Construction 101: Building Materials

Constructing a building sounds complicated and difficult. Physically and mentally exhausting because you need to know the standards and regulations concerning building a safe and habitable building that can withstand environmental factors (e.g. storms and floods). It is very overwhelming, especially for beginners who haven’t worked in the field.

In this blog post, the fundamentals or the basic things you need to know about the materials used in construction such as concrete, mortar, clay and timber will be discussed.

Concrete

Concrete is the most commonly used material in a construction site. It can be used as a cast in situ or a pre-cast.

A cast in situ are concrete poured on site while the pre-cast are made in a factory. Both can be used as foundation, walls, floors, building frames, roofs, window sills and beams.

The components of concrete are as follows:

• Cement - serves as the matrix or glue in the mixture made from burned limestone under extremely high temperature. If not enough cement is in the mixture, low strength and shrinkage will develop (Le Bow, 2018).

• Water - acts as the catalyst. Too much water will weaken the concrete while too little water will lessen workability (Illinois University, 2020).

• Aggregates - acts as fillers and influences workability. Rounded, small aggregates will mean high workability due to more water but is less strong than larger, coarser aggregates which are thicker and stronger but harder to work with (Neil Sullivan and Sons, 2020).

These components are mixed in certain proportions depending on the purpose or use of concrete.

The quality of concrete produced can be judged according to its characteristics such as workability and strength. Workability relates to the ease of placing, transportation and finishing of concrete and is affected by many factors such as the proportion of water, temperature and the aggregates.

Another important characteristic of concrete is strength. The strength of a concrete is measured in Newton/mm2 (e.g. 42 N/mm2) and it refers specifically to its compressive strength. Concrete has weaker tension (refer to diagram below).

Diagram from Concrete Decor.

There are 2 common tests that can be done to measure the workability and strength of concrete.

Slump Test - performed to asses workability and it gives a warning that concrete may have been significantly overdosed with water, thereby alerting the contractor that the strength may be lower and the durability characteristics may be decreased (Irish Concrete Society, 2002).

It is performed by using an inverted cone in a flat surface and 3 equal parts of fresh concrete is poured inside the cone then poked 25 times. This repeated on every layer of concrete poured into the cone to remove air bubbles and void. The slump test can be influenced by several factors like temperature, cement and water ratio and also the grading of the aggregates.

Cube/Cylinder Test - measures strength of concrete. It is performed by pouring 3 equal parts of freshly mixed concrete into a cylinder and poking it 25 times or tapping the side of the cylinder before pouring the next layer to make sure there is no void or air bubbles. It is also important to make sure that the top is smooth. any void or air bubble will compromise the strength of the concrete cube. After finishing the top and making sure there are no voids, close the cap and the sample is then cured for 28 days then sent to the laboratory.

Picture from Leighton Broadcasting, 2020

Mortar

Mortar is another material commonly used in construction. It acts as a paste that binds bricks together and provide support to make the whole structure stronger against weathering and other environmental factors. It is used to form screeds and also for rendering or plastering building and walls to protect against weathering and improve appearance.

Components of mortar

Mortar is composed of the cement, water, aggregates and hydrated lime in specific proportions depending on use or purpose.

• Cement or hydraulic lime acts as the matrix that binds all the components together.

• Water acts as the catalyst to activate other components like the cement and lime and helps improve workability.

• Aggregates are the fillers and aids in mobility, strength, water retention and resistance to rain. It can either be soft sand which is usually used when building bricks and blocks while the sharp sand is used for rendering walls, floor screeds and pavements because of its improve drainage.

• Hydrated lime/ plasticizer is used to improve workability.

Characteristics of mortar

The characteristics of mortar includes strength, resistance to rain penetration, mobility and water retention (CivilBlog, 2020).

Strength

Mortar needs to be strong by binding the blocks and provide support by spreading even weight.

Resistance to rain penetration

Mortar used for plastering should protect the brick joints and should not let water in.

