strength must be at least 170 kPa (3550 lb/ft2). In
The above materials were first evaluated for
frost-heave susceptibility, then for thaw-weaken-
freezethaw areas, the weight loss has to be less
ing. Since laboratory tests were not conducted to
than 14% (ASTM D560).
determine properties, we assumed some of the
material properties from information in the litera-
P-306 econocrete subbase course
ture.
P-306 econocrete subbase course is a mixture of
subbase quality aggregate, cement, and water. The
aggregate can be crushed or not. The limits of the
Frost heave
Chamberlain (1981), after a thorough review of
subbase material gradation is shown in Figure 1h.
existing frost-susceptibility index tests used in the
The cement specified is ASTM C150 Type I. Admix-
U.S. and abroad, decided that the criterion devel-
tures that are pozzolanic (fly ash), air-entraining
oped by Casagrande in the early 1930s was the
(not less than 4% and not more than 9%), or water
best indicator of frost-susceptibility. Based on
reducing can be used. The compressive strength
field tests, Casagrande (1931) found that the
after 7 and 28 days must at least be 3445 and 5167
kPa (500 and 750 lb/in.2), respectively. An upper
amount of material in the soil finer than 0.02 mm
(0.78 103 in.) was a fairly good indicator of
limit of 8268 kPa (1200 lb/in.2) is recommended
since compressive strengths greater than that may
frost-susceptibility in terms of rate of heaving.
induce cracking in the overlying pavement. A mini-
Based on this, the Corps of Engineers (COE) has
mum amount of cement of 119 kg/m3 (7.43 lb/ft3) is
developed a frost-susceptibility classification as
also specified. In freezethaw areas, the maximum
shown in Table 3. In most cases for granular mate-
weight loss should not exceed 14% and the air con-
rials, if the amount of material finer than 0.02 mm
tent should be between 6 and 10% ( 2%).
is kept at less than 3%, the material could be clas-
Table 3. Corps of Engineers (COE) frost-susceptibility classification.
Percentage finer
Typical soil types
Frost
than 0.02 mm
under Unified Soil
group
Soil
by weight
Classification System
NFS*
(a) Gravel
01.5
GW, GP
Crushed stone
Crushed rock
(b) Sands
03
SW, SP
PFS†
(a) Gravel
1.53
GW, GP
Crushed stone
Crushed rock
(b) Sands
310
SW, SP
S1
Gravely soils
36
GW, GP, GW-GM,
GP-GM
S2
Sandy soils
36
SW, SP, SW-SM,
SP-SM
F1
Gravely soils
610
GM, GW-GM, GP-GM
F2
(a) Gravely soils
1020
GM, GW-GM, GP-GM
(b) Sands
615
SM, SW-SM, SP-SM
F3
(a) Gravely soils
over 20
GM, GC
(b) Sands, except
over 15
very fine silty sands
SM, SC
(c) Clays, PI > 12
--
CL, CH
F4
(a) Silts
--
ML, MH
(b) Very fine
silty sands
Over 15
SM
(c) Clays, PI < 12
--
CL, CLML
(d) Varved clays and
other fine-grained,
CL, ML and SM,
banded sediments
--
CL, CH and ML,
CL, CH, ML and SM
* Non-frost-susceptible.
† Possibly frost-susceptible, requires lab test to determine frost design soil classifi-
cation.
7
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