Specifying manufactured sands for concrete applications

pcm_admin19/03/2020, 3:54 am19/03/2020

In Australia, research conducted by Cement Concrete Aggregates Australia (CCAA) has provided greater confidence in the specification of manufactured sands for general applications in Australian Standard AS2758.1 (Aggregates and rock for engineering purposes) and in identifying suitable manufactured sands for use in concrete pavements.

Manufactured sand is defined as a purpose-made crushed fine aggregate produced from a suitable source material. Earlier users of manufactured sand have raised concerns about the effect of the shape and grading on water demand, the deleterious clays on both the water demand and early-age performance of hardened concrete and mineralogy on the skid and abrasion resistance of concrete pavement.

A comprehensive CCAA research project (2007) has demonstrated a workable grading envelope of manufactured sands that differ from those previously found workable for natural sands. The identification and control of deleterious fines were found to be effected by limiting the deleterious fines index (DFI) that is the multiple of the methylene blue value (MBV) and the percentage of material passing a 75-micron sieve. These important measures are being incorporated into the revised Australian Standard AS2758.1.

The identification of non-reactive manufactured sands to alkali silica reactivity (ASR) will be greatly enhanced by the development of Australian Standard AS1141.60.1 accelerated mortar bar test (AMBT), to be released by Standards Australia for public comment in the coming months.

In concrete pavement, it was found by the CCAA (2012) that the free silica limit used in the selection of natural sand to provide good skid and abrasion resistance to concrete pavement does not necessarily apply to manufactured sands.

A sand durability test, based on the Micro-Deval abrasion test method, has been found to be effective in identifying suitable sands (both natural and manufactured sand) that provide good skid and skid after wear to the micro-texture of concrete pavement.

This finding agrees with that of parallel research conducted by the International Centre for Aggregates Research (ICAR) at the University of Texas in Austin.

The Australian premixed concrete industry consumes more than an estimated 20 million tonnes of sand in the manufacture of concrete annually. Manufactured sands can now be specified for a broad range of concrete applications.

The greater and efficient use of manufactured sands, however, can be significantly enhanced by the production of manufactured sands with better shape and grading by improved crushing and blending of sands.

Vute Sirivivatnanon is the research manager for Cement Concrete Aggregates Australia and associate professor of construction materials at the University of Western Sydney.