NSF Convergence Accelerator Track I: Revolutionizing the manufacture of Portland cement concretes towards a circular and carbon-negative future

混凝土是世界上应用最广泛的建筑材料。然而，目前普通波特兰水泥（OPC）基混凝土的生产造成了当今社会面临的三大挑战：气候变化、资源枯竭和固体废物。这项融合研究将通过利用循环经济原则的协同作用和一种革命性的混凝土制造方法，将混凝土转化为最大的二氧化碳汇之一，为解决所有这些挑战建立一条途径。通过生物分子调节碳化（BioCarb）技术，这种新的制造方法将水泥浆转化为有效的二氧化碳吸收剂，它可以吸收并永久储存比现有技术多25到50倍的二氧化碳。更重要的是，原位制备的纳米颗粒可以显著提高混凝土的抗压强度。同样，富含钙的工业废料-如再生混凝土细粒、钢渣和煤灰-可以转化为负碳的补充胶凝材料，这可以大大减少混凝土生产所需的OPC量。此外，BioCarb中使用的功能性生物分子将从农业废弃物中提取，这为混凝土中使用的化学外加剂脱碳提供了一种新的解决方案。如果成功，该项目可以释放混凝土作为碳酸盐矿物永久储存二氧化碳的巨大潜力，并使混凝土的所有成分脱碳。因此，混凝土的二氧化碳足迹可能会减少50%以上。如果提议的技术得到全面部署，全球每年可减少20多亿吨二氧化碳，每年可将30多亿吨固体废物转化为有用的胶凝材料和骨料，同时避免开采等量的自然资源。混凝土可以通过矿化过程作为二氧化碳汇，在矿化过程中，二氧化碳与混凝土中富含钙的矿物质反应产生CaCO3并永久储存二氧化碳。然而，包括扩散障碍和边际强度改善在内的关键挑战阻碍了现有技术充分发挥混凝土的二氧化碳封存潜力。为了充分发挥这一潜力，我们提出了一项突破性的技术，BioCarb，以最大限度地提高二氧化碳的吸收，同时在混凝土硬化之前就地生产纳米级性能增强剂。这是通过使用生物分子作为小剂量添加剂来实现的，该添加剂通过以下方式调节富钙矿物的碳化过程：1)与钙螯合以促进矿物的碳化；2)控制碳酸钙的结晶成核、取向、大小和多晶型；3)使生成的CaCO3纳米和微颗粒均匀分散。因此，混凝土可以直接吸收更多的二氧化碳，而不会影响其性能。更重要的是，通过BioCarb产生的亚稳CaCO3可以与水泥反应形成新的矿物质或溶解再沉淀，在混凝土中起到结合相的作用。因此，一种新型水合硅酸钙-碳酸钙混合粘合剂可以在混凝土中形成，从而提高了混凝土的机械强度、体积稳定性和耐久性。同样，该工艺可用于处理其他富钙固体废物，将其转化为负碳的补充胶凝材料和骨料，分别最大限度地替代水泥和自然提取骨料。这意味着脱碳的潜力更大。该项目采用了一种融合的研究方法，通过融合多个学科——土木工程、材料科学与工程、环境工程、化学、食品科学与加工、环境正义——以及BioCarb的最终用途，以及对环境和经济可持续生产混凝土的全生命周期考虑，将BioCarb转化为实际应用。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Concrete is the most widely used construction material in the world. However, current production of ordinary Portland cement (OPC)-based concrete contributes to three main challenges that our society is facing today: climate change, resource depletion, and solid waste. This convergence research will establish a pathway to address all these challenges by leveraging the synergy of circular economy principles and a revolutionary manufacturing method of concrete which converts concrete into one of the largest sinks for CO2. Through a biomolecule-regulated carbonation (BioCarb) technology, this new manufacturing method transforms cement slurry into an effective CO2 absorbent, which can absorb and permanently store 25 to 50 times more CO2 in fresh concrete than existing technologies. More importantly, the compressive strength of the produced concrete can be drastically increased by in-situ produced nanoparticles. Similarly, calcium-rich industrial wastes – such as recycled concrete fines, steel slag, and coal ashes – can be converted into carbon-negative supplementary cementitious materials, which can substantially reduce the amount of OPC needed for concrete production. In addition, the functional biomolecules used in BioCarb will be extracted from agricultural waste, which provides a new solution to decarbonize chemical admixtures used in concrete. If successful, this project can unlock the enormous potential of concrete for permanent storage of CO2 as carbonate minerals and decarbonize all ingredients of concrete. As a result, the CO2 footprint of concrete will potentially be reduced by more than 50%. If the proposed technology is deployed at full scale, over 2 billion metric tons of CO2 can be reduced per year globally, and more than 3 billion metric tons of solid wastes can be converted into useful cementitious materials and aggregate every year and avoiding extraction of the same amounts of natural resources.Concrete can serve as a CO2 sink through mineralization processes, in which CO2 react with calcium-rich minerals in concrete to produce CaCO3 and permanently store CO2. However, key challenges including diffusion barriers and marginal strength improvement impede existing technologies to reach full potential of concrete for CO2 sequestration. To fully unlock this potential, we propose a breakthrough technology, BioCarb, to maximize CO2 uptake while n-situ produce nanoscale performance enhancers before concrete hardens. This is achieved by using a biomolecule as small-dose additive, which regulates the carbonation process of calcium-rich minerals through: i) chelating with calcium to facilitate the carbonation of the minerals, ii) controlling the crystal nucleation, orientation, size, and polymorph of calcium carbonate, and iii) enabling uniform dispersion of the produced CaCO3 nano- and micro-particles. As a result, much more CO2 can be absorbed by concrete directly without compromising performance. More importantly, the metastable CaCO3 produced through BioCarb can react with the cement to form new minerals or dissolve and re-precipitate to function as a binding phase in concrete. As a result, a novel calcium silicate hydrate-CaCO3 hybrid binder can form in the concrete, leading to improved mechanical strength, volumetric stability, and durability. Similarly, this process can be used to process other calcium-rich solid wastes and convert them into carbon-negative supplementary cementitious materials and aggregate for maximal substitution of cement and naturally extracted aggregate, respectively. This implies an even bigger potential for decarbonization. A convergent research approach is employed in this project to transit BioCarb into practical use, by fusing multiple disciplines – civil engineering, material science and engineering, environmental engineering, chemistry, food science and processing, and environmental justice – and the end uses of BioCarb and full life cycle considerations for the environmentally and economically sustainable production of concrete.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.