Engineering Geology

Chapter 6
one of the shortcomings of the test since specific reference stones are seldom available.
Leary used the two types of acid immersion test and two types of crystallization test to
classify sandstones into six grades, as follows:
1. Class A sandstones pass a severe acid immersion test and a severe crystallization
test.
2. Class B sandstones pass a mild acid immersion test and a severe crystallization
test.
3. Class C sandstones pass a severe acid immersion test and a mild crystallization
test.
4. Class D sandstones pass a severe acid immersion test but fail a mild crystallization
test.
5. Class E sandstones pass a mild acid immersion test but fail a mild crystallization
test.
6. Class F sandstones fail a mild acid immersion test and a mild crystallization test.
Damage can occur to stone by alternate wetting and drying. What is more, water in the pores
of a stone of low tensile strength can expand enough when warmed to cause its disruption.
For example, when the temperature of water is raised from 0 to 60∞C, it expands some
1.5%, and this can exert a pressure of up to 52 MPa in the pores of a rock. Indeed, water can
cause expansion within granite ranging from 0.004 to 0.009%, in marble from 0.001 to
0.0025% and in quartz arenites (sandstones) from 0.01 to 0.044%. The stresses imposed
on masonry by expansion and contraction, brought about by changes in temperature and
moisture content, can result in masonry between abutments spalling at the joints, blocks may
even be shattered and fall out of place.
Frost damage is one of the major factors causing deterioration in a building stone (Ingham,
2005). Sometimes, small fragments are separated from the surface of a stone due to frost
action but the major effect is gross fracture. Frost damage is most likely to occur on steps,
copings, cills and cornices where rain and snow can collect. Damage to susceptible stone may
be reduced if it is placed in a sheltered location. Most igneous rocks, and the better quality
sandstones and limestones, are immune. As far as frost susceptibility is concerned, the
porosity, tortuosity, pore size and degree of saturation all play an important role. As water
turns to ice, it increases in volume, thus giving rise to an increase in pressure within the
pores. This action is further enhanced by the displacement of pore water away from the
developing ice front. Once ice has formed, the ice pressure rapidly increases with decreasing
temperature, so that at approximately -22∞C, ice can exert a pressure of 200 MPa
(Winkler, 1973). Usually, coarse-grained rocks withstand freezing better than the
fine-grained types. Indeed, the critical pore size for freeze–thaw durability appears to be
about 0.005 mm. In other words, rocks with larger mean pore diameters allow outward
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