binder (HEAB) with different components can help control costs and facilitate its promotion and application in engineering. In this study, through the tensile test, viscosity test, laser scanning confocal microscope (LSCM), and Fourier transform infrared spectroscopy (FTIR), the properties of HEAB with different epoxy resin (EP) content were studied, the appropriate EP content was explored, and the curing degree was evaluated by the epoxy conversion rate. Meanwhile, the pavement performance of the HEAB mixture was studied and compared with the stone matrix asphalt (SMA) mixture. The results showed that the tensile properties of HEAB were significantly improved when the EP content reached 30% by weight, and the phase transition occurred when the EP content was 50% by weight. The appropriate content of EP in HEAB was recommended to be 40% by weight, and the mixing temperature of 160°C can ensure sufficient construction allowable time range. The epoxy conversion rate gradually rose with the increase of curing time, and the early curing reaction rate was faster than the later ones. The HEAB mixture had excellent comprehensive properties, and its high-temperature stability was particularly outstanding, but the water stability and skid resistance were inferior to the SMA mixture. Hence, an upper layer of SMA and lower layer of HEAB as a composite structure of a steel bridge deck pavement are worthy of further study in the future.

This paper experimentally studies the drying shrinkage and creep deformation of sustainable self-compacting concrete (SCC) prepared by substituting natural aggregates with recycled concrete aggregates and cement with supplementary cementitious materials (SCMs). A total of 11 mixes with two recycled coarse aggregate (RCA) replacement ratios (50% and 100% by volume) and two SCM replacement ratios (50% and 75% by weight) were manufactured, including binary mixture (cement and fly ash), ternary mixture (cement and fly ash, and slag) and quaternary mixture (cement and fly ash, slag, and silica fume). The influence of various RCAs and SCMs as well as the SCM combinations on the shrinkage and creep characteristics were analyzed in detail. The test results indicate that the shrinkage and creep characteristics of recycled aggregate SCC (RA-SCC) are significantly affected by RCA and SCM, as well as by SCM combinations. Compared to the control SCC, the addition of 100% RCAs increased the shrinkage deformations up to 37.2% and creep deformations up to 33.5% at 420 days, respectively. In addition, the inclusion of fly ash and slag reduced the shrinkage deformation by 27.6% and the addition of SCMs using a combination of fly ash, slag, and silica fume reduced the specific creep of RA-SCC mixes by 27.9%. A comparison between the measured shrinkage and creep strains and calculated values using existing prediction models was conducted. Based on the American Concrete Institute (ACI) prediction models, modified shrinkage and creep models were proposed by considering the influence of RCAs and SCMs.

Since the conventional asphalt concrete will release many harmful gases including greenhouse gas in the construction process and it is prone to early diseases leading to long-term performance deficiencies, in recent years, polyurethane (PU) has been gradually considered to replace the asphalt binder used in road due to its excellent performance, such as mechanical properties, durability, elasticity, environmentally friendly, low energy, etc. However, the PU concrete has been found to have poor water stability due to the poor moisture damage resistance of the PU-aggregate interface. To improve the water stability of PU concrete, the evolutions in the moisture damage resistance of PU-aggregate interface subjected to water immersion and freeze-thaw cycle were investigated, and the technique to improve its moisture damage resistance was preliminarily explored. For this purpose, a method for evaluating the PU-aggregate interfacial bonding property was first proposed. Under the two aging conditions of water immersion and freeze-thaw cycle, both the interfacial tensile strength and shear strength decreased rapidly in the early stage of aging, followed by a steady and incredible great degradation ratio. In contrast to interfacial tensile strength, interfacial shear strength is more sensitive to freeze-thaw cycle than water immersion. The decrease of moisture damage resistance of PU-aggregate interface is mainly ascribed to the destruction of the weak van der Waals forces caused by the invasion of water, plasticization of PU binder, hydrolysis of –NHCOO– and possible incomplete curing, among which the first two factors are inescapable. The best way to improve the moisture damage resistance of the PU-aggregate interface is to develop a PU that can be highly cured in a short time at ambient temperature and does not readily hydrolyse. The present research provides a solid theoretical basis for the research and development of PU suitable for pavement.

The ultrahigh-performance concrete (UHPC)-normal strength concrete (NSC) composite has been increasingly used for improving mechanical performance and durability of engineering structures. The UHPC-NSC composite structures in operation will be subjected to environmental loading (i.e., seasonal temperatures). The present study aimed to investigate the bond strength of the high-early-strength ultrahigh-performance concrete (HESUHPC)-NSC composite using a designed tensile specimen within normal seasonal temperatures (summer, autumn, and winter), in Changsha, China. The effect of the HESUHPC age and typical seasonal temperatures on the bond strength is discussed. It was found that in extreme conditions (i.e., 1-day age in winter), the pure interface failure occurred in the HESUHPC-NSC composite. The tensile bond strength of the HESUHPC-NSC composite increased with the age, and the early strength increased rapidly. However, the increase rate was affected by the typical seasonal temperatures. Moreover, the tensile bond strength of the HESUHPC-NSC composite decreased from summer to winter, and the differences were significant at the early age. The present study might provide valuable data for the application of the HESUHPC-NSC composite in different seasons.