ACI 2008 Concrete Projects Competition Winners

 

1st Place:
 Developing a Novel pH Buffer Methodology to Inhibit Concrete Corrosion
Author:
 Michael J. Loy  
Faculty Advisor:
 Rosa Hemphill
Abstract:
 Concrete deterioration costs billions of dollars each year in the U.S. in repair, replacement, and environmental impact. The major cause of deterioration is corrosion of steel reinforcing bar in concrete that occurs when concrete pH is reduced by high acidic attack or when chloride ions penetrate concrete, destroying the natural passivation layer surrounding reinforcing bar.

This innovative study developed a pH buffer methodology to maintain a high pH environment to protect reinforcing bar's passivating layer from acidic and chloride corrosion. Previous studies and mitigation strategies have focused on creating additional passivation layers or developing coatings, sealants, or coverings for concrete to inhibit corrosion.

Sodium borate and sodium carbonate-based buffers, both highly alkaline and nonchloride, were mixed into concrete by replacing the mixing water with 25%, 50%, and 100% concentrations of each buffer, then compared against a non-buffered control. Samples were placed in a 100% carbon dioxide chamber to accelerate acidic corrosion attack and immersed in a 2M sodium chloride solution to accelerate chloride corrosion. The effects of pH buffers on compressive strength, pH levels, half-cell potential, flowability, air content, and reinforcing bar surface were studied.

Results indicated that pH buffers maintained high pH and reduced probability of corrosion with sodium borate at 50%—the most effective buffer solution. It exceeded the control in compressive strength, maintained consistently high pH, and tested second-best in low probability of acidic and chloride corrosion with moderate flowability. The study supported an efficient, cost-effective nontoxic buffer methodology to extend the service life of concrete, improve durability, and promote a sustainable environment.
 
  
2nd Place:
 The Use of Mexican Natural Pozzolans for Preventing Corrosion in Reinforced Mortar Specimens: A Laboratory Study  
Author:
 José Pacheco
Faculty Advisors:
 Gerardo Fajardo San Miguel and Pedro L. Valdez Tamez
 
  
3rd Place:
 The Use of Macro-synthetic Fibre-Reinforced Concrete  
Author:
 Peter Hughes
Faculty Advisor:
 C.J. Hill