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By harnessing the benefits of lowering cost and reducing CO 2 emission, employing geopolymer as the repair materials have been gaining interest. This article investigated the bond strength and degradation of metakaolin-based geopolymer mortar subjected to rapid efflorescence exposure, acid attack, freeze-thaw cycles, wet-dry cycles, and heat-cool cycles. The slant shear strength tests evaluated the new-old mortar bond strength. FTIR, XRD, and TGA were conducted to monitor the deterioration of geopolymers. Visual observation and ICP-OES tests were performed to quantify the efflorescence risk. Results showed that acid exposure mainly reduces bond strength by degrading the geopolymer framework. In aggressive environments involving moisture and temperature changes, i.e., freeze-thaw, wet-dry and heat-cool cycles, geopolymers exhibit negligible deterioration. However, the shrinkage induced by water migration and the volume expansion caused by elevated temperatures significantly decrease (up to 90%) the bond strength of geopolymer repair mortar. The negative effect imposed by the efflorescence should not be neglected. A significant bond strength reduction (up to 20%) was observed for geopolymer repair mortar suffering from efflorescence. Samples with higher granulated blast furnace slag (GGBS) addition show lower strength loss, benefiting from their lower efflorescence extent. Stoichiometrically designing the geopolymer repair binder to avoid efflorescence is recommended. [ABSTRACT FROM AUTHOR]

[Display omitted] • The properties of ITZ in geopolymer-stabilized RAP were investigated. • A model representing the interaction between geopolymer, aged asphalt, and aggregate was developed. • The impacts of RAP aging degrees on interfacial bonding were examined. • The simulation findings were corroborated by SEM-EDS results. Geopolymer technology offers significant advantages in stabilizing recycled asphalt pavement (RAP), allowing its repurposing as road construction materials. This study employs a combination of molecular dynamics simulations and experimental characterization to investigate the properties of the interfacial transition zone (ITZ) in geopolymer-stabilized RAP. A composite model of geopolymer-aged asphalt-aggregate was established using molecular dynamics (MD) to access the effects of aging degrees of RAP on the interfacial bonding. The findings revealed that aging asphalt molecules on the RAP surface exhibit an affinity for Na+ present in geopolymers. Na+ ions migrate to the interfacial region, forming electrostatic interactions with double-bonded oxygen atoms in the aging asphalt molecules. The interfacial interaction energy and nanomechanical performance grow up and then reduced with the aging degree of RAP. SEM-EDS results verified these simulation findings, indicating that C(N)-A-S-H might grow at the interface, leading to a strong affinity and external chemical bonding. [ABSTRACT FROM AUTHOR]

We studied the upper-bound ultimate bearing capacity of smooth strip shallow footings with symmetrical and asymmetrical horizontal confinements on purely frictional sand within the framework of upper-bound limit analysis. The subsoil follows the associated flow rule, and no surcharge on the soil surface is assumed. The contact between the soil and the horizontal confinement walls is assumed to be perfectly rough. The upper-bound solutions for the objective functions are obtained using nonlinear sequential quadratic programming. The results for the different internal friction angles φ are provided in terms of the variation of two parameters, namely, the bearing capacity factor Nγ and the correction factor of bearing capacity Kγ, with respect to the change in the clear spacing between the edge of smooth footing and the rigid vertical walls. The values of Nγ and Kγ increase with φ and decrease with the clear spacing between the edge of the smooth footing and the rigid vertical walls. Nγ and Kγ are more sensitive to this confining effect as φ increases. The numerical results, a comparative analysis with the results from previous studies, and design charts are also included. [ABSTRACT FROM AUTHOR]

As a by-product of steel making, the chemical composition of steel slag makes it prone to hydration, which may induce adverse impacts on steel slag asphalt mixture when exposed to moisture surroundings. In this study, a finite element model was developed to explore the effect of moisture damage considering steel slag hydration on the fracture properties of steel slag asphalt mixture. Then the numerical model was validated with experimental results. The effect of water on damage, horizontal stress distribution, as well as scalar stiffness degradation (SDEG) values were computationally analyzed. Moreover, some influencing factors such as the loading rate and aggregate morphology were considered. It is concluded that the presence of water would lead to the generation of hydration products, which results in reduced adhesion between fine aggregate matrix (FAM) and coarse aggregate. The unfavorable effect of water on strength is more significant at the FAM-coarse aggregate interface. A declined degree of 30.7% in the horizontal stress along the vertical centerline of the specimen is found by treating with water for 5 days. By changing the loading rate in the model, it could be found that immersion time has a significant impact on the proportion of damaged cohesive elements and damaged adhesive elements. While for the aggregate morphology, though the difference in aggregate morphology would lead to various degrees of stress concentration, the adverse of water has little impact on the stress concentration phenomenon. Based on mentioned above, the deterioration characteristics of water on steel slag asphalt mixture would provide guidance for the application of steel slag asphalt mixture in the future. • Fracture of steel slag asphalt mixture subjected to moisture damage was analyzed. • The adverse impact of water on interfacial strength is more significant. • The generation of hydration products would lead to a decline in adhesion. • The presence of water would lead to a rise in the proportion of cohesive damage. [ABSTRACT FROM AUTHOR]

