The future of crushed sands?

Influence of the sand grain shape on the working properties of SCC mortars

Grain size distribution with combination of the results of the CPA and air jet screening

Grain size distribution with combination of the results of the CPA and the Coulter

Relationship between packing density and Fuller exponent n – corresponds to Fig. 1

$Relationship between packing density and Fuller exponent n – measured with CPA and laser diffraction$

Relationship between packing density and Fuller exponent n – measured with CPA and laser diffraction

Measured values for natural and crushed sands in comparison with the curves calculated after Peronius and Sweeting

Relationship between the packing density and V funnel flow time at the same slump

Bingham approximation of typical sands with different grain shape

Influence of the roughness on the rheological parameters yield point and plastic viscosity

Estimation of the working properties for a formulation with w/z = 0.6

Dumps of crushed sands at a quarry

Summary: In this paper, as the culmination of extensive tests, a method is presented which can be used to estimate the behaviour of crushed sands in SCC mortars in advance. The algorithm described provides an initial basis for an empirical model that enables the derivation of information on the working properties of SCC mortars from only the results of analysis of the grain shape and grain size distribution of the starting sands. The key parameters are the Fuller exponent n of the grain size distribution and the shape parameters sphericity and roughness.

1 Introduction

Crushed sands are usually a by-product of the production of ballast and chippings, accounting for up to 20% of the yield. With simple comminution methods, crushed sands with a fine grain content of 15-25 mass % are produced “by the way”. They are only used in high-grade applications providing the entire comminution and processing flow undergoes cost-intensive optimization. Depending on the regionally dependent availability of extracted materials, however, they are currently either just dumped or used for inferior backfilling, as cable sands or in frost protection courses.

The...