The course of deterioration lime mortar in the

The
setting and hardening of lime mortar plaster were slow processes due to the
reactions between lime and water. Different quantities of heat are released out
for different components of reaction materials and their reaction rates.
Initially, glue gel binders of poorly organized layers are formed, latter they
are recrystallized. The EDS analyses at different parts of samples show wide
compositional variations. Co-existing dihydrate and anhydrate occur together.
The volatile components in these minerals varied widely. The analyses were
enriched with CO3, SO3 and H2O. About 10
samples did not have any water molecules (anhydrites). The remaining 8 samples
were enriched water molecules (hydrates up to 64%). Carbonates are subordinate
to sulphates CaO and SO3 maintain the proportion of 1:1. However H2O
increases significantly to 64% in some sulphate minerals.  The portlandite Ca(OH)2 was seen
as hexagonal stacks of plates. It can bring pH value to over 12 and the rate of
reaction with water was rapidly increased (Balkstein, 2007). The water content
of these sulphate bearing hydrate minerals were varied from gypsum (20.67%) to
ettringite (64.25%). Gypsum contains 2 moles of water for each 1 mole of
calcium sulphate. The water molecule in gypsum distorts its structure
vibrationally by its potential environment (Cyhang, et.al. 1996). All these
sulphate bearing minerals were impure by accommodation of Si, Al, Fe+3,
Mg, Na and K in their lattices to compensate SO4 tetrahedron. Using
Rittman’s normative proportion 4 of ettringite (Ca6Al2(SO4)3
(OH)12.26H2O) and Thaumasite (Ca3Si6H6CS.12H2O)
were calculated that assuming enough water molecules were available during the
course of deterioration lime mortar in the course of time. From the spot
analyses of the sample the maximum concentration of ettringite was reached 91%
and thaumasite 48.51%. Contrastingly, the volume percentage of anhydrite
exceeded over 96% in an analysis. These features indicated that the
orientations and exposures of mineral grains for reacting with pore-fluids in
wet and dry state has played critical roles on co-existences of these minerals
under crystal field stabilization. Ettringite formation is associated with
expansion because of its higher water of crystallization.  As lime mixes have low viscosity they
penetrate even minute pores and voids than other binders. The pressure from
crystal growth will lead to cracking and damage. Particle size distribution and
crystal morphology were determined under SEM.