Prague to turn slag into building material

Prague is preparing to transform the slag produced by incineration into building materials for the construction industry.

Each year, incineration produces 65 to 75,000 tonnes of slag, according to Prague’s deputy mayor for the environment, Petr Hlubuček.

In 2017, 5.7 million tonnes of municipal waste were produced in the Czech Republic.

Of this total, 45.5% went to landfill, with only 37.5% being extracted for waste recovery and only 12% being converted into energy. In comparison, the EU’s average landfill rate in 2019 was 23%.

In a move towards a more circular economy, the city of Prague intends to use the large amounts of slag and residual ash produced as by-products of incineration in a more sustainable way.

Generated as a secondary material through the thermal treatment of solid waste, slag consists primarily of silicon dioxide as well as a mixture of metal oxides. The advantages of using slag in cement mixes range from greater durability and strength of the material to lower permeability. Its inherent durability and resilience allow it to be used on highways, roads and sidewalks as well as on bridges, marine constructions and hydraulic dams.

Hlubuček claims that the use of slag for construction purposes would not only reduce carbon emissions, but also be more cost effective, bringing the capital further to meet its broad arched 2030 climate goals.

At the moment, construction with slag cement is not possible due to the current legal situation in the country. The slag is classified as waste rather than a raw material, something that must be changed before construction using the industrial by-product can begin.

Concerns about the potential use of slag as a construction material have already been expressed by the environmental NGO Arnika. The group argued that slag from incinerators contains toxic chemicals that can seep into the environment and contaminate groundwater supplies. Arnika also pointed out that a previous experience using slag from the metallurgical industry for construction purposes had a less than favorable impact on the environment.

The City of Prague’s Climate Plan 2030 aims to reduce carbon emissions by 45% by 2030. The policies adopted to achieve this objective relate to four areas, which are: energy and sustainable buildings, sustainable mobility, savings circulars and adaptation measures. Over the next few years, the municipality will focus on producing energy from renewable energy sources, creating low-emission public transport, as well as building the city’s first biogas plant, among others.

Regarding waste management across the country, the Czech government intends to increase the national recycling rate as well as capacity while imposing taxes on landfills to launch a more circular economy.

Berta D. Wells