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[SEAOC] RE: [SEAOC] Durability of Lightweight concrete

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Our experience in researching lightweight concrete durability was similar to 
yours.  The literature on tire-wear durability is inconclusive.  However, 
there appear to have been many successes using lightweight concrete for 
exposed bridge decks, even though many others were built with AC or normal 
weight wearing surfaces.  We were convinced enough to specify lightweight 
concrete with no additional wearing surface (there is a 15 mm integral 
wearing surface assumed for design) for a 690 meter cast-in-place concrete 
box girder bridge over the American River (Folsom, CA) to be bid next March. 
 Caltrans is also planning on using lightweight for the new Benicia- 
Martinez bridge, although I'm not sure if they are using it exposed.

Some questions come to  mind for your case:
1.   Do you know the concrete strength, type of lightweight aggregate 
(natural or manufactured), and if the fine aggregate was also lightweight? 
 These may give some indication of the wear-resistance to be expected.
2.   What is the current condition of the beamway after 30 years?
3.   How much would it cost if it was necessary to overlay it later?

Not knowing the answer to these questions, my feeling from reading the 
literature is that there is no reason to assume that the performance would 
be worse than for a normal weight overlay. It seems to depend heavily on the 
type of aggregate used.

A good place to start if you don't already have it:

FHWA Report No. FHWA/RD-85/045, "Criteria for Designing Lightweight Concrete 
Bridges", August, 1985.

Finally, if you happen to be in Sacramento tomorrow (Sept. 10) there is an 
"International Symposium on Lightweight Concrete Bridges" sponsored by 
Caltrans and Pacific Custom Materials (a lightweight aggregate 
manufacturer).  You could probably get a set of proceedings from:

715 N. Central Ave., Suite 101
Glendale, CA

Tony P.

From: seaoc
To: 'seaoc(--nospam--at)'
Subject: [SEAOC] Durability of Lightweight concrete
Date: Thursday, September 05, 1996 3:56PM

I have a 30 year old lightweight concrete beamway in an amusement park
that was never intended to bear direct vehicle traffic.  The ride that
has now been removed ran on a steel rail bolted to the beamway.  The
proposed vehicle will ride tires directly on the lightweight concrete.

The question is, how durable is lightweight concrete to tire traffic?
The prevailing wisdom from the literature that I have investigated (ACI,
PCA, etc.) is muddled at best.  When durability of lightweight concrete
is discussed, resistance to freeze/thaw cycles is usually all that is
addressed.   At present, I have specified a cement-based overlay on the
wear surface, but this is no small cost.  Any thoughts out there on the
durability of lightweight concrete to tire traffic?  The vehicle is
comparable to a car or truck.  Is it a common practice for bridges that
use lightweight concrete to use it for the wearing surface?  Any good
references that address this question?