Over the past three years, the Human Environment and Transport Inspectorate (ILT), together with several environmental agencies, has conducted research into the production and application of immobilisate. This is a building material largely composed of contaminated recycled waste materials. Many improvements have since been initiated.
For example, the Ministry of Infrastructure and Water Management has stipulated in the draft Circular Materials Plan (CMP) that bottom ash from waste incineration plants (AVI-bottom ash) must be cleaned before it can be reused circularly. There is also a legal obligation to provide information prior to its application.
Nevertheless, the ILT still sees risks. In 2024, 7 producers received a warning from the ILT. It was also announced that a re-inspection would take place in 2025.
Immobilisate mainly consists of bottom ash from waste incineration plants, contaminated soil, and several secondary components, such as blasting grit and sorting sieve sand. By adding cement and water, it hardens into a concrete-like building material. In the Netherlands, immobilisate has been widely used at hundreds of locations as a foundation under industrial buildings and nearby outdoor areas. In 2020, over 1.5 million tons of immobilisate were produced. In 2023, this decreased to 400 thousand tons.
ILT Inspections
In the Netherlands, there are 8 recognized producers of immobilisate. The ILT found major shortcomings among them in recent years. In 2023, the ILT identified 50 violations. The ILT found that the product certificates issued by the certifying body based on the assessment guideline BRL 9322 (version 2016) did not sufficiently guarantee the quality of the produced immobilisate. As a result, new types of immobilisate were made without proper controls. Moreover, the proportions of raw materials in the immobilisate were stretched too far. Following these findings, the industry has initiated improvement measures. For example, an industry association has been established, and work is being done on a clearer assessment guideline.
In 2024, the ILT conducted further inspections. The number of identified violations then dropped to 19. 7 of the 8 producers received a written warning, and it was simultaneously indicated that a re-inspection would take place in 2025. These re-inspections will take place in the coming months.
Risks of Immobilisate
In building materials, harmful substances such as chloride, bromide, and sulfate are always released within legal limits. If legal requirements are met, these substances are bound in the immobilisate, reducing risks. However, if immobilisate does not harden properly or crumbles, harmful substances can exceed the norm and spread into the soil and groundwater.
Developers receive money from producers if they use immobilisate as a building material. In contrast, the use of primary building materials such as sand, gravel, or concrete must be paid for. This provides a perverse incentive to use more immobilisate than necessary or when it is not necessary, useful, or functional.
Since 2024, there has been a national obligation to inform the relevant environmental agency at least 4 weeks before the start of the work. Immobilisate may only be used if the material contributes to the foundation of a structure or road. This contribution must be substantiated civil-technically. However, it is difficult for environmental agencies to determine how much immobilisate is technically needed for a sufficiently strong foundation.