New Type of Crushed Sand to replace natural Sand in Concrete Production
The availability of natural sand for concrete production is facing challenges, while the so-called waste stockpiles at aggregate crushing areas are causing problems for producers. This means that the industry has a huge need to solve this challenge by finding suitable technology for usable crushed sand production.
Issues related to aggregates prices, sales and technical issues of the production are usually among the topics of concern to coarse aggregate quarry managers. Another issue is the mass balance of production because, as part of a normal production process of crushed aggregates, up to 30% (rock dependent) of the material acquired from the bedrock is reduced to sizes smaller than 4 mm and thus cannot be used as coarse aggregates.
This co-generated material has long been the most unfavorable fraction in terms of assuring a profitable mass balance, since it can be hard to sell or even to get rid of at any price. As a result, in many places there are huge stockpiles of this “waste” that not only affects the profitability of the aggregate operation, but also causes environmental issues.
In the past few decades, the availability of suitable natural sand for concrete production near the point of consumption has been exhausted around many populated regions in the world. This has led to a search for a replacement material; the aforementioned surplus fines from crushing operations are expected to be the next best alternative – due to both great availability and suitable physical properties.
Natural Sand and Surplus Quarry Fines – Differences
Early attempts to use this co-generated material as fine aggregate were mainly unsuccessful. However, today the important differences between natural sand and surplus quarry fines are well known by aggregate producers, and there are examples of the producer successfully overcoming the challenges after working in close cooperation with with the quarrying machinery supplier, e.g. Metso Minerals.
With respect to particle shape, this includes optimizing the crushing process along with vertical shaft impact (VSI) crusher, rock-on-rock shaping at the end. This can result in a particle shape that closely resembles that of natural sand.
Fig. 2: Different types of fine aggregates: (1) High-quality, 0/8 mm natural glaciofluvial sand from Norway; (2) Low-quality, 0/8 mm co-generated material of coarse crushed aggregate production (should not be called crushed or manufactured sand); (3) High-quality, 0/8 mm crushed sand, produced using an optimized crushing circuit and VSI shaping.
The issue of the high fines content can be resolved with either wet or dry processing, i.e. different washing techniques or air classification. Finally, if the sand particles are sieved and classified into reasonably narrow particle sizes of a good shape, they can be successfully used as high-quality manufactured sand already today.