The When a hydrate is heated; it absorbs

The
recalculation of EDS analyses (Table 5 and 6) of weight percent in the element
form into oxides, the analyses showed a great deficiency of cations with
abundance of free anions; indicating that the analyzed material is composed of
significant amount of hydroxides and water of crystallization.  The analyses are very similar to the chemical
composition of saline solutions or groundwater. Normally, a small number of
substances constitute the chemical composition of water (major ions), but other
ions (minor ions) can also be found in low concentrations. The identification
of saline minerals based on their morphology of crystal forms was rather
complex and difficult. They often grow as distorted crystals as needles and
radiating aggregates in pore spaces. Owing to their small size in the range
around 5?m, it is not possible to identify under polarizing microscope.

 

Hydrates
are composed with water of crystallization in their structures 6. When a
hydrate is heated; it absorbs enormous quantity of heat (endothermic) and forms
anhydrous mineral. When an anhydrate is immersed into water; it absorbs water
and releases enormous quantity of heat transforming into a hydrate mineral 6.
In other way, it can be expressed that a hydrate is formed by releasing
enormous quantity of heat from its anhydrous product. The heat released might
promote evaporation of pore fluids. Ice is formed by removing heat from the
freezing water is a typical example for a hydrate transition. The most hydrates
are stable and soluble in water at room temperature. Some hydrates spontaneously
loss water of crystallization by efflorescence. Others absorb water into their
structure forming hydroscopic hydrates. Some deliquescent mineral like sodium
hydroxide absorbs huge quantities of water and form as a liquid. The
decomposition of carbohydrates generally releases water. Thus, water of
crystallization in a hydrate mineral play critical role on their changes in
their specific gravities and in turns their volumes 7. Hydration is not a
reversible reaction, however, the environment in which the crystallization of
hydrates plays critical role for the formation of hydrates and anhydrates 8.  Repeated hydration and dehydration changes
the volume of saline minerals which in turn affects the volume of pore spaces
and hairline cracks are induced. Most pores are partially or completely filled
with saline pore fluids 9. The evaporation of saline fluids precipitates
saline minerals initially at peripheral portions of saline droplets inside the
pores.

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Figures13-20 provide distribution of ionic
components in the pore fluids present in the lime-plaster, derived from EDS
analyses and represent chemical variation of binary components. The
ions of various chemical components are calculated on the basis of 6(Cl) ions
(Deer.et.al. 5). Rittman’s norm 4 is used to calculate the normative
proportions of calcite, gypsum and halites. linear distributions were seen in the distributions of Al
against Si, Cl against CO2, Na against Ca (Figures 13-15).  A low concentration of sulphate ions in the
tri-linear diagram shows a linear distribution of Cl ions against CO2.
Figure 16 represents the linear distribution of carbonate ions against
chloride ions in the lime mortar.  Low concentration of gypsum shows
linear distribution for normative calcite (Figure 17). NaCl (halite) against Cl
and aluminum carbonate against silicon carbonate exhibited positive linear
distribution (Figures 18 and 19). The Figure 20 elucidates initial random
distribution of Na ions against Ca ion and more linear when Na ions enriches at
late stages of crystallization.