Fracture toughness of alkali-sensitive rocks in alkaline solution

• Alkali-sensitive rocks like quartz porphyry, graywacke and quartzite show severe degradation in alkaline environment.
• Fracture toughness and modulus of elasticity decrease up to 75% in potassium hydroxide solution after 560 days.
• The rocks tested are used as aggregate in concrete and may cause severe distress due to alkali–silica reaction (ASR).

There are certain types of rocks which can crack in alkaline environment. If they are used in concrete which is highly alkaline they may cause great distress to the concrete structure. The cause of cracking of so-called slow/late aggregates is supposed to be due to gel pressure in the grain. The cracking of grains can be approached with the aid of fracture mechanics and the decisive parameter for crack extension is the critical stress intensity factor. To this end, various types of rocks were stored in alkaline solution and the critical stress intensity factor was determined as function of exposure time.