Water treatment contributes to ambitious environmental construction
Proper management of soil and construction aggregate masses brings economic and environmental benefits. However, there are too few suitable sites for the temporary storage of soil and aggregates.
For every construction project we need soil and aggregate, but very rarely can it be obtained on site or even close by. Usually, the aggregate travels a long way before it is processed into construction materials such as asphalt or crushed stone. The volumes that are transported are huge, says YIT’s environmental manager Jame Welin.
“For example, in metro and underground car park construction sites, the excavated volumes can be up to 100,000 cubic metres. Even in smaller building sites we are talking about large volumes of up to 10,000 m3.”
Recycling refers to the transfer of soil and aggregate between construction sites. In this way, there is no need to quarry the aggregate. For example, if several construction projects are under way in Helsinki, aggregate can be transferred between the sites instead of being transported from outside the metropolitan area.
“This will reduce emissions, as well as disruptions to traffic caused by logistics,” Welin says.
A construction site may be accumulating huge heaps of land while at the same time other sites are in desperate need of more construction aggregate. Welin mentions mass balance, referring to the ideal situation where there is neither shortage nor surplus of aggregate at construction sites. If necessary, masses are shifted directly between construction sites, but this is not an optimal solution. Digital tools can be used to find room for small volumes of aggregate at construction sites, but there usually is no room for larger volumes.
“It is difficult to store heaps of soil and aggregate on a construction site to wait for use on the next site. We need more recycling areas where the surplus can be transported and then delivered where needed. Such multi-hectare areas for intermediate storage of soil cannot be easily found in the Helsinki metropolitan area.”
Not all soil is of equal value, and there are differences in aggregates. Only first-class aggregate that is hard enough to withstand the traffic wear is suitable on the road surface. Clay, on the other hand, is rarely transferred from one site to another, as there is more than enough clay everywhere. The usefulness of clay is greatly enhanced when it is first stabilised by adding a stabilising agent such as cement or ash. This increases its load-bearing capacity so that it can be used for creating landforms, for example.
Sometimes the soil is contaminated and cannot be used as such. Contaminated soil temporarily blocks construction in the area affected, but the situation can be remedied through decontamination, as Mikko Moilanen, Construction Manager at YIT, explains.
“Soil can be contaminated for many reasons, such as spillage of oil, metals or solvents. Old landfills and industrial sites are typical examples of sites that must always be decontaminated before construction begins.”
Contaminated soil can be partially cleaned on site, but most of the fine material is transported to special facilities for decontamination. Rock, or mineral aggregates, can be sorted on site, crushed and then used as crushed stone.
Decontamination is often a huge task. Moilanen tells that YIT is currently in the process of decontaminating a 5,000-m2 site in Hermanni, which will later be used for the construction of an apartment block.
“The decontamination work will take from four to six months. In the pre-war years, the Hermanni area housed wood-treatment facilities, and now we find impregnated wood and other waste there.”
A site in its own class is Verkkosaari in Kalasatama, where homes and offices will be built. Before the construction work can begin, the site has to undergo a massive decontamination process.
“The decontamination alone will take four years. The area contains a terrible amount of wood waste. It remains to be seen whether there is enough capacity in the southern Finland to receive all that waste,” Moilanen says.
The methods of soil recycling and decontamination have remained relatively unchanged, and new technologies have hardly changed the industry. One major change has been that the importance of soil recycling has now been widely recognised, as sustainable development has become an increasingly important theme in the construction industry.
“Previously, soil was shuffled back and forth without any proper management. The situation changed when the City of Helsinki started managing the soil masses and made huge savings. From Helsinki the practice then spread to the rest of Finland,” Welin explains.
According to Welin, it is increasingly important that information on shortages and surpluses and the quality of the soils in question is passed between construction sites. Proper management of soil and construction aggregate masses brings economic and environmental benefits. However, as mentioned above, there is a big but resolvable challenge, namely zoning, in the way of the new approach.
“The problem is with zoning: we do not have enough recycling sites for intermediate storage. This often hinders action, even if there is a desire and the required expertise in the field,” Welin sums up.