UK: Tarmac has demonstrated a new concrete product using a high proportion of slag with Align, the joint venture building part of HS2, a new high-speed railway line. It demonstrated the potential to use very high ground granulated blast furnace slag (GGBS) content in excess of 90%, as an alkali activated cementitious material conforming to BS EN197, the standard for cementitious materials allowed to be used in ready mixed concrete, to significantly reduce carbon emissions, whilst still producing a quality finish and allowing normal construction and demoulding times.

Demonstration and testing at full scale used one of three Tarmac concrete batch plants at a Chalfont Lane construction site in Hertfordshire. A structural slab forming part of the new viaduct pre-cast factory and a vertical wall were poured. Tarmac says that the mixes, designed to Align concrete specification, exceeded expectations in both fresh and hardened properties, and showed that the new concrete can be produced in normal concrete plants and placed via mixer truck and by skip with a tremie pipe. The new low carbon concrete has a carbon footprint following industry BSI PAS2050 calculation rules that gives a 62% reduction in CO₂e per cubic metre of concrete, compared to a standard CEM I concrete, meeting the same specification in the same raw materials. The footprint covers all aspects of the concrete production and supply with no carbon off-setting applied, delivering an actual footprint of 133kg/m³ CO₂e. This represents a saving of 220t CO₂e for every 1000m³ produced.

“Together we’ve shown this new concrete is fit for purpose in slabs and walls, with good repeatability and works with standard production and construction methods. This product is a great step along the industry zero carbon routemap, and the demonstration will help accelerate adoption of this new concrete,” said Robert Gossling, head of commercial engineering solutions at Tarmac.

Tarmac is supplying concrete for the construction of the Central 1 section of HS2 Phase One that is being built by Align. This includes a 22km section of high-speed rail infrastructure incorporating a 3km viaduct across the Colne Valley, a 16km twin-bored tunnel, and five vent shafts handling both intervention and tunnel ventilation facilities.

Austria: Neuson Hydrotec is promoting its MRP40300 type mobile screener and crusher. The tracked product was developed to screen waste slag-containing material on site using magnetic separators and then crush it for reuse. The unit consists of: a vibrating feed and dosing unit, for converting discontinuous feed into continuous feeding of the bulk material into the plant; a vibration sieve for separation into up to four fractions; up to three magnetic separators for separating bulk materials; and discharge belts for the continuous discharge of the individual fractions.

“With the MRP, we were able to create the missing link between breaking steel slag and the finished, sorted end product. It was important to us not only to crush the steel-containing slag with our patented jaw crusher, but also to be able to subsequently separate the iron-containing material and slag into different fractions. Our customers can now look after several company locations with our mobile machines. The construction of stationary systems at each location is no longer absolutely necessary,” said Markus Zweimüller, head of the business machines division at Neuson Hydrotec.

Linz-based Neuson Hydrotec is a manufacturer of hydraulic and drive technology products for mobile and stationary applications.

South Korea: Continental New Materials has awarded a granulated blast furnace slag (GBFS) supply contract to steel producer POSCO. Continental New Materials applies technology developed at the Ulsan National Institute of Science Technology (UNIST) to produce clinker-free cement.

POSCO's hot rolled and wire rod marketing manager Kim Dae-Up said "We will continue to provide support so that POSCO's steel by-products can become eco-friendly cement materials and contribute further to carbon reduction."

US: The United States Geological Survey (USGS) estimates that the US sold 17Mt of ferrous slags in 2021, a rise of 31% year-on-year from the estimate in 2020. Blast furnace slag represented about 49% of the volume sold and accounted for 87% of the total value ofslag, most of which was granulated. Steel slag produced from oxygen and electric arc furnaces accounted forthe remainder of sales. Slag was processed by 28 companies servicing active iron and steel facilities or reprocessing old slag piles at about 124 processing plants, including some iron and steel plants with more than one slag-processing facility, in 33 States, including facilities that import and grind unground slag to sell as ground granulated blast furnace slag (GGBFS).

A further 2.2Mt was imported, a slight decline from 2020. From 2017 to 2020 the USGS reports that 42% of imported slag came from Japan, 18% from Brazil, 11% from China and 10% from Italy.

The USGS noted that during 2021, domestic GGBFS remained in limited supply because granulation cooling was known to be available at only two active US blast furnaces while, elsewhere, only one domestic plant produced pelletised slag in limited supply. Grinding of granulated blast furnace slag was only performed domestically by cement companies. However, following Covid-19 related decrease in availability in 2020, supply of steel slag increased in 2021.