Lozano-Valcarcel Juan M, Ov David, Kränkel Thomas, Gehlen Christoph, Breitenbücher Rolf
Chair of Materials Science and Testing, Centre for Building Materials, School of Engineering and Design, Technical University of Munich, 80333 Munich, Germany.
Institute for Building Materials, Ruhr University Bochum, 44801 Bochum, Germany.
Materials (Basel). 2023 Jun 10;16(12):4306. doi: 10.3390/ma16124306.
Chloride ingress and carbonation pose a significant risk of steel rebar corrosion in concrete structures. Various models exist to simulate the initiation phase of rebar corrosion, addressing both carbonation and chloride ingress mechanisms separately. These models also consider the environmental loads and material resistances, typically determined through laboratory testing based on specific standards. However, recent findings show significant differences between material resistances obtained from standardized laboratory specimens and those extracted from real structures, with the latter exhibiting inferior performance on average. To address this issue, a comparative study was conducted between laboratory specimens and on-site test walls or slabs, all cast using the same concrete batch. This study encompassed five construction sites featuring different concrete compositions. While laboratory specimens adhered to European curing standards, the walls were subjected to formwork curing for a predetermined period (typically 7 days) to simulate practical conditions. In some instances, a portion of the test walls/slabs received only one day of surface curing to emulate inadequate curing conditions. Subsequent testing of compressive strength and resistance to chloride ingress revealed that field specimens exhibited lower material resistance compared to their laboratory counterparts. This trend was also observed in the modulus of elasticity and carbonation rate. Notably, shorter curing periods further compromised performance, particularly resistance to chloride ingress and carbonation. These findings highlight the importance of establishing acceptance criteria not only for concrete delivered to construction sites but also for ensuring the quality of the actual structure.
氯离子侵入和碳化对混凝土结构中的钢筋腐蚀构成重大风险。存在各种模型来模拟钢筋腐蚀的起始阶段，分别针对碳化和氯离子侵入机制进行研究。这些模型还考虑了环境荷载和材料抗性，通常通过基于特定标准的实验室测试来确定。然而，最近的研究结果表明，标准化实验室试件获得的材料抗性与从实际结构中提取的材料抗性存在显著差异，后者平均表现较差。为了解决这个问题，对实验室试件与现场测试墙或板进行了对比研究，所有试件均使用同一批混凝土浇筑。该研究涵盖了五个具有不同混凝土成分的建筑工地。实验室试件遵循欧洲养护标准，而墙体则进行了预定时间（通常为7天）的模板养护以模拟实际情况。在某些情况下，部分测试墙/板仅进行了一天的表面养护以模拟养护不足的情况。随后对抗压强度和抗氯离子侵入性能的测试表明，现场试件的材料抗性低于实验室试件。在弹性模量和碳化速率方面也观察到了这种趋势。值得注意的是，养护期越短，性能下降越明显，尤其是抗氯离子侵入和碳化性能。这些发现凸显了不仅要为运至施工现场的混凝土制定验收标准，还要确保实际结构质量的重要性。
