Deterioration Reduction through Multi-scale crack Control (DRMC)
University of California, Berkeley
Problems
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.
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.
Findings
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.
Impact
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.
Core competencies
- Fracture mechanics of quasi-brittle materials
- Durability mechanics
- Nano and microstructure design and modeling
- Forensic Analysis and Nondestructive Evaluation of Damage in quasi-brittle and metallic materials
Current research team members:
- Gabriel Jen (Ph.D. Candidate)
- William Trono (Ph.D. Candidate)
- David Lallemont (Ph.D. Candidate)
- Cagla Meral (Ph.D. Candidate)
- Jessica Jones (M.Eng Candidate)
Recent graduates and co‐workers:
- Joshua Blunt (Ph.D. 2008) now at Exxon Mobil
- Margarita Constantinides (Ph.D. 2008) now at McKinsey and Company Inc.
- Fariborz Vossoughi (Ph.D. 2008) now at Ben C. Gerwick Inc.
Current Research Collaborations:
- Corrosion assessment and modeling: Thomas Devine (MSE Department, UC Berkeley)
- Alkali silica reaction mechanisms: M. Garci-Juenger (University of Austin, Texas) and L. Turanli (University of Ankara, Turkey)
- Confinement and tension stiffening modeling of high performance fiber reinforced composites: Sarah Billington (Stanford)
- HyFRC for seismic applications: Marios Panagiotou (UC Berkeley)