## 4 Conclusions  
A series of laboratory investigations were conducted to explore the effects of calcium hydroxide and magnesium hydroxide particles on the geotechnical and microstructural properties of the residual soils. The following conclusions are summarized based on the results obtained:  
1. The Atterberg limits of both treated soil samples reduced as a result of decreased DDL thickness. The change in the Atterberg limits caused a transition in soil plasticity classification from high plasticity clay (CH) to intermediate plasticity clay (CI).
2. Calcium hydroxide and magnesium hydroxide nanoparticles showed different effects on the compaction characteristics of the treated soil samples. The MDD of CS decreased with increased OMC due to the pozzolanic reactions between the soil and calcium ions. The compaction characteristics of MS portrayed a different trend whereby their MDD decreased with increased OMC as a result of reduced DDL thickness.
3. The hydraulic conductivity of calcium and magnesium hydroxide nanoparticles-treated samples reduced significantly with permeation time. This is probably due to the clogging of soil pores by the cementing gels formed. These phenomena retarded the movement of water along the compacted soil matrix and resulted in lower hydraulic conductivity.
4. The UCS of nanoparticles-treated samples increased with increasing curing time due to enhanced interlocking between the soil particles. It is quite likely that the flocculation of soil particles  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Elements**} & \multirow{2}{*}{**Natural Soil, NS (\%)**} & **Calcium Hydroxide** & **Magnesium Hydroxide** \\  & & **Treated Soil, CS (\%)** & **Treated Soil, MS (\%)** \\ \hline C & 10.74 & 11.96 & 10.23 \\ O & 61.91 & 61.20 & 59.67 \\ Al & 10.34 & 9.71 & 10.50 \\ Si & 12.85 & 11.41 & 12.61 \\ Fe & 1.09 & 1.12 & 3.40 \\ Pt & 3.08 & 3.01 & 2.56 \\ Ca & - & 1.01 & - \\ Mg & - & - & 0.46 \\ Na & - & 0.25 & 0.25 \\ Cl & - & 0.32 & 0.32 \\ Al/Si & 0.80 & 0.85 & 0.83 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Elemental compositions of treated and untreated soils after 14 days curing time.  
and the formation of cementing gels enhanced the bonding of the soil particles and gave rise to a denser soil structure.
5. The appearance of denser and compacted soil structure as shown in the VP-SEM images of CS and MS justified the explanation of the reduced hydraulic conductivity and increased UCS of treated soil samples. In addition, the formation of new cementing gels such as calcium silicate hydrate, calcium aluminate hydrate, magnesium silicate hydrate, and magnesium aluminate hydrate, which act as soil binders, were observed from the XRD analysis of treated soil samples.  
In conclusion, magnesium hydroxide and calcium hydroxide nanoparticles produced from the quick precipitation method can be utilized as environmental-friendly stabilizers in improving the geotechnical properties of poor soils. Nonetheless, the calcium hydroxide treated sample showed better performance compared to the magnesium hydroxide treated sample in terms of lower hydraulic conductivity and higher UCS.  
Conceptualization, V.A. and L.L.Y.; Methodology, L.L.Y. and E.E.; Investigation, L.L.Y. and S.V.A.D.N.J.P.; Resources, V.A.; Data Curation, L.L.Y. and S.V.A.D.N.J.P.; Writing-Original Draft Preparation, L.L.Y. and S.V.A.D.N.J.P.; Writing-Review and Editing, E.E.; A.S.; S.C.P. and V.A.; Visualization, L.L.Y. and V.A.; Supervision, A.S.; S.C.P. and V.A.; Project Administration, A.S. and S.C.P.; Funding Acquisition, V.A.  
This research was funded by Ministry of Higher Education in Malaysia, grant number FRGS/I/2017/TK01/MUSM/03/01. This support is gratefully acknowledged.  
The authors declare no conflict of interest.