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close this bookAppropriate Building Materials: a Catalogue of Potential Solutions (SKAT; 1988; 430 pages)
View the documentPreface
Open this folder and view contentsIntroduction
close this folderFundamental information on building materials
View the documentStone
View the documentEarth, soil, laterite
View the documentSoil stabilizers
View the documentFired clay products
View the documentBinders
View the documentLime
View the documentCement
View the documentPozzolanas
View the documentConcrete
View the documentFerrocement
View the documentFibre and micro concrete
View the documentNatural fibres, grasses, leaves
View the documentBamboo
View the documentTimber
View the documentMetals
View the documentGlass
View the documentPlastics
View the documentSulphur
View the documentWastes
Open this folder and view contentsFundamental information on building elements
Open this folder and view contentsFundamental information on protective measures
Open this folder and view contentsExamples of foundation materials
Open this folder and view contentsExamples of floor materials
Open this folder and view contentsExamples of wall materials
Open this folder and view contentsExamples of roof materials
Open this folder and view contentsExamples of building systems
Open this folder and view contentsAnnexes
 

Sulphur

General

Although there are several very useful applications of sulphur as a building material, the technology is not yet widely known. This is probably because research and development has taken place almost exclusively in Canada and the United States and only few prototype buildings have been constructed in developing countries. However, the increasing supplies of sulphur, mainly from the desulphurization of petroleum and natural gas, are causing disposal problems in some countries, problems that can be solved if sulphur is used extensively as a building material.

Sulphur also occurs naturally in volcanic regions and has since long served as a basic material for the chemical industry, particularly for producing sulphuric acid, a primary material for large-scale industrialization. Sulphur is also used in the production of fertilizers and insecticides.

At normal temperatures, pure sulphur is a yellow crystalline material, which melts at about 119° C and hardens rapidly on cooling. In the molten state it adheres firmly to a wide range of materials rendering them waterproof and resistant to salts and acids. Sulphur can be stored indefinitely and recycled any number of times by heating and recasting.

The use of sulphur also has several limitations which must be recognized. Further research is needed, preferably in sulphur producing developing countries, especially with a view to the use of low-cost additives, development of practical, inexpensive equipment and simple construction methods.

Sulphur products

• Sulphur concrete, comprising elemental sulphur (about 30 % by weight) and coarse and fine inorganic aggregate (about70 %), forming a concrete-like material that can tee moulded and which is impervious to water. It contains neither water nor cement. The powder sulphur and aggregates can be mixed in a conventional mixer equipped with a heater, which raises the temperature of the mix to 140° C in a matter of minutes. Preheating the aggregates to about 180° C and addition of silica flour produces a more homogeneous flowable mixture and more uniform products. The colour can be varied with different aggregates. Sulphur concrete can be cut with a saw and drilled.

• Sulphur coating on weak, flexible and porous materials makes them strong, rigid and waterproof. By dipping, spraying or painting, almost any material can be impregnated with sulphur.

• Sulphur bonding, by using molten sulphur as an adhesive, or applying it externally over non-adhering joints, can produce extremely strong bonds between two components.

• Sulphur foams, produced by introducing small amounts of foaming agents, are light (weighing about 170 kg/m3), rigid, and have excellent thermal resistance, low shrinkage and water absorption.

• Sulphurized asphalts, in which either the aggregate or the asphalt (as used in road and pavement construction) is partially replaced by sulphur, thus raising the viscosity at high temperatures or lowering it at lower temperatures.

• Sulphur-infiltrated concrete, produced by introducing molten sulphur into moist-cured lean concrete, in order to increase its strength and water resistance.

Applications

• Blocks, bricks and tiles of any desired shape mace from sulphur concrete for load-bearing floor and wall constructions. Blocks are most appropriately made hollow and interlocking, facilitating accurate and quick constructions, and the cavities to be filled with reinforced concrete (eg in earthquake regions) or with insulating material (eg in colder climates).

