In Scotland, we’re spoilt with architectural gems everywhere. In Edinburgh and Glasgow in particular, we walk through streets surrounded by buildings that are hundreds or even thousands of years old on a daily basis without a second thought. These buildings have survived because they were originally built with high quality materials and have been cared for over the years by owners and tenants. The people who have lived there understood the value of the buildings and because of this, the buildings have been used time and time and time again.
The same thought process should be applied to the aggregates that we use in our construction projects. If we take care of our materials, manufacture them to the highest possible quality and treat them as we should, then they can be reused almost endlessly. State-of-the-art wash plants ensure that recycled aggregates are free of anything that could hamper their longevity. Just like houses, the better we design for reuse and take care of our aggregates, the better they will perform and the longer they will last.
Not all aggregates are created equal
There are several different ways that we can produce the spectrum of grades of recycled aggregates demanded by the construction industry, and they all produce very different results. This range is needed in recycled aggregates due to the vast applications that they are used in.
Basic crushed products like 6F5 are extremely popular and don’t go through the washing process. It’s still recycled from CDE waste, but it is an unwashed product created from oversized material, generally ranging in size from 75mm all the way down to dust. 6F5 is a reliable product generally used for low value applications such as capping layer for roads and buildings, where high-performing aggregates are not needed.
Washed recycled aggregates like our sand and gravel are also made from materials that have been reclaimed and repurposed from construction, demolition and excavation sites. The key difference between these aggregates and products like 6F5 is that the washed products have been thoroughly cleaned and graded by our state-of-the-art wet processing recycling facility which removes any contaminants within the material. This washing and recycling process helps produce the highest possible quality product.
Testing and quality
You might worry that continuing to reuse the same product over and over again and only ‘washing’ it would deteriorate its quality. Our recycled washed aggregates undergo the same testing as quarried materials, being held to British Standards and the Specification for Highway works. It is still important to ensure that your supplier meets all the appropriate product and application standards.
At Brewster Brothers, all aggregate product samples taken for testing will be sampled from stockpiles to BS EN 932-1 (‘Tests for general properties of aggregates’) and are tested weekly. In addition, we have also achieved accreditation ISO 9001 for our Quality Management System.
The benefits of washing aggregates
Dry screening has long been widely accepted as the norm, and for many other suppliers it is still very much the way they produce aggregate. To produce a high performing aggregate comparative to virgin aggregates, requires the material to go through the thorough washing process to remove contaminants and grade the sand and gravel into appropriates sizes. Dry processing can result in a dustier material, however for products like 6F5 where the main applications are for drainage or subbase, this is compliant with the testing requirements.
Crushed recycled material
Wet processing has several additional benefits. As well as removing excess fines via attrition and scrubbing, washing allows the effective removal of organics and lightweight contamination from sand and gravel via density separation.
Looking at wider benefits, washing ensures the waste can be fully recycled and not downcycled into lower value applications.
Widespread use of aggregate washing facilities helps to address local (and global) natural sand shortages by producing manufactured sand from crushed CDE waste.
Virgin aggregates are finite, and are energy intensive to procure, which can have a significant impact on the natural environment. Washed aggregates represent a very practical alternative. Unwashed products like recycled 6F5 play an important role in lower value applications like drainage and subbase, but for the highest performing recycled aggregates, and in order to extract the maximum value from CDE waste, the washing process is vital.
Washed recycled aggregates look (almost) identical, perform the same and are tested to the exact same standards as their virgin equivalents. They represent a viable, high-performing and sustainable solution to our dwindling natural resources.