Engineersdaily | Free Engineering Database

Masonry column is a structural element which is one of the main load bearing element in a masonry structure. Process of reinforced and unreinforced masonry column construction is discussed.

Usually, the column construction is carried out by concrete to order to accommodate all the axial and compression forces coming over it under severe load action. Constructing a masonry column is the conversion of the masonry structure into a complete load bearing structure.

Mainly the column constructed by masonry can be reinforced or unreinforced to bring similar behavior to that of a complete concrete column. Different Ideas and concept behind masonry column design and construction are discussed below.

Features of Brick Masonry Columns

The construction of brick columns over concrete columns helps in increasing the architectural beauty. The constructed brick columns can either be round, rectangle or square or elliptical in cross-section. These can be constructed to the needful height. These columns can act as corner pillars, porch columns, boundary gate pillars or free-standing columns.

Fig.1. Brick Masonry Column

The construction of brick columns is fast and easy with less tools and labor compared with the concrete column construction. When compared with R.C.C columns, the brick column construction is more economical in nature.

Process of Construction of a Brick Column

As mentioned above, the bricks columns can be constructed either reinforced or unreinforced based on the load-bearing capacity required. The construction process of a brick column is summarized below:

Unreinforced Brick Column Construction

1. Preparing Layout on the Ground
Initially, the place and the center of the pillar or the column must be located on the ground by a temporary marking with a rod. This marking will help in supporting the vertical alignment and the horizontal alignment within the adjacent pillars.

2. Excavation and Foundation
The excavation is performed for constructing the ground support. The thickness of the excavation is based on the thickness of the foundation and the type of the masonry construction.

If there is no reinforcement to be placed on the masonry, a simple concrete bed of suitable mix is poured into the excavated area. The rod that is used as a marker of center is projected outside as shown in figure-2.

Fig.2. The Rod representing the center of the column projected after laying the concrete mix for foundation

3. Brickwork for Masonry Column 

Once the foundation layer is dried, the brickwork is started. The first-class bricks with a cement mortar of 1:4 ratio is used. This is sufficient to transfer the loads to the foundation safely.

The laying of the bricks must be done only after wetting them by dipping it in water. Certain brick column layer requires damp proof layer, for severe moisture conditions.

The brick is laid vertically upwards by maintaining the verticality and the horizontal alignment with the help of a plumb bob and compass.

Fig.3. Laying of Bricks over the Concrete Foundation

4. Curing Works

 Properly curing the brickworks for 7 to 10 days is required based on the construction.

5. Plastering, Finishing and Painting
Most of the brick column construction would give a good appearance without plastering. But if required, it can be plastered and finished. If necessary they can be painted.

Reinforced Brick Columns

The columns can be constructed by brick masonry by incorporating reinforcement into the same. This process of placing reinforcement in brick masonry will help in the increase in the load bearing capacity of the column.

As this type of construction have a requirement of placement of reinforcement bars unlike the case of concrete design. Special grooved bricks are employed that will have the provision for the placement of the reinforcement.

The figure-4 below shows the construction details of the reinforced brick column. The cavity space through which the reinforcement is passed through is filled with grout/mortar that makes the whole unit monolithic.

Fig.4. Plan and Cross-Sectional View of a Reinforced Brick Column

As shown in the figure, special cavities are intentionally made during the brick manufacturer for the placement of the reinforcement. Every fourth layer is provided with a steel plate as shown in the figure-1.

These will have a thickness of 6 mm. The vertical reinforcement that is placed through the masonry is fixed at the bottom concrete foundation block.

The main application of reinforced masonry is for the construction of the retaining walls, lintels, load-bearing columns, the walls constructed on the soils that are subjected to more settlement. All these structures incorporate columns within it that too is constructed with brick masonry.

Although most masonry surfaces will be colonised by various organisms, damage is usually restricted to porous stone and is usually associated with atmospheric pollution. The main pollutant today is sulphur dioxide which dissolves in rainwater to produce sulphurous acid and reacts with the calcium carbonate of limestones to form calcium sulphite. However, sulphite is never found on limestones, but only sulphate which is produced by much more aggressive sulphuric acid. Various chemical explanations have been given for this oxidation from sulphite to sulphate, such as ultra-violet radiation, but it is a fact that sulphate deposits are always associated with the presence of sulphating bacteria, particularly Thiobacillus species. In areas where coal fires are still used extensively and in some industrial areas, nitrous oxide pollution also occurs which should give nitrous acid and nitrites on limestones, but only nitrates are actually found, indicating oxidation to the more aggressive nitric acid. In these circumstances nitrating bacteria, particularly Nitrobacter species, are always found.
 

Urban areas appear to be cleaner since the introduction of the Clean Air Act, but this is only because particulate emissions have been reduced from industrial chimneys and there has been a progressive decline in most areas in the use of coal for domestic heating. Unfortunately sulphur dioxide pollution has become steadily worse, partly through the increasing use of less expensive heavy oil for heating large commercial and industrial premises as this fuel has a relatively high sulphur content, but also partly through a feature of the Clean Air Act which limits only emission concentrations rather than amounts; if an operator is emitting excessive sulphur dioxide concentrations these can be easily reduced by injecting air into the flue, but the total emissions of sulphur dioxide remain unchanged.

Image courtesy: Historic environment Scotland Slime producing algae may result in slippery surfaces.

