Many
different methods are used in order to predict the life span of a concrete
structure. The test methods do not per se measure the life span of the
concrete but measure the concrete's ability to prevent ingress of undesirable
elements. Most of the test methods give results at 28 days which will
vary depending upon the binder content, binder type, and water content
in the mix. The following results are indicative and comparative of what
can be expected when incorporating Super-Pozz®
into concrete. |
Permeability
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While strength
development is an important criterion for concrete performance, it fails
to give an insight into durability. Durability was assessed by means of
a series of tests designed to measure the density and impermeability of
the binder paste microstructure. Water permeability and absorption as
well as chloride permeability were measured. Probably the most important
consideration when using Super-Pozz®, is it ability
to improve the durability of concrete by decreasing the water demand without
adversely affecting the workability. |
Water
Absorption
In this
test the cubes are initially water cured for 28 days, following which
cores are drilled out and oven dried for 72 hours before once again being
immersed in water. The increase in mass resulting from the immersion is
expressed as a percentage of the dry specimen. Higher water absorption
figures are indicative of permeable concrete.
As can be seen from
the results below, concrete specimens containing Super-Pozz®
have the lowest absorption values. This is indicative of a denser microstructure.
The decrease in values from 28 to 56 days reflects an increase in density
as the result of the refinement of the pore structure.
Chloride attack
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Concrete exposed
to marine environments is very susceptible to chloride ion ingress into
the concrete which in turn corrodes the steel reinforcing. This expansion
of the reinforcing causes the concrete to crack and break off. Various
laboratory tests methods measure the chloride ion conductivity through
a concrete specimen. Super-Pozz® contains a high percentage
alumina which is known to bind the chloride ions in concrete. The in-situ
performance of a concrete containing Super-Pozz® is
therefore better than expected when comparing to the laboratory results. |
Sulphate attack
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Concrete exposed
to aggressive soil and sewage normally fail due to the presence of sulphate
in the relevant solution. The sulphate in turn forms expansive ettringite
crystals causing the concrete to crack. Laboratory tests measure the overall
expansion of concrete specimens submersed in MgSO3
and NaSO3 solution. These results are often used
to demonstrate the resilience of a concrete exposed to these environments.
The resilience and
durability of concrete containing mineral additives like fly ash is well
documented and tested. It is therefore expected that concrete containing
Super-Pozz® to be comparatively durable.
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