Concrete accounts for almost 10% of global CO₂ emissions, and the raw materials it requires are running out. At the same time, millions of tonnes of existing concrete disappear into the ground and under roads every year. We believe that can change — and we have proved it must. Where others see demolition rubble as waste, we see raw material.
With our technology, we liberate sand, gravel, and cement from existing concrete. We use them again in new concrete of the same quality — but without new extraction and without CO₂. We do this together with demolition companies, contractors, architects, and scientists who believe that circular should be the norm. Not someday, but now.
Our vision is straightforward: circular concrete should be the norm. We envisage a construction sector in which every new building automatically becomes the raw material for the next one. Where demolition rubble no longer exists. Where circular is not an alternative, but the standard. That future is being built. The question is not whether construction will change. The question is how quickly.
Sixty years building towards an idea. From a transport company in 1965 to the launch of SL Materials in 2026: every step brought us closer to circular concrete.
Founding of Rutte, an Amsterdam family business specialising in the transport of concrete paving materials.
Production of the first concrete units made from 100% recycled material. This is where the dream of truly circular concrete begins.
Partnership with Koos Schenk to bring his Smart Crushing technology from laboratory to industrial scale.
Launch of Freement — the first circular cement from our own production. The NOS Eight O’Clock News (the main Dutch national news broadcast) is there to cover it. Circular concrete is put on the map.
Official incorporation of Urban Mine as an independent company, focused on the transition to 100% circular concrete.
Launch of SL Materials. No longer just a producer, but the catalyst making circular concrete the norm across the entire construction sector.
We ask the construction sector to go circular. So we must do the same ourselves. Our factory in Zaandam is built on the same principles as our concrete: reuse wherever possible, waste nothing.
The solar park on the roof of our Zaandam site generates all the electricity our machines require. The surplus charges electric boats, among other things.
The noise barriers surrounding our factory came from the Badhoevedorp interchange. Their posts now support the foundation of the concrete plant.
The city is our source of raw materials, so that is where our factory belongs. Through full enclosure and noise reduction, we cause less disruption than an average neighbourhood (noise levels within environmental category 3.2).
The rainwater that falls on our roof is collected in concrete rainwater tanks. We reuse that water in the production of new concrete. What others discharge, we process.
Our entire factory operates under a roof enclosure. No dust reaching the neighbourhood, no rainwater damaging our raw materials. Cleaner working for everyone.
What we make, we draw from the immediate surroundings. Demolition rubble from Amsterdam and the surrounding area is liberated in Zaandam into raw materials for new concrete.
Find the answers to frequently asked questions here.
SL Materials grew out of the Rutte Group, an Amsterdam family business that began in 1965 as a transporter of concrete paving materials. In 2002, we produced the first concrete units made from 100% recycled material. In 2016, we started working with Koos Schenk to scale his Smart Crushing technology to industrial level. In 2018, we launched Freement, the first circular cement from our own production. In 2026, we launched SL Materials as an independent brand.
The SL stands for Smart Liberated, a reference to our core method: liberating high-quality raw materials from existing concrete using smart technology. The name is also a tribute to Koos Schenk, who conceived the Smart Liberator.
SL Materials grew out of the Rutte Group. We work with a team of skilled professionals, scientists and entrepreneurs who share the conviction that circular concrete should be the norm. For specific contacts, please visit our contact page.
SL Materials grew out of the Rutte Group, an Amsterdam family business with more than sixty years of experience in transport and concrete materials. The knowledge, network and infrastructure of the Rutte Group form the foundation on which SL Materials has been built.
To make circular concrete the standard in construction — as an obvious choice. We are working towards a sector in which every demolished building becomes raw material for the next one. We are doing that today, together with demolition companies, contractors, architects and scientists.
Whether it’s circular concrete, a tender, or a potential partnership — or you simply have a question for our team — we’re ready to talk.
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