## 4 Results and Discussion
### Effect of PG on Lime-Soil Reactions  
The addition of PG to the lime-stabilization of soil results in modifications in the end products formed during the pozzolanic reactions. The primary constituent of PG is calcium sulfate (CaSO\({}_{4}\).2H\({}_{2}\)O) [22]. As a result of this, sulfate ions are introduced into lime soil reactions. The mechanism of strength development due to the addition of PG can be attributed to the formation of the mineral ettrin  
Figure 8: SEM Micrograph of (**a**) LPI (**b**) LP2.  
Figure 7: SEM Micrograph of LP3.  
formation of ettrinigite in lime sulfate systems [35; 36; 37]. In most of the cases, the ettrinigite formed was associated with swelling, resulting in the poor performance of the stabilized soils. However, several researchers who had earlier worked on PG admixed systems have attributed the formation of ettrinigite as the reason for the early strength gain [21; 22; 38; 39]. With increasing curing periods, PG is consumed in the formation of ettrinigite. [PERSON] and [PERSON] [39] identified increasing peaks of ettrinigite coupled with decreasing peaks of gypsum in their X-ray diffraction study indicating the consumption of PG in PG-fly ash- limestone systems. PG also hastens the pozzolanic reaction in PG-time-fly ash systems [21]. [PERSON] et al. [22] report that the formation of ettrinigite hastens the pozzolanic reactions. [PERSON] and [PERSON] [40] also reported increased strength in PG admixed cement systems due to the formation of ettrinigite. The formation of ettrinigite in sulfate systems is given by (2), (3) and (4) [22; 38].  
\[\mathrm{xCa(OH)_{2}+SiO_{2}+nH_{2}O}\rightarrow\mathrm{xCaO\cdot SiO2\cdot(n+x)H _{2}O} \tag{2}\]  
\[\mathrm{yCa(OH)_{2}+Al_{2}O_{3}+nH_{2}O}\rightarrow\mathrm{yCaO\cdot Al_{2}O_{ 3}\cdot(n+y)H_{2}O} \tag{3}\]  
\[\mathrm{3 Ca(OH)_{2}+Al_{2}O_{3}+3 CaSO_{4}\cdot 2H_{2}O}+26H_{2}O\rightarrow \tag{4}\]  
\[\mathrm{3 CaO\cdot Al_{2}O_{3}\cdot 3 CaSO_{4}\cdot 32H_{2}O} \tag{5}\]  
[PERSON] et al. [39] had also given a similar chemical reaction (5) for the formation of the ettrinigite in lime- or cement-stabilized sulfate-rich soils.  
\[\begin{array}{c}6\mathrm{Ca^{2+}+2 Al(OH)_{4}-44(OH)^{-}+3(SO4)^{2-}+26H_{2}O} \\ \rightarrow\mathrm{Ca_{6}[Al(OH)_{6}]_{2}\cdot(SO_{4})_{3}\cdot 26H_{2}O}\end{array} \tag{6}\]  
It has been reported by researchers that ettrinigite formed in such stabilized soil systems has both positive as well as detrimental effects. Whether ettrinigite can cause expansive damage depends not only on the quantity but also on the condition under which ettrinigite forms. In a high CaO concentration solution, ettrinigite packs densely adjacent to other solid particle surfaces, and this gel tends to expand; in a low CaO concentration solution, ettrinigite is produced dispersedly, and this gel has less tendency to expand [39]. In the present work, the addition of PG to the lime-stabilized soil has resulted in an increase in the strength of the soil, and thereby it can be concluded that the reactive conditions in the soil have been favorable for the formation of ettrinigite that helps in better packing of pores in the stabilized soil matrix.