The characteristics of shotcrete mix proportions are as follows:
- The slump of wet sprayed concrete should be controlled between 8 and 12cm.
- The sand content of wet sprayed concrete is much higher than that of concrete.
The sand ratio for wet spraying concrete should be controlled between 55% and 65%. The sand content of wet sprayed steel fiber reinforced concrete should be controlled between 60% and 70%.
- The cement to aggregate ratio (referred to as the cement to bone ratio) of sprayed concrete is higher than that of ordinary concrete.
The cement to bone ratio of wet sprayed concrete should be controlled between 1:3.5 and 1:4.0, and the cement to bone ratio of wet sprayed steel fiber reinforced concrete should be controlled between 1:3.0 and 1:4.0.
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- Water cement ratio of sprayed concrete.
The water cement ratio of wet sprayed concrete should be controlled between 0.42 and 0.50, and the water cement ratio of wet sprayed steel fiber reinforced concrete should be controlled between 0.40 and 0.45.
- The amount of cement used in shotcrete is higher than that in ordinary concrete, generally ranging from 400 to 450 kg/m3, with a maximum of 500kg/m3.
- The design method for the mix proportion of shotcrete is different from that of ordinary concrete, and its strength calculation should consider the difference in strength between the benchmark concrete (without adding accelerators) and the shotcrete slab specimens. Shocked concrete does not contain any admixtures.
The compressive strength test specimen of shotcrete is made by spraying large plates on site and processing them into cubic specimens with a side length of 100mm or cylindrical specimens with a diameter of 100mm*100mm using the mix proportion of shotcrete, it is not possible to test the compressing test specimens on site. Generally, benchmark concrete specimens is much higher than that of on-site sprayed slabs.
- The mix proportion of sprayed concrete must pass on-site spraying tests, and processing strength specimens must be made using the spraying plate cutting method or drilling core method to conduct sprayed concrete performance tests. The test results should meet the construction mix proportion determined after meeting the design requirements.
