To ensure a long service life in
harsh environments, wood requires
preservative treatment.
on a designated length of pile. There is also a table that specifies
minimum tip size. Timber piles in the United States and Canada
classify this butt measurement by a Class. Sizes of Class A (14-inch
butt) and Class B (12-inch butt) piles are for designers that prefer
those designations. The American Wood Council publishes design
values for timber piles conforming to ASTM D25 titled, “National
Design Specification for Wood Construction.” These strength values
are used in determining the bearing capacity, lateral capacity
and allowable driving stress of a pile.
To ensure a long service life in harsh environments, wood
requires preservative treatment. Standards are written by the
American Wood Protection Association (AWPA), a group of consumers,
scientists and wood preserving companies to ensure
consistency of treatment for all variations of preservatives, wood
species and treatment processes. AWPA has published these
standards for over 110 years. A Use Category System for all wood
products is provided in the front of their Book of Standards. The
guide describes minimum treatment levels for various exposure
conditions to ensure long service life for all treated wood products.
The Use Category System Standard U1 is used by specifiers to
determine the appropriate treatment for a particular service condition.
There are five major Use Categories depending on service
conditions where the wood will be used. Timber piles are found
in two of the Use Categories. Foundation piles and piles used on
QA/QC – TIMBER
land or in fresh water are listed in UC4C, Commodity Specification
E: Round Timber Piling. Piling used in saltwater environments are
listed in UC5, Commodity Specification G: Marine Applications.
Timber piles used in marine applications are further divided into
subcategories UC5A, UC5B and UC5C. These subcategories are
based on geographical regions and specify the amount of preservative
needed to provide optimum protection. The Use Category
subdivisions for timber piles in marine applications list the prescribed
treatments that are approved by the EPA and the retention
levels for the common preservatives used. These preservatives are
Creosote and Creosote solutions, Chromated Copper Arsenate
(CCA) and Ammoniacal Copper Zinc Arsenate (ACZA).
When using specifications for round timber piles, a sample
specification may be written, such as: Southern Pine/Douglas Fir
Piles shall conform to ASTM D25, unused, clean peeled, uniformly
tapered, one piece from butt to tip. Specify butt or tip diameters
from tables listed in the ASTM D25 standard, including the pile
length. The preservative portion could be addressed as follows:
Pressure treatment shall be in accordance with the following
AWPA Use Category Standard: UC4C, UC5A, UC5B or UC5C.
Handling, storage, and field fabrication, including the treatment of
cut ends or penetrations, shall be in accordance with AWPA M4.
To properly preservative treat timber piles, moisture must first
be removed from the cellular structure (lumens) of the wood so
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