Washing of aggregates : Influence on aggregate properties and mortar rheology

Aggregates (0-2 mm) produced by blasting and cruching of bedrock often contains rough and flaky particles with free mica and other minerals in finer fractions. Consequently, concrete produced with this type of aggregate displays a higher water demand and lower workability than the corresponding concrete with glaciofluvial aggregate. In order to achieve the desired workability changes in the mix design and/or processing of the aggregate, e.g. sieving and washing, are required. In this paper, the effect of washing on the material properties, i.e., particle size distribution, specific surface area and sand equivalent value (SE-value), of aggregates from crushed bedrock has been studied. The effect of the washed aggregates on the water demand of mortars was also studied with rheological methods. The results show that the used washing procedure mainly removed particles below 125 µm with emphasis on particles smaller than 40 µm. Consequently, this resulted in a decrease in the specific surface area of the fine particles and, thus, a lower water demand of the mortar. This is verified in the mortar tests where the yield stress of mortars was significantly reduced when the washed aggregates were used. Godkänd; 2006; 20071121 (palle)