Opportunities and limitations of concrete recycling

Figure: Kerkhoff, Siebel

Carbonation depth of concretes containing defined recycled aggregates produced for the tests [49]. Ra: recycled aggregates from a three-month old concrete of strength class B 15 with w/c = 0.68; Rb: recycled aggregates from a three-month old concrete of strength class B 45 with w/c = 0.48

Figure: Kerkhoff, Siebel

Figure: Bödefeld, Reschke

Carbonation depth of concretes containing recycled aggregates produced from concrete rubble [43]. 01: reference; 03: CEM I, 75 m.-% RC 2/32 mm; 05: CEM III/A, 75 m.-% RC 2/32 mm; 06: CEM I, 75 m.-% RC 2/32 mm + 12.5 m.-% RC 0/2 mm; 08: CEM III/A, 75 m.-% RC 2/32 mm + 12.5 m.-% RC 0/2 mm; 09: CEM I, 75 m.-% RC 2/32 mm + 25 m.-% RC 0/2 mm

Figure: Bödefeld, Reschke

Figure: Cement and Concrete Research

Expansion of concrete prisms containing recycled aggregates produced from concretes that contained alkali-reactive aggregates [50]. Aggregates; spratt: alkali-reactive siliceous lime; coarse RCA: coarse recycled aggregates from concretes containing alkali-reactive aggregates; fine RCA: fine recycled aggregates from concretes containing alkali-reactive aggregates

Figure: Cement and Concrete Research

Phase diagram for recycled aggregates (data for technically reprocessed recycled aggregates [56], recycled coarse aggregates from concretes with defined parameters [57], model concretes [28])

Dependence of mechanical properties of the recycled-aggregate concrete on the characteristics of the original concrete [44] [58]

Dependence of relative compressive strength and modulus of elasticity of recycled-aggregate concretes on the amount of old cement paste introduced into the concrete mix [28] [27] [59] [60]

In the future, concrete production could increasingly rely on the use of recycled aggregates (see BFT International 04/2013, pp. 78). Part 2 of this article deals with concrete durability and the modeling of recycled-aggregate concrete.

Unlike concrete based on natural aggregates, recycled-aggregate concrete contains two types of cement paste: the “new” paste creating concrete strength and the “old” paste whose parameters – such as its composition, water/cement ratio and degree of carbonation – are unknown. In addition, such concretes contain the “old” aggregates whose origin and properties are usually unknown, too. Both the components of recycled aggregates and the new cement paste and new aggregates may comprise compounds that may become involved in deleterious chemical reactions. Furthermore, the recycled aggregates cause...