Mobility/workability

This refers to the workability of mortar and its consistency how easy it is to spread. It is dependent on the proportions of its components.

Water retention

Mortar with good water retention would allow easier workability and improve binding of components. It also can't develop a strong bond with the brick surfaces if there is not enough water.

Clay

Clay is one of the materials used in building the frame of a building that is naturally- occurring. It is sticky, mouldable and is used to make bricks that are used as pavers, floor tiles and roof.

Components of clay

Clay are made from small articles of eroded/weathered rocks which settled and built up overtime. Particles of clay looks like 'stacks of plaques', also know as mica.

Characteristics of clay

The unique characteristic of clay is called 'plasticity'. It is the ability of clay to form and retain a shape even after outside force is removed. According to Elsevier's Applied Clay Science, mineralogical composition, particle size distribution, organic substances and additives can affect the plasticity of clays. This characteristic enables clay to be moulded into shape and use it, not just in construction but also in pottery and ceramics.

Timber

Timber is another naturally- occurring material with inherent defects that are used in construction. It is used as a frame to form the entire building, walls, floors, widows, doors and foundations. Timber can either be from hardwood or softwood based on their botanical classification and not correlated to the durability, hardness and weight of wood.

Hardwood

- deciduous trees

- hard covering on seed

- angiosperms (able to flower)

- examples are oak, beech and maple trees

Softwood

- evergreen

- absence of hard covering on seeds

- gymnosperms (not able to produce flowers)

-examples are pine, conifers and cypress

Picture from Zukzik

Heartwood and Sapwood

Heartwood is the inner portion of the trunk. It is darker in colour compared to sapwood because it is composed of older, dead cells and is no longer involved in physiological processes (i.e. transportation and storage of food). It provides support to the whole tree . Timber from the heartwood are more durable compared to timber from sapwood.

Sapwood, on the other hand, is the outer, younger layer of cells in the trunk. It is involved in transport and storage of food and water. It is composed of living cells and water, therefore, it is prone to fungal attacks which decreases its durability. However, preservatives are applied or drying is done to increase durability when used as timber.

Benefits of seasoned timber

Seasoned timber means controlled drying of timber either using air, which takes longer up to 2 years or kiln, which is faster, usually up to days. Seasoning is required for sapwood while heartwood requires less seasoning or not as often due to its natural durability but, depending on where it is going to be used, it may require seasoning. The benefits of seasoning timber are explained below.

Increase durability

Durability increases when moisture decreases. Moisture content of above 20% increases susceptibility to fungal attacks and rot.

Enhances workability

Dry wood is easier to cut and adheres easily when glue is applied.

Stabilizes and prevents moisture release and absorption.

Timber is naturally 'hygroscopic'. It absorbs and release moisture depending on the moisture content of its surroundings. Dry timber inhibits this and makes the timber more stable.

Increases strength

Drier timber is more durable and strong due to less than 20% water content.

References

Illinois University, 2020. Concrete. [Online] Available at: http://matse1.matse.illinoisedu/concrete/prin.html [Accessed 2020].

Irish Concrete Society, 2002. Irish Concrete Society Seminar. [Online] Available at: http://concrete.ie/wp-content/uploads/2018/10/BackToBasicsHandoutApril15th2002.pdf [Accessed 24 October 2020].

Le Bow, C. J., 2018. Effect of Cement Content on Concrete Performance. [Online] Available at: https://scholarworks.uark.edu/cgi/viewcontent.cgi?article=4553&context=etd [Accessed 21 October 2020].

Neil Sullivan and Sons, 2020. The Role of Aggregates in Concrete. [Online] Available at: https://www.neilsullivanandsons.co.uk/news/role-aggregates-concrete/ [Accessed 24 October 2020].

https://blog.leightonbroadcasting.com/blog/an-intro-to-bricks-mortar-and-the-importance-of-consistency-in-advertising-part-1-of-3