Page 250 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

228 CORROSION CONTROL AND PREVENTION

use of inhibitors may increase the expected life of 20–25 years more while compared
to the use of black steel rebar and conventional concrete.

4.9.1.5 Multiple Protection Systems Corrosion inhibitors are used in multi-
ple corrosion protection systems in conjunction with epoxy-coated rebars and
low-permeability concrete, in particular, for marine applications. Epoxy-coated
seven-wire strands are not commonly used for prestressed concrete bridge members.
Corrosion inhibitors are used in place of coated seven-wire strands in the prestressed
highway construction industry.

4.9.1.6 Methods of Controlling Corrosion in New Bridge Construction Methods
based on current practice in research, field performance, and emerging technologies
may be described as follows (16): the preferred primary corrosion protection system is
fusion-bonded epoxy-coated rebars that have been used in 20,000 reinforced-concrete
bridge decks and nearly 100,000 total structures. Epoxy-coated rebar has performed
very well in combating the corrosion-induced deterioration of concrete bridge decks.
This does not perform well in severe marine applications.
With constant updates in the American Association of State Highway and
Transportation Officials (AASHTO) and American Society for Testing and Materials
(ASTM) specifications for epoxy-coated rebar, this corrosion protection system
will continue to improve. The specifications involve all aspects of fabrication of
epoxy-coated rebar. All these will result in improved performance of epoxy-coated
rebar and more durable new concrete structures.
To provide longer service life to the concrete decks of the order of 75–120 years
without the need to repair corrosion-induced concrete damage, a number of solid and
clad corrosion-resistant 304 and 316 stainless steel rebars have been developed. Both
alloys provide excellent corrosion protection but at higher cost. Type 316 stainless
rebar requires more detailed studies.
Epoxy-coated rebar together with calcium nitrite may be a favorable corrosion
protection system especially for marine applications such as piles. The long-term
stability is still not confirmed and research is in progress to identify new inhibitors.
∘
Temperatures such as 38 C and 75% humidity or moisture have been identified
as conditions leading to high corrosion rates for steel in concrete. Use of a low
water-to-cement ratio concrete, use of mineral admixtures, proper selection of
cement type and aggregates contribute to the production of high-performance
concrete with significant corrosion resistance (19).
For the protection of high-strength, seven-wire strands encased in ducts, mix
designs for corrosion-resistant grout for filling the grouts have been developed.
A new rapid method for evaluation of grouts has been developed (24). These
developments led to new grout specification documented by the Post-Tensioning
Institute in 2001.
With the recent collapse of two posttensioned bridges in the United Kingdom
and one in Belgium the impact-echo nondestructive evaluation (NDE) technique
was developed to detect voids in posttensioned ducts. In addition, a complementary
magnetic-based nondestructive technique (NDT) for assessing section loss in