Calcium aluminate silicate hydrate (CASH) is a principal binding phase in Al-doped cement systems, with the upper limits of macroscopic cementitious performance ultimately determined by its intrinsic nanoscale mechanical properties. Understanding the multiscale structure-property relationships is essential for guiding the design of improved CASH performance.The unclear submicron structure of CASH as a critical bridge between nanoscale behavior and macroscopic properties hinders the understanding of the evolution of multiscale mechanical properties. This study was to develop a CASH texture model from single crystals to polycrystals and to reveal the impacts of coupled Ca/Si and Al/Si ratios and water states on its physical and mechanical properties.

An upscaling algorithm was developed to remap coarse-grained models to all-atom models, overcoming barriers in constructing submicron textural structures, bridging experimental observations and molecular simulations, and providing some insights into CASH. This approach could enable the exploration of emergent cement phenomena in scales up to 100 nanometers with millions of atoms, offering a realistic representation of CASH pore structure, packing density, water content and state, as well as surface roughness. The resulting submicron-sized CASH was composed of randomly packed nanostructural units, reproducing structural features that were consistent with experimental observations. Molecular dynamics simulations were employed to reveal the multiscale structural evolution, the coupled effects of Ca/Si ratio and Al/Si ratio as well as the influence of multiple water states on the physical and mechanical properties of CASH.

The results indicate that a structural homogenization serves as a fundamental mechanism driving the transition of CASH from nanoscale anisotropy to submicron isotropy, with a disordered packing mitigating the interlayer fragility of single crystal CASH. When the Al/Si ratio increases from 0.05 to 0.10, Al–O bonds facilitate silicate chain polymerization, resulting in an enhancement of 15.40% in tensile strength. The submicron-sized CASH structure achieves an optimal mechanical performance at a Ca/Si ratio of 1.50 and an Al/Si ratio of 0.10. Further increasing the Ca/Si ratio leads to a reduction in strength due to a decrease in bridging Si–O bonds, whereas increasing the Al/Si ratio exerts an limited influence on the chain connectivity and framework stability. The cohesion of CASH is governed by intergranular contacts, and adsorbed water in the grain boundary regions is released as free water under humid conditions, significantly weakening cohesion and reducing strength by 40.80%.

In this study, an upscaling algorithm was developed to overcome barriers in constructing CASH textural models. Molecular dynamics simulations were employed to elucidate the multiscale structural evolution, Ca/Si and Al/Si coupling, and water governing the physical and mechanical properties of CASH. The findings could advance the atomic scale understanding of the submicron polycrystalline structure and mechanical behavior of CASH, paving a way for the design of more sustainable and durable cementitious composites.

The shrinkage cracking of concrete structures in arid regions such as plateaus becomes increasingly complex under the context of global climate change. This study utilized climate simulation data to analyze the coupled evolution characteristics of temperature, humidity, and atmospheric pressure across China. Based on a comprehensive analysis of 4662 sets of concrete shrinkage test data, the influence of atmospheric pressure on humidity was introduced and a modified CEB-FIP 2010 concrete shrinkage model was proposed that incorporated temperature-humidity-pressure coupling effects. The spatiotemporal evolution patterns of concrete shrinkage deformation nationwide were investigated. For a bridge pier concrete, the strain-stress-damage evolution process was simulated, and spatiotemporal dynamic zoning maps for shrinkage-induced cracking damage risks were developed. A risk of concrete shrinkage cracking damage by 2050 was projected to intensify significantly, with medium-to high-risk zones expanding by over 15% compared to current levels with increasing temperatures and decreasing humidity in arid regions.

The CMIP6 climate model was used to predict future temperature and humidity trends, with data spatially smoothed using cubic interpolation and the Gaussian filtering. The coupling relationship between temperature and humidity was analyzed by the Pearson correlation coefficients, Spearman correlation coefficients, and mutual information. The CEB-FIP 2010 model was improved via introducing a linear relationship between concrete strength and shrinkage development rate, combined with a barometric correction factor. The FEniCS finite element library was used to simulate stress and crack propagation in typical concrete components under different shrinkage strains, thus establishing a risk zonation framework for climate change scenarios.

According to the CMIP6 climate model predictions, the average temperature in northwest China will rise significantly over the next 30 a, especially in summer, with some areas exceeding 305 K (i.e., 32 ℃). Simultaneously, the relative humidity will decrease markedly, with some regions of humidity below 40% increasing in the north. These trends will intensify concrete drying shrinkage, particularly in arid regions. The analysis using the Pearson and Spearman correlation coefficients and mutual information reveals a negative correlation between temperature and humidity. In the north of 45°N, the correlation coefficients both approach -0.9, and the mutual information values approach 0.9, indicating a negative linear and monotonic relationship. This coupling will exacerbate concrete shrinkage effects.

Based on 4662 sets of concrete shrinkage experimental data, the CEB-FIP 2010 model is refined via introducing a linear relationship between concrete strength and shrinkage development rate, along with a barometric correction factor. The improved model shows an enhanced prediction accuracy, with a nearly 1:1 ratio of overestimation to underestimation, particularly in high-temperature and high-strength concrete scenarios. The results of finite element simulations using the FEniCS library show that concrete cracking initiates at a shrinkage strain of 5.5 ζ ×10^-4, with stress concentration at nodes at 7.5 ζ ×10^-4, stable surface crack development at 9.0 ζ ×10^-4, and widespread crack propagation at 1.1 ζ ×10^-3. Based on climate change scenarios, China is divided into five risk zones for concrete shrinkage and cracking damage. From year 2020 to year 2050, medium-and high-risk areas centered on arid regions show a significant outward expansion. By year 2050, the medium-and high-risk zones in the northwest plateau region are notably larger than in year 2020, more than 15%, demanding priority crack-resistant measures to ensure a long-term concrete structural stability.

Future temperature in arid regions could increase, while relative humidity decreased significantly, with highly coupled temperature and humidity changes that would an exacerbate concrete shrinkage. Atmospheric pressure changes nationwide could be relatively stable, but the low-pressure environment in northwest arid regions could further increase a concrete shrinkage. The improved shrinkage model showed a significant enhancement in prediction accuracy, with a more uniform distribution of shrinkage values and a nearly 1:1 ratio of overestimation to underestimation. Concrete cracking occurred at a shrinkage strain of 5.5 ζ ×10^-4, with stress concentration at nodes at 7.5 ζ ×10^-4, stable surface crack development at 9.0 ζ ×10^-4, and widespread crack propagation at 1.1 ζ ×10^-3. China, could be divided into five risk zones, with medium-and high-risk areas centered on arid regions significantly expanding more than 15% outward from year 2020 to year 2050.