The many lives of rock material
YIT CORPORATION News, May 8, 2019 08:00
Finnish bedrock consists mainly of durable rock material. YIT’s operations involve many phases in the life cycle of rock, such as extraction, mineral aggregate refining, as well as the recycling and reuse of aggregates in asphalt, for example.
The story of rock material starts deep in the core of Finnish bedrock, which can be up to 3,000 million years old.
Finnish bedrock is durable and it mainly consists of solid bed. Rock has been used as material for as long as mankind has built constructions. Today, rock material is used in nearly all constructions, such as roads, railways, bridges, buildings and tunnel bases. The responsible use of rock material means avoiding excess use of mineral aggregates, optimising material consumption and recycling whenever possible.
The bedrock material used in construction often comes from a quarry, i.e. an extraction site, as it is called in professional terminology.
“When choosing the rock material extraction site, the first thing to consider is its location with regard to residential areas, water systems and other natural values. The next step is surveying the quality of the material, i.e. the properties of the rock. In an ideal situation, the extraction site is located as close to the usage site as possible,” says SVP Juha Arvola, Head of Mineral Aggregates, YIT Finland.
The extraction of rock material is highly regulated and always subject to permission. For example, in Finland, the Government decree on environmental protection at rock quarries, other rock quarrying operators and crushing plants (800/2010) sets the minimum distance between extraction sites and residential buildings: for quarries subject to environmental permit, it is 300 metres. In addition, any noise, dust and landscape effects must be surveyed before setting up an extraction site. After completing the required surveys, a mineral aggregates permit and environmental permit must be obtained. YIT can purchase the land or sign a lease with the land owner.
However, obtaining the extraction site does not mark the start of mineral aggregate crushing and other refining activities, let alone sales.
A geologist carries out a rock material survey, which is followed by test blasting. The material extracted in test blasting is tested in a laboratory in order to define its quality and possible usage purposes. Rock material is classified in terms of suitability for different purposes based on its mechanical and physical properties. The mineral content of the material is often measured by an external operator, such as Tampere University.
Aggregate grades planned according to use
Once the quality of the rock material has been defined, the actual extraction process starts by felling trees and removing soil at the extraction site in order to reveal the bedrock. The next step is drilling and blasting the bedrock to create blast rock, which is then fed into a crushing plant. The output of the crushing plant, the finished products, are then moved to separate stockpiles. A Drone equipped with a camera is used in the aggregate inventory-taking.
“The rock is crushed into various grades at the site. The finest grade has a diameter of 0–2 mm, whereas the coarsest one is 250 mm. The grade sizes are always planned according to usage needs,” Arvola tells us.
For example, the crushed stone used for anti-slipping purposes in the winter is typically 3–6 mm or 3–8 mm in diameter, and typical grade sizes used in foundation construction are 0–16 mm, 0–31 mm, 0–56 mm, 0–90 mm and 0–150 mm, depending on the object constructed. The crushed stone products are transported from the extraction site to end-users by lorries.
The service life of a quarry or extraction site can vary from a few years to decades, depending on its size and the available reserves. Restoration work is carried out in the area as the extraction proceeds.
“The quarry or gravel site is sloped as outlined in the mineral aggregates permit, and other planned landscaping measures are also taken. We plant tree saplings according to the permit stipulations and monitor the area’s gradual reunification with the surrounding landscape,” Arvola explains.
As regards aggregate use, the construction industry is better than its reputation
Mineral aggregates can be divided into three different types. Natural stone is an overall term for all rock material extracted from the bedrock (e.g. rock, gravel and sand). Secondary stone is rock material generated as a by-product of the process, and recycled stone refers to mineral aggregate that has already been used once.
The transportation of rock material is expensive and environmentally burdensome, so aggregates are seldom transported more than 25 kilometres from their selling point. However, concrete gravel, railway ballast and high-grade asphalt aggregates may be transported over distances longer than 100 km, if suitable material is not available anywhere closer to the usage site. This is why many major construction projects aim at a so-called mass balance, which means self-sufficiency with regard to rock material.
