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Moravian College • Preservation Master Plan
not properly installed in monolithic cast-in-place
concrete construction, leading to cracking. Metal
reinforcement was often installed too close to the
surface, causing rapid reinforcement corrosion.
Concrete mixes contained too much or too little
aggregate, producing shrinkage cracks or spalling.
Harmful additives, such as chloride containing
compounds, were added to alter setting times.
Air-entrained concrete evolved in the mid-1930s
and significantly improved concrete’s ability to
withstand freeze/thaw deterioration. This process
creates air bubbles in the mix, which form a system
of fine, discrete pores that aid in relieving freeze/
thaw stresses. Concrete installed prior to this
invention is therefore inherently more vulnerable.
Cracking in concrete can range from overall hairline
cracks to large gaping cracks and may be caused by
a combination of deterioration mechanisms. Overall
map cracking, an interlocking system of fine cracks,
is caused by shrinkage of the concrete during
installation or internal stresses, such as occurs
with the alkali-silica reaction of certain aggregates.
Vertical cracks may be caused by natural expansion
forces in the material or by shrinkage during the
original concrete set.
Delamination is the loss of concrete material in thin
sheets. Delamination is caused by inherent flaws in
the original material, such as too much aggregate in
the mix, and is exacerbated by freeze/thaw cycling,
salts, and structural stresses. Many of Moravian
College’s historic buildings have concrete parging
on the foundations, which is delaminating in places,
often due to water damage.
Concrete Inspection
As with all exterior envelope materials, routine
inspection is the best method of identifying
potential problems in order to avoid any major
failures. A thorough visual inspection should look
for the following potential signs of deterioration:
• Discernable crack patterns.
• Rust staining or efflorescence associated with
cracking.
• Delamination of surface material.
• Spalling or loss.
• Rust staining.
• Efflorescence.
• Water leakage, ponding, or areas of poor
drainage.
• Exposed and/or corroding reinforcement.
• Foundation settlement.
If an inspection identifies major deterioration, a
structural engineer with experience in historical
concrete construction should conduct an in-depth
assessment.
Causes of Concrete Deterioration
Freeze/Thaw
Deterioration from freeze/thaw cycles is dependent
on the permeability and porosity of the concrete.
Damage will not occur unless there is a sufficient
amount of water in the capillary pores of the
concrete. The entire volume of the concrete does
not need to be saturated to cause damage as surface
layers can spall and delaminate from freezing
pressure. Air-entrained concrete reduces these
pressures by allowing expansion within the small,
discrete voids. The introduction of air-entrained
concrete dates to the mid-1930s, and much of the
failure of earlier concrete was caused by freeze/
thaw deterioration.
Salts and Effl orescence
Solutions of salts or carbon dioxide percolating
through concrete can cause leaching and
deterioration of the concrete. The type of
efflorescence depends on the rate of evaporation
of the solution when it reaches the surface of the
concrete. If the evaporation is rapid, salts can
be deposited within the pore system inside the
concrete. The pressures caused by crystallization
and hydration of salts in the presence of a saturated
solution can then disrupt the cement paste. Finally,
damage occurs on surfaces where drying takes
place.
If the rate of evaporation is fairly slow, efflorescence
will appear on the surface of the concrete. The
formation of efflorescence requires that water laden
with certain elements move through or flow over
the concrete. These deposits come from elements
that were carried in the water. In particular,
calcium carbonate in the water is problematic.
It forms on the surface of concrete when carbon
dioxide in solution percolates through the concrete,
dissolving the carbonates in the cement paste, and
then depositing them on the surface. This leads to
unsightly masses on affected surfaces.
John Milner Associates • October 2009 • Chapter 9 • Building Guidelines • 282