Concrete Degradation Analysis: Material Design and Procedures

This report examines the structural integrity of concrete in buildings, focusing on the causes and prevention of concrete degradation. It identifies factors such as aggregate expansion (alkali-silica reaction, dedolomitization), chemical damage (carbonation, chloride action, sulfate), and physical damage (de-shuttering issues) as key contributors to degradation. The report also highlights visible signs of concrete degradation, including cracks, sagging beams, and exposed steel reinforcements. To improve concrete durability, the report proposes proper mix design adhering to ASTM standards, strategic placement of construction joints, and ensuring low permeability to prevent harmful reactions. Waterproofing is also recommended in water-prone environments. This analysis aims to provide insights into maintaining the longevity and stability of concrete structures, and students can find similar solved assignments on Desklib.

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1 March 2019
Material Design and Procedures
Structural integrity of any building is only fairly evaluated when structural components,
and masonry which essentially consists of concrete is stable, durable, and hence stronger.
Nevertheless, for some reasons, the durability and hence stability of the structure may be
shortened following failure of degradation of concrete components. This is familiarly termed as
concrete degradation.
The causes of concrete degradation include but not limited to chemical damage, physical
damage, aggregate expansion, bacterial corrosion, calcium leaching, and sea water effects. Some
of these causes are explored in the following section:
i. Aggregate expansion
This mainly consequence chemical reaction of the concrete termed as alkali-silica reaction in
most instances causing damaging and expensive phenomena. Reactive silica in concrete react
with alkali in concrete in the presence of water. Alkali component significantly constitute cement
inform of oxides of calcium and potassium. Most aggregates in concrete consists of reactive
mineral constituents such as strained quartz, opal, flint and chalcedony. Alkali-silica reaction
results in the formation of expansive gels which create extensive cracks in concrete hence
causing damage to concrete. Certain kinds of aggregates consists of dolomite minerals. When
such aggregates are used in the concrete mix design, dedolomitization reaction results when
hydroxyl ions react with magnesium carbonate component forming carbonate ions and
magnesium hydroxide. This reaction similarly triggers expansion of cracks causing concrete
degradation.
ii. Chemical damage
This entails concrete degradation from chemical exposure and processes such as carbonation,
chloride action, sulfate, decalcification or leaching etc. For instance, Carbonation is a slow and
continuous process developing from the concrete surface to the interior components of concrete.
Carbonation has two notable effects on concrete. It increases the mechanical strength of
concrete, but in the process causes drop in alkalinity hence exposing steel reinforcements to

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corrosion. Reinforcement steel are used to enhance tensile strength of concrete hence their
corrosion and hence exposures significantly affects the overall condition and strength of
concrete.
iii. Physical damage
This mainly results during the processes of de-shuttering and casting of concrete. Also, when
steel shuttering are used without base plates, concrete degradation occurs. The top surface of the
concrete slab is pinched by the steel shuttering from the weight of the preceding slabs under
construction.
For example, evidences of concrete structure showing signs of concrete degradation include
cracks on slabs, beams, and masonry of concrete compositions, re-orientation of building
placement and service, sagging beams and slabs, exposed steel reinforcements in building,
popping out on concrete surfaces, just to mention but a few.
To improve concrete durability, I propose the following ways:
a. Proper mix design: this should strictly adhere with ASTM standards to achieve needed
strength by ensuring correct proportions of cement, sand and coarse aggregates. In
unnatural conditions, suitable concrete admixtures should be included in the mix design.
b. Construction joints: expansion and construction joints should be provided at sufficient
intervals to allow room for expansion or shrinkage under prevailing circumstances and
causes hence protecting concrete degradation.
c. Low permeability: the mix design should ensure low permeability which would otherwise
trigger reactions such as silica-alkali reactions, leaching etc. resulting in concrete
degradation. In environments where exposure to water in poised, adequate water proofing
should be conducted on concrete surfaces to check on permeability.

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Bibliography
George B. (2010) Diagnosis of deterioration in concrete structures: identification of defects,
evaluation and development of remedial action, 2010. Crowthorne, Berkshire, England: Concrete
Society.
Dyer, T. (2014) Concrete durability. Boca Raton, US: CRC Press, Taylor & Francis Group.
Schutter, G. (2013) Damage to concrete structures. Boca Raton, Florida, US: CRC Press.
Scrivener, K. & Young, J. (2011) Mechanisms of chemical degradation of cement-based
systems: proceedings of the Material Research Societys Symposium on Mechanisms of Chemical
Degradation of Cement-based Systems, Boston, USA, 27-30 November 1995. Abingdon, Oxon:
Taylor & Francis.