Environmental Engineering Reference
In-Depth Information
4.2
Comparison of simulated regolith
and real lunar soil
The simulated regolith Jsc-1 is composed of basal-
tic ash with a typical composition of most terres-
trial basalts (as described previously for vacuolar
basalts from the canary islands). The lunar basalts
and soils from lunar maria, are quite similar to
the simulated regolith in terms of its main com-
pounds. however, the lunar samples have no water
and low contents of some volatile compounds such
as na
2
o. in addition, lunar rocks were formed in
highly reducing environments and contain iron as
Fe
2
+ and Feo (the Fe
2
o
3
was only found as traces
of the mineral hematite in some lunar meteorites,
but not in samples from the space missions).
The minerals found in the majority of simulated
regolith (plagioclase, pyroxene, olivine, ilmenite
and chromite) are also characteristic of soils from
v maria. lunar soil also contains a significant
proportion of crystals produced by the impacts
of micrometeorites (formed under highly reducing
conditions) with a certain amount of microscopic
particles of native iron. By contrast, crystals of
simulated regolith Jsc-1 have a higher content of
plagioclase and metal oxides than the lunar soil,
but do not contain native iron. it should be noted
that the micrometric textures of the lunar aggluti-
nates are complex and may not accurately match
with any terrestrial analogue, so the comparison is
made under macroscopic point of view.
other interesting geotechnical features of simu-
lated lunar regolith compared to the real lunar soil
are:
• Density: for Jsc-1 has a value of 2.9 g/cm
3
,
being in the range of the lunar soil, which gave
values between 2.9 g/cm
3
and 3.5 g/cm
3
.
• internal friction angle: between 25° and 50˚ for
the real lunar soil, while the value obtained for
the simulated regolith is 45˚.
• internal cohesion: varies from 0.26 kPa and
1.8 kPa for lunar soil, while the value obtained
for the simulated regolith is 1.0 kPa.
accordingly, it can be concluded that the
simulated regolith Jsc-1 is a good chemical and
mechanical analog of the real lunar soil. in fact,
it is a material that has already been produced in
large quantities to meet the needs required by sci-
entists and engineers in their investigations.
Table 8.
Physical properties of molten lunar basal.
2.6-2.7
Molten density at 1473°k (g/cm
3
)
solid density (g/cm
3
)
2.9-3.0
Water absorption (%)
0.1
Tensile strength (MPa)
35
compressive strength (MPa)
54
equivalente Mösh hardness
8.5
840
specific heat (J/kg ⋅k)
1400-1600
Melting temperature °k
heat of fusion (J/kg)
4,2 ⋅ 10
5
(±30%)
Thermal conductivity, solid (W/m ⋅k)
0.8
Thermal conductivity, molten
at 1500°k (W/m ⋅ k)
0.4-1.3
surface resistivity (Ω ⋅ m)
10
10
internal resistivity (Ω ⋅ m)
10
9
2300
sonic velocity, molten at 1500°k (m/s)
sonic velocity, solid at 1000 k (m/s)
5700
Basically, the experiment consisted on heating
samples to 1100°c, after pretreatment to try to get
the desired results. initially, the regolith samples
were compacted to reach a density of 2.45 g/cm
3
.
subsequently, the samples were sintered increas-
ing their density to a maximum of 2.68 g/cm
3
. The
results were a few blocks of 13.1 cm long, 5.6 cm
wide and 4.6 cm in height, uniform and cracks-free
(likely, the abundance of crystals on Jsc-1 allowed
an optimal adhesion between grains of the rock).
consequently, it has been demonstrated that with
earth analogues is achievable the use of lunar
basalt as building material.
5
conclUDinG ReMaRks:
aPPlicaTions oF The lUnaR
BasalT FoR “in siTU” BUilDinG
The lunar basalt, because of their abundance, ease
of management and structural strength, is the best
material for the construction of roads, tracks and
even blocks for armour of dwellings and facilities
for the lunar base that require it.
The raw lunar soil could be melted at a tem-
peratures of 1550°k, then to be cooled and sub-
sequently solidify in a hard and resistant material.
Depending on how the cooling is done, the resist-
ance will be different (nasa, 1980):
• Rapid cooling (within minutes): the basalt would
become a liquid crystal polymer substance. it
would be a hard material but slightly brittle,
so cracks may propagate easily. if this option
is selected, it would be necessary to divide the
material into small plates to isolate potential
fractures, allowing easier maintenance.
• slow cooling (several hours): the basalt would
became from a fully liquid state at 1570°k
4.3
Using simulated regolith JSC-1
for brickmaking
There have been several experiments with this
material to check the possibility of sintering in
small blocks or plates for the “in situ” construction
on the Moon (allen et al., 1992).