• Impregnation of weak and porous materials (such as thatch roofs; panels of reeds, woven mats, cloth or paper stretched on wooden frames; timber components; and even low-strength concrete) to provide strength and water resistance. For example, a large piece of cloth, stretched on a frame and impregnated with sulphur, forms a bowl shape, which hardens and - when turned upside down - becomes a strong, waterproof dome-shaped panel.

• Rigid walls made by laying bricks or concrete blocks dry and then applying a sulphur coating onto the internal and external surfaces. Strong lintels have also been made by laying hollow concrete blocks in a row and bonding them by applying molten sulphur across the joints on the two vertical outer surfaces.

• Thermal insulation of buildings with sulphur foams, or production of lightweight, non-loadbearing wall and ceiling panels.

• Paving of courtyards and other outdoor surfaces, walkways, etc. with sulfurized asphalts.

• Pipes, cisterns and a variety of precast elements made of sulphur-infiltrated concrete for better chemical resistance, higher mechanical strength and impermeability, despite lower proportion of cement.

Advantages

• Pure elemental sulphur is abundantly available in many regions; can be stored indefinitely and reused any number of times; requires relatively little energy and only simple equipment to melt; adheres to a wide range of materials; has no taste or smell (except when heated or cut with an electric saw) and does not act on the skin; and is a poor heat and electricity conductor.

• Sulphur concrete gains 90 % of its ultimate strength in 6 to 8 hours (normal portland cement requires 30 to 60 days to gain the same strength); it is not attacked by salts (hence unwashed aggregates and even sea sand can be used); it does not require water (of special significance in desert regions, which incidentally also produce large amounts of by-product sulphur from oil refining); it can be cast to produce building components with precise dimensions and sharp edges (especially suitable for the manufacture of interlocking blocks, which can be assembled without the use of mortar or special skills); it has a chemically resistant, non-absorbing, smooth, hard and appealing surface (which is easy to keep clean by merely washing), eliminating the need for plastering or painting; and it retains most of the characteristics of pure elemental sulphur.

• Sulphur coating can considerably increase the strength and prolong the service life of many materials.

• Sulphur surface bonding reduces construction time, saves cement and produces strong, waterproof bonds.

• Sulphur foams have similar thermal insulation characteristics, but higher compressive strengths than conventional rigid foams, such as expanded polyurethane.

• Sulfurized asphalts can be stronger and cheaper than standard paving materials.

• Sulphur-infiltrated concrete requires less cement than concretes of the same strength and impermeability.

Problems

• Sulphur has a low melting point (about 119° C) and ignites at about 245° C. Sulphur combustion is self-sustaining and thus, once ignited, will continue to burn until extinguished. Burning sulphur produces sulphur dioxide, a toxic gas.

• Pure sulphur becomes brittle and powdery (orthorhombic crystalline form) on cooling, making it unsuitable for a variety of applications.

• Sulphur has a much higher coefficient of thermal expansion than portland cement concrete, and sulphur concrete tends to contract on cooling.

• Under humid or wet conditions, reinforcing steel tends to corrode in the presence of sulphur, making sulphur concrete unfit for structural uses.

Remedies

• Sulphur should not be used as a building material where temperatures are likely to exceed 80°C.

• A sulphur fire in an enclosed structure can be smothered by closing all entrances and denying it air; it can also be extinguished with water or sand.

• Apart from avoiding all potential sources of fire (eg cookers, heaters) close to sulphur-based components, a precautionary measure is to add a fire resistant material to the molten sulphur. A suitable material is dicyclopentadiene.

• The tendency of sulphur to become brittle and powdery is overcome by adding a plasticizer which retards the crystallization of sulphur. Dicyclopentadiene was also found to be effective for this purpose, as well as to increase the thermal stability of sulphur concrete.

• Shrinkage of sulphur concrete in precast components (eg hollow blocks) is best overcome by overfilling the mould, and after cooling, sawing off the extra concrete.

• Thermal expansion of sulphur concrete should be taken into account by providing sufficiently wide joints.

• The brittleness and thermal movement of sulphur-based materials can be reduced by fibre reinforcement, but further research is needed on this aspect.

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