Materials selection for concrete overlays : the final report Page: 19
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If the existing pavement is overlaid with AC layers, these layers must be removed by
milling prior to surface preparation and repair of distresses. Remnants of AC will hinder the
bond between concrete layers and are likely to trigger delaminations, because AC works as a
bond-breaking layer between concrete layers. Complete milling of these layers will ensure that
all surface contaminants such as oil, carbonates, and acids are removed.
Three typical means of surface preparation for BCOs are shotblasting, milling, and sand
blasting. The most efficient method is by means of shotblasting equipment, such as the
SkidabraderTM machine. Unlike cold milling, shotblasting can achieve adequate depth without
causing microcracking. It can remove concrete matrix leaving the CA intact undamaged.
Sandblasting is suitable for small and hard to reach areas. It is not recommended for
large areas because of its uneven removal of surface material. Surface preparation procedures
are listed in Table 2.1.
Table 2.1: Surface preparation procedure [11]
Removal Principle Depth Important advantages Important disadvantages
method behavior action
(mm)
Shotblasting Blasting with steel No (12) No microcracking, dust. Not selective.
shot.
Milling (scari- Longitudinal tracks Yes Suitable for large volume Microcracking is likely,
fying) are introduced by (75) work, good bond if reinforcement may be
rotating metal followed by water damaged; dust development,
lamellas. flushing. noisy; not selective. Newer
machines can cause less
microcracking.
Sandblasting Blasting with No No microcracking. Not selective; leaves
sands. considerable sand.
Scabbling Pneumatically No (6) No microcracking, no Not selective.
driven bits for dust.
impacting the
surface.
Grinding Grinding with No (12) Removes uneven parts. Dust development, not
(planning) rotating lamella. selective.
Flame-cleaning Thermal lance No Effective against pollution The reinforcement may be
and painting, useful in damaged; smoke and gas
industrial and nuclear development; safety
facilities, considerations limit use; not
selective.
Pneumatic (jack) Compressed-air- Yes Simple and flexible use, Microcracking, damages
hammers (chip- operated chipping large ones are effective, reinforcement; poor
ping), hand-held working environment; slow
or boom- production rate; not
mounted selective.
Explosive Controlled blasting Yes Effective for large removal Difficult to limit to solely
blasting using small, volumes, damaged concrete; safety
densely spaced and environmental
blasting charges. regulations limit use; not
selective.19
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Kim, Dong H.; Fowler, David W.; Ferron, Raissa P.; Trevino, Manuel M. & Whitney, David P. Materials selection for concrete overlays : the final report, report, July 2012; Austin, Texas. (https://texashistory.unt.edu/ark:/67531/metapth303706/m1/39/?rotate=270: accessed July 18, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting UNT Libraries Government Documents Department.