Students will be able to do the following after this module:

  • Learners will be able to identify the pros and cons of using concrete in structural designs, where it is necessary and why it is a popular building material.
  • Learners will be able to identify the sustainability and life cycle analysis aspects of using concrete.

Introduction of Concrete

Concrete is found in almost every civil engineering project, its ease of use and durability make it a popular choice. Concrete is a mixture of materials to create a thick paste-like consistency. The below diagram shows the relative amounts of materials used to make it.

Image Source: The Construction Specifier, found here

Its most basic form is aggregates, cement and water. The addition of supplementary cementitious materials (SCM’s) such as slag cement and fly ash is to help enhance the hydration reactions to strengthen hardened concrete properties [13]. Similarly, the admixtures are used to enhance specific properties such as workability, early or final strength, and durability [14]. All these ingredients are mixed together and then ready for use. It is important to remember that concrete sets with time so when in transportation it needs to be continually moving until it reaches its destination and can be placed into the desired form.

Image source: NRMCA, found here

Material Testing 

Since concrete is mixed on request it is important to be quality checking the batches to ensure they meet code requirements. This is done using a slump test, air content test, and compressive strength testing. 

Slump Test

Slump is performed to evaluate the consistency of the concrete. This is done because if the mixture is too wet or too dry this will impact the workability and the strength of the concrete [15]. The video below shows how a slump test is performed.

Air Content Test

This test checks the amount of air entrained in the concrete, essentially how much air is in the mixture. Generally, this is done when the concrete will be used in locations/climates where frost-related damage can occur. There needs to be enough air void space that any water that gets in is allowed to expand when freezing and thaw and phase out without damaging the hardened concrete [16]. This is where admixtures like an air-entraining admixture can be used to ensure there is a tolerable about of void space. The following video further explains this and shows how a test for air content is conducted.

Compressive Strength Test 

Lastly, compressive strength is one of the most important criteria when evaluating concrete quality. This is done when the concrete batch is made, additional cylinders are cast and then will be kept to test at different time intervals (usually at 7 and 28 days) to ensure the strength is developing correctly [17]. Again, the below video explains the testing process.

Concrete Building Pros and Cons

The concrete used in building systems is reinforced, typically with steel rebar. This is because concrete on its own is very strong in compression (compaction) but does not have adequate tensile (pulling) strength, so the rebar is added to make up for this. Like any building material, the following sections will go over the pros and cons of using concrete [18][19].

Pros

  • Very strong and durable with human and equipment traffic and weather conditions.
  • Fire resistant.  
  • Long-lasting and low maintenance.
  • Can be used in many places of the building: flooring, walls, etc.
  • Energy-efficient – Concrete acts as a good insulator and will help regulate temperatures.

Cons

  • Concrete does not have tensile strength, and needs the addition of rebar to achieve adequate strength.
  • Concrete is very heavy relative to its strength.
  • Requires continual testing and monitoring to ensure proper curing, if cured improperly will need to be redone.
  • Requires professional installation for buildings.

Environmental Impacts

While concrete is a widely used and good building material, it is important to also evaluate the environmental impacts of materials. The concrete industry accounts for 8% of the total global emissions, producing 4 billion tonnes of carbon dioxide (CO2) annually [20].

Contributing factors

  • Production requires a significant amount of energy for the extraction and processing of raw materials, such as limestone, clay, and sand. This process contributes to the overall environmental footprint through the use of machinery and equipment. 
  • Cement production is a significant source of CO2 emissions. The process of converting limestone into cement releases CO2 as a byproduct
  • Concrete can not be recycled therefore demolition activities generate substantial amounts of waste.  
  • Since large amounts of concrete can not be made on-site they require special large rotating concrete trucks to be transported from the plant to site.

Each of the above factors contributes to greenhouse gas emissions which has a negative impact on climate change. Read the following article to learn more about the impacts of concrete and some solutions that are being pursued to reduce emissions.

https://psci.princeton.edu/tips/2020/11/3/cement-and-concrete-the-environmental-impact

Test Your Learning!

Module Quiz