Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 46
46
corrosion rates, and corresponding probability and reliabil- Update Experience with Different
ity analyses. These issues are related to reliability of metal Reinforced Fills
loss modeling, quantification of the effect of construction
An example of the experience gained from collecting and
practice on performance, and understanding the cost bene-
analyzing data relates to the use of reinforced fills that may or
fits of using different materials. All of these are important
may not meet AASHTO specifications for electrochemical
components of asset management. For example, the data-
properties. The database was divided into two primary groups
base can be used to
including data from reinforced fill conforming to AASHTO
criteria and from reinforced fill not conforming to AASHTO
· Study the mean and variance of corrosion rates for data
criteria. The AASHTO corrosion model was applied to esti-
sets grouped according to different climate, site conditions,
mate reinforcement corrosion rates and to compare them to
and reinforced fill conditions;
measured corrosion rates. The observations below were made
· Quantify performance for marginal reinforced fills; and
from the existing database. These observations may be updated
· Evaluate the performance of different materials (e.g., steel
as more data become available.
vs. zinc, other forms of metallization, and the use of poly-
meric coatings).
· For reinforced fills conforming to AASHTO criteria, the
AASHTO corrosion model overestimates steel corrosion
These applications will lead to better estimates of service life
rates for 98% of the data. It should be noted that most of
and can help to quantity the benefits of selecting higher quality
the data in this group are associated with reinforced fills
backfill for construction or the costs associated with using mar-
that meet AASHTO requirements by a wide margin.
ginal quality fill. Performance data can also facilitate evaluation · For reinforced fills conforming to AASHTO criteria, marine
of alternative materials, including use of galvanized versus plain environments have minor to no effect on measured cor-
steel, or other corrosion protection measures that may include rosion rates of galvanized reinforcements, but marine
epoxy or polymer coatings. Practices that may lead to poor per- environments accelerate corrosion rates of plain steel
formance may also be identified and quantified, including the reinforcements.
impact that poorly maintained drainage inlets may have on · For reinforced fills that do not satisfy AASHTO criteria,
service life, or the effect of fill contamination during service. The marine environments are associated with relatively high
database needs to be continuously updated and should include corrosion rates.
performance data from sites where good practice has been · Reinforced fills that do not meet AASHTO criteria (i.e., soil
followed as well as from sites with questionable conditions. resistivity values < 3,000 -cm and pH values < 5) can
significantly affect steel corrosion rates, which tend to dra-
Maintenance, Rehabilitation, matically increase beyond rates estimated by the AASHTO
and Replacement corrosion model.
· Based on available data, organics content, chlorides, sul-
Issues that can address future needs for maintenance, reha- fates, and relatively high values of pH have much less effect
bilitation, retrofit, or replacement include on measured corrosion than do relatively low resistivity
and low pH.
· Spatial variations of element condition and corrosion rate · Review of the latest research information confirms the safety
(e.g., top vs. bottom of wall), of the electrochemical requirements for fill and associated
· Special areas that may deserve increased maintenance (e.g., metal loss rates in the current AASHTO standards.
in proximity to drainage inlets), and
· Effects of different climates, use of deicing agents, and so
forth.
Recommendations for
Future Research
Improved knowledge of spatial variations and special prob- NCHRP Project 24-28 assessed and improved the predictive
lems can lead to improved allocation of resources. For exam- capabilities of existing computational models for corrosion
ple, in some cases, extended service life may be best achieved potential, metal loss, and service life of metal-reinforced systems
by retrofitting areas surrounding drainage inlets, or the ben- used in retaining walls and highway cuts and fills. Methodology
efits of improved maintenance of drainage inlets may be real- was developed that incorporates the improved predictive mod-
ized in terms of increased service life. In areas where deicing els into an LRFD approach for the design of metal-reinforced
salts are used, corrosion monitoring can demonstrate the need systems. Recommended additions and revisions were prepared
to maintain pavements, improve drainage, or install and to incorporate the improved models and methodology in the
maintain impervious barriers. AASHTO (2009) LRFD Bridge Design Specifications.
