THE ROLLER-COMPACTED CONCRETE GRAVITY DAM 175
- the development of rapid continuous construction techniques based
on the use of special concretes.
Neither of the first two approaches is capable of offering other than a
token reduction in cost. The third option offers the greatest potential
through financial benefits associated with a shortening of construction
period by up to 35% combined with a lower-cost variant of concrete.
The concept of dam construction using roller-compacted concrete
(RCC), first developed in the 1970s, is based primarily on approach 3.
Several variants of RCC have now been developed and offer the prospect
of significantly faster and cheaper construction, particularly for large
gravity dams.
3.7.2. Alternatives in roller-compacted concreteResearch has resulted in the emergence of three principal approaches to
developing RCCs. In the first, RCC is conceived as a low-cost fill material,
offering the maximum possible economy consistent with satisfactory
strength and durability and suitability to continuous construction tech-
niques, i.e. compaction by roller. An example of this is provided by rolled
dry lean concrete (RDLC) (Moffat, 1973; Moffat and Price, 1978). The
second approach, developed in Japan, is closer to conventional lean heart-
ing concretes. It is confusingly identified as the rolled-concrete dam, or
RCD, concept of RCC. The third approach to RCC is the concept of a
dense, high-paste content material, and is exemplified by high PFA
content concrete (Dunstan, 1981). Variants of RCC are the subject of
continuing development, particularly in the USA, Japan, China and South
Africa.
Two distinct approaches to the design of an RCC dam have
developed. In the traditional or concrete technology approach, RCCs of
the high-paste and RCD types are employed to build what is in all import-
ant respects a conventional gravity dam. The more radical ‘geotechnical’
approach is based upon optimizing the design profile to construction in a
lean RCC such as RDLC. In this approach the concrete is handled as an
earthfill, and compacted at or near its optimum moisture content in thin
layers. The logical extension of this approach is to draw upon embank-
ment dam design principles in developing an optimum profile. The dam
following this approach is therefore optimized for construction using a
lower strength and relatively permeable RCC gravity profile in conjunc-
tion with a horizontally slipformed high-quality upstream concrete mem-
brane. A profile for an RDLC dam constructed on this principle is
illustrated in Fig. 3.22(a). An equivalent high-paste RCC profile is shown
in Fig. 3.22(b).