Constructing the fragment size distribution of a bench blasting round, using the new Swebrec function

The blasting at the Vändle aggregate quarry has been investigated in order to predict the effect of the specific charge on fragmentation and to assess the contribution of blasting and primary crushing to the -32 mm fines. Two 25000 ton blasts divided into halves were monitored. Each half had an expanded or a shrunken pattern in order to lower or raise the specific charge. A normal round uses Ø90 mm drill-holes on a 34 m pattern with a gassed bulk emulsion blend with 20-25 % of AN prills. The test rounds lay directly behind each other, with a shrunken pattern behind an expanded one and vice versa to minimize the influence of geology.From the muck piles, four test piles of about 500 tons were extracted and photographed for image processing. About a quarter of each was sieved in four steps and fines samples taken. The material was replaced and the whole pile fed to the primary crusher while measuring the effect and the fines produced. Crushability and grindability data were measured.All lab samples and crushing test samples follow the new Swebrec distribution extremely well. The fragmentation size distribution of the muck piles is constructed using the sieving data and the lab samples, conforming to the Swebrec function. Image analysis gives a fragmentation curve with a distinctly different character. Of the total of 28 % of -32 mm fines after primary crushing, blasting and crushing contribute about half each. Based on these data a set of design curves are constructed that allow the prediction of how any given fraction changes when the specific charge in the round is changed.Godkänd; 2006; 20061208 (ysko)