Opportunities and limitations of concrete recycling

Granulated concrete in various compositions taken from a rubble stockpile. Top: composite particles from aggregates bonded by cement paste. Bottom: mortar particle (left) and almost mortar-free gravel particle (right)

Amount of concrete accumulated in existing buildings and structures (cement production data taken from [1], simplified calculation of the concrete volume excluding the use of cement in other products)

Recycled amounts of construction waste and fields of use of recycled building materials produced from this waste [3]

Effects of various
surface treatment methods on relative compressive strength, with untreated recycled-aggregate concretes used as a reference [15] [17] [18]

Mixing process applying the two-stage mixing approach (TSM) according to Tam [30]

Mixing process applying the triple mixing method according to Deyu Kong [33]

Mixing process with integrated coating according to Jiusu Li [34]

Effects of various mixing processes on relative compressive strength, with recycled-aggregate concretes produced in a conventional mixing process used as a reference [30] [31] [32] [33] [34]

Dependence of relative compressive strength and elastic modulus on the ratio of recycled aggregates after 28 days [38] [39] [40] [41] [42] [43] [44]

Dependence of compressive strength on concrete bulk density when using recycled aggregates [45]

In the future, concrete production could increasingly rely on the use of recycled aggregates. Part I of this article deals with the optimization of the mix design and mixing process and refers to the mechanical properties of recycled-aggregate concrete.

Concrete is the most commonly used construction material worldwide. When considering the cement quantities manufactured in Germany since 1950 for determining the produced concrete volumes and calculating the amount of concrete that has accumulated in existing buildings and structures, this exercise results in a notional volume of over 12 billion t (Fig. 1).

However, the actual amount of concrete built up since 1950 is smaller because the volumes removed by demolition need to be subtracted. If we assume that this concrete volume was equivalent to 18% of annual concrete production until 1995 and...