ICRI Introduces Hydrodemolition Technical Guideline

“Before anything else, preparation is the key to success.” Alexander Graham Bell (1847 – 1922).  And so it is for the success of a concrete repair:  Without proper surface preparation, a concrete repair will be seriously compromised with the possibility of an immediate failure.  ICRI recently published Technical Guideline No. 03737, “Guide for the Preparation of Concrete Surfaces for Repair Using Hydrodemolition Methods”.  While surface preparation techniques are discussed in ICRI Technical Guideline No. 03732 “Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings and Polymer Overlays”, this new guideline focuses specifically on the use of hydrodemolition for concrete removal and surface preparation.

Hydrodemolition is the only non-mechanical method of removing deteriorated concrete in preparation for a repair material or overlay.  Hydrodemolition has been in use in the US for over twenty years and has been widely accepted for over ten years.  Engineers and many State Departments of Transportation specify hydrodemolition for concrete removal.  They recognize the significant improvement in bond strength obtained using the hydrodemolition method.  The quality of the surface preparation insures the long-term success and durability of the concrete repair. 

Mechanical removal equipment, such as jackhammers and rotomills, impact the repair surface causing micro-fractures to develop.  The micro-fractures can extend ¼” to ½” into the surface damaging (bruising) the substrate.  This weak zone in the substrate will result in a reduction in the bond strength between the substrate and repair materials.  Direct tensile bond tests show bond failure in this weaken zone with tensile strengths only a fraction (10%-50%) of the tensile strength of either the substrate or the repair material.
 

 

Hydrodemolition does not introduce micro-fractures into the substrate.  During hydrodemolition the coarse aggregate is exposed and not damaged.  The surface texture is rough with partially exposed aggregate protruding.  The elimination of micro-fractures and increased surface area from the rough texture creates and excellent bond with the repair material.  Direct tensile tests typically show failure deep within the existing substrate (often the weaker of the two materials) and not at the bond line.

The new Technical Guideline contains information on the entire hydrodemolition process including:

• Benefits and limitations;
• The system and how it works;
• Safety;
• Applications;
• Issues to consider when using hydrodemolition;
• Wastewater control;
• Debris cleanup and disposal;
• Test areas and methods of measuring the removal.

The new guideline No. 03737 explores other benefits of hydrodemolition, such as:

• Deteriorated concrete is selectively removed;
• Reinforcement is cleaned and undamaged;
• Structural vibration is minimal;
• Dust (silicosis) is minimized;
• The construction time can be accelerated;
• Robotic equipment reduces jobsite injuries.

As ICRI and the concrete repair industry looks to the future, we will seek repair methods and procedures that enhance the quality of the repair, are less labor intensive, and improve the work environment.  The use of high-pressure water to remove concrete represents a step forward.  Technical guideline No. 03737 will assist the reader in understanding how the hydrodemolition process works and how it can be use to enhance the quality and durability of concrete repairs.