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RETURN TO HOMEPAGEDry Sprayed Concrete (Gunite)
When installed properly by experienced applicators, sprayed concrete provides designers with a cost effective and adaptable method to create and repair structures. Sprayed concrete exhibits certain properties that in some respects makes it superior to poured concrete. However, it must be remembered that these properties are largely as a result of the different methods of mixing, transporting and placing rather than fundamental differences in component materials. Low Water /Cement RatioSprayed concretes generally have a lower water/cement ratio than poured concrete. This is particularly true in the dry process where a low slump mix capable of supporting itself without sagging is quite normal. High Strengths with Rapid Strength GainSprayed concretes can be expected to attain high compressive strengths particularly with a low water/cement ratio and the dense compaction achieved by the high velocity of application. Rapid strength gain is also achieved, especially when using factory batched materials. Compressive strengths 30% higher than conventionally placed concretes can be expected. High Density /Low PermeabilityThe high velocity of placement ensures good compaction and high density coupled with low permeability and water absorption. This results in a durable homogeneous material with excellent freeze/thaw resistance, low surface cracking and a high degree of abrasion resistance. These properties may be further enhanced by the use of fibre reinforcement in the mix. Enhanced Adhesion and Bond StrengthAs with so many operations in construction, good surface preparation is vital. Assuming that the substrate is properly prepared then the bond strength with sprayed concrete is generally excellent. Furthermore, the use of bonding agents and coatings is usually unnecessary and, under certain conditions, damaging to the bond. High Speed High OutputSprayed concrete can deliver high volumes quickly and economically. Free formed tunnel linings or retaining walls can be sprayed immediately after excavation. Walls up to lm thick have been constructed in the USA using the wet process even with very high reinforcement densities. Multiple layer application can reduce the generation of thermal stresses in construction. Reduction in Formwork CostsIn comparison with conventionally poured concrete, sprayed concrete requires far less formwork. This is especially so if curved or organic shapes are favoured by the designer which may be impossible to achieve using conventional formwork. Virtually any shape can be formed especially thin shells and linings. Ease of AccessThe ease of application of sprayed concrete means that material can be applied in restricted areas, often considerable distances from the point of access. Without the need to transport and erect bulky formwork only the operator and delivery hoses need to be able to visit the workface. The cement and sand mixture can be transported over long distances from the production plant.
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