USE OF RECYCLED SAND AND EXPANSIVE AGENTS FOR THE PRODUCTION OF MORE DURABLE AND SUSTAINABLE CEMENT-BASED MATERIALS

The availability of resources for the construction industry is becoming increasingly uncertain, while at the same time the amount of construction and demolition waste is growing. Reconciling needs and secondary resources as well as contributing to reuse is a useful and motivating scientific challenge. Legal and regulatory barriers have to be overcome in order to allow a real circular economy in the construction industry. Working locally and developing an appropriate treatment of Construction and Demolition Wastes is favouring upcycling and valorization of secondary materials for prefabricated, 3D printed concrete or repair materials. It is becoming increasingly difficult to ensure the availability of good quality sand for the production of concrete. Recycled concrete sand, when properly produced, can be a serious alternative for low- to medium-range mortars and concretes. Technical properties of recycled sands are analysed, and proposals are made for increasing the rate of incorporation into mortars. In the same time, minimum requirements are proposed for using recycled sand in 3D mortars. Final properties are compared with classical materials and durability of end products is analysed. Accelerated carbonation process seems to increase recycled sands properties (before and/or after manufacturing concrete). Expansive agents may also help to manage the various types of shrinkage, which can be exacerbated in mixtures with recycled sands. On the long run, a broader and more systematic use of recycled materials calls for adapted regulations and specifications: this is essential for lowering in a significant manner the environmental impact of the construction industry.