CONCRETE, ONE FOR ALL?
Updated: Apr 30, 2021
I can still remember when, running my first building site, we used to mix our own concrete in place; it was kind of naive: we didn´t have any check on the “ingredients” and they changed every new batch delivered; we had just three mix recipes: one for the foundations, one for the floor ballast and one for all the rest; we never checked on the hardened concrete quality if not during the final structural testing….real ignorance in power!
Concrete technology is not a new science of this century, but can be defined as a relatively new field of interest when it comes to applications in the building market.
Of course, all of you readers of P-Concrete, are not looking for in-depth articles about concrete technology, because, like me, you are more “concrete” oriented (sorry for the pun). That´s why in this post I am just going to list some specific kind of concrete with a brief explanation of how they are made and what they are for. Some more details will be discussed in linked posts, but if you need more insight, I invite you to share your curiosity, doubts and facts on P-Concrete forum. It´s free, you only need to register and waiting to receive your approval as a member (it will take few moments don´t worry) and as a reward for your patience you´ll get a free copy of the brochure “Concrete flooring tips and tricks”, you are going to love it! (Sorry for these advertising lines). One last thing: in this post I don´t list all the several Fck or Rck concrete…. you already know about them, aren´t you?! Let´s get started:
STRUCTURAL LIGHT WEIGHT CONCRETE
The main aggregate is structural expanded clay, which is a particularly light, rigid, non-deformable material refractory to high temperatures and with high thermal resistance. The weight benefit while used in concrete is around 30% weight saving. This specific kind of concrete can express high strength, high fire resistance and a certain degree of sound absorption. The use is advisable in foundation on soils with poor bearing capacity, when raising existing structures, in renovations and restorations. Read more in the post “Light weight structural concrete”.
NON-STRUCTURAL LIGHT WEIGHT CONCRETE
The main aggregate is non-structural expanded clay, which has the same physics characteristics of the structural one with exception of strength to compression. Normally low diameter aggregate is used for this specific mix. This concrete is a great allied when it comes about fills and light ballasts. Its good thermal resistance contributes to a proper building insulation and being made out of natural row materials can be considered eco-friendly to some extent.
There are basically three different types of fiber-reinforced concrete: Synthetic, structural synthetic, metallic. The first type is characterized by super-thin fibers available in different measures which contributes to containing plastic shrinkage, for this reason they are widely used in precast structures as well as in flooring. The second type is characterized by bigger fibers, both in length and section. They can have different shapes and physical characteristics. These fibers are designed to cooperate in reducing hygrometric shrinkage and to increase concrete ductility, therefore concrete flooring is the main field of action as per the third type, metallic fibers; the main difference is just the material. More details on these fiber-reinforced concrete types on the related post.
THWARTED SHRINKAGE CONCRETE
These kinds of mixes are designed to thwart the natural concrete tendency to shrink, due to internal tension, related with the water laying into the capillary porousness. The result is a sort of “self-curing” concrete that minimize hygrometric shrinkage (read my post “Concrete shrinkage part 2”). All kind of structure can be realized with this specific concrete, especially the horizontal ones.
COMPENSATED SHRINKAGE CONCRETE
The situation here is quite similar to the previous one, meaning the final goal is the same: reducing hygrometric shrinkage. But this time the goal is reached by adding expanding admixtures. It is quite a thin equilibrium, the one the mix-designer has to reach, because he has to equalize the shrinkage in absolute value with the same expansion value focusing at the same time on timing, since the expansion has to be developed before the shrinkage process starts.
UNDERWATER CASTING CONCRETE
Normal concrete cannot be casted underwater because it will be immediately washed-out. These family of mixes are absolutely more cohesive and viscous than regular ones and while keeping their results in terms of strength performance and workability, they can easily be casted underwater even by means of concrete pumps. More about Underwater casting concrete in the related post.
LOW PERMEABILITY CONCRETE
While low permeability values are always related to low w/c ratio (see post “Concrete permeability”), it is possible to lower them even more when pozzolanic fillers are added to the mix, they will not only fill the voids normally occupied by water (which tends to evaporate, while filler stays) but developing chemical hydration products, will increase dramatically the internal connections reducing capillary porousness and increasing strength and durability, all with the same w/c ratio. They can be used in every kind of structure where low permeability is a requirement. Read more in the post “Low permeability concrete”.
True, a good fair-faced concrete is the result of a perfect compaction work (see my posts “Concrete compaction” and “Concrete quality is a team work”). Nonetheless specific mix-design can help and this is the goal of fair-faced concrete.
The main “aggregates” are polystyrene or “air”. In the first case, a specific mix is designed in order not to have polystyrene pearls floating on the surface, but remain homogeneously mixed with all the other components. Several densities are available, the lower the density the higher the insulation but the lower the load. If “air” is the main “aggregate” the mix cannot be defined as a concrete but more as a mortar, very light in weight and with medium-low insulation property. It is easy to break under concentrated load, like the load of a man, that´s why it is quite difficult to keep it intact before casting on top of that a thin ballast, for the floor tiles.
This is only a short list, several other types are already available or under experimentation not to mention the possibility to access to a virtually infinite creation of tailor-made mixes, where the focus is the specific expected performance. Don´t be trapped in the misconception that concrete is just defined by a value of Fck or Rck. Technology is moving fast and when we are up to date, we can get unexpected benefits in terms of quality, money saving and final client satisfaction.