High-performance concrete (HPC) is currently widely used in water-related structures. The incorporation of nano-silica (nano-SiO₂, NS) can further refine its pore structure, thereby enhancing the compressive strength and durability of HPC without necessitating a reduction in the water-to-binder (w/b) ratio. However, the addition of nano-materials significantly increases the autogenous shrinkage (AS) of concrete, leading to elevated tensile stresses and making the concrete more susceptible to early-age cracking. To mitigate AS, superabsorbent polymers (SAPs) can be introduced to internally cure the concrete, thereby improving the internal relative humidity (IRH) and reducing the AS in NS-reinforced concrete. In this study, we experimentally investigate the setting behavior, pore structure, compressive strength, IRH, and AS properties of concrete with a w/b of 0.3, incorporating both NS and SAP. The results demonstrate that the addition of NS advances setting time, significantly densifies the pore structure, markedly enhances compressive strength, accelerates the decline in IRH, and increases AS strain. Conversely, the incorporation of SAP exhibits opposite effects on these properties, particularly in substantially mitigating AS strain. The combined incorporation of 1.5% NS and 0.15% (or 0.30%) SAP achieves both higher compressive strength and lower AS strain compared to plain concrete at 28 days. These findings suggest that the simultaneous introduction of NS and SAPs into concrete formulations is recommended to achieve an optimal balance between shrinkage and strength properties. Such advancements are particularly beneficial for applications in hydraulic and water-related structures, where enhanced durability and reduced cracking are critical for maintaining structural integrity and ensuring longevity.

This study investigated mineral admixtures that are often utilized as replacements for cement in high-performance concrete with a view to enhancing their durability and workability. The properties of concrete are closely related to the structure of its pores. This research employed low-field nuclear magnetic resonance technology to explore the influence of water-to-cement ratio, curing time, and mineral admixture content on the pore structure of early-age cement pastes. The findings indicated that the pore size distribution curves of all composite cement pastes display a distinct bimodal nature. The size of gel pores increases with a higher water-to-cement ratio, but decreases as the curing period extends. Fly ash, slag, and silica fume improve the pore structure at 14 days, 7 days, and 3 days, respectively. The addition of admixtures has little effect on the most probable pore diameter, but raises the proportion of gel pores with increasing content. In order to better fit the experimental data, a bimodal model integrating Shimomura and Maekawa’s model with the Weibull distribution function was introduced to describe the pore structure of cement pastes with or without fly ash, slag, and silica fume.

For the problem of high intensity, low efficiency and poor accuracy in the artificial classification of navel oranges, a detection method is proposed based on machine vision technology. In defect detection, we analyze the color information of navel oranges surface, and obtain surface defect with a proper ratio of R/B and G/B. In the detection of color and luster, we calculate the texture information of the grayscale image, and propose three characteristics such as smoothness R, "consistency" measure U and entropy descriptor e. Finally, a hierarchical model is established based on BP neural network. The test results show that this method can be used for detecting the color and luster of navel orange with a high recognition rate.

1. Cement-based materials are among the most widely used civil engineering materials due to their advantages such as low cost, abundant raw materials, and high compressive strength [1–4]. However, ...