Prefabricated concrete structures have gained widespread use and promotion in developed regions such as Europe, America, and Japan. Here, we introduce the stone reverse casting process for precast concrete. In simple terms, this involves factory precasting decorative stone for a building’s exterior walls into concrete, creating integrated prefabricated components such as columns, beams, and walls. The benefits of this method include a smooth surface, strong adhesion, and, most importantly, a significant boost in overall construction efficiency.
The stone reverse casting technique for precast concrete is now a well-established technology. However, in its early stages, experts conducted extensive testing on factors like stone expansion rates, bonding strength with concrete, exposure to weather, and water immersion before achieving the current level of technological maturity.
Granite is the most commonly used decorative stone for concrete, though sandstone, marble, limestone, and others are also utilized. Regardless of the stone type, it is crucial to avoid materials prone to cracking, long-term weathering, freezing damage, or rust.
The stone panels typically have a thickness of 30mm, with some variations down to 25mm. Attention must be given to potential warping or deformation during firing, penetration or discoloration around back anchor holes during integrated decoration, and the risk of breakage during transportation.
Now, let’s focus on some critical points. The stone must undergo a back treatment for three reasons:
1. To prevent the alkali white birch phenomenon caused by direct contact between the stone and concrete surface;
2. To absorb minor relative displacement between stone and concrete due to differing thermal expansion rates;
3. To prevent stones from falling off if cracks or fractures occur, especially when there is no anchoring. (Materials used include resin adhesive, silica sand, and waterproof sealant.)
Production process of exterior wall panels:
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After production, the surface should be cleaned thoroughly using a high-pressure water jet.
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During storage and transport to the construction site, it is essential to implement protective measures to prevent surface damage from collisions.
Construction hoisting site:
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Prefabricated concrete buildings utilizing stone reverse printing technology:
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With technological advances, materials like ceramic tiles are now also used alongside natural stone to complement prefabricated concrete components. This process involves more than simply laying tiles in molds and pouring concrete; it requires meticulous attention to detail.
First, it is important to select tiles that have mortise and tenon grooves on the back, which significantly enhance the bonding strength between the concrete and the tiles.
Typically, ceramic tiles are arranged in small sections with a curtain, with rubber isolation strips placed between the joints. This setup facilitates tile laying on the steel plate surface by prefabricated manufacturers. The adhesive tape serves not only to maintain consistent gaps but also to prevent cement mortar from seeping onto the tile surfaces. Additionally, a small amount of mortar is applied beforehand to the gaps between edge formwork and tiles, as well as between tile joints, to ensure proper filling during concrete pouring and prevent unsightly gaps.
After pouring the concrete and allowing it to cure, the surface tile protection paper and isolation rubber strips are removed, followed by thorough cleaning to reveal the finished product. Besides aesthetics, all ceramic tiles undergo inspection using diagnostic tools. Tiles producing hollow sounds are considered defective and must be replaced.
To prevent secondary contamination, a protective film can also be wrapped around the finished components. This reflects the commitment to treating customers’ products with care.
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It is important to highlight another key test: the ceramic tile pull-out test. This involves creating test samples using the same ceramic tiles and concrete grades as the final product, then testing the samples with specialized instruments. The specification requires that the pull-out strength of ceramic tiles exceeds 0.6 MPa.
What does 0.6 MPa mean in practice? It means that a force of 3 kN (approximately 300 kg) or more is required to break a ceramic tile measuring 100 × 50 mm. However, the pull-out resistance for ceramic tiles in precast concrete reverse printing usually reaches about 10 kN (around 1 ton).
Prefabricated concrete buildings featuring tile reverse printing technology:
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