CMMI-EPSRC RENACEM: Response to CO2 exposure of concrete with natural supplementary cementitious materials

混凝土传统上被认为是矿物骨料、水和波特兰水泥的混合物。然而，现代混凝土混合物要复杂得多，还含有化学外加剂和辅助胶凝材料（SCM），以增强流体和硬化状态下的性能。SCM在美国、英国和国际上广泛用于替代部分波特兰水泥，提高混凝土的长期耐久性，降低成本，并减少与混凝土生产相关的CO2排放。最常用的SCM是废物衍生的，包括燃煤灰和炼铁产生的高炉炉渣。然而，工业过程的变化（例如煤与生物质的共烧，可再生能源的使用，全球钢铁工业的结构变化）以及对SCM需求的增加导致了高质量传统SCM的短缺。广泛使用的天然SCM，如煅烧粘土和火山矿物质的使用正在急剧增加，因为它们的化学和矿物学更均匀，与废物衍生的SCM相比有助于质量控制。美国和英国正在推进标准化，以使这些材料得到更广泛的使用，但其使用的基础科学需要进一步研究。天然SCM，如废物衍生的，通常对混凝土的耐久性，成本和环境足迹有积极的影响。然而，所有SCM的一个问题是，它们往往会增加混凝土碳化的脆弱性。当CO2进入材料时发生碳酸化，发生化学反应并降低pH值，导致钢筋腐蚀以及水泥基质完整性的变化。在具有天然SCM的混凝土中，控制碳酸化和相关降解的机制在很大程度上是未知的。考虑到该领域正在推动在混凝土中使用越来越多的天然SCM（所谓的LC3系统），了解天然SCM对碳酸化降解的贡献对于未来证明该技术至关重要。此外，操纵系统的组成以减少或防止碳酸化是可能的，但先前尚未探索。RENACEM是领先的基础设施材料研究人员之间的美英联合合作，旨在阐明解释天然SCM生产的混凝土长期性能的基础科学。我们将了解混凝土和大气二氧化碳之间的化学相互作用及其运输，以确定用于评估的有意义的方法。这将支持采用新的方法来测试混凝土的碳化与自然SCM和预测模型。

Concrete can traditionally be thought of a mixture of mineral aggregates, water, and Portland cement. However, modern concrete mixtures are much more complex, also containing chemical admixtures and supplementary cementitious materials (SCMs) to enhance properties in the fluid and hardened states. SCMs are widely used in the US, UK and internationally to replace a portion of the Portland cement, improving concrete long term durability, reducing cost, and reducing CO2 emissions associated with concrete production. The most commonly used SCMs are waste-derived, including coal combustion ashes and blast furnace slags from iron-making. However, changes in industrial processes (e.g. co-firing of coal with biomass, use of renewable energy, structural changes in the global iron industry) and increasing demand for SCMs are leading to a shortage of high quality, conventional SCMs. The use of widely-available natural SCMs, such as calcined clays and volcanic minerals, is rising dramatically, as their chemistry and mineralogy are more homogeneous, aiding in quality control compared to waste-derived SCMs. Standardization is advancing in the US and the UK to enable broader use of these materials, but the fundamental science of their use needs further investigation. Natural SCMs, like waste-derived ones, generally have positive impacts on concrete durability, cost, and environmental footprint. However, one concern with all SCMs is that they often increase the vulnerability of concrete to carbonation. Carbonation occurs when CO2 enters the material, chemically reacting and reducing pH, leading to corrosion of steel reinforcement as well as changes in the integrity of the cementitious matrix. In concretes with natural SCMs, the mechanisms governing carbonation and related degradation are largely unknown. Considering that the field is pushing toward use of increasing volumes of natural SCM use in concrete (so-called LC3 systems), understanding the contribution of natural SCMs toward carbonation degradation is critical for future proof this technology. Furthermore, it is possible that manipulating the composition of the systems to reduce or prevent carbonation is possible, but has not previously been explored. RENACEM is a joint US-UK collaboration between leading infrastructure materials researchers to elucidate the fundamental science explaining the long-term performance of concretes produced with natural SCMs. We will understand the chemical interactions between concretes and atmospheric CO2, and its transport, to identify meaningful methodologies to be used for their assessment. This will underpin the adoption of new methods for testing carbonation of concretes with natural SCMs and prediction models.