Collaborative Research: In-situ Production of Calcium Carbonate Nanoparticles in Fresh Concrete

波特兰水泥混凝土仍然是世界上使用最广泛的建筑材料，其性能的改进可能会在民用基础设施的设计和寿命方面带来重大好处。在混凝土中掺入纳米颗粒可以显著提高混凝土的特定性能，例如强度和耐久性。然而，纳米颗粒在混凝土中的实际应用受到了很大的限制，因为纳米颗粒的制造成本高，使用效益成本比低，分散困难。本研究旨在研究在新拌混凝土中原位生成纳米颗粒，以提高其工程性能。两步混合工艺将用于在新混凝土中以低成本生产纳米碳酸钙，并提供良好的分散性。由于纳米颗粒触发的机制，通过这种工艺制成的混凝土将具有明显更高的强度和更好的耐久性。对民用基础设施、国民经济和环境效益的潜在好处可能是巨大的。设计了一项积极的教育计划，以补充研究活动，重点是让一群传统上代表性较低的(妇女、少数民族和/或社会经济上处于不利地位的)学生和高中教师参与研究活动。将开发一系列课程模块和专题讲座，将研究工作整合到两所院校的课堂教学中。原位生产纳米碳酸钙克服了阻碍纳米颗粒在混凝土中实际应用的主要障碍。1)原位生成的纳米碳酸钙促进水泥水化并调节水化产物的局部堆积和生长；2)纳米颗粒从无定形或亚稳态转变为稳定的相变在混凝土中形成粘结机制；3)掺入纳米碳酸钙的混凝土由于水化水泥矿物学的变化而表现出较低的孔隙率和较高的强度。综合的实验和数值方法将被用来检验这些假设。特别是，分子动力学模拟将用于解释该方法对水泥早期水化的影响；热力学模拟将用于量化对矿物相组合的影响；先进的材料表征技术(X射线衍射、核磁共振、背散射电子成像等)。将能够验证模拟并量化微观结构。工程表现将通过机械性能评估和耐久性测试来确定。该奖项反映了NSF的法定使命，并已通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Portland cement concrete remains the most widely used construction material in the world, and improvements in its properties have the potential for significant benefit in the design and longevity of civil infrastructure. Incorporating nanoparticles to concrete can significantly enhance specific properties, for example strength and durability. However, real applications of nanoparticles in concrete are very limited because of low benefit-cost ratio of using nanoparticles induced by the high manufacturing cost, and difficulty of dispersing nanoparticles. This research studies the in-situ production of nanoparticles in fresh concrete to enhance the engineering performance. A two-step mixing process will be used to produce calcium carbonate nanoparticles in fresh concrete at low cost, as well as to provide well dispersion. Concrete made by this process will have significantly higher strength and better durability due to mechanisms triggered by the nanoparticles. The potential benefit to civil infrastructure, national economy and environmental benefits can be substantial. An aggressive educational plan is designed to complement the research activities, with an emphasis on involving a group of traditionally underrepresented (woman, minority and/or socio-economically disadvantaged) students and high school teachers in the research activities. A series of course modules and special topics lectures will be developed to integrate the research endeavors into classroom teaching at both institutions.In-situ production of calcium carbonate nanoparticles overcomes the major barriers preventing practical applications of nanoparticles in concrete. Three hypotheses have been identified for revealing the working mechanisms of this method: 1) the in-situ produced calcium carbonate nanoparticles promotes cement hydration and tunes the local packing and growth of hydration products, 2) the phase change of nanoparticles from amorphous or metastable to a stable one creates a binding mechanism in concrete, and 3) concrete with calcium carbonate nanoparticles exhibit lower porosity and higher strength due to changing in mineralogy of hydrated cement. A comprehensive experimental and numerical approach will be applied to test these hypotheses. Especially, molecular dynamics simulations will be used to explain the effects of the method on the early hydration of cement; thermodynamic modeling will be employed to quantify the effects on the mineral phase assemblage; advanced material characterization techniques (x-ray diffraction, nuclear magnetic resonance, backscattered electron imaging, etc.) will enable validation of the simulations and quantification of the microstructure. The engineering performance will be determined by the evaluation of mechanical properties and durability testing.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.