Building Material

Building material is any material that can be used for construction purposes. It includes concrete, mortar, clay, and timber. Selection is based on budget and the effectiveness and suitability of the materials in the building project.

Image - Pinterest

CONCRETE

Concrete is used extensively in the construction industry in foundations, walls, floors, roofs and windowsills due to its strength and durability. It may be used as a cast in-situ (poured on site) eg. foundations or in factory-produced precast forms eg. bricks and blocks. When poured concrete takes the shape of its mould and at controlled humidity and temperature levels sets (cures) to form a solid mass. The three components of concrete are cement, water, and aggregates (rock or sand) and are mixed in different proportions according to what the resulting mix is to be used for.

Cement is manufactured by burning a mixture of limestone and shale at 1500°C . The resulting clinker is ground to form a powder to which gypsum is added to control how quickly the mix sets. Cement acts as a binding agent when mixed with water and aggregates forming a paste. The paste hardens and binds the aggregates or sand together.

Water chemically reacts with the cement (hydration) and provides workability within the concrete. The amount of water in the mix compared with the amount of cement is called the water/cement ratio. The lower the w/c ratio, the stronger the concrete giving higher strength with less permeability. Water used should be of potable quality and the minimum amount used to eliminate possible evaporation which could affect the durability and strength of the concrete.

Aggregates act as fillers and influence workability. They should be free of impurities and graded according to size. Sand is a fine aggregate with gravel or crushed stone a coarse aggregate. Larger aggregates are stronger but harder to work with, while finer aggregate is less strong but easier to work with.

Properties of Concrete

The most used terms to describe the properties of concrete are workability, strength and durability.

Workability relates to the ease of transportation, placing, compaction and finishing of fresh concrete. It can be affected by water content, temperature, aggregate properties, cement content, mixing time and elapsed time after mixing. Workability can be measured by the Slump Test. This is where a slump or Abrams cone of specific measurements is placed on a non-absorbent surface and filled with concrete in three stages. After each addition, the concrete is tamped 20 times to remove any air. After the third addition the concrete is levelled at the top and the cone removed carefully. The resultant ‘slump’ is measured, and the results are interpreted to evaluate if the mix is fit for purpose.

Images - Wikipedia Slump Test Cone & Measurement

Strength in concrete terms usually relates to compressive strength measured in Newtons per square millimetre, or N/mm2. Concrete is strong in compression but weak in tension, so steel is often used as reinforcement. Strengths range from as low as 20N/mm2 to as high as 65N/mm2 for structural concrete. Concrete strength increases with time where moisture is available. 80% of the strength is reached at an age of 28 days. The standard for foundations is 30N20 or 3N10 where the 20 or 10 relates to the size of the aggregate in mm. Concrete block strength range from 5 to 20N . The strength of concrete can be determined by the cylinder test where force is applied until the concrete fails. The cylinder is filled with concrete in the same way as in the slump test, allowed cure for 28 days and then analysed in a lab.

Durability Concrete can be affected by weathering, chemical attack, abrasion and freeze/thaw attack. It is important that the thickness of concrete covering steel reinforcement (or ‘cover’) is sufficient to prevent the ingress of moisture and air, which may lead to corrosion.

Images Kilsaran

MORTAR

4 & 5 Mortar is used in construction to fill the gaps between the bricks or blocks keeping them both level and plumb. Mortar can also be used for screeds on floors or for

rendering walls or buildings. It is a mixture of aggregate, a binder such as cement or lime, and water and is applied as a paste which then sets hard, providing support and preventing damage from weathering. Different mixes of mortar can be prepared depending on use eg. strength, workability, location and structures being built.

Cement Water Sand

Images: Wikipedia & Wix

Cement acts as the matrix which combines the mix together. Water is required as the catalyst for the hydration of the cement to occur. Hydrated lime is used as a plasticiser for improved workability. Aggregates (either soft or sharp sand) are use as the filler. Soft sand gives a smooth and plastic mortar which is easy to spread when building bricks or blocks. Sharp sand is used for rendering on walls, floor screeds and paving as it allows good drainage when used under paving.

The mixing of mortar may be done by volume batching (mostly used on-site) or by weight batching (usually used in factories). Water is added dependent upon workability requirements.

