Civil Engineering Reference
In-Depth Information
5
3. Low water-cementing materials ratio (0.20 to 0.45 by
mass)
4. Higher freshly mixed concrete temperature
5. Higher curing temperature
6. Chemical admixtures
7. Silica fume (or other supplementary cementing mate-
rials)
8. Steam or autoclave curing
9. Insulation to retain heat of hydration
10. Special rapid hardening cements.
High-early-strength concrete is used for prestressed
concrete to allow for early stressing; precast concrete for
rapid production of elements; high-speed cast-in-place
construction; rapid form reuse; cold-weather construction;
rapid repair of pavements to reduce traffic downtime;
fast-track paving; and several other uses.
In fast-track paving, use of high-early-strength mix-
tures allows traffic to open within a few hours after con-
crete is placed. An example of a fast-track concrete
mixture used for a bonded concrete highway overlay con-
sisted of 380 kg (640 lb) of Type III cement, 42 kg (70 lb) of
Type C fly ash, 6
1
⁄
2
% air, a water reducer, and a water-to-
cementing materials ratio of 0.4. Strength data for this 40-
mm (1
1
⁄
2
-in.) slump concrete are given in Table 17-4. Figs.
17-2 and 17-3 illustrate early strength development of con-
cretes designed to open to traffic within 4 hours after
placement. Fig. 17-4 illustrates the benefits of blanket
curing to develop early strength for patching or fast-track
applications.
When designing early-strength mixtures, strength
development is not the only criteria that should be evalu-
ated; durability, early stiffening, autogenous shrinkage,
drying shrinkage, temperature rise, and other properties
also should be evaluated for compatibility with the
project. Special curing procedures, such as fogging, may
be needed to control plastic shrinkage cracking.
700
600
4
500
3
400
300
2
200
1
100
0
0
3 hours
4 hours
28 days
Time
Fig. 17-2. Strength development of a high-early strength
concrete mixture using 390 kg/m
3
(657 lb/yd
3
) of rapid
hardening cement, 676 kg/m
3
(1140 lb/yd
3
) of sand, 1115
kg/m
3
(1879 lb/yd
3
) of 25 mm (1 in.) nominal max. size
coarse aggregate, a water to cement ratio of 0.46, a slump
of 100 to 200 mm (4 to 8 in.), and a plasticizer and retarder.
Initial set was at one hour (
Pyle 2001
).
7
1000
Type III
6
800
Type II/III
5
600
4
3
400
2
200
1
0
0
3 hours
6 hours
7 days
Time
Fig. 17-3. Strength development of high-early strength
concrete mixtures made with 504 to 528 kg/m
3
(850 to 890
lb/yd
3
) of Type III or Type II/III cement, a nominal maximum
size coarse aggregate of 25 mm (1 in.), a water to cement
ratio of 0.30, a plasticizer, a hydration control admixture,
and an accelerator. Initial set was at one hour (
Pyle 2001
).
Table 17-4. Strength Data for Fast-Track Bonded Overlay
Compressive strength,
Flexural strength,
Bond strength,
Age
MPa (psi)
MPa (psi)
MPa (psi)
4 hours
1.7 (252)
0.9 (126)
0.9 (120)
6 hours
7.0 (1020)
2.0 (287)
1.1 (160)
8 hours
13.0 (1883)
2.7 (393)
1.4 (200)
12 hours
17.6 (2546)
3.4 (494)
1.6 (225)
18 hours
20.1 (2920)
4.0 (574)
1.7 (250)
24 hours
23.9 (3467)
4.2 (604)
2.1 (302)
7 days
34.2 (4960)
5.0 (722)
2.1 (309)
14 days
36.5 (5295)
5.7 (825)
2.3 (328)
28 days
40.7 (5900)
5.7 (830)
2.5 (359)
Adapted from
Knutson and Riley 1987
