In this article we will discuss about:- 1. Production of Sulphur Infiltrated Concrete (SIC) 2. Uses of Sulphur Infiltrated Concrete (SIC) 3. Durability.
Production of Sulphur Infiltrated Concrete (SIC):
Sulphur infiltrated concrete was developed as an economical alternative to polymer impregnated concrete (PIC) to be used for higher strength and durable precast elements. Sulphur is considerably cheaper than polymers and the technique of impregnation is more simple. These factors result in cost benefits.
The concrete to be infiltrated should be produced using normal aggregates with aggregate/cement ratios between 3:1 to 5:1. The water/cement ratio should be high between 0.7 and 0.8. The size of coarse aggregate should be 10 mm and below. It should be well graded. The fine aggregate should be of good quality. Sulphur also should be of high purity of 99.9%.
Infiltration Procedure:
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Procedure A:
After moist curing of elements for 24 hours at about 23°C, they are dried at 121°C to 125°C for another 24 hours. After drying, the specimens arc immersed in molten sulphur at 121°C under vacuum for 3 hours. The specimens are removed from container, wiped clean of sulphur and allowed to cool to room temperature for one hour and weighed to determine the weight of sulphur infiltrated in concrete.
The period of immersion depends upon the type and size of the member. For lean concrete the period of immersion is 2 hours under vacuum. After this period the vacuum is released and the specimens are soaked for an additional half an hour in the molten sulphur under atmospheric pressure. After this period the elements are removed from the molten sulphur wiped clean and allowed to cool. It is weighed to determine the weight of sulphur infiltrated in concrete.
In case of low water/cement ratio concretes which are relatively dense, external pressure is applied after the release of vacuum to force sulphur into the concrete. The above procedure may be modified to suit the individual job conditions.
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However following points should be kept in mind:
1. For concretes with a water/cement ratio of the order 0.65, the one day old elements must be handled with care to avoid damage.
2. The drying temperature should be kept as high as possible, but not exceeding 150°C, as the higher temperature may damage the gel structure of the young hydrated cement paste. The period of drying will depend on the type and size of the element.
3. The period of vacuum (evacuation time) appears to be less critical than the immersion time in molten sulphur after evacuation. For concretes with water/cement ratio of about 0.55 increased immersion times is essential to achieve full infiltration.
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Procedures B:
In this case, the dried concrete specimen is placed in an air tight container and subjected to vacuum pressure of 2 mm of mercury for 2 hours. After releasing 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, cooled to room temperature for about an hour. The specimen is weighed and the weight of sulphur impregnated in concrete is determined.
The specimens made by both the procedures are tested in compression and tension by splitting method.
From the results it has been observed that:
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1. The compressive strength of sulphur infiltrated specimens (cubes and cylinders) is enormously higher than the strength of plain moist cured specimens. It is found that with water/cement ratio 0.7, the increase in compressive strength of cubes prepared by procedure B is found about 7 times higher. With the use of 0.8 water/cement ratio, cubes prepared by procedure B gave about 10 time’s higher strength.
2. Similarly specimens prepared by procedure B gave more than 4 times increase in splitting tensile strength.
3. The elastic properties of sulphur infiltrated concrete improved by 100%.
4. Sulphur infiltrated concrete showed a very high resistance to freezing and thawing. The sulphur infiltrated concrete was found in good condition even after 1230 cycles when prepared by procedure B, while plain moist cured concrete disintegrated after about 40 cycles. Concrete made with procedure A, deteriorated after about 480 cycles.
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The improvement in the strength of sulphur impregnated concrete may be due to the fact that randomly distributed pores in the body of the concrete have regions of stress concentration when loaded externally. The impregnation of these porous bodies by some material would modify the stress concentration. The extent of modification will depend how well the impregnant has penetrated into the smaller pores. The test results of specimens prepared by both procedures are shown below in Table 23.2.
Details of Mix:
Water/cement ratio = 0.70
Aggregate/cement ratio = 8.5:1
Ratio of C.A. to F.A. = 1:1
Uses of Sulphur Infiltrated Concrete (SIC):
The techniques of production of this concrete are simple, inexpensive and effective. The attainment of strength in about 2 days makes this process all the more attractive.
As the high strength of concrete can be achieved in a very short interval of time, the sulphur infiltrated concrete can be used for the manufacture of precast roofing elements, fencing posts, sewer pipes and railway sleepers. It can also be used in industry, where high corrosion resistant concrete is required.
However this method cannot be employed conveniently to cast in-situ concrete. Further it has been observed that the sulphur infiltrated pre-cast concrete units are cheaper than normal concrete. The added cost of sulphur and process may be offset by the savings in the concrete.
Durability of Sulphur Infiltrated Concrete (SIC):
1. The performance of the sulphur infiltrated concrete generally has been found satisfactory against freezing and thawing, sea water attack, wetting and drying conditions.
2. It is more durable than conventional concrete in high concentrations of H2SO4 and HCl.
3. The strength properties are not significantly affected when exposed to short term temperatures upto 100°C. At these temperatures it shows certain amount of ductility before failure.
4. The increase in abrasion resistance depends on the sulphur loading in the concrete. The sulphur filling of the pores of the concrete provides an un-interrupted path for heat flow resulting in increased thermal conductivity over that of normal dry concrete.
5. This concrete provides a corrosive protection cover to the embedded steel. The sulphur loading required for a given corrosive protection depends upon the water/cement ratio used in the concrete. Higher the water/cement ratio, higher the sulphur loading required. The minimum sulphur loading for 0.7 water/cement ratio is 10% and for 0.4 water/cement ratio 5% sulphur loading is sufficient.
6. When left in stagnant water for a long time, slight leaching of sulphur has been observed and the concrete showed undesirable expansion followed by cracks.