Microwave Fragmentation of Concrete

Metna Co.

Problems & Needed Improvements

• Problems with existing methods of removing damaged pavement

• Time-consuming

• Labor-intensive

• Generate abrasive dust & noise

• Cannot effectively avoid undamaged parts

• Require heavy equipment

• Needed Improvements

• Speed & precision

• Dust and noise control

• Reduced/eliminated need for on-site labor

• Value-added use of debris in follow-up repair

Alternative Concrete Removal Technologies

• Pneumatic concrete breakers

• Hydraulic breakers

• Expansive agents

• Hydro-demolition

• Abrasive jetting

• Sponge blasting

• CO2 (dry ice) blasting

• Electrohydraulic scabbing

• Shot blasting

• Laser ablation

• Microwave fragmentation

• Differential thermal stresses & vapor pressure

• Volumetric (versus superficial) removal

• Selectivity

• Dust and noise control

• Efficient and expedient

• Beneficiation of fragmented concrete

• Potential for remote control

Pneumatic Breaker Hydraulic Breaker Expansive Agents Hydrodemolition Abrasive Jetting

Microwave Heating of Concrete

Curing

• Lower frequencies (0.915 & 2.45 GHz) for uniform heating

• ~1 kW microwave power

• Significantly reduced cure time & rate of strength gain

Selective fragmentation & recycling

• Higher microwave frequencies (>2.45 GHz) to induce differential thermal stresses, localize the microwave power and improve selectivity.

Electromagnetic Spectrum

Concrete Application of Microwave

• Accelerated microwave curing of concrete

• Selective microwave demolition and drilling of concrete

• Microwave recycling of concrete

• Concentration of energy in the demolition zone

• A waveguide forms a narrow beam of energy that can be directed to a targeted area.

System Components

Microwave Generator

Microwave Transmission Line • Control Unit

Waveguides

Dimensions of Standard Waveguides

Schematics of the Transmission Line and the Applicator

Applicator

Working Principles

• Main Causes of Concrete Demolition

• Differential Thermal Stresses in bulk concrete

• Differential Aggregate-Paste Interfacial Stresses

• Pore Water Pressure