Although the pore network is critical for the stable low-temperature performance of concrete, research on the mechanisms linking multi-scale pore structures to low-temperature performance remains limited. This study employed pumice to modulate the pore network of ultra-low water binder ratio cementitious materials (ULWC). LT-DSC, 1H NMR, and CT were used to investigated the relationships between pore characteristics (including pore size, uniformity, fractal dimension, and pore shape) and low-temperature performance from micro-, meso-, and macroscopic perspectives. Additionally, nanoindentation and finite element simulations were employed to reveal the control mechanisms of the pore network on the low-temperature performance of ULWC. The result showed that the addition of pumice increased the compressive strength growth rate at −80 °C from 44.38 % to 97.05 %. Pore structure analysis indicated that pumice promoted the aggregation of the fractal space of the gel pores and induced the matrix to form more prolate spheroid-shaped pores. Among them, the fractal dimension and porosity were strongly correlated with low-temperature compressive strength, and the low-temperature strength prediction model based on these factors achieved an accuracy of 0.95. Furthermore, microstructural analysis and simulation results suggested that the stress dissipation characteristics of prolate spheroid-shaped pores, in conjunction with low-temperature pre-stress, collaboratively enhanced the low-temperature performance of ULWC. And the low modulus of pumice and its improvement of micropore network uniformity can reduce the low temperatures damage rate of the UHD C-S-H modulus from 22.62 % to 0.82 %. These findings provide theoretical guidance for the targeted optimization of low-temperature performance of concrete in the future.

中文翻译：

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超低水结合比水泥基材料 （ULWC） 的多尺度孔隙优化在低温性能中的提升：孔隙网络的缓冲机制


尽管孔隙网络对于混凝土的稳定低温性能至关重要，但关于多尺度孔隙结构与低温性能之间的联系机制的研究仍然有限。本研究采用浮石调控超低水结合剂比水泥基材料 （ULWC） 的孔隙网络。使用 LT-DSC、1H NMR 和 CT 从微观、细观和宏观角度研究孔特性 （包括孔径、均匀性、分形维数和孔形状） 与低温性能之间的关系。此外，采用纳米压痕和有限元模拟来揭示孔隙网络对 ULWC 低温性能的控制机制。结果表明，浮石的添加使 −80 °C 时的抗压强度增长率从 44.38 % 提高到 97.05 %。孔结构分析表明，浮石促进了凝胶孔分形空间的聚集，诱导基质形成更多的长球状孔。其中，分形维数和孔隙度与低温抗压强度强相关，基于这些因素的低温强度预测模型达到了 0.95 的精度。此外，微观结构分析和模拟结果表明，长球形孔隙的应力耗散特性与低温预应力相结合，共同增强了 ULWC 的低温性能。浮石的低模量及其对微孔网络均匀性的提高可以将 UHD C-S-H 模量的低温损伤率从 22.62 % 降低到 0.82 %。 这些发现为未来混凝土低温性能的针对性优化提供了理论指导。