Self-healing Concrete

Concrete is the largest commodity chemical used in the world, with 2.35 billion metric tons of concrete produced annually today. This quantity has increased each year since the 1970's and is projected to approach 5 billion metric tons by 2030. Concrete used in buildings, bridges and highways are expected to last for decades without damage or major loss of structural strength. However, because of environmental exposure and repeated cyclic loadings, defects and cracks develop in these materials. Multiple problems arise if these cracks are allowed to stay after they have been initiated. Water ingress through the cracks causes corrosion of steel reinforcement bars and stresses the concrete even further because of freeze-thaw cycles. The mechanical properties of the concrete also get degraded substantially, leading to premature and sometimes catastrophic failure. There is a critical need to produce 'smart' concrete materials that have a capacity to self-repair (at least partially) cracks, thus leading to more durable materials. When viewed as a whole, the process of blasting, mining, transporting and producing concrete is an energy intensive process that releases a significant amount of carbon dioxide. Concrete production is responsible for almost 10% of the carbon dioxide present in the atmosphere. Thus, both from the perspective of mechanical properties and direct environmental impact, there is a significant motivation to produce concrete that has self-healing capability, and thus has a greater useful lifetime than the concrete that is used today.