Sulphate formed from sulphur dioxide in this way is a source of crystallisation damage, but damage is not confined to limestones. On mortar the sulphate in urban areas may be sufficient to react with the tricalcium aluminate in ordinary Portland cement to cause the expansion and cohesion failure usually known as sulphate attack. However, deterioration problems attributable to bacteria are not confined to urban areas. In rural areas ammonia generated by bacteria from urine in stables and byres can be absorbed on stone walls or asbestos-cement roofs where it is converted by Nitrosomonas species to nitrites and then by Nitrobacter species to nitrates, frequently causing spalling damage.

Bacteria are not the only organisms which colonise damp masonry surfaces. If the surfaces are warm with sufficient light, algae will develop in the water film on the surface, typically producing a bright green coloration, although sometimes dark green, brown and pink colorations occur. Algae often colonise a surface within one or two hours of rainfall, but the algal coloration disappears just as rapidly as the surface dries. Many of the algae are killed by drying but sufficient remain to redevelop and multiply when dampness returns. The humus accumulating on the masonry surface from dead algae and other sources eventually allows mosses, liverworts, grasses and even trees to develop, their root systems often causing serious damage. Organic deposits on the surface also encourage fungi to develop, such as Cladosporium, Phoma, Alternaria and Aureobasidium species; some species are associated particularly with the high nitrogen levels that develop on masonry contaminated by bird droppings.

Serious masonry deterioration is sometimes associated with growth of lichenised fungi or lichens, symbionts of algae growing within fungi, usually Ascomycetes. The fungal hyphae penetrate deeply into stone, exploring fractures but also generating organic acids such as oxalic acid. Oxalates are formed in carbonaceous stones which are usually deposited in or near the thallus or surface growth; eventually these accumulations of phosphates can kill the thallus, leaving a lichen ‘fossil’ of calcium oxalate on the surface of the stone which is sometimes mistaken for lichen growth; repeated applications of biocide sometimes fail to control lichen growth because the growth is, in fact, a dead calcium oxalate fossil formed in this way. If the calcium oxalate is deposited just below the surface, densification can occur which is similar in texture to the calcium sulphate densification that can occur on limestones in urban atmospheres, causing similar spalling damage to the surface of the stone, particularly if it is also microporous and subject to frost or salt crystallisation damage. Where lichens grow on roofs, the oxalic and other lichen acids can cause severe damage to lead, copper, zinc and aluminium roof coverings and gutters; these acids can even cause etching on glass and apparently resistant stones, such as granites.

There are basically three types of lichen, classified according to the shape of the thallus. In the crustose lichens the thallus forms a flat crust on the surface of the stone, the diameter of the thallus giving an accurate indication of the age of the growth; the diameter of the largest growths in millimetres will indicate approximately the years since the stone was installed, a useful feature for identifying original and replacement stones in old masonry. The crustose lichens cause densification of the stone surface on limestones and sandstones, the stone within the centre of the thallus often spalling away to leave bare stone which is then rapidly colonised by the growth. Sensitive species cannot develop in polluted atmospheres, but resistant species become very active in the absence of competition, particularly on limestone, cast stone and concrete surfaces on which acid pollutants are neutralised; Lecanora and Candelariella species are particularly common in these circumstances. Crustose lichens vary greatly in size from minute growths within pores to enormous plates 300mm (12") or more across.

Foliose lichens have thalli like leaves or scales projecting as a group from a point of attachment to the stone. Fruticose lichens also originate from a point in this way but their thalli are branched. Foliose and fruticose lichens are not so common on buildings, except in exposed and relatively unpolluted areas on western coasts, conditions that actually encourage the development of many different lichens. Particular species tend to be associated with particular conditions. Lecanora and Candelariella have previously been mentioned as species which tolerate pollution, particularly when growing on acid neutralising substrates such as limestone, carbonaceous sandstone, asbestos-cement tiles, render and concrete. Calaplaca species are also commonly found on limestones in reasonably unpolluted conditions, whilst Tecidia and Rhizocarpa species are more often found on sandstones.

It will be appreciated from these comments that identification of lichen growths can often indicate both the nature of the substrate on which it is developing and the pollution to which it is subject. Very heavy lichen growth on limestone headstones in a cemetery was found to be causing continuous and rapid stone erosion and spalling damage, each sequence of spalling removing the lichen thallus layer with a thin layer of attached stone, thus exposing a fresh stone surface with lettering still engraved in it but with the detail becoming blurred. Identification of the lichen suggest that it was a species which particularly favoured surfaces with a high nitrogen content and which was usually associated with contamination through bird droppings, although none were present on the headstones and all surfaces were virtually identically affected. The explanation for the abnormal growth was pollution through dust discharges from a neighbouring fertiliser factory.

This abnormally heavy lichen growth was associated with Portland limestone headstones, but adjacent memorials constructed in French Euville limestone with a rather different texture developed instead a heavy coating of black slime fungus. Slime fungi are strange organisms which form a heavy gelatinous coating over the stone in which algae are trapped, giving the coating a colour characteristic of the algae involved. Slime fungi can develop externally or internally on building materials. Green, brown or red slime fungi commonly develop on masonry surfaces in churches in humid areas where the periodic heating results in excessive condensation; this is a common problem in churches in Cornwall.