# Stabilisation of Soft Clay, Quick Clay and Peat by Industrial By-Products and Biochars
## 2 Materials and Methods
### Binders  
A Portland cement of type CEM I 52.5 R (EN 197-1 [44]), produced by Norcer at Brevik, near Porsgrunn, Norway, was used. The CEM I cement was chosen to avoid any content of fly ash or slag that could interact with the biochars and IBPs.  
Four different types of biochars (BCs) were used, all produced in a full-scale microwave-assisted pyrolysis (MAP) unit with a residence time of \(\sim\)20 min. The reactor temperature was approximately 470-600 \({}^{\circ}\)C. The four biochars were as follows:  
* BC1: originated from demolition wood, i.e., wood panels, furniture and composite wood materials, which hence contained some metals and glue remains.
* BC2: originated from municipal sewage which had been sedimented to a bottom sludge and thereafter left to decay for some time. Approximately 39 wt.% of limestone (CaCO\({}_{3}\)) was added for hygiation and workability before the sludge was used for biochar production.
* BC3: originated from sewage and food waste. To speed up the sedimentation, iron chloride (FeCl\({}_{3}\)) was added for flocculation. The bottom sludge was used to produce the biochar.
* BC4: originated from garden waste, i.e., branches, leaves and grass, but also contained some soil and sand.  
The five types of IBPs included two types of bioashes, one paper-sludge ash and two ladle slags:  
* The bioashes were one fly ash (FA) and one bottom ash (BA) obtained from the Bergene Holm's combustion plant at Brandval, near Kongsvinger, Norway. This plant is a grate-fire combustion plant where the boiler temperature is 1000-1200 \({}^{\circ}\)C. The resulting fly and bottom ash account for approximately 10% and 90%, respectively, of the total ash generated. The biomass consisted of a mixture of \(\sim\)35-40% dry wood chips and \(\sim\)60-65% bark. Bioash is mostly used for agricultural purposes [45]; however, a few studies have also been made on soil stabilisation [46, 47, 48, 49, 50, 51].
* One type of paper-sludge ash (PSA) was used, originating from the Norske Skog factory at Skogn, mid-Norway, where paper production and recycling is performed. A mixture of \(\sim\)58% biofuel (demolition wood), \(\sim\)25% deinked pulp sludge, \(\sim\)14% bio sludge and \(\sim\)3% plastic/juice cartons, etc., was combusted at a temperature of approximately 850 \({}^{\circ}\)C. In this study, fly ash from the combustion was used. PSA has been used as an alternative binder in both mortars and concrete [52, 53, 54] and in soil stabilisation [55, 56, 57, 58, 59, 60, 61].
* The two ladle slags originated from Celsa Steel Services, where the recycling of steel is carried out to produce reinforcement steel bars. Both electric arc furnace slag and steelmaking slag are generated from different stages of the melting process. The ladle slags used herein were a mixture of these slags and were extracted from two different locations: at the melt shop (LS1), i.e., a fresh ladle slag, and from an intermediate repository (LS2). Since LS is cooled rather slowly, it develops a high crystallinity and thus possesses relatively low hydraulic reactivity compared to GGBS [62]. LS can be alkali-activated using, e.g., sodium hydroxide, sodium silicate ('waterglass'), QL, CEM or reactive magnesia [63; 64; 65], albeit somewhat less effectively than GGBS [65; 66]. LS has also been used for research purposes in soil stabilisation [67; 68; 12; 69; 70; 71].  
All biochars and IBPs were ground and sieved to a <1 mm fraction and dried before being used for soil stabilisation. Figure 1 shows the IBPs and an example of one biochar.