Mieke De Schepper

Life Cycle Assessment of Completely Recyclable Concrete

Since the construction sector uses 50% of the Earth’s raw materials and produces 50% of its waste, the development of more durable and sustainable building materials is crucial. Today, Construction and Demolition Waste (CDW) is mainly used in low level applications, namely as unbound material for foundations, e.g., in road construction. Mineral demolition waste can be recycled as crushed aggregates for concrete, but these reduce the compressive strength and affect the workability due to higher values of water absorption. To advance the use of concrete rubble, Completely Recyclable Concrete (CRC) is designed for reincarnation within the cement production, following the Cradle-to-Cradle (C2C) principle. By the design, CRC becomes a resource for cement production because the chemical composition of CRC will be similar to that of cement raw materials. If CRC is used on a regular basis, a closed concrete-cement-concrete material cycle will arise, which is completely different from the current life cycle of traditional concrete. Within the research towards this CRC it is important to quantify the benefit for the environment and Life Cycle Assessment (LCA) needs to be performed, of which the results are presented in a this paper. It was observed that CRC could significantly reduce the global warming potential of concrete.

Use of Secondary Slags in Completely Recyclable Concrete

A completely recyclable concrete (CRC) is designed to have a chemical composition equivalent to the one of general raw materials for cement production. By doing so, this CRC can be used at the end of its service life in the cement clinkering process without need for ingredient adjustments, and with improvement of the resource efficiency of cement and concrete production. Copper slag is interesting as an iron source for the production of such a CRC and can be added to concrete, either as alternative binder or as aggregate. By isothermal calorimetry and compressive strength tests it was found that the addition of copper slag as cement replacement is of minor interest. But a study toward the compressive strength and durability of concrete with copper slag as aggregate replacement had promising results. The performance of these concretes was comparable with or even better than the reference concrete, regarding strength and most durability aspects such as porosity and permeability, and resistance against carbonation and chloride ingress. Only the resistance to freeze-thaw attack with deicing agents was inferior.

Setting Control of Completely Recyclable Concrete with Slag and Aluminate Cements

A completely recyclable concrete (CRC) is designed to have a chemical composition equivalent to the one of general raw materials for cement production. By doing so, this CRC can be used at the end of its service life in cement manufacturing without the need for ingredient adjustments. In one of the designed CRC compositions, blast-furnace slag cement (BFSC) was combined with calcium aluminate cement (CAC), which resulted in fast setting. In an attempt to control this fast setting, different retarders and/or the combination of lime and calcium sulfate were added to the system. The workability (slump and flow), setting time (ultrasonic transmission measurements and Vicat), strength development (compressive strength tests), and hydration behavior (isothermal calorimetry) were studied. It was found that the combined addition of lime and calcium sulfate results in a workable mixture that becomes even more workable if a retarder is also added to the system.