Civil Engineering Reference
In-Depth Information
cracking than conventional concrete (
Grube and Rickert
2001
). Research indicates greater tensile creep for SCC,
resulting in a reduced tendency to crack (
Bickley and
Mitchell 2001
). The use of fly ash as a filler seems to be
advantageous compared to limestone filler; it results in
higher strength and higher chloride resistance (
Bouzoubaa
and Lachemi 2001
and
Ludwig and others 2001
).
The production of SCC is more expensive than reg-
ular concrete and it is difficult to keep SCC in the desired
consistency over a long period of time. However, con-
struction time is shorter and production of SCC is envi-
ronmentally friendly (no noise, no vibration).
Furthermore, SCC produces a good surface finish. These
advantages make SCC particularly interesting for use in
precasting plants. SCC has been successfully used in a
number of rehabilitation projects in Canada (
Bickley and
Mitchell 2001
).
REACTIVE-POWDER CONCRETE
Reactive-powder concrete (RPC) was first patented by a
French construction company in 1994. It is characterized
by high strength and very low porosity, which is obtained
by optimized particle packing and low water content.
The properties of RPC are achieved by: (1) eliminating
the coarse aggregates; just very fine powders are used
such as sand, crushed quartz, and silica fume, all with par-
ticle sizes between 0.02 and 300 µm; (2) optimizing the
grain size distribution to densify the mixture; (3) post-set
heat-treatment to improve the microstructure; (4) addition
of steel and synthetic fibers (about 2% by volume); and
(5) use of superplasticizers to decrease the water to cement
ratio—usually to less than 0.2—while improving the rhe-
ology of the paste. See Fig. 17-8 for a typical fresh RPC.
The compressive strength of reactive-powder con-
crete is typically around 200 MPa (29,000 psi), but can be
produced with compressive strengths up to 810 MPa
(118,000 psi) (
Semioli 2001
). However, the low compara-
tive tensile strength requires prestressing reinforcement in
Fig. 17-8. Freshly-mixed reactive-powder concrete.
severe structural service. Table 17-6 compares hardened
concrete properties of RPC with those of an 80-MPa
(11,600-psi) concrete.
RPC has found some applications in pedestrian
bridges (Fig. 17-9) (
Bickley and Mitchell 2001
and
Semioli
2001
). Also, the low porosity of RPC gives excellent dura-
bility and transport properties, which makes it a suitable
material for the storage of nuclear waste (
Matte and
Moranville 1999
). A low-heat type of reactive-powder
concrete has been developed to meet needs for mass con-
crete pours for nuclear reactor foundation mats and
underground containment of nuclear wastes (
Gray and
Shelton 1998
).
Table 17-6. Typical Mechanical Properties of Reactive Powder Concrete (RPC)
Compared to an 80-MPa Concrete (
Perry 1998
)
Property
Unit
80 MPa
RPC
Compressive strength
MPa (psi)
80 (11,600)
200 (29,000)
Flexural strength
MPa (psi)
7 (1000)
40 (5800)
Tensile strength
MPa (psi)
8 (1160)
Modulus of Elasticity
GPa (psi)
40 (5.8 x 10
6
)
60 (8.7 x 10
6
)
Fracture Toughness
10
3
J/m
2
<1
30
Freeze-thaw, ASTM C 666
RDF
90
100
Carbonation depth: 36 days in CO
2
mm
2
0
Abrasion
10
-12
m
2
/s
275
1.2
