Field exposure experiments on the influence of low air pressure environment on the air-void structure of air-entrained concrete and its deterioration mechanism

IF 7.4 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Construction and Building Materials Pub Date : 2024-11-12 DOI:10.1016/j.conbuildmat.2024.139067

Chaohua Jiang , Yi Wang , Youling Ouyang , Weitai Cai , Wenxun Qian , Limin Xia

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Abstract

Field exposure experiments were conducted in Nanjing (101.2 kPa) and Lhasa (65.3 kPa) to comparatively analyze the performance of polyether-based air-entraining agent (AEA-P) and rosin-based air-entraining agent (AEA-R) in low air pressure (LAP) environments. The effects of LAP environments on the air-void structure and pore structure of air-entrained concrete (AEC) with 3 %, 5 %, and 7 % air content were studied using the air-void parameter testing and NMR. Finally, the relative dynamic elastic modulus change of the AEC was investigated in relation to freeze-thaw resistance tests. The results indicate that the bubble stability of the AEA-P is superior to that of the AEA-R. The initial bubble diameter of the AEA-P under LAP conditions is 8–12 % smaller than that of the AEA-R. After 15 minutes of standing, the bubble diameter of the AEA-P is nearly half that of the AEA-R. LAP significantly deteriorates the air-void structure of AEC. These effects are primarily manifested as a reduction in the proportion of air-voids smaller than 200 μm and an increase in the proportion of air-voids larger than 200 μm. Compared to NAP, the proportions of air-voids smaller than 200 μm decreased by 3.8 %, 5.8 %, and 10.2 %, while the proportions of air-voids larger than 200 μm increased by 2.5 %, 3.0 %, and 4.6 % for the three different AEA dosages in LAP. Additionally, LAP reduces the specific surface area of the air-voids, increases the average air-void diameter, and reduces the number of air-voids. Consequently, the air-void spacing factor increases by 23–35 μm compared to normal air pressure (NAP), with the variation ranging from 12.5 % to 28.5 %. Regardless of whether the AEC was molded under LAP or NAP, the total porosity increased with higher air content. Additionally, the number of capillary pores larger than 200 nm was higher in concrete molded under LAP conditions. Under the same air content, the frost resistance of AEC molded in LAP is inferior to that of AEC molded under NAP, after 300 freeze-thaw cycles, the relative dynamic elastic modulus of the AEC decreased by 2.4 %, 3.1 %, and 4.8 % for the different air content levels, respectively. This study offers valuable insights into the freeze-thaw damage mechanisms of concrete in high-altitude cold environments. It also provides measures to enhance the frost-resistant durability of concrete in plateau areas.

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低气压环境对引气混凝土气泡结构的影响及其劣化机理的现场暴露实验

在南京（101.2 kPa）和拉萨（65.3 kPa）进行了现场暴露实验，比较分析了聚醚型引气剂（AEA-P）和松香型引气剂（AEA-R）在低气压（LAP）环境下的性能。利用气泡参数测试和核磁共振研究了低气压环境对含气量为 3%、5% 和 7% 的引气混凝土（AEC）的气泡结构和孔隙结构的影响。最后，结合抗冻融试验研究了引气混凝土的相对动态弹性模量变化。结果表明，AEA-P 的气泡稳定性优于 AEA-R。在 LAP 条件下，AEA-P 的初始气泡直径比 AEA-R 小 8-12%。静置 15 分钟后，AEA-P 的气泡直径几乎是 AEA-R 的一半。LAP 会明显恶化 AEC 的气泡结构。这些影响主要表现为小于 200 μm 的气泡比例减少，而大于 200 μm 的气泡比例增加。与 NAP 相比，在 LAP 中的三种不同 AEA 剂量下，小于 200 μm 的气泡比例分别减少了 3.8%、5.8% 和 10.2%，而大于 200 μm 的气泡比例分别增加了 2.5%、3.0% 和 4.6%。此外，LAP 减少了气泡的比表面积，增加了气泡的平均直径，并减少了气泡的数量。因此，与正常气压（NAP）相比，气泡间距系数增加了 23-35 μm，变化范围在 12.5 % 到 28.5 % 之间。无论 AEC 是在 LAP 还是 NAP 下成型，总孔隙率都会随着空气含量的增加而增加。此外，在 LAP 条件下成型的混凝土中，大于 200 nm 的毛细孔数量较多。在相同含气量条件下，LAP 条件下模压的 AEC 的抗冻性不如 NAP 条件下模压的 AEC，在经过 300 次冻融循环后，不同含气量水平的 AEC 的相对动态弹性模量分别降低了 2.4%、3.1% 和 4.8%。这项研究为了解高海拔寒冷环境下混凝土的冻融破坏机制提供了宝贵的见解。它还为提高高原地区混凝土的抗冻耐久性提供了措施。

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来源期刊

Construction and Building Materials 工程技术-材料科学：综合

CiteScore

13.80

自引率

21.60%

发文量

3632

审稿时长

82 days

期刊介绍： Construction and Building Materials offers an international platform for sharing innovative and original research and development in the realm of construction and building materials, along with their practical applications in new projects and repair practices. The journal publishes a diverse array of pioneering research and application papers, detailing laboratory investigations and, to a limited extent, numerical analyses or reports on full-scale projects. Multi-part papers are discouraged. Additionally, Construction and Building Materials features comprehensive case studies and insightful review articles that contribute to new insights in the field. Our focus is on papers related to construction materials, excluding those on structural engineering, geotechnics, and unbound highway layers. Covered materials and technologies encompass cement, concrete reinforcement, bricks and mortars, additives, corrosion technology, ceramics, timber, steel, polymers, glass fibers, recycled materials, bamboo, rammed earth, non-conventional building materials, bituminous materials, and applications in railway materials.