All natural and man made materials react to the environment differently, some substances have stronger stress thresholds than others. Two of the most concerning forces on materials that engineers face throughout the year are compression (that can cause the substance to shrink or buckle) and expansion (that causes the material to widen).
Heavy loads placed on top of a material can cause if to compress and changes in temperature can cause a material to either compress of expand. Each substance (listed in the periodic table of elements, as well as complex compounds) has its own temperature coefficient. Hot weather causes materials to expand, while cold weather caused them to contract.
Over time, these dynamic forces can cause the material to become less effective and consequently, can result in a major defect in the overall integrity of the structure it is built in.
Compressive and Tensile Strength
Compressive strength is the amount of force that is exerted on a specific material that would cause it to compress or ‘shrink’. Concrete has a rather high compressive strength compared to other materials. That’s why concrete is the prominent element that is used in construction of buildings, since its high threshold of compression allows greater loads to be placed on top of it; however, concrete does not fare well regarding tensile strength.
Tensile strength represents the amount of stress on a material that would cause it to expand or ‘stretch’. Steel has a higher tensile strength than many other materials.
Integrating with Steel
In order to circumvent defects from extreme load stresses or temperature variations, a combination of concrete and steel is used. This helps both materials to stand up to these pressures and work as one unit. The steel helps to prevent the concrete from expanding due to temperature variations or other external stresses. Subsequently, we have increased compression strength and increased tensile strength, as the two components bond together to resist both forces that would otherwise cause them to fail if the components were used separately.
The result is reinforced concrete. In the pictures below, steel rods are strategically positioned before the concrete is poured.
One cannot just throw the necessary components in the mix and expect a perfect batch of concrete to appear. It is important that contractors follow the guidelines for producing concrete. There must be the right proportion of water needed to mix with the concrete. If too much water is added, the tensile strength of the concrete is reduced. The result will be an acceleration of the expansion process and subsequently, cracks can begin to appear much sooner than expected. When this happens, the concrete can actually break apart.
We’ve all read about building collapses. Inappropriate amounts of water mixed with concrete could have been part of the reason.
The Concrete Foundations Association provides the guidelines necessary for preparing concrete.
To ensure you have a contractor that adheres to all the requirements for constructing a house, always check that the contractor you are hiring is trustworthy.