Abstract :
Reactive Powder Concrete (RPC) is a special
type of ultra high strength, superplasticized, silica
fume concrete, often fibre-reinforced, with improved
homogeneity because the traditional coarse and fine
aggregate are replaced by fine sand with particle sizes
in the range of 100-400 μm [4-16 thousandths of an
inch]. RPC properties are attractive because compressive
strengths up to 800MPa [116 ksi] have been
recorded, but more typically in excess of 200MPa
[29 ksi]. Flexural strengths up to 141MPa [20.4 ksi]
and fracture energy of 40 kJ/m2[kJ/in.2] have been
reported—the latter achieved when steel or stainless
steel fibres were included in themix (Baché (1998) Proceedings
of the 2nd international conference on superplasticizers
in concrete, Ottawa, pp 35-41; Coppola et al.
L’Industria Ital Cemento 707:112-125 (1996); Blais
and Couture PCI J 44(5):60-71 (1999); Richard and
Cheyrezy (1994) Proceedings of V. Mohan Malhotra
symposium on concrete technology: past, present, and
future (SP 144). American Concrete Institute, Detroit,
pp 507-518; Richard and Cheyrezy Cement Concrete
Res 25(7):1501-1511 (1995)). Ductal , a commercial
RPC, has a compressive strength of approximately150MPa [22 ksi] with metallic or organic fibres. All
tests described here were performed on 40 × 40 ×
160mm [1.6×1.6×6.3 in.] (Width (b) × Depth (d) ×
length (L)) prisms with Poly Vinyl Alcohol
(PVA) fibres. Ductal is a family of RPC and microdefect-
free concretes containing micro silica, silica
fume, cement, Quartz sand, superplasticizer, and PVA
fibres.Mechanical and fracture parameters were investigated
using four point bending. Low and high cyclic
fatigue tests were conducted in three stages, starting
from low to high strain cycles. Cracks generated by
cyclic fatigue testsweremonitored periodically in order
to evaluate the rate of crack propagation. Cracks were
also investigated using a high magnification microscope.
Three pairs of specimens were tested, notched
and un-notched to evaluate fracture parameters. Four
point bending was used again because determination
of the J-Integral (JIC) requires the application of pure
bending over a portion of the beam. Load was applied
at the third points over a span (S) of 120mm [4.7 in.],
providing a span to depth ratio (S/d) of 3.0. Specimens
were notched using a 1mm [0.04 in.] thick diamond
saw. The crack tip generated was circular and the crack
length (s) was approximately 10mm [0.4 in.]. Tests on
the notched specimens included measurement of the
crack mouth opening displacement (CMOD). Closedloop
testing was developed using a feed back signal
from the (CMOD) clip gauge attached to the notched
specimens and from strain gauges attached to the unnotched
specimens. The weight (w) of each specimen
was obtained prior to testing. Fracture parameters werecalculated from the load-deflection curves obtained
from the notched and un-notched specimens
