As a kind of cement-based composite material with ultra-high strength, ductility, and durability, ultra-high performance concrete (UHPC) is a promising repair material to strengthen existing concrete infrastructures like bridges and tunnels. To achieve reliable and effective reinforcement, the interfacial performance and failure mechanism between UHPC and normal concrete (NC) becomes a critical issue. A series of experimental work was conducted to test the UHPC-NC interfacial behavior under various stress states and the interfacial morphology was measured by 3d scanning to obtain the roughness parameters, providing a basis for further numerical investigations. Then, a numerical framework on multi-scales was established to analyze the mechanical behavior of the NC-UHPC interface, considering effects of the meso-structure of UHPC and the treated interface roughness. NC was regarded as a homogeneous matrix whose failure was described by the elastic-plastic damage model in form of coupled gradient-enhanced damage evolution. UHPC is characterized by the second-order mean-field homogenization (MFH) method to consider its components on meso-scale. The interface is represented by the cohesive zone model (CZM), whose load transfer capability was described by the effective traction-separation law (TSL). Resultantly, mechanical behavior and deboning failure mechanism of the UHPC-NC interface was revealed, and the influence of the roughed interface morphology and the meso-structure of UHPC was evaluated. The loading resistance of a UHPC-NC composite element would benefit from the increased interfacial bonding strength. The interface roughness, the substrate concrete strength have positive effects on the mechanical properties of the interface.

Uncertainties in rock properties are primarily divided into aleatory uncertainties, caused by inherent randomness, and epistemic uncertainties, resulting from limited or subjective data. This study introduces an integrated reliability method that employs both probabilistic and non-probabilistic models to characterize input uncertainties, based on their available information. Statistical parameters and best-fit pdfs are used to model inputs with sufficient data whereas a super-ellipsoid convex model with minimised volume is used to model inputs with limited data. The super-ellipsoid model is transformed into a unit hyper-sphere. The non-probabilistic reliability index ( is defined as the minimum distance from the origin to the failure surface. A double loop algorithm, combining Monte-Carlo simulations and convex-model based reliability measure, is developed to estimate the probabilistic distribution of in the presence of mixed inputs. The methodology is illustrated using a rock tunnel as a case study. Unlike conventional reliability methods, this approach can address mixed uncertainties based on the exact information available. Further, the method estimates the uncertainty in reliability measure i.e., statistical measure and pdf of by truly propagating the impreciseness of mixed inputs, instead of its fixed value based on assumed probability distributions. The current approach can be viewed as more advanced than traditional methods because it accurately accounts for input uncertainties due to limited information, without incorporating subjective data. This provides users with a more informed understanding of tunnel stability.

Temperature changes and the resulting thermal stresses may be a threat to the long-term durability of concrete structures. Thermal stresses in concrete structures can be stimulated by constrained thermal eigenstrains on different scales of observation. Taking concrete beams, as an example, three different scales are defined, namely, the microstructural scale of the concrete material, the cross-sectional scale, and the macrostructural scale of the beams.

In order to quantify the multiscale thermal stresses, the scale transition (i) from cement paste, sand, and aggregates to the material scale of concrete, (ii) from the material scale of concrete to the cross-sectional scale of the beam considered, and (iii) from the cross-sectional scale to the macrostructural scale of the beam was established. Microstructural stresses in concrete constituents of a thermally-loaded concrete beams were quantified. Furthermore, the influence of different heating speeds, different concrete constitutions, different internal relative humidities, and different geometric dimensions of the beams were discussed in the framework of sensitivity analyses. This helps in understand of the multiscale nature of thermal stresses in concrete structures.

This study presents a 3D numerical investigation into a road integrated with a shallow geothermal energy system (SGES) in East England. An SGES uses the upper few metres of the ground as a heat source and sink to provide heating/cooling and energy storage efficiently by circulating fluid through the ground heat exchanger. This study focuses on the inter- seasonal heat harvesting processes inside the road system and its impact on the performance of the pavement. A time-dependent numerical model was developed using COMSOL Multiphysics to simulate these processes, accounting for heat transfer between the pavement, adjacent soil, and the fluid within the embedded pipes. The model also incorporated phase change materials (PCMs) in the soil to enhance thermal conductivity and energy storage potential. The SGES modelling used realistic UK climate data and soil temperature profiles to define the boundary conditions. This study evaluated the impact of various design parameters on the SGES, such as pipe diameter, burial depth of the pipes, fluid flow rate, and soil thermal conductivity, particularly with the inclusion of PCMs. The goal is to ascertain the influence of these variables on energy storage efficiency during the summer. Furthermore, the stored energy can be harnessed to warm the pavement in winter, thereby enhancing climate resilience and reducing weather-related road maintenance costs.

The high temperature in geothermal tunnels not only brings challenges to the construction but also a reflection of the large amount of heat energy stored in these tunnels. This study applies the phase change materials (PCMs) to geothermal tunnels combined with the ground source heat pump (GSHP). The system is expected to mitigate the challenges resulted from geothermal hazard, such as high environmental temperature and additive thermal stresses in the support structure, and show advantage in heat energy storage. A finite element model is established to investigate the performances of system, and the validation of model is conducted by comparing with in-situ experimental results. Furthermore, the performances of system are evaluated by parametric analysis, including the operation mode, phase transition temperature, and latent heat. The simulation results reveal that the combination of PCMs and GSHP can adjust the environmental temperature and decrease the thermal stresses in the construction period of tunnels compared with common support structures. This can bring more thermal comforts to workers in geothermal tunnels. Meanwhile, the system increases the efficiency and sustainability in heat energy storage in the operation period. The longer time for the rest of GSHP and larger latent heat increases the efficiency in energy extraction.