Out of all civil engineering work, industrial concrete floors are most certainly considered the easiest to create. This has often led to an underestimation of the importance of certain basic aspects which, while not being crucial for other structures, are essential in the case of concrete floors. Using high quality (and therefore durable) concrete is clearly a necessary condition but alone is not sufficient to guarantee good flooring. In addition to the design, the technological and executive aspects – which sometimes are linked to problems that are difficult to assess, should also be considered.
Keywords related to concrete floor slabs
The quality of an industrial concrete floor is highly dependent on obtaining a strong, durable, flat, and crack-free surface.
The surface properties of the floor are affected not only by the quality of the concrete, but also by the quality of the pouring and placement.
Time in casting and finishing is a critical variable on which the success or failure of the work in meeting the end user's expectations depends. Setting and hardening times, plastic and drying shrinkage deformations, segregation tendency, water/cement ratio, and workability are all extremely important factors to control when creating flooring as they affect the finishing process and, ultimately, the performance of the floor slab itself.
The execution itself, especially in finishing the concrete surface, can also affect the quality of the flooring. For example, a premature finishing operation or the presence of bleeding water on the surface of the concrete leads to a localised increase in the water/cement ratio with the formation of a layer of mortar with low mechanical strength values, low wear resistance and a strong tendency to crack and delaminate. Furthermore, a finish that is not performed at the right time with respect to the setting and hardening of the concrete, can result in defects in the planarity of the surface (curling).
Common challenges with concrete floors
In general, the characteristics of a concrete surface determine the serviceability of the flooring. Because of this, all phenomena that can lead to cracks in the concrete surface must be controlled.
Cracks, curling, and delamination are the main problems that can occur in a concrete floor, damaging the work and compromising the service life.
Plastic shrinkage, drying shrinkage, alkali-aggregate reaction, freeze and thaw cycles, and dimensional variations due to temperature changes are all phenomena that can induce stresses within the concrete leading to the formation of cracks that could compromise the performance of the flooring.
Plastic shrinkage
Plastic shrinkage is a phenomenon that occurs in the first few hours of a concrete’s service life because of surface capillary stresses that develop when the evaporation rate of the water is faster than the bleeding rate. Concrete structures with very large surface areas exposed to air, such as industrial floors, are particularly prone to plastic shrinkage.
Drying shrinkage
Concrete deforms when the relative ambient humidity changes. More specifically, if the humidity is low, it contracts.
Since the tensile strength of concrete is much lower than its compressive strength (approx. 1/10), shrinkage in a confined structure induces a tensile stress that causes cracking. The extent of this shrinkage depends on the water/cement ratio and the aggregate/cement ratio, as well as on the shape and size of the structure:
- The increase in the water/cement ratio causes greater shrinkage, because/as both the degree of water evaporation from the concrete and the level of concrete porosity increase.
- A reduction in the aggregate/cement ratio, on the other hand, induces an increase in shrinkage due to the greater volume of cement paste in the concrete mixture.
- As the surface/volume ratio increases, shrinkage also increases because more surface area is exposed to water evaporation.
Along with relative ambient humidity, temperature is the major driving factor when it comes to the shrinkage and cracking phenomena of the floor. Significant temperature differences within the thickness of a concrete structure lead to thermal cracking as a consequence of different contraction among the portions.
Curling
Curling of floor slabs is a direct consequence of shrinkage. This phenomenon occurs as a result of increasing contractions along the thickness of the slabs due to differential shrinkage, leading to defects of planarity and cracks along the edges of the joints.
The action of freeze-thaw cycles
If the temperature drops below 0°C, the water freezes and its volume increases causing a pressure capable of damaging the concrete. This phenomenon occurs cyclically in areas with a harsh climate and its effects can gradually worsen the top surface layer until it crumbles and delaminates. A typical example of structures subject to this phenomenon are industrial floors located outdoors in areas where the climate is very cold.
There are many factors that can cause a concrete floor to deteriorate prematurely. It should also be considered that the problems described above can add up, producing cracks, curling, and delamination very quickly.
For these reasons, it is always recommended to adopt a Flooring System that is the most appropriate combination of different products, each one specialized in solving a single problem. As a full solution, this System can tackle all the problems that can arise when creating an industrial floor.
The Flooring System is an effective tool for the contractor and ready-mix concrete supplier that enables them to deal with and provide the best flooring solution.
In the next blog article, our experts Nicoletta and José will explain in detail all the components of the Flooring System from Master Builders Solutions.
