Slag aggregates

By-products of the steel and iron industries, slag aggregates have many valuable properties that can be used in construction and infrastructure projects.

Steel aggregates have a high abrasion and crushing resistance for road applications; air-cooled blast furnace products bond particularly well to cement and bituminous binders. They also offer significant environmental benefits such as the re-use of secondary materials and avoidance of the need to quarry natural aggregates.

Yes, where applicable. Slag aggregates produced by Tarmac are supplied as CE marked products under the Factory Production Control Process of BS EN ISO 9001:2008 for the production of products to BS EN 12342-Aggregates for Unbound and Hydraulically Bound Mixtures, BS EN 13043-Aggregates for Unbound Bituminous Mixtures and BS EN 12620-Aggregates for Concrete.

One of the minerals (beta dicalcium silicate) present in some crystalline blast furnace slags can undergo a transformation in its crystalline structure on cooling that can cause disintegration of the product in a phenomenon known as ‘falling’, ‘dicalcium silicate unsoundness’ or ‘lime unsoundness’. Chemical equations and microscopic tests are intended to exclude slags that might contain this compound from use as aggregate.

When it does occasionally occur, ‘falling’ happens only during cooling and will not affect slag aggregates in service.

Steel slag contains oxides of calcium and magnesium (lime and magnesia) that expand upon reaction with water. Expansion issues in service are avoided by process control measures which subject the steel slag to long periods of natural weathering in exposed stockpiles before use.

As part of this quality protocol the steel slag’s volumetric expansion is tested during the weathering process at monthly intervals using in-house developed test methods and measured against set limits, with a minimum of three months weathering per windrow.

The quarantined windrows of steel slag are released for sale when expansion test data complies with internal control limits to ensure fitness for purpose as part of the CE and FPC requirements of BS EN 13242, the testing for volume stability of steel slag using BS EN 1744-1 19.3 is carried out at a minimum of six monthly intervals.

Tarmac have a team of experienced Technical Product Support Managers who can provide advice on specific site requirements and offer valuable technical support. Use the contact section of this website for further information.