Evaluation of the quality of fine materials and filler from crushed rocks in concrete production

• The fine material in crushed rocks is very variable.
• The fine materials from crushed rocks reflect the mineralogy of the rock.
• Mica minerals are flaky and detrimental for concrete workability.
• Clay size micas may accumulate in the ultrafine material and adversely effect concrete workability.
• By appropriate mortar tests, the quality of the fine material can be evaluated.

Crushed rocks are, in general, more flaky and irregular in shape than natural aggregates. Especially granitic rocks display variable amounts or flaky free micas in the finer fractions when crushed. Moreover, the crushed rocks result in more fine material. Fillers can, in combination with superplasticizers and if the quality is appropriate be used to expand the paste phase of the concrete and thus be used to lower the cement consumption. To utilize the filler optimally one needs to evaluate the filler quality.There are several methods to evaluate the filler. In this article different methods both in regards to the material properties and the behavior in mortar and micro mortar tests are compared and evaluated. The analysis shows the importance of understanding the effect of both the particle shape and flakiness in the fine fractions and the properties of the material in the finest fraction i.e. <10 μm. This is very much related to the mineralogy of the rock.