# Influence of Some Additives on the Properties of OPC Solidified Sandy Silt
## 2 Experimental Work
### Preparation and Test Methods  
Previous studies conducted on sandy silt indicated that oven drying could change the plasticity and properties of the soil [(23)]. Therefore, in this test, air-dried undisturbed sandy silt was selected and was ground into smaller sizes using a sieve, and sandy silt with a moisture content of 20% was disposed of. The mix proportion of OPC was first determined through trail mixing so that the stabilized soil had good mechanical properties and a moderate setting time. All solidified soil specimens were prepared under the condition of 11% OPC inclusion. The proportion of additives is shown in Table 3 (sandy soil weight basis). OPC and different types of additives were dry mixed in a Hobart mixer. The liquid components of the soil specimens and the concrete were gradually added to the solid particles over the next one minute and were then further mixed for 3 min for homogeneity. The paste was cast into molds (cylinder specimens with a diameter of 50 mm and a height of 50 mm for unconfined compression and tensile strength tests; 40 \(\times\) 40 \(\times\) 160 mm prisms for flexural and cylinder specimens with a diameter of 100 mm and a height of 100 mm for compressive resilient modulus test) in three layers on a table vibrator and were then wrapped using a thin plastic sheet to prevent the evaporation of the solution. The specimens were stored in a standard curing chamber (temperature = 18 \({}^{\circ}\)C-22 \({}^{\circ}\)C; relative humidity \(>\) 95%). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Initial Setting** & **Final Setting** & **Compressive Strength/(MPa)** & **Flexural Strength/(MPa)** \\
**Time/(min)** & **Time/(min)** & **3d** & **28d** & **3d** & **28d** \\ \hline
150 \(\pm\) 3 & 210 + 5 & 27.5 \(\pm\) 1.4 & 49.6 \(\pm\) 2.0 & 5.5 \(\pm\) 0.6 & 9.0 \(\pm\) 1.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Physical properties of the OPC. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Material** & **SiO2** & **Fe2O3** & **Al2O3** & **CaO** & **MgO** & **SO2** & **SO3** & **Others** & **LOI \({}^{\text{a}}\)** \\ \hline OPC & 21.14 & 2.70 & 4.70 & 63.66 & 2.61 & — & 2.53 & 1.21 & 1.45 \\ Gypsum & 2.68 & 0.37 & 0.54 & 36.12 & 1.03 & 42.7 & — & 14.51 & 2.05 \\ Lime & 1.74 & — & 0.56 & 93.64 & 1.37 & — & 1.14 & 0.90 & 0.65 \\ Fly ash & 58.05 & 4.32 & 30.10 & 1.53 & 2.81 & — & 0.43 & 1.82 & 0.94 \\ \hline \hline \end{tabular} \({}^{\text{a}}\) Loss on ignition.  
\end{table} 
Table 2: Chemical compositions (wt.%) of raw materials used. Unconfined compression and tensile strength tests for the specimens were executed according to GB/T 50123-2019 [24] using a WEW-2000D universal testing machine. Specimens were loaded at a rate of 0.5 mm/min under displacement control. A flexural strength test was conducted by using a YDW-10 cement bending machine (loading speed = 40 N/s). The strengths were calculated using Equations (2)-(4). \[\mathrm{f_{tuncon}}=\frac{\mathrm{P_{max}}}{\mathrm{A}} \tag{2}\]  
\[\mathrm{f_{fen}}=\frac{2\mathrm{P_{max}}}{\mathrm{\pi dh}}\left(\sin 2\alpha- \frac{\mathrm{a}}{\mathrm{d}}\right) \tag{3}\]  
\[\mathrm{f_{flex}}=\frac{\mathrm{P_{max}L}}{\mathrm{b^{2}h}} \tag{4}\]  
where, \(\mathrm{P_{max}}\), \(\mathrm{A}\), \(\mathrm{d}\), \(\mathrm{h}\), and \(\mathrm{b}\) are the peak load (N), the cross-sectional area (mm\({}^{2}\)), the diameter (mm), the height (mm), and the width (mm) of the specimen, respectively; \(\alpha\) and a are the central angle of the half-width and the width of the pressing strip. For the compressive resilient modulus tests, the loading gradually increased from a low load to a high load. The maximum values of the loading band were collected as well as their corresponding displacement variations [25]. \[\mathrm{E_{c}}=\frac{\sigma}{\varepsilon}=\frac{\mathrm{P_{0}h}}{\mathrm{I_{0 }A}} \tag{5}\]  
where, \(\mathrm{P_{0}}\) is the load amplitude (N), \(\mathrm{I_{0}}\) is the deformation amplitude (mm).