Shotcrete mix design components

Shotcrete has been used on a large scale for tunneling works and fire protection is also used for architectural purposes. There are two types of application shotcrete, the wet and dry. Shotcrete is a concrete with the help of air under pressure to be transported at high speed. It is applied and compacted at the same time against a surface.

Shotcrete components

As mentioned above, other than the permanent shotcrete from the way in applying it. Here are somePoints must be observed and respected in the production of shotcrete mix.

Cement

It 'obvious that the quality characteristics of cement play a dominant role in the behavior at high initial resistance. The specific surface (Blaine value) must not be less than 3500 cm2 / g. compressive strength of cement, lime should be greater than 10 MPa after 2 days and more than 35 MPa after 28 days. First stiffening of cement and lime should not be 1.5 hours before and after 4 hoursstart of mixing with water. The choice of cement is, however, as long as the desired properties of hardened concrete and not subject to their suitability for spraying. The requirement of initial strength would be for the content of cement. Usually dry process, we dose of 280-350 kg per 1 m3 of mix in bulk. Able for the contents of wet cement process varies from 425 kg/m3 to 500 kg/m3. Cement content suitable for the force required may be revised only with the study shotcrete. Aslight slowing of the setting is through the Tri observed in calcium sulfate-aluminate cement. Blast furnace cements cause the same problem.

Water

Any use of water for the mixing of mineral components must be cleaned, as it occurs in nature. Spring water must be analyzed to determine their compatibility with other components of the mixture. The water-cement ratio should not exceed 0.40, if there is a high strength and durable shotcreterequired.

Sand

The sand must be clean. It is always combined with a total. S / A ratio varies from 55% - 65%. Despite the sand determines the classification of himself as an arbitrator for a particular label for a certain standard, in a combination of sand and an entire set, which must be used in accordance with the standard.

Aggregate

Aggregates are usually crushed whole you would think that could be produced from tailings.But we must avoid flaky aggregate elongated.

Sand / gravel ratio

This relationship must meet several conditions. S / A ratio have a mild or shotcrete pump rotor filling. In general, it is clear that lead to fines of more dust, increasing the demand for water is mixed. Any other mixed with aggregates of more rest would rise, too. E 'was observed that a good pumping properties are achieved when the particles less than 1.18 millimetersrepresents about 40% of the sand / aggregate mix.

Superplasticiser / Stabilizer

Are taken into account for the production of wet-mix alone. These are mainly naphthalene or polycarbonate superplasticiser base. Only some specific superplasticiser could be used to Lignosulfate base. Because the normal concrete, allowing a reduction in consumption of water by processing appropriate to maintain. However, it should be noted that lower the W / C is faster at the beginningStrengths are achieved. The dosage depends on the required functionality. Are usually measured by 1,0-1,7%.

Accelerator

I'm definitely for wet-mix is not required. They are used in some cases, dry-process. They are included for various reasons. They enable the spraying of thick layers, if made, is high, and the band shotcrete is not reached within the substrate. This allows the development of early strength, which minimizesdeformation of the surrounding rock. Limit the reason for the return. Some types of accelerators allow sealing of work when substrate indicates discharge of water. They exist in the form of powder or liquid. They are either alkaline or alkaline-free. Typical doses of modern accelerators of 3-8% by weight of cement.

Roadworks Civil Engineering Overview