# Stabilisation of Soft Clay, Quick Clay and Peat by Industrial By-Products and Biochars
## 2 Materials and Methods
### Geotechnical Testing  
The preparation of stabilised soil specimens was performed by first remoulding the natural clays and peat until they were visually considered homogeneous, whereupon the dry binder mixture was added and homogenised for \(\sim\)3-5 min. The soil-binder mixtures were then moulded in plastic cylinders (diameter 54 mm; height 100 mm) using a roding technique, i.e., tamping or pushing a rod onto the material to minimise the air content [75; 76]. Three replicate samples from each mixture were produced and cured for 28 days in the sealed cylinders at a room temperature of approximately 20 \({}^{\circ}\)C [77]. Unconfined compression (UC) tests were then performed with a strain rate of \(\sim\)3.7%/min. From the UC tests, the strength was interpreted as the maximum shear stress (\(\tau_{max}\)), which is typically used in Nordic practice instead of the unconfined compressive strength (\(\tau_{max}=UCS/2\)). Stiffness was interpreted as secant Young's modulus (\(E_{50}\)) up to 50% of the peak stress.  
Table 1 shows the complete laboratory strength testing programme. Based on the results from previous research [27; 29; 46], different binder quantities (\(\alpha\)) and combinations were used for the clays and peat and for the IBPs and biochars. For the clays stabilised with IBPs, mixtures of 50 wt.% CEM and 50 wt.% IBP were used, with a total \(\alpha\) of 60 kg/m\({}^{3}\). For comparison, specimens with 100% CEM were also prepared with \(\alpha\) of 30 and 60 kg/m\({}^{3}\). For clays and biochar (BC), mixtures of 33 wt.% CEM and 67 wt.% BC were prepared with \(\alpha\) of 150 kg/m\({}^{3}\), i.e., 50 kg/m\({}^{3}\) of CEM and 100 kg/m\({}^{3}\) of BC. For comparison, specimens with 100% CEM with \(\alpha\) of 50 kg/m\({}^{3}\) were prepared.  
For the peat specimens, all mixtures were prepared with 33 wt.% CEM and 67 wt.% IBP or BC with a total \(\alpha\) of 300 kg/m\({}^{3}\). Again, for comparison, specimens with 100% CEM with \(\alpha\) of 100 kg/m\({}^{3}\) were prepared.  
To further investigate the stabilisation effect of the IBPs and biochars, testing according to the'strength activity index' (SAI) [78] was performed, although not using the same recipe and geometry as specified in the ASTM standard due to available laboratory equipment. Specimens with mixtures of 12.5 wt.% water, 25 wt.% dry binder and 62.5 wt.% clean quartz sand were manufactured. One reference specimen with 100% CEM was prepared, followed by mixtures where 20% of the CEM was replaced with the respective IBP and biochar. Thus, in total, 10 mixtures were prepared, all moulded in cylinders (diameter 54 mm; height 100 mm) and cured for 14 days before being subjected to UC tests.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Binder** & & **Onsey Clay** & **Tiller-Flotten Clay** & **Peat** \\ \hline \multirow{3}{*}{Cement} & & CEM-30 & CEM-30 & \\  & CEM 1 & CEM-50 & CEM-50 & CEM-100 \\  & & CEM-60 & CEM-60 & \\ \hline Sludge & PSA & CEM-30/PSA-30 & CEM-30/PSA-30 & CEM-100/PSA-200 \\ \hline \multirow{3}{*}{Bioash} & FA & CEM-30/FA-30 & CEM-30/FA-30 & CEM-100/FA-200 \\  & BA & CEM-30/BA-30 & CEM-30/BA-30 & CEM-100/BA-200 \\ \hline \multirow{3}{*}{Ladle slag} & LS1 & CEM-30/LS1-30 & CEM-30/LS1-30 & CEM-100/LS1-200 \\  & LS2 & CEM-30/LS2-30 & CEM-30/LS2-30 & CEM-100/LS2-200 \\ \hline \multirow{3}{*}{Biochar} & BC1 & CEM-50/BC1-100 & CEM-50/BC1-100 & CEM-100/BC1-200 \\  & BC2 & CEM-50/BC2-100 & CEM-50/BC2-100 & CEM-100/BC2-200 \\ \cline{1-1}  & BC3 & CEM-50/BC3-100 & CEM-50/BC3-100 & CEM-100/BC3-200 \\ \cline{1-1}  & BC4 & CEM-50/BC4-100 & CEM-50/BC4-100 & CEM-100/BC4-200 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Laboratory strength testing programme. Mixtures were designated by binder quantity of CEM and binder quantity of biochar or IBP. For example, CEM-30/BC4-30 denotes a mixture of 30 kg of CEM and 30 kg of BC4 per m\({}^{3}\) of natural soil, i.e., a total binder quantity of 60 kg/m\({}^{3}\). For all mixtures, three replicate specimens were prepared.