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

传统上，混凝土可以被认为是矿物集料、水和波特兰水泥的混合物。然而，现代混凝土混合料要复杂得多，还含有化学外加剂和辅助胶凝材料(SCM)，以增强其在流体和硬化状态下的性能。SCMS在美国、英国和国际上被广泛使用，以取代部分波特兰水泥，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二氧化碳排放。最常用的SCM是从废物中提取的，包括燃煤灰烬和炼铁产生的高炉炉渣。然而，工业过程的变化(例如，煤与生物质共烧、可再生能源的使用、全球钢铁行业的结构性变化)以及对SCM日益增长的需求正在导致高质量、常规SCM的短缺。广泛使用的天然超临界流体材料，如煅烧粘土和火山矿物，其使用正在急剧增加，因为它们的化学和矿物学更均匀，与废物衍生的超临界流体材料相比，有助于质量控制。美国和英国正在推进标准化，以便更广泛地使用这些材料，但它们使用的基础科学需要进一步研究。天然SCM与废物衍生SCM一样，通常对混凝土耐久性、成本和环境足迹有积极影响。然而，所有SCM的一个问题是，它们经常增加混凝土的碳化脆弱性。当二氧化碳进入材料时，会发生碳化作用，化学反应并降低pH值，导致钢筋的腐蚀以及水泥基质的完整性改变。在使用天然SCM的混凝土中，碳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对碳化降解的贡献对于未来证明这项技术至关重要。此外，有可能操纵体系的组成以减少或防止碳化，但以前没有人探索过。RENACEM是美国和英国领先的基础设施材料研究人员共同合作的项目，旨在阐明解释用天然SCM生产的混凝土的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传输，以确定用于评估它们的有意义的方法。这将为采用天然SCM和预测模型测试混凝土碳化的新方法奠定基础。

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.