Sulphur - Inflitrated Concrete
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 concrete.
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 infiltrated concrete.
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 strength.
Similarly, the 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 test conducted.
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 - Infiltrated concrete
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 place concrete.
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.