Clay-and-concrete floor slab

A composite floor in which reinforced (or prestressed) concrete joists work together with a cast-in-place topping slab, while clay infill blocks lighten the non-structural zones. A solution that combines load-bearing capacity, reduced self-weight and continuity with the Italian building tradition.

The clay-and-concrete (laterocemento) floor is the most common horizontal structure of mid-to-late 20th-century Italian construction: a composite system that uses concrete where strength is needed (compression in the slab, reinforcement in the joists) and clay where the only job is to lighten and shape the pour (the infill blocks). Its logic is that of the T-beam: the closely and regularly spaced joists act with the collaborating slab as a sequence of small bending beams.

The structural behaviour rests on the composite T-section: the upper concrete slab, cast in place over the blocks, takes the compression stresses, while the bottom reinforcement of the joists takes the tension due to bending. The clay infill blocks carry no load: they cut the self-weight and act as permanent formwork for the pour. For the composite action to be effective the slab must be thick enough (typically 4-5 cm) and reinforced with a welded mesh that distributes point loads and counters shrinkage cracking.

Cast in place, the floor is born monolithic: the joists are tied into the perimeter ring beams and, over the supports, top reinforcement (negative moments) and solid block-free bands are arranged to take the shear. The quality of the result depends on the concrete cover, the compaction of the pour and moist curing: insufficient cover or poorly compacted concrete expose the bars to carbonation and corrosion, the leading cause of decay in existing floors. Solid bands and transverse rib-beams also govern the lateral distribution of loads and the deflection.

Structurally efficient as it is, laterocemento is a heavy, stiff floor with two recurring weak points. Acoustically it readily transmits impact noise: meeting the legal requirements calls for a floating screed on a resilient layer, isolated from the walls. Thermally, on the roof or towards unheated spaces, the mass must be paired with insulation. Fire resistance (REI class) is instead provided by the cover to the bars and the thickness of the elements, to be checked against the use. Services, finally, are housed within the screed, not within the structure.