Durability Mechanics at the University of California Berkeley
Deterioration Reduction through Multi-scale Crack Control (DRMC)
There is a pressing need to enhance the sustainability of our infrastructure. Concrete structures are deteriorating at a much faster rate than expected resulting in a massive need for repairs and premature replacement and costing billions of dollars annually. Deterioration is caused by mechanical loading conditions and expansive deterioration processes (corrosion, frost action, alkali‐silica reaction, and sulfate attack) which create tensile stresses that eventually lead to crack formation. Cracks in concrete due to expansive deterioration processes initiate as small microcracks. Once these microcracks become interconnected and form macrocracks ingress of water and aggressive ions is enhanced and the deterioration process accelerated. In order to enhance the service life of concrete structures, the concrete needs to be designed in such a way that it complies with certain performance criteria such as crack resistance, high durability, and deflection or tension hardening behavior. Our research group developed such a material through a materials science and fracture mechanics approach.
We developed a performance based materials approach referred to as Deterioration Reduction through Multi‐scale crack Control (DRMC) to enhance the durability and service life of concrete structures. The multi‐scale crack control is achieved through the combined use of micro and macrofibers. The microfibers control microcracks and macrofibers resist and delay subsequent macrocrack formation. The DRMC approach is a holistic approach and provides multiple lines of defense against damage due to mechanical and environmental conditions by reducing the rate of damage initiation and damage propagation. It concentrates on cracking which is common to all deterioration processes independent of their reactants. Hence, it differentiates itself from the traditional approach which treats each deterioration process in isolation and proposes different remedies for each expansive deterioration mechanism.
The DRMC approach limits the ingress of aggressive agents and water to the reaction sites since crack formation is delayed up to strain levels exceeding the yield strain of conventional steel reinforcing bars. It also limits the egress away from the reaction sites due to the presence of microfibers in close vicinity to the reaction sites. The control of microcracks is essential for enhancing the durability of reinforced concrete structures. The microfibers pin the crack surfaces which confines the reaction product (i.e. alkali silica reaction gel or corrosion product) and prevents it from leaving. The lack of egress modifies the density, the composition, and the amount of the alkali silica gel and corrosion products and furthermore reduced their reaction rates. In case of alkali silica reaction (ASR) it was the change in the ASR gel composition that starved the reaction.
The DRMC approach which was based on materials science and fracture mechanics principles has the potential to provide us with materials that enhance the service life and the sustainability of concrete structures. It is a rich new research area that has the potential of spawning several new directions to investigate the DRMC’s impact on the various deterioration mechanisms. Hybrid fiber reinforced concrete (HyFRC) composites developed according to the DRMC approach and tested under severe environmental and seismic loading conditions exhibit superior performance in regards to durability, crack resistance, and ductility.
- CK. Yi & C.P. Ostertag, “Mechanical Approach in Mitigating Alkali Silica Reaction,” Cementand Concrete Research, Vol 35, pp.67-75, 2005
- J. Grupp, J. Blunt, C.P. Ostertag, T. Devine, “Effect of Crack control on Corrosion”, Cementand Concrete Research, Vol 37, pp. 1115-1126, 2007
- J. Blunt and C.P. Ostertag, “A Performance Based Approach for the Design of a Deflection Hardened Hybrid Fiber Reinforced Concrete,” Journal of Engineering Mechanics, ASCE 2009, Vol 135, pp. 978-986.
- Blunt, J. and C.P. Ostertag, “Deflection hardening and workability of hybrid fiber composites,” ACIMaterials Journal, 2009, Vol. 106, pp. 265-272