Concrete is a necessary and very useful material for construction work.
It has been critical in structural engineering throughout history – from the Great Pyramids of Giza to the structures of Ancient Rome to Gothic Architecture of the 18th century.
While technology and materials have advanced since it was first developed, concrete continues to be one of the most widespread materials used throughout the world to build cities, roads, bridges etc.
Despite its ubiquity – we’re rarely more than a few feet from concrete these days – there are many complexities when it comes to concrete, in part due to it many applications (from skyscrapers to roadside kerbs).
What is concrete made from?
Concrete is a stone-like product that is created by mixing binding material (cement, flyash or lime) along with an aggregate (sand, gravel, stone, brick chips, etc.), water and admixtures. It is critical to apply the correct portions of each product in the mix as per the initial design and predetermined outcomes from the laboratory.
It’s strength and quality are dependent on the consistency of all the individual products and the mixing proportions. Because of this, on-site monitoring of the wet concrete is undertaken with samples taken and then tested once the concrete has hardened. After many days this process confirms the strength and durability.
Cement is a key constituent of concrete. The most common is known as Portland cement – obtained by heating limestone and clay or other silicate mixtures at high temperatures (>1500°C) in a rotating kiln, then grinding them into a fine powder. It is used for general construction purposes where special properties are not required. It has great resistance to cracking and shrinkage but dependent on the density and final strength of the concrete has less resistance to chemical attacks.
Portland cement cures not through drying or evaporation of the water, but through a chemical reaction called hydration. This means it is important that adequate levels of water are used to ensure the concrete reaches its full strength. Too much water could reduce the strength and durability of the concrete therefore water reducing chemicals are included in the mixed concrete.
Why test concrete?
There is good reason that engineers pay close attention to the composition of concrete – because selecting the exact quantities and characteristics of the ingredients needed can be very complex. Testing concrete (either in the field or a laboratory) is an essential process.
1. Quality control
Concrete testing can ensure it meet required standards, design specifications for its use and the batching equipment used to mix the concrete remains within their tolerances.
2. Assurance and due diligence
Testing can confirm that your structure (road, bridge, building) will perform to the specified standards and that the materials match the product being used.
3. Rule out variability
As concrete is made from raw materials that contain natural variabilities, testing the materials each time will ensure the product is consistent and meets the intended civil design parameters
Key testing methods
When it comes to concrete, the two main tests are the tests for compressive strength on the hardened concrete in the laboratory and slump tests on the wet concrete on-site.
Compressive strength tests indicate the capacity of the concrete to support the load of the building or structure. The slump test, meanwhile, assesses the consistency of the concrete and confirms that the correct volume of water has been added to the mix before the concrete is placed within the structure.
To be used, concrete must meet the requirements of the National Construction Code (NCC) and any specifications which are given by clients, architects, engineers, or builders. Important Australian standards in respect to concrete are:
AS 3600 – sets out minimum requirements for the design and construction of concrete building structures
AS 3700 – sets out minimum requirements for the design and construction of masonry elements
AS 1012 – methods of testing concrete