Soundless cracking agent is a new type, environmental and convenient construction material that can crack rock and concrete without exploding. An experimental research was conducted to investigate the performance of soundless cracking agent. The experimental results show that the soundless cracking agent has a fast reaction velocity, big expansive pressure. And the testing results reveal that its reaction velocity and expansive pressure strength are associated with proportion of water to cement. Finally, it was applied to crack rock in hard-rock tunnel in high gas coal mine. There is a big rock (11.6m long, 2.3m wide and 0.7m high) at the shaft station of Panbei coal mine need to be removed, and it is very near to a coal seam. It can not be removed by blasting; therefore soundless cracking technique was chosen. Hundreds of holes were drilled with a diameter of 42mm, a depth of 500mm, and the distance between each two holes were 200mm. At last, the big rock mass was cracked into crushed stone. The application results in practice indicate that the performances of the soundless cracking agent meets the demands of constructing design; and the static cracking effect was excellent.
The static cracking agent (SCA) is a new kind of cracking material using expansive pressure to cut or crack concrete, rock and other precious brittle solid materials. SCA has many advantages in application process, which includes no blasting wave, no quake, no flying stone, no noises and no poisonous gas[1–3].
Expansive pressure and reaction speed are the two important indexes to determine the property of the static cracking agent. Therefore, expansive pressure and reaction speed are tested.
Resistance measurement method has been employed to test expansive pressure. The static cracking agent was placed in a thin-wall circular steel tube, and resistance strain gauges were bonded to the outer surface(Fig.1). Fig.1 Picture of expansion pressure measure After the hydration reaction of SCA, expansive pressure occurred in the thin-wall circular tube because of the volume expansion of SCA, which caused the extension deformation in circumferential direction. The circumferential deformation of outer surface can be measured by the resistance strain gauges. Finally, the expansive pressure can be calculated by using the elastic mechanics theory. By using the elastic theory, the expanded pressure formulae for the inner wall of the steel pipe was derived. Specimen G02: the air temperature was 8.6_; the water SCA ratio was 0.24; the SCA and water were 2.2kg and 0.529kg, respectively; the water temperature was 15.1°C. The biggest expansive pressure was only 10.72MPa(Fig.3). The expansive pressure was very small because some SCA was ejected from the tube. Specimen G03: the air temperature was 8.6_; the water SCA ratio was 0.26; the SCA and water were 2.75kg and 0.715kg, respectively; the water temperature was 14.0°C. The biggest expansive pressure was only 38.87MPa(Fig.4).