Civil Engineering Reference
In-Depth Information
Table 18-2. Examples of Lightweight Insulating Concrete Mixtures
28-day compressive
Ratio: portland
Ovendry
Type I
strength, MPa (psi),
cement to aggregate
density,
portland cement,
Water-cement
150 x 300-mm
Type of concrete
by volume
kg/m
3
(pcf)
kg/m
3
(Ib/yd
3
)
ratio, by mass
(6 x 12-in.) cylinders
1:4
480 to 608 (30 to 38)
362 (610)
0.94
2.75 (400)
1:5
416 to 576 (26 to 36)
306 (516)
1.12
2.24 (325)
Perlite*
1:6
352 to 545 (22 to 34)
245 (414)
1.24
1.52 (220)
1:8
320 to 512 (20 to 32)
234 (395)
1.72
1.38 (200)
1:4
496 to 593 (31 to 37)
380 (640)
0.98
2.07 (300)
1:5
448 to 496 (28 to 31)
295 (498)
1.30
1.17 (170)
Vermiculite*
1:6
368 to 464 (23 to 29)
245 (414)
1.60
0.90 (130)
1:8
320 to 336 (20 to 21)
178 (300)
2.08
0.55 (80)
Polystyrene:**
sand:
0 kg/m
3
(0 lb/yd
3
)
1:3.4
545 (34)
‡
445 (750)
0.40
2.24 (325)
73 kg/m
3
(124 lb/yd
3
)
1:3.1
625 (39)
‡
445 (750)
0.40
2.76 (400)
154 kg/m
3
(261 lb/yd
3
)
1:2.9
725 (44)
‡
445 (750)
0.40
3.28 (475)
200 kg/m
3
(338 lb/yd
3
)
1:2.5
769 (48)
‡
474 (800)
0.40
3.79 (550)
Cellular*
—
625 (39)
524 (884)
0.57
2.41 (350)
(neat cement)
—
545 (34)
468 (790)
0.56
1.45 (210)
—
448 (28)
396 (668)
0.57
0.90 (130)
—
368 (23)
317 (535)
0.65
0.34 (50)
Cellular
†
(sanded)
††
1:1
929 (58)
429 (724)
0.40
3.17 (460)
1:2
1250 (78)
373 (630)
0.41
5.66 (820)
1:3
1602 (100)
360 (602)
0.51
15.10 (2190)
*
Reichard (1971)
.
** Source:
Hanna (1978)
. The mix also included air entrainment and a water-reducing agent.
† Source:
Gustaferro (1970)
.
†† Dry-rodded sand with a bulk density of 1600 kg/m
3
(100 pcf).
‡ Air-dry density at 28 days, 50% relative humidity.
air voids of 20% to 35%, and a cement content of about 280
kg per cubic meter (470 lb per cubic yard).
preferred sequence is to first introduce the required
amount of water into the mixer, then add the cement, air-
entraining or foaming agent, aggregate, preformed foam,
and any other ingredients.
Excessive mixing and handling should be avoided
because they tend to break up aggregate particles, thereby
changing density and consistency. Segregation is not usually
a problem (though it could be for Group II) because of the
relatively large amounts of entrained air in these mixtures.
Pumping is the most common method of placement,
but other methods can be used. Finishing operations
should be kept to a minimum; smoothing with a darby or
bullfloat is usually sufficient. Placement of insulating
concretes should be done by workers experienced with
these special concretes.
Periodic wet-density tests (ASTM C 138 or AASHTO
T 121) at the jobsite can be performed to check the unifor-
mity of the concrete. Variations in density generally
should not exceed plus or minus 32 kg/m
3
(2 pcf). A close
approximation of the ovendry density can be determined
from the freshly mixed density.
Workability
Because of their high air content, lightweight concretes
weighing less than 800 kg/m
3
(50 pcf) generally have
excellent workability. Slumps of up to 250 mm (10 in.) usu-
ally are satisfactory for Group I and Group III concretes;
appearance of the mix, however, may be a more reliable
indication of consistency. Cellular concretes are handled
as liquids; they are poured or pumped into place without
further consolidation.
Mixing and Placing
All concrete should be mechanically mixed to produce a
uniform distribution of materials of proper consistency
and required density. In batch-mixing operations, various
sequences can be used for introducing the ingredients; the
