Warping of Terrace Pavers at the U.S. Capitol Building.
Warping of Terrace Pavers at the U.S. Capitol Building.
(1329 K)
Ferraris, C. F.; Stutzman, P. E.; Clifton, J. R.
NISTIR 5847; 25 p. May 1996.
Available from:
National Technical Information Service
Order number: PB96-193651
Keywords:
building technology; aggregates; alkali-silica reaction;
cements; concretes; construction materials; expansion;
pavers; warping
Abstract:
The terraces of the U.S. Capitol are covered with
cement-based pavers designed to emulate the granite
pavers used elsewhere on the Capitol grounds. The
pavers were warped after three years of service. These
pavers are composed of two layers; an upper, decorative
white-cement-based mortar with crushed micaceous quartz
aggregate supported by a base of conventional concrete.
Field inspection and laboratory testing indicates the
warping is probably due to the high cement content,
environmental exposure conditions, and possibly
differences in hydraulic length changes of two layers
comprising the pavers. A cement content of nearly twice
that found in typical concretes, leads to higher levels
of moisture-driven swelling and shrinkage. This coupled
with the different exposure environments of the two
materials, i.e., higher relative humidity under the
paver and faster drying on the top of the paver, and the
differential hydraulic length changes of the two
materials used in the pavers leads to warping.
Alkali-silica reactivity (ASR) tests indicate that the
base layer aggregate is marginally reactive and the
upper layer aggregate is non-reactive. While some
reaction products were observed in the base layer,
expansion due to alkali-silica reaction was not thought
to be a significant cause of the warping of the pavers.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899