The broken fraction

Every morning in Rotterdam, a truck picks up the previous night’s roadwork debris and takes it out of the city. Slabs of pavement that cracked under a delivery van, kerbstones that shifted after a winter freeze, tiles broken during utility repairs, brick that snapped when a tree root reached it. In the standard maintenance stream, this material is roughly sorted into recyclable fractions: the whole slab reused where possible, the broken material crushed into road base or sent to landfill. The pieces that fall between whole and dust are the ones the system is worst at handling. Too broken to reinstall. Too shaped to disappear into aggregate. That gap between whole-object reuse and bulk recycling is the broken fraction.

For the last year, LLA has been trying to work out what to do with it. The Broken Fraction is a ten-month research project, supported by the Creative Industries Fund NL under its Kick-start Grant Scheme, in partnership with The Green Village at TU Delft. It runs from August 2026 to March 2027. What it produces will be a material library (thirty to fifty small cast samples, each documenting a specific combination of Rotterdam-sourced aggregate, low-carbon binder, and surface treatment) and a visual atlas: Rotterdam rebuilt, on paper, in its own broken fragments.

This is a preliminary research, not a finished design. The grant funds the work that has to happen before a serious material proposition can be brought to a client. But the argument it advances is not new. It is the recovery of one.

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Two chains, and a missing third

Contemporary reuse practice in construction has organised itself into two dominant chains.

The first is whole-object reuse. Rotor, in Brussels, has led this field for over a decade with de-mounting, cataloguing, and re-selling architectural components (doors, radiators, floorboards, stone slabs) that would otherwise be demolished. Superuse Studios in Rotterdam works in a related register. This chain functions best where components are structurally intact, geometrically standard, and locatable in a supply chain.

The second is bulk recycling. Broken concrete becomes road base. Crushed brick becomes fill. Waste glass becomes cullet. This chain absorbs vast quantities and functions industrially, but at the cost of the material’s specificity: a Rotterdam brick loses its Rotterdam-ness the moment it enters the crusher.

Between whole and bulk sits the fraction the two chains are equally bad at handling: broken enough that it cannot be reinstalled as a slab, specific enough that it should not be pulverised into anonymous fill. This is the fraction the project treats as its material. Not as fill but as surface.

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Cocciopesto, granito, and the long precedent

Casting aggregate into a binder to produce a surface is not an invention. It is one of the oldest continuous techniques in Mediterranean building culture. Cocciopesto (crushed terracotta bound in lime) is a Roman-era floor and wall surface, still legible at Pompeii, still the basis for a specific school of Italian conservation. Granito, or terrazzo, is its late-nineteenth-century descendant: broken marble bound in cement, polished flat, the surface of a thousand hospital corridors and municipal foyers.

Both techniques treat the broken fragment as a legible surface, not as hidden mass. The fragment is the point. You see it and the floor is a small archive of where the marble or the terracotta came from.

The Broken Fraction takes this logic and applies it, deliberately, to Rotterdam’s maintenance stream. A slab broken on the Coolsingel becomes aggregate in a bench on the Nieuwe Binnenweg. A brick from a Delfshaven renovation becomes surface in a paving unit two streets away. The material stays in the neighbourhood it was made in, carrying its former meaning and memory.

------The binder is the point

The reason this is a landscape architecture project and not a purely material-research one is that the public floor and space are a landscape’s medium. A pavement is not simply a surface but a settled sign about what the ground is for. The binder that holds the fragment together is also a part of it.

Portland cement, the default binder, is one of the most carbon-intensive materials in the construction sector. Producing one kilogram of Portland cement releases roughly 0.9 kilograms of CO₂. Cement production accounts for around 7-8 percent of global CO₂ emissions and if it were a country, it would be the third-largest emitter in the world.

The project’s second research axis is the binder shortlist: what alternatives exist, at what performance, at what carbon cost. Natural hydraulic lime (potentially combined with metakaolin) or blast-furnace slag cement (CEM III) each has a specific chemistry, a specific supply chain, and a specific relationship with the aggregate. This is the terrain where landscape architecture meets material science, and where the Green Village partnership becomes essential.

A broken fraction bound in Portland cement is a compromised proposition. A broken fraction bound in a binder that itself embodies the carbon logic of the project is a design proposal.

------The memorial dimension

There is a third argument, and it is the one that gives the project its cultural stake beyond its technical claims.

Materials from renovation (bricks pulled from a specific demolished house, tiles from a specific stripped kitchen, stone from a specific replaced kerb) carry their address with them. In the standard recycling stream, this address is lost. In the surface application the project proposes, it is not. A grinding pass at the end of the casting reveals the fragment. The neighbourhood becomes legible in the floor of the neighbourhood.

This is not nostalgia but a specific counter-move against the smoothing of cities. Every new public surface installed in Rotterdam looks increasingly like every other new public surface installed anywhere. The broken fraction proposes that the floor of a place should carry the history of the place, visibly, physically, at the scale of a fragment you can identify.

Between the paving slab and the aggregate pile, there is a whole material that no supply chain currently knows how to handle. The Broken Fraction begins the work of naming it, testing it, and giving it back to the city it came from.

FURTHER READING
Jane Hutton, Reciprocal Landscapes: Stories of Material Movements (Routledge, 2019).
Pierre Bélanger, Landscape as Infrastructure: A Base Primer (Routledge, 2017).
Alan Berger, Drosscape: Wasting Land in Urban America (Princeton Architectural Press, 2006).
Kevin Lynch, Wasting Away: An Exploration of Waste (Sierra Club Books, 1990).
Cyrille Simonnet, Le béton: Histoire d’un matériau (Parenthèses, 2005).
Kiel Moe, Empire, State & Building (Actar, 2017).

ARTICLES & RESOURCES
Rotor DC - salvage and reuse cooperative, Brussels.
BC Materials - excavated earth as construction material, Brussels.
Superuse Studios - circular architecture and material harvesting, Rotterdam.
StoneCycling / FRONT Materials - reprocessed construction waste into new bricks and tiles.
The Green Village - living lab for sustainable construction, TU Delft.