“When it comes to recycled mineral aggregates, the construction industry is better than its reputation; the recycling rate is high. For example, rock material blasted out in conjunction with tunnelling can be used at another site run by the same construction operator in a nearby area, or transported to other sites,” says geologist Akseli Torppa from the Geological Survey of Finland. He specialises in mineral aggregates surveys.
Recycled mineral aggregate can be obtained from such sources as old asphalt or concrete from demolished buildings. The quality of such material is tested in a similar manner as that of pure natural stone, and the applied quality requirements are based on the same standards.
Reclaimed asphalt is YIT’s feat
YIT is particularly renowned for the use of reclaimed asphalt. Old asphalt is ground off at the site and some of it is blended into a new asphalt mix using the REMIX method. Asphalt consists of hard rock material and the binding agent, bitumen.
“In principle, the amount of reclaimed asphalt can be a full 100 percent, but in this case, the ageing of bitumen and certain issues in the manufacturing process pose challenges. At the moment, we can use 50 percent of reclaimed asphalt in the wearing course of the pavement and 70 percent in the lower layers,” says Vesa Laitinen from YIT’s laboratory.
Laitinen tells us that if the content of reclaimed asphalt exceeds 50 percent, this can help reduce the carbon dioxide emissions of asphalt by more than 20 percent.
Geologist Akseli Torppa has also noticed the increase in mineral aggregate recycling among construction industry operators.
“Apart from hard rock material, aggregates can be recycled for such purposes as the mass filling and banking of construction sites. The majority of scrap rock material taken to landfill is environmentally harmless. I believe that the use of recycled mineral aggregates will increase in the future, because when well planned, it is a cost-efficient and environmentally sustainable approach,” Torppa says.
YIT is continuously developing new methods that would enable increasing the proportion of reclaimed aggregates in asphalt and other products. The rock material used in asphalt, as well as bitumen, which is made from oil, are non-renewable natural resources. This means that the higher the recycling rate, the better for the preservation of natural resources.
Through recycling and reuse, rock material goes through many lives.
Fact: YIT’s mineral aggregates business
The extraction of rock material is highly regulated and always subject to permission. Before setting up an extraction site, any noise, dust and landscape effects must be surveyed. The minimum distance between quarried object and residential buildings is 300 metres and for gravel extraction sites, it is 100 metres.
YIT utilises an IoT-based data collection software tool in its crushing operations for such purposes as supervision, maintenance planning and product development.
Automation has been introduced into use in the weighing of rock material at the extraction site. The automation system enables transmitting the weight of the dispatched rock material’s weight directly from the wheeled loader to invoicing.
We are particularly proud of our aggregates recycling rates and the use of reclaimed asphalt in our REMIX method. When the content of reclaimed asphalt exceeds 50 percent, this can help reduce the carbon dioxide emissions of asphalt by more than 20 percent.
We optimise our use of mineral aggregates from the perspectives of both construction efficiency and the environment. We strive to use any hard rock material generated as the by-product of our processes at the same site or in the nearby areas, or sell it to other users. Aggregates other than hard rock can be recycled for such purposes as the mass filling and banking of construction sites.
For further information, please contact:
Juha Arvola, SVT, Head of Mineral Aggregates, YIT Finland, tel. +358 (0)400 151 739, juha.arvola@yit.fi
Pauliina Pykälä, Communications Manager, YIT Corporation, tel. +358 (0)40 354 3360, pauliina.pykala@yit.fi
YIT is the largest Finnish and significant North European construction company. We develop and build apartments and living services, business premises and entire areas. We are also specialised in demanding infrastructure construction and paving. Together with our customers, our nearly 10,000 professionals are creating more functional, more attractive and more sustainable cities and environments. We work in 11 countries: Finland, Russia, Scandinavia, the Baltic Countries, the Czech Republic, Slovakia and Poland. The new YIT was born when over 100-year-old YIT Corporation and Lemminkäinen Corporation merged on February 1, 2018. Our pro forma revenue for 2018 was approximately EUR 3.8 billion. YIT Corporation's share is listed on Nasdaq Helsinki Oy. www.yitgroup.com
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