New types of composites have been produced by the
recently developed techniques of impregnating porous materials like concrete
with sulphur. Sulphur impregnation has shown great improvement in strength.
Physical properties have been found to improve by several hundred per cent and
large improvements in water impermeability and resistance to corrosion gave
also been achieved.
In the past, some attempts have been
made to use sulphur as a binding material instead of cement. Sulphur is heated
to bring it not molten condition to which condition to which coarse and fine
aggregates are poured and mixed together
. On cooling, this mixture gave
fairly good strength, exhibited acid resistance and also other chemical
resistance, but it proved to be costlier than ordinary cement concrete.
Recently, use of sulphur was made
to impregnate lean porous concrete to improve its strength and other useful
properties considerably. In this method, the quantity of sulphur used is also
comparatively less and thereby the processes is made economical. It is reported
that compressive strength of about 100 MPa could be achieved in about 2 days
time. The following procedures have been reported in making sulphur-infiltrated
A coarse aggregate of size 10 mm
and below, natural, well graded, fine aggregate and commercial sulphur of
purity 99.9 per cent are used. A large number of trail mixes are made to
determine the best mix proportions. A water/cement ratio of 0.7 or over has
been adopted in all the trials. A number of 5 cm cubes, 7.5 cm x 15 cm
cylinders and also 10 mm x 20 cylinders are cast from each batch of concrete.
These samples are stored under wet cover for 24 hours, after which they are
removed from moulds and the densities determined. Control specimens are moist
cured at 240C for 26 hours.
Two procedures are
adopted. In procedure 'A' after 24 hours of moist curing, the specimen is dried
in heating cabinet for 24 hours at 1210C. Then the specimen are
placed in a contained of molten sulphur at 1210C for 3 hours.
Specimens are removed from the container, wiped clean of sulphur and cooled to
room temperature for one hour and weighed to determine the weight of sulphur
In procedure 'B' the
dried concrete specimen is placed in an airtight container and subjected
to vacuum pressure of 2mm mercury for two hours. After removing the vacuum, the
specimens are soaked in the molten sulphur at atmospheric pressure for another
half an hour. The specimen is taken out, wiped clean and cooled to room
temperature in about one hour. The specimen is wighed and the weight of
sulphur-impregnated concrete is determined.
The specimens made adopting
procedure A and B tested by compression and splitting tension tests. It is seen
that the compression strength of sulphur-infiltrated cubes and cylinders are
enormously greater than the strength of plain moist cured specimen. It is found
that when water/cement ratio of 0.7 is adopted an achievement of about 7 fold
increase in the strength of the test cube when procedure B is adopted and
five-fold increase in strength when procedure A is adopted was obtained. When
water/cement ratio 0.8 is adopted, procedure B gave about a tenfold increase in
sulphur-infiltrated concrete showed more than four times increase in splitting
tensile strength when procedure B was adopted.
It was also found that the
elastic properties of sulphur-infiltrated concrete have been generally improved
100 per cent and also sulphur-infiltrated specimen showed a very high
resistance to freezing and thawing. When the moist cured concrete was
disintegrated after about 40 cycles, the sulphur impregnated concrete was found
to be in fairly good condition, even after 1230 cycles, when procedure b was
adopted and the sample deteriorated after 480 cycles when the sample was made
by procedure A. table 12.8 and table 12.9 show the typical values of strength
The improvement in strength test
attributed to the fact that porous bodies having randomly distributed pores
have regions of stress concentration when loaded externally. The impregnation
of a porous body by some material would modify these stress concentrations. The
extent of modification will depend on how well the impregnant has penetrated
the smaller pores.
Application of Sulphur -
The sulphur-infiltration can be
employed in the precast industry. This method of achieving high strength can be
used in the manufacture of pre-cast roofing elements, fencing posts. Sewer
pipes, and railway sleepers, sulphur-infiltrated concrete should find
considerable use in industrial situations. Where high corrosion resistant
concrete is required. This method cannot be conveniently applied to cats-in
Preliminary studies have
indicated that sulphur-infiltrated precast concrete units are cheaper than
commercial concrete. The added cost of sulphur and process should be offset by
considerable savings in concrete.
The techniques are simple,
effective and inexpensive. The tremendous strength gained in pressure
application, where in immersion accompanied by evacuation may also offset the
extra cost. The attainment of strength in about two days time makes this process
all the more attractive.