• The retardation mechanism of ZnO in AAS was investigated. • The effects of ZnO on the reaction and performance of AAS were studied. • Retardation mechanisms of 'dissolution inhibition' and 'calcium depletion' were denied. • The retardation of ZnO in AAS could be attributed to nucleation inhibition. • Zinc was immobilized in AAS through various physicochemical approaches. The relatively fast setting of alkali-activated slag (AAS) greatly restricts its wide application. ZnO can serve as the retardant for AAS. However, the role of ZnO in AAS is not well understood. This paper investigates the retardation mechanism of ZnO in the AAS system and the effects of ZnO on the reaction and performance of AAS. Results showed that a ZnO dosage of 2 wt% prolonged the setting of AAS paste by 72 min and inhibited the growth of C-(A)-S-H gels within the first 6 h of the reaction. The retardation of ZnO in AAS could be attributed to the 'nucleation inhibition', in which Zn2+ inhibits the generation of calcium hydroxide precipitation owing to the preferential incorporation of Ca in the calcium zincate (CZ) phase, thus reducing the nucleation sites and slowing down C-(A)-S-H gels growth, until all Zn ions are transformed into CZ phase or bonded in the AAS framework. ZnO slightly reduced the compressive strength and reaction extent of AAS, and was immobilized in AAS through various physicochemical approaches. This study provides a new look into the interaction between ZnO and AAS systems. [ABSTRACT FROM AUTHOR]

Icy pavement surface significantly reduces the skid resistance of roads, and is an important cause of traffic accidents in winter. Reliable road surface icing prediction models are of great significance for decision making in winter road maintenance. This paper developed a finite difference model for predicting road surface ice formation based on heat transfer and phase transition theory. The input data included the meteorological data and road material properties. The output of the model included not only the road surface temperature, but also the road surface condition and ice thickness. To achieve this, the governing equation and boundary conditions were established based on the heat transfer theory. The energy exchanges during the transformation between ice and water were considered by calculating the latent heat based on the phase transition theory. The finite difference method was used to solve the above heat transfer problem. A series of laboratory experiments were designed and conducted to verify the accuracy of the prediction model. And an equation was established to estimate the time required for all surface water to condense into ice when necessary climatic factors were available. With the validated model, the effects of road materials and climatic factors on pavement surface ice formation were analyzed. The results show that cement concrete pavements are more likely to freeze than asphalt concrete pavement. Pavement consisted of a low-conductivity bottom layer, and high-conductivity surface and middle layers, is more suitable for preventing road surface ice in winter. The prediction model is useful for transportation agencies to understand the mechanism of road ice formation and ensure traffic safety in winter. • Road ice formation is predicted trough FDM considering phase change latent heat. • Cement pavements are more likely to freeze than asphalt pavements. • Cement concrete pavements are more likely to freeze than asphalt concrete pavement. • Higher thermal conductivity in pavement surface layer tends to alleviate road ice. [ABSTRACT FROM AUTHOR]

Safety factor of slope is often calculated based on the conventional linear Mohr–Coulomb failure criterion. However, many experimental results show that the strength envelopes of almost all of geomaterials are characteristically nonlinear. This paper presents a method (upper bound limit analysis method) to analyze the stability of a homogeneous slope based on a general nonlinear failure criterion, in which different shear strength reduction strategies ( SSRS ) can be used. Based on the presented method, three SSRSs (i.e. by factoring the unconfined shear strength c 0 only, by factoring the tensile strength σ t only, by factoring both the unconfined shear strength c 0 and the tensile strength σ t ) are used to calculate the safety factors of a homogeneous slope under a general nonlinear failure criterion. Compared results show different SSRSs have significant influence on the calculated safety factor. [ABSTRACT FROM AUTHOR]

• Measured CTC/CTE of FAM, aggregate, and asphalt concrete. • Developed 3-D microstructure-based FE model to calculate CTC/CTE. • The simulation results were compared to experimental measurements with close agreements. • Analyzed effects of microstructure feature on CTC/CTE of asphalt concrete. The coefficient of thermal expansion (CTE) and contraction (CTC) are critical parameters for pavement design and thermal analysis. This paper develops a 3-D microstructure-based FE model to evaluate the CTE and CTC of asphalt concrete. The 3-D random microstructure of asphalt concrete was generated with an image-aided algorithm. In the presented algorithm, the random 3-D geometry of a single aggregate was generated with a single 2-D image captured by Aggregate Image System 2 (AIMS2). The randomly generated 3-D aggregates were packaged with PFC 3D to construct the 3-D microstructure for asphalt concrete with prescribed gradation. Then the 3-D microstructure of asphalt concrete was imported into FE software ABAQUS to calculate the CTE and CTC. To validate the results from the numerical simulation, a laboratory experiment was conducted to test the CTE/CTC of the asphalt concrete with the same material composition. With the validated FE model, the effect of aggregate type, shape, and spatial orientation on the CTE/CTE was analyzed. Results show that the relative differences between the average values of numerical and experimental data were 1.63%∼4.64% for the CTE, and 3.01%∼7.20% for the CTC. With the increase of temperature, the CTE first decreased and then increased, while the CTC first increased and then decreased. Compared with the 3-D microstructure-based model, both the 2-D plain stress and plain strain models tended to overestimate the CTE of asphalt concrete. When the aggregate orientation tended to be inclined to a certain direction, the CTC and CTE of the asphalt concrete parallel to that direction tended to be smaller. Asphalt concrete prepared with quartz gravels and sand stones tended to have higher CTC and CTE. While the CTC and CTE of asphalt concrete could be reduced by using limestones. [ABSTRACT FROM AUTHOR]