Precast concrete is a type of building component that is cast and cured in a controlled environment at a factory (or off-site), and then transported to the construction site for assembly once it has reached the required strength.

It is the counterpart to ‘cast-in-place concrete’ and constitutes a core technology of construction industrialisation and prefabricated construction.

Key Advantages

• Controllable Quality: Manufactured in a factory, it is unaffected by weather conditions (rain, snow, high temperatures). With a high degree of mechanisation, precise dimensions, and a constant curing environment (temperature and humidity), strength distribution is more uniform.
• Extremely Fast Construction: Component production can proceed simultaneously with foundation excavation on-site. On-site work involves simply hoisting and connecting components like ‘building blocks’, significantly reducing construction time (by up to 50%).
• Smooth Surfaces: Using high-precision moulds, the components produced (such as exposed concrete slabs) have extremely high surface flatness, often eliminating the need for secondary plastering and allowing direct progression to the painting stage.
• Environmental Sustainability and Cost Efficiency: Moulds can be reused hundreds of times, reducing the consumption of timber formwork on site and minimising construction waste.

Shotcrete (Shotcrete / Sprayed Concrete) is a building material in which a pre-mixed concrete mixture is conveyed through pipes using compressed air and sprayed at high speed onto a surface where it sets and hardens.

Its most notable feature is that formwork is not required (or only single-sided formwork is needed), and automatic compaction is achieved through the force of high-speed impact.

1. Why use shotcrete? (Advantages)

• No formwork required: Saves time and material costs associated with erecting and dismantling formwork, making it particularly suitable for irregular shapes (such as cavities and circular arches).
• Immediate support: Forms a load-bearing layer rapidly after spraying, bonding with the rock or soil to form a monolithic structure and prevent collapse.
• Compact structure: The kinetic energy generated by high-speed impact makes the concrete extremely dense, providing strong impermeability.

2. Typical Applications

• Tunnels and Mines: As part of ‘anchor-spray support’, it is central to tunnel construction (New Austrian Tunneling Method, NATM).
• Slope Stabilisation: Prevents landslides and rock weathering.
• Renovation Projects: Reinforces and thickens the surfaces of ageing bridges and dams.
• Landscape Architecture: Creates artificial rockeries, swimming pool structures or skate parks.

Fair-faced concrete is synonymous with a ‘sense of sophistication’ in architectural design and is regarded as the ultimate expression of concrete architecture.

Its defining characteristic is: structure as decoration. Once the walls have been cast, no secondary finishing such as painting or tiling is carried out; instead, the natural texture of the concrete, along with construction joints, expansion joints and bolt holes, is utilised directly as the decorative surface.

1. Core characteristics

• Natural Finish: It displays the characteristic bluish-grey hue of concrete, with a uniform and smooth texture.
• Construction Marks: Formwork joints (formwork joints) and tie-rod holes (exposed holes) are its signature geometric aesthetic elements.
• Exceptional Durability: The surface is typically coated with a layer of transparent silane sealer, which is both waterproof and stain-resistant whilst maintaining breathability, resulting in a lifespan far exceeding that of standard decorative materials.

2. Construction Challenges (Why is it expensive?)

Exposed concrete demands almost exacting construction techniques; it must be ‘cast in one go’ and cannot be repaired:

• High-precision formwork: High-strength laminated plywood or steel formwork is typically used to ensure a mirror-smooth surface.
• Precise mix proportions: The ratios of water, cement, aggregate and water-reducing admixtures must be absolutely precise; otherwise, colour variations, honeycombing or pitting may occur.
• Compaction process: Air must be expelled evenly to prevent the formation of air bubbles, and segregation must be avoided.
• Protective measures: Curing after formwork removal is crucial; even the slightest impact or contamination can result in irreversible damage.