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The Portland Cement Association (PCA) maintains a database
on many roller-compacted concrete (RCC) water resource projects
completed in the United States. The database includes in-place unit
costs for RCC. This information maybe useful in estimating costs
on proposed projects. To assist in estimating costs, PCA has developed
cost curves based on actual unit bid prices for the two most common
uses for RCC in water resources applications: gravity dams and dam
rehabilitation projects in which RCC is used for spillways, overtopping
protection, and as a concrete buttress.
Gravity Dams
 Figure
I plots cost data from actual RCC gravity dam projects. The
RCC unit prices include all material costs (i.e., aggregate, cement,
pozzolans, water and admixtures); plus mixing, conveying, placing,
formwork, cleanup and curing. Also included are labor and equipment
costs to mix and place the RCC. Project mobilization costs are not
included.
The cement and pozzolan content for each project varies widely. To minimize the effect of this variable, unit costs for each project were adjusted to assume 150 pcy of cement and 90 pcy of fly ash or simply 195 pcy of cement with no fly ash. When using Figure I to develop preliminary cost estimates, the unit price derived from the curve should be adjusted to reflect the actual cementitious content of the particular project.
Rehabilitation and Spillways
 Figure
2 provides a baseline for projects where RCC is used in the
rehabilitation of existing dams and for new project spillways. The
curve was developed from actual projects in which RCC was used for
emergency spillways, overtopping protection, and the buttressing
of existing concrete and masonry dams. Unlike the gravity dam analysis,
no efforts were made to adjust project unit prices to a baseline
cementitious quantity. Typically, projects represented in Figure
2 generally have cement contents between 250-325 pcy.
 The
cost curves serve as a baseline but the specifics of each project
must be taken into account and appropriate adjustments made to the
unit cost to reflect the uniqueness of the project. A variety of
factors can influence the unit price of RCC as can be seen from
the scatter of the data points in the figures. These factors include
contractor's experience, availability and size of access and staging
areas, contractor's flexibility in choosing conveyance and mixing
equipment, the extent of RCC forming, the length of the allowable
RCC placement window before special methods have to be employed
for temperature control, and the availability of the aggregate source,
to name a few.
In developing the two cost curves, each project's bid unit price
was adjusted from the year it was bid to the current year using
a construction cost index developed by the U. S. Bureau of Reclamation.
The index accounts for inflation from the time the project was bid
to the year shown on the figure. For gravity dams, PCA used the
USBR's cost factors for concrete dams. For the rehabilitation and
spillway projects, an average was taken of cost factors for concrete
dams and embankment dams. Averaging the cost factors was thought
to provide a better representation of the type of work performed
for dam rehabilitation and spillway construction.
Latest Cost of In-Place RCC on Recent Dam
Projects
Bid tabulations from several RCC dam projects completed after 2003
show that the unit cost of in-place RCC approximately ranges from
$75 to $142 per yd3 (from $98 to $186 per m3).
This unit cost includes cost of materials, mixing, transporting,
placing and curing. It is based on reported bid prices of successful
bidders. For detailed cost information on
eight recent projects, click here.
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