The quality of your concrete mix plays a fundamental role in every build project, not only in its finished look but in how well the structure weathers over time. By highlighting five key issues that can impact the quality and finishing of concrete, Sephaku Cement aims to ensure that you are able to address any concrete quality issues you might have before it’s too late.
The first problem to keep an eye out for is bleeding. The bleeding of concrete refers to a process in which free water in the concrete mix settles on the surface of the poured mixture.
Once this water has evaporated, it creates air voids in the concrete and as a result, diminishes the bond between the cement paste and aggregates. While some bleeding is to be expected, excessive bleeding can affect the durability and strength of the concrete which makes the cement porous and prone to micro cracking.
Owing to the fact that bleeding is a result of the wrong measurement of water for your set of materials in your cement mixture, the cement-to-water ratio is critical to get right and to do this, it is important to use a proper method of mixing.
Spalling, a phenomenon which separates, cracks and exposes the aggregate on the surface of the concrete, is the second obstacle that affects the finishing quality of your concrete. There are a number of reasons why spalling occurs but one major reason is freeze thaw cycling or porous concrete with reinforcing steel that will rust expand and cause spalling.
The catalyst of this issue is water seeping into the cracks of the concrete.
During the colder months of the year, that water freezes overnight and expands, resulting in the opening of the concrete which creates a gap and ultimately leaves the concrete cracked. This happens predominantly close to the surface as it is considered that concrete with strength of higher than 5,0 Mpa will withstand forces exerted by freezing expansion.
These cracks leave the surface of the concrete patchy and expose the aggregate. So how can you avoid ending up with cracks in your concrete due to spalling? Importantly, apply a good water sealant to finish the surface of your concrete as this will help prevent water from entering the concrete, which can ensure a long lasting finished concrete look.
The third and one of the most common cement challenges is cracked concrete. A crack is characterised as a fracture in the concrete that may extend partly or completely through a slab of concrete.
This cracking is often due to the formation of tensile or bending stresses. While the tensile stress prevents the concrete structure from expanding and bending, if the stress applied to the concrete is greater than the tensile strength it may result in cracking.
It is therefore very important to do a tensile stress test. One test that can be conducted is applying uniaxial tension that is done by moulding a concrete block of your concrete which is then placed in a machine that applies a tension load. This goes a long way to assist you in ensuring your concrete is crack proof.
In the event of bending of a slab it must be noted that the bottom of a slab is in tension, therefore the tensile strength should be sufficient to overcome the tensile stress. Reinforcing steel is often used to assist with this type of stress.
Honeycombing is the fourth sign of bad concreting. This dilemma arises from a lack of mortar filling in the voids in the concrete between the coarse aggregates. This results in the formation of voids in the concrete which reduces the compressive strength of the concrete and increases the porosity of the concrete, making it prone to the ingress of various damaging materials and gasses.
There are a variety of different tools to ensure that honeycombing does not occur. Firstly, you must ensure you use a concrete with the right workability and then, once poured, make sure that your cement is fully compacted.
The delamination of concrete is the final concrete quality issue that you must know how to spot in the “Big 5 of Building”.
Delamination results in the separation of the surface layer of the concrete which detaches from the concrete element. This problem occurs if you seal your concrete surface while the underlying concrete is still bleeding and releasing air.
Delamination becomes a common issue when conditions like humidity, sun or wind make it seem like the underlying concrete is ready for trowelling. Yet this potential problem can be prevented by ensuring that the surface of the slab has the finishing completed straight after the bleeding process has ended.
This approach guarantees that the finishing of your concrete will be of a strong quality.
Bleeding, spalling, honeycombing, delamination, and cracking. These are the “Big 5” that you do not want to miss seeing clearly when you’re in the on-site build phase of your infrastructure project. The Sephaku Cement Technical team is always available to help you spot these, and any other potential issue, as you bring your building plan to life and take it to new heights.