Plastic waste management is now a major environmental issue. According to the UN, more than 430 million tonnes of plastic are produced each year, two-thirds of which quickly become unrecycled waste ending up in landfills or the marine environment, illustrating the urgent need for innovative recycling solutions [1] . At the same time, the construction sector, a major consumer of resources, is responsible for 6% to 8% of global CO₂ emissions, mainly due to cement manufacturing [2] . These findings have stimulated the search for sustainable solutions, such as the use of recycled plastic-based components as composite materials in the construction sector. This work explores the possibility of completely replacing cementitious binders with plastic binders, while ensuring reliable adhesion between the reinforcement and the matrix. This mechanical bond is essential to the strength of reinforced structures and determines their overall performance, durability and compliance with current technical standards.

The analysis focuses on comparing the adhesion of standard concrete and concrete made from recycled plastics. This study aims to complement the very interesting mechanical properties obtained in particular in compression and tension [3] [4] .

This approach is part of a circular economy approach, aiming to limit greenhouse gas emissions while recycling plastic waste for constructive use.

The methodology is based mainly on pull-off tests on cylindrical specimens, in accordance with standards [5] . These tests make it possible to quantify the bond stress and identify the modes of failure in order to evaluate the quality of the steel-polymer matrix bond in each of the formulations studied.

Figure 7 shows the average results obtained for each type of concrete.

Analysis of Figure 7 highlights significant differences in adhesion between the reinforcement and the matrix depending on the type of binder used.

Cementitious concrete performs well with an average pull-off stress of 6.59 MPa, accompanied by concrete failure illustrated in Figure 8(a) , indicating excellent adhesion between the steel and the cementitious matrix.

For plastic concrete, the PET + flint formulation offers the highest strength (8.06 MPa). This demonstrates PET's strong ability to develop an effective bond with the reinforcement, to the point of causing the concrete to break. The pull-out strength of HDPE-based plastic concrete remains good (3.23 MPa) as it is higher than the usual reference values, despite being lower than other plastic concrete formulations. The slip failure mode shows in Figure 8(b) [8] , and indicates a less effective interface, with no deterioration of the matrix. PP + silex has an intermediate performance (5.45 MPa) exceeding the standards for conventional concrete. Although the mode of failure is also related to slippage, the presence of an effective mechanical bond gives it a balanced profile, potentially viable for moderate or semi-load-bearing structural applications.

The pull-out test results indicate that certain specimens, notably cementitious concrete (2), HDPE + flint (3) and PET + flint (3), have significantly lower pull-out resistance values than the other samples in their category. This behaviour can be explained by poor centring of the reinforcing bar in the matrix, as illustrated in Figure 9 , which promotes an asymmetrical distribution of adhesion stresses, reducing the efficiency of load transfer and leading to early slip initiation or localised failure without complete mobilisation of the matrix.

Plastic pollution is now one of the most pressing environmental challenges worldwide, particularly due to the slow degradation of polymers and their accumulation in natural environments. With this in mind, our study is part of a drive for innovation and sustainable development in the construction sector, exploring the use of recycled plastics as an alternative binder to cement in reinforced concrete. Through a rigorous experimental approach, it was possible to compare the adhesion performance between reinforcement and matrix in two types of concrete: one conventional, cement-based, and the other melted plastic-based.

The comparative study of adhesion between reinforcement and matrix revealed good adhesion in plastic concrete, although slightly lower than that observed in cement-based concrete. However, this difference remains within a tolerable margin for certain non-structural applications, and even structural applications under controlled conditions. This solution could therefore be a reliable alternative to traditional concrete, particularly in contexts where sustainability is sought.

Nevertheless, the introduction of these plastic concretes into the construction industry represents a promising prospect. It offers a concrete response to the challenges of plastic pollution while paving the way for lighter, more resistant building materials that are adapted to local resources.

Looking ahead, studies on ageing and fire behaviour will be required to ensure its applicability on a large scale.

We would like to thank the International Development Research Centre (IDRC) and the MESRI Department of Research and Technological Development (DFRSDT) for funding this project.