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MC Magazine |
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Testing
for Leaks
What makes an “Engineer’s
review of documents” a feasible alternative to physically
testing precast concrete products for leaks at joints?
By Gary K. Munkelt,
P.E.
Gary Munkelt is a consulting
engineer with Gary K. Munkelt & Associates in North Wales,
Pa. Contact him at gkm2001@verizon.net.
Machine tooling for
making joints
Precast concrete manufacturers are competitive because they
make the same product over and over again. Steel forms are
used to make the product because many hundreds of pieces can
be produced with the same form. The steel pallets used to
form the joints are machined to tight tolerances that provide
products with consistent dimensions and fit.
A review of the dimensions of the pallet
and the resulting joint is not necessary. Confidence (that
a watertight joint is possible) is gained by knowing that
the precaster uses machined steel pallets to make joints in
precast products.
Quality control procedures
For several decades, the precast community has disciplined
itself to continually improve its products. Quality control
programs have been established at many precast plants. The
most widely recognized quality standard in the precast industry,
however, is the NPCA Plant Certification Program. The program
includes an annual inspection by an independent engineering
firm. It is intended to make engineers who must approve products
feel confident that their jobs will contain products of high
quality. Those precast plants that have gained “certified
plant” status have demonstrated:
- They have established an effective quality
control program, which applies not only to their products
but also to materials in the product.
- Record keeping is in order.
- Procedures are reviewed annually by
an unbiased policing group indicating that QC practices
are continually being followed (as opposed to being started
and then forgotten).
There are many precast plants capable of
manufacturing quality products that do not have “certified
plant” status. Those precasters can prove good quality
control practices by submitting documents describing their
procedures and record keeping systems. The “Engineer
of Record” responsible for final operations can feel
comfortable that the products from quality control-oriented
producers should be leak proof when installed properly. An
effective field inspection program can then be a substitute
for expensive physical testing of all units installed.
Effective sealant
materials
Concrete against concrete does not provide watertightness.
A flexible material must be inserted into the joint to prevent
migration of water from one side of the joint to the other.
The sealant needs to remain flexible during the life of the
structure. Two materials are popular today:
- Rubber gaskets with a profile to fit
into special grooves in a machined joint. The rubber stays
flexible and the groove keeps the gasket at a specific location
to effectively prevent water movement.
- Flexible joint sealants manufactured
to meet the requirements of ASTM Specification C 990. These
materials come in preformed coils, caulking gun cartridges
or trowelable grade. They adhere to the concrete and remain
flexible for the life of the joint.
Preformed coils are popular because they
are easy to apply and avoid waste. The simplicity of installing
these materials can give the reviewing engineer confidence
that this material will provide a watertight joint.
This technical information is available
on the NPCA Web site at www.precast.org under Precasters Notebook.
NPCA members may visit the Web site’s Members Only section
to view the Precasters Notebook library.
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