The concrete used for greenpipe channels

The design of Greenpipe drainage channels is the result of meticulous work carried out by the technical department in collaboration with partner companies.

A simple recipe

It is a very versatile material and seemingly very simple; in fact, its “recipe” consists of water, cement (binder), and aggregates of different grain sizes (sand and gravel) with the addition, as needed, of chemical additives or fibers and/or reinforcement. The type of cement and, above all, the presence of additional elements (such as reinforcement or chemical substances) influence its physical characteristics and mechanical performance.
Therefore, behind the word “concrete” lie multiple facets: it can be “normal” or NSC (Normal Strength Concrete), lightweight, high-performance or ultra-high-performance (HPC or UHPC), reinforced, fiber-reinforced, etc.

Classification of concrete: based on compressive strength

Concrete is classified according to its compressive strength, its main mechanical characteristic. This strength is indicated by a pair of numbers in its class designation. The second value of the pair (for example, 60 in C50/60) is known as Rck (characteristic strength) and is measured in N/mm².

From 20 to 55 for normal concrete
From 60 to 75 for high-performance concrete
From 85 to 120 for high-strength concrete

The compressive strength (minimum class) of the concrete used by Greenpipe for the production of its drainage channels varies, depending on the models, between C50/60 (R_ck equal to 60 N/mm², NSC – Normal Strength Concrete) and C55/67 (R_ck equal to 67 N/mm², HPC – High Performance Concrete).

UNI EN 1433: design guidelines for drainage systems

There is also the reference technical standard for drainage systems, UNI EN 1433, which provides guidelines on the design and production of products and also establishes the minimum criteria for the materials used.

For concrete channels, the UNI EN 1433 standard introduces additional requirements and tests:

the water absorption test, whose average value in % by mass resulting from the test must be less than 6.5 (in this case the products can be marked “W“)
the material resistance test to freezing and thawing in the presence of standing water containing de-icing salts, the results of which, if compliant with the UNI EN 1433 standard, entitle the channels to be marked “+R“.

Regarding the production of concrete used for its channels, Greenpipe relies on fixed industrial plants in which the ingredients of the “recipe” are mixed according to a “mix design” specifically developed to meet different design challenges, taking into account numerous variables such as:

mechanical strength, durability, modulus of elasticity, etc.
available materials such as type of cement, aggregates, additives, additions, etc.
execution requirements such as workability, casting method, curing, etc.

Vibro-compacted concrete

The mix, in the case of “vibro-compacted” concrete, consists of stone aggregates with grain sizes between 0.2 and 10 mm and Portland cement, and is characterized primarily by a low water-cement ratio.
This material is used to fill special molds for the serial production of channels: thanks to its “damp” consistency, it is possible to demold the concrete inside the mold after just a few minutes (i.e., the product can be extracted from the formwork) without losing its “shape”.
This allows for high daily output using a single mold, and it is simultaneously “mechanically vibrated” and “hydraulically compressed,” giving the finished product mechanical strengths that are on average higher than those of the same product made using the casting method. On the other hand, the surfaces will be rougher and more porous.

Cast concrete

In the case of “cast” concrete, the mix is more fluid and involves the use of stone aggregates with a maximum grain size of 15 mm but with an appropriate percentage of filler that serves as a filling agent. The water/cement ratio is much higher compared to “vibro-compacted” concrete.
This mix is poured by gravity into special molds and extraction of the piece is delayed by a few hours to allow the concrete to initiate the chemical reactions of setting and hardening that will ensure, once completed after 28 days, maximum mechanical performance. This type of process requires the use of multiple molds simultaneously to achieve good daily productivity; however, without ample space and a large mold inventory, it will never be possible to achieve the same number of pieces per day as with the vibro-compaction process. On the other hand, for the production of special pieces (complex and numerically limited), cast production is widely preferable.
Products made with this type of raw material are particularly smooth and therefore water flow is enhanced.

Self-Compacting Concrete (SCC)

A particular type of concrete used in cast production is “self-compacting concrete” (Self-Compacting Concrete or SCC): the mix possesses extremely high fluidity as well as high resistance to segregation; in fact, it compacts under its own weight alone (without mechanical vibration), regardless of the shapes of the molds into which it is poured, the dimensions of the castings, and the density of metal reinforcement.
SCC concrete completely fills the formwork, eliminating macro-voids and excess air within the mix, and flows through tight spaces and around obstacles without blocking. This translates into a reduction in macro-defects in the concrete that cause deterioration of its mechanical properties, i.e., greater durability of the product, greater adhesion of the concrete to the reinforcement bars, and greater aesthