This grant provides funding for the development of virtually "crack-free" concrete materials capable of elevating material durability and extending structural service life by self-sealing porous cracks and autogenously regenerating mechanical performance after damage. This will be accomplished through experimental studies examining the physical and chemical material requirements and environmental exposures that best promote self-healing. Material design based on micromechanics of crack initiation and propagation to control crack width to below 60 m under typical structural service conditions will be emphasized. Nano and microscale phenomena of ion transport, crystal formation and growth into self-healed products will be determined. Supporting this work is a set of existing and newly developed experimental tests to evaluate the reliability, quality and repeatability of self-healing. These tests include dynamic modulus measurements, uniaxial tensile test, water permeability test, nano-indentor and XEDS. As a result, the extent of self-healing both in transport as well as in mechanical properties will be determined.
If successful, this research will provide a systematic methodology for designing robust concrete material which is virtually "crack-free." This have significant economic, social and environmental impacts on the United States, through enhancement of the durability and reduction of maintenance needs and cost of infrastructures such as bridges and roadways. Apart from durability, self-healing concretes offer higher performance in structural safety and cost-effectiveness by regenerating after damage, becoming a powerful tool for engineers charged to create structures conforming to increasingly higher requirements. The impacts of this research look to promulgate a significant design paradigm shift not only among construction engineers, but the larger engineering design community through methods for development of robust self-healing composites.
The poor durability of concrete structures worldwide is a growing concern as repeated maintenance of these structures become more and more expensive. This research involves the development of virtually "crack free" concrete materials capable of elevating material durability and extending service life by sealing porous cracks and regenerating mechanical performance after damage, without human intervention. This is accomplished through experimental studies examining the material requirements and environmental exposure conditions that best promote self-healing. These conditions then guide the design of tailorable bendable concrete for robust material self-healing. Supporting this work is a set of existing and newly developed experimental tests to evaluate both the rate and quality of self-healing at the macro, micro and nano-scales. Specifically, this research accomplishes the following objectives: 1. Understand the effects of environmental conditions (i.e. wet/dry cycles), physical properties (i.e. crack width less than 50 micron, and preferably less than 20 micron), and chemical compositions (i.e. available chemical species - unhydrated cement grains, unused pozzolans and calcite nucleation sites such as fiber surface) on self-healing processes 2.Develop testing techniques (using resonant frequency changes to detect healing – or reversal of damage) to rapidly and accurately determine the level and quality of self-healing, either self-sealing against fluid transport or complete recovery of material properties. The experiments establishes without a doubt that robust self-healing in cementitious material is practically feasible. 3.Design robust self-healing cementitious composites using self-healing criteria (from objectives 1), testing techniques (from objective 2), and micromechanics based concrete materials design philosophies as guides toward crack-free concrete for durable structures. Bendable concrete with crack width self-controlled to less than 20 micron reveal self-healing in the laboratory and outdoor environments. Intellectual Merits: The introduction of an integrated material design approach coupling experimental testing, development of new testing techniques, and material microstructure analyses, with emerging materials design philosophies is a major advancement for construction materials. The development and application of such an approach to self-healing composites serves as a watershed innovation in concrete materials. Additionally, this integrated approach is a leap forward for self-healing materials among all fields of materials engineering. The rapid resonant frequency based rehealing detecting technique also allows future researchers to build upon this fundamental work. The PhD students and post-doc trained on this project serve to champion new design principles in the development of durable "crack free" self-healing concrete structures both in the United States and abroad. Broader Impact: The durability of civil infrastructures has significant economic, social and environmental impacts on the United States. Poor durability leading to repeated repairs is decidedly unsustainable. Apart from durability, self-healing concretes offer higher performance in structural safety and cost-effectiveness by regenerating after damage, becoming a powerful tool for engineers charged to create structures conforming to increasingly higher requirements. Beyond the construction community, the self-healing lessons learned in this research are immediately applicable to other fields using engineered materials, such as advanced composites and polymers, which are subject to damage and require both costly and time intensive maintenance. The impacts of these findings look to promulgate a significant design paradigm shift not only among construction engineers, but the entire engineering design community through methods for development of robust self-healing composites. Additionally, this project fostered collaborative international research initiatives with Delft University in the Netherlands. Several women students were mentored in this project.
