DESIGN FEATURES OF LONG-SPAN HOLLOW-CORE FLOOR SLABS USING SILICA FUME
DOI:
https://doi.org/10.55287/22275398_2026_60_29Keywords:
Long-span slab, hollow-core slab, silica fume, flexible layout, high-strength concrete, modulus of elasticity, heat-and-moisture treatmentAbstract
The transition to modern housing with flexible layouts requires increasing floor span lengths. Conventional hollow-core slabs with a depth of 220 mm are designed for spans of up to 9 m, whereas a 12 m span traditionally requires increasing the section depth to 250–400 mm, which results in greater weight and material consumption.
The aim of this study is to substantiate the possibility of maintaining the standard slab depth of 220 mm while increasing the design span to 12 m through the use of concrete modified with silica fume. A combined methodology was applied, including experimental selection of concrete mix proportions with the addition of ultrafine silica fume MKZ-85 at 10–30% of the cement mass and SP-1 superplasticizer, testing of specimens for strength after heat-and-moisture treatment, and a design assessment of slab load-bearing capacity and deformability according to the first and second limit states.
The results showed that the addition of silica fume increases concrete strength by 40–70% and the modulus of elasticity by 10–15%, while reducing cement consumption by up to 50%. The design assessment demonstrated that slabs made of Class B35 silica-fume-modified concrete meet strength and crack-resistance requirements for a 9 m span. For a 12 m span, deformability is the governing factor; however, owing to the increased modulus of elasticity, the calculated deflection is reduced to the allowable value of 45 mm ().
The economic analysis revealed a reduction in the cost of 1 m³ of concrete mix by RUB 200–450 and a reduction in heat-and-moisture treatment time by 3–4 hours. The use of silica fume makes it possible to increase the design span of hollow-core slabs by 33%, from 9 to 12 m, without increasing their section depth or reducing their load-bearing capacity. This solution enables the construction of buildings with flexible layouts, including open spaces of up to 9 × 9 m without intermediate columns, increases the functional service life of housing to 80–100 years, and contributes to the utilization of industrial by-products. The technology is considered technically and economically justified for implementation at precast reinforced-concrete plants.
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