The use of recycled crushed concrete sand as basis for alkali-activated concretes

Figure: Harnisch/Ufermann/Judith

Fig. 1: Project steps

Figure: Harnisch/Ufermann/Judith

Fig. 2: Compressive strength of the mortar mixture with 75 wt.-% (left) and 50 wt.-% (on the right) of metakaolin after 7, 14 and 28 days for the WGM between 1.7 and 2.0

Figure: Harnisch/Ufermann/Judith

Fig. 3: Workability tests by means of hand kneading tests; bad cohesion (left) and good cohesion (right)

Figure: Harnisch/Ufermann/Judith

Fig. 4: Tests on the green strength; no green strength (left) and sufficient green strength (right)

Figure: Harnisch/Ufermann/Judith

Fig. 5: Production of the paving block prototype: Single block making machine (left) and prototypes after production (right)

Figure: Harnisch/Ufermann/Judith

Fig. 6: Dry densities after 28 days for laboratory test specimens (gray) and specimens made of the paving block prototypes. Columns: mean values, Marker: scatter band

Figure: Harnisch/Ufermann/Judith

Fig. 7: Compressive strength after 28 days for laboratory test specimen (gray) and specimen made of paving block prototypes (yellow) as well as after 42 days with water saturation (blue). Columns: mean values, Marker: scatter band

Figure: Harnisch/Ufermann/Judith

Fig. 8: Splitting tensile strength after 28 days for laboratory test specimen (gray) and specimen made of paving block prototypes (yellow) as well as after 42 days with water saturation (blue). Columns: mean values, Marker: scatter band

Figure: Harnisch/Ufermann/Judith

Fig. 9: Comparison of the calculated CO₂ equivalents

Figure: Harnisch/Ufermann/Judith

This paper examines selected findings of a research project funded by DBU as part of which practice-oriented applications of alkali-activated binder systems based on recycled crushed concrete sand were investigated in respect of the production of concrete products.

The cement industry and concrete manufacturers together are appealed for reducing the consumption of resources as well as the carbon emissions related to the production of cement. This paper examines selected findings of a research project funded by DBU (German Federal Environmental Foundation) as part of which practice-oriented applications of alkali-activated binder systems based on recycled crushed concrete sand were investigated in respect of the production of concrete products.