Relevant cost savings with recycled aggregates

With the exception of special qualities such as pure concrete waste, recycled building materials are, in general, significantly more economical than natural mineral materials. The total cost savings of a construction project through the use of secondary aggregates produced from construction waste depends mainly on factors such as the transport distance between the construction site and the nearest possible supply plant, existing capacities of natural and recycled building materials, the local competitive structure and technical requirements pertaining to the construction materials.

Economic advantage

As a rule, the use of recycled building materials pays off financially, as there is now a widespread network of suppliers. In the example shown here, an average cost advantage of 6 €/t for remexit® 0/32 and 0/45 compared to use of primary aggregates in lower base and subbase of a road is assumed, on the assumption of identical transport routes for both material alternatives.

Assumptions for benefit calculation

The following sample calculation considers the construction of a 3-lane motorway with the execution of the lower base and subbase with remexit® recycled aggregates.

Recycled aggregates calculation example for use in base course and subbase

Excerpt from Table 1, Line 3 of the Guidelines for the standardisation of pavement structures of traffic areas (RStO 12) 

For the execution of an exemplary motorway section according to table 1 of RStO 12, line 3 (Guidelines for the standardisation of pavement structures of traffic areas) with asphalt base course and crushed rock base course on frost blanket course, a base course of 15 cm is required. Asphalt surface course and asphalt base course are 30 cm thick.. 

The necessary thickness of the frost resistant pavement structure depends on the frost sensitivity of the subsoil or subgrade. For a frost sensitivity class F3 according to table 6 of RStO, the basic thickness of the frost resistant pavement structure for a motorway amounts to 65 cm. If, for example, the motorway was to be built in the frost zone III (e.g. southern Bavaria), an additional thickness of 15 cm would be necessary according to table 7 RStO. A further 5 cm would be necessary, for example, in case of additionally unfavourable climatic influences. This would mean a minimum thickness of 85 cm for the frost resistant pavement structure. In the chosen example, this is achieved by a 40 cm thick frost blanket course. 

In the case of a new construction, the entire width of the carriageway is included in the material demand calculation. Assuming the three-lane standard cross section RQ 36 according to the Guidelines for the construction of motorways RAA of the FGSV, the minimum width for crushed base and frost blanket course amount to approx. 29 m for the carriageways plus an additional 4 m if the central reservation is identically constructed. 

Standard cross section RQ 36 for three-lane motorway according to the Guidelines for the construction of motorways RAA, extract from figure 3

Summary of the benefit calculation

Recycled/Secondary aggregate benefit calculation in road works

Assumptions for the benefit calculation per km

When using remexit® in the frost blanket course and crushed base course, the following quantity of primary building materials can be replaced based on the above assumptions:

(0.40 + 0.15) m x 33 m x 1,000 m = 18,150 m³.

Assuming a gross density of recycled aggregates of 2.0 t/m³, this corresponds to a quantity of 35,300 t of recycled aggregates for a motorway section of 1 km in length. 

The cost saving per km results from the following calculation:

6 €/t x 36,300 t = 218,800 €/km