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.