There are 5 different types of mortar depending on intended use:

1. Cement, Hydrated Lime, Sand Ratio 1:1:5, the standard mix with good workability used on the superstructure of buildings

2. Cement & Sand 1:5, a durable mix used where there is a high moisture content eg. below the damp proof course

3. Cement, Plasticiser & Sand 1:5 used on the sub- and superstructure of buildings

4. Hydraulic Lime & Sand 1:3 used on renovation and preservation work. Its properties help avoid condensation.

5. Trowel-ready mortar, ready mixed and delivered onsite for use in boundary walls & brickwork.

CLAY

Clay forms very slowly as a result of weathering and erosion of rocks. It differs in composition from area to area but is generally composed of finely grained natural rock or soil material sometimes with small quantities of quartz, metal oxides or organic matter. It demonstrates high plasticity when mixed with water until dried when it becomes hard, showing good robustness, stability and durability.

Bricks, roof tiles and pavers may be manufactured from clay, but pavers and roof tiles are usually not used in Ireland due to cost. To manufacture bricks the clay is ground in mills, mixed with water and then moulded, either by hand or machine (hydraulically pressed), to the shape and size of a standard size (215mm x 102.5mm x 65mm). The bricks are then fired at high temperatures yielding hard, durable products with strength ranging from 20 to 100N.

Image Wix, Clay Brick & Mortar

Specs are generally classified by

1. Variety

(a) Commons used in general building work

(b) Facings which gave a decorative finish, and

(c) Engineering with defined specifications for strength, density and moisture.

2. Quality

(a) For internal use only

(b) Ordinary, for external facings and

(c) Engineering, where a durable specification is required

3. Types

(a) Solids – small holes do not exceed 25% of brick

(b) Perforated – Small holes in excess of 25% of brick

(c) Hollow – Large holes exceeding 25%, and

(d) Cellular (Frog) – Holes closed at one end exceeding 20% of brick

TIMBER

Timber is a natural occurring material which can be used to form the entire fabric of the building walls, floors, roofs, windows, doors and foundations. Timber is mainly classified as either hardwood (deciduous eg. oak, maple) or softwood (evergreen eg. pine, cypress) but this categorising does not have a direct bearing on the weight, hardness, or durability of the wood. Heartwood (inner trunk) is more durable, but sapwood (outer trunk) accepts impregnation with preservative more easily.

Images - Wix

Properties of Timber

Timber displays excellent thermal qualities, is resistant to electrical currents, contains acoustic properties and displays tensile strength (can bend under pressure without breaking). Its strength makes it a perfect choice as a heavy-duty building material eg. structural beams. Different species of wood have different properties for weight, moisture content and durability. The weight of wood tissue is approx. 1500kg/m3 but densities vary widely. The moisture content (MC) of timber has a large effect on weight, durability, workability, strength, stability and fungal attack. Durability refers to the resistance to fungal decay (from perishable to extremely durable).

Why should we season timber?

Seasoning timber is the controlled drying of the wood (to ˂20%MC) either using air which can take up to two years or in a kiln can be completed in 10 days. Seasoning improves the workability of the timber, it becomes more stable and increases in strength as it dries. Sapwood always requires seasoning as it is considered perishable whereas heartwood requires less seasoning due to its natural durability. Timber can be treated with preservative which makes it poisonous to fungi and insects, preventing the timber rotting.

References

1 Concrete Network. 2021. Available at: www.concretenetwork.com/concrete.html [Accessed 21.02.2021]

2 Howden Group.2021. Available at: www.howden.com/en-gb/articles/cement/how-is-cement made [Accessed 21.02.2021]

3 Irish Cement Society. 2018. Available at: www.concrete.ie/about-concrete/concrete-properties-testing [Accessed 21.02.2021]

4 The Concrete Centre. Available at: www.sustainableconcrete.org.uk/Sustainable-Concrete/What-is-Concrete/Mortar.aspx [Accessed 24.02.21]

5 Civil Knowledges. 2020. Available at: www.civilknowledges.com/what-is-mortar [Accessed 26.02.2021]

6 Designing Buildings. 2021. Available at: www.designingbuildings.co.uk/wiki/Clay_in_construction [Accessed 26.02.2021]