TM 5-822-7/AFM 88-6, Chap. 8
cient frequency and amplitude to fully consolidate
D-6. Thickness design.
the sample. Some commercially available tables
a. General. The thickness design procedure for
have been found unsuitable without the use of a
RCCP is the same as that used for conventional non-
reinforced concrete pavements with no load transfer
sample surcharge weight. A suggested minimum
amplitude and frequency necessary to consolidate an
considered as outlined in Army TM 5-822-6/AFM
RCC sample without using a surcharge weight is
88-7, chapter 1, and Army TM 5-824-3/AFM 88-6,
0.0625 inch and 60 Hz, respectively.
chapter 3. Beams sawn from RCCP at Fort Stewart,
Fort Hood, and Fort Lewis and tested for flexural
d. Sample fabrication. The strength of an RCC
strength indicate that the actual flexural strength of
mixture is controlled primarily by the water-cement
the pavement is 20 to 50 percent higher than the
ratio and the degree of compaction attained. All
typical strength assumed in design for those
RCCP mixtures placed by the Corps of Engineers to
pavements. This suggests that the thickness design
date have had water-cement ratios ranging from
for compacted RCCP should be modified based upon
0.30 to 0.40. Laboratory strength determinations are
the 28-day strength of beams sawn from a test
made using fabricated flexural, compressive, and
section constructed, using the same aggregate,
splitting tensile strength specimens. Conventional
cement, and construction procedure as planned for
ASTM testing methods cannot be followed when
the entire work. However, until additional perfor-
fabricating these specimens due to the dry consistency
mance records and testing procedures are developed
of the concrete. The procedure being used is to fill
for RCCP, conventional pavement thickness design
cylinder molds in two layers and beam molds in a
will be used.
single layer, and consolidate each layer of concrete
b. Lift thickness. The maximum thickness of a lift
on a vibrating table. Vibration of each layer is
of RCCP is governed by the ability of the pavers to
continued until paste is discernible over the entire
place the RCCP in a smooth and continuous fashion.
surface area. Use of a surcharge weight may be
This maximum uncompacted thickness is usually 10
to 12 inches. The maximum uncompacted thickness
specimens fabricated in the laboratory are to be
can be approximated by multiplying the design
cured according to ASTM C 192.
thickness by 1.25, thus accounting for the reduction
e. Strength results. Test specimens fabricated and
in thickness due to compaction. The minimum
cured in the laboratory generally exhibit higher
thickness of any lift should be 4 inches.
strengths than those cored or sawn from an RCCP.
c. Two-lift construction. If the total uncompacted
This is probably due to the higher unit weights
thickness exceeds the capacity of the paver, the
normally obtained with the fabricated specimens
RCCP should be placed in two or more lifts, thus
and the more efficient laboratory moist curing.
creating a horizontal joint (or horizontal plane
Laboratory test specimens generally have unit
between the layers) in the RCCP. Sufficient bond
weights which are 98 to 99 percent of the theoretical
develops at a fresh horizontal joint in RCCP (top lift
(air-free) weight of the mixture, while core samples
placed within 1 hour of bottom lift) to allow the use of
taken from RCCP normally have unit weights ranging
a monolithic thickness design. If the top lift is not
from 95 to 98 percent of the theoretical weight.
placed within 1 hour of the bottom lift, the thickness
Therefore, fabrication of a companion set of test
should be designed as a rigid overlay of a rigid base
specimens having the lowest relative density allowed
pavement. The surface of the lower lift should be
by the contract specifications should be considered
kept moist and clean until the upper lift is placed,
during the laboratory mixture proportioning studies.
and the upper lift should be placed and compacted
f. ASTM D 558 method. Studies are currently being
within 1 hour of compacting the lower lift to insure
conducted to determine whether a proportioning
that a bond between lifts is formed. In two-lift
method similar to ASTM D 558 is viable for RCC.
construction, the uncompacted thickness of the first
Such a method would produce the optimum moisture
lift should be two-thirds the total uncompacted
content necessary to obtain maximum density for a
height of the RCCP (or the maximum lift thickness
particular set of materials and compaction procedures.
the paver can handle, whichever is smaller). The
Previous tests indicate that the optimum moisture
thinner section in the upper lift aids in creating a
content obtained by Method 100 (CE 55) of MIL-
smoother final surface, and because of the smaller
STD-621 may produce a mixture too wet to allow
volume of material, allows the paver placing the
efficient operation of a vibratory roller.
second lift to move quicker than and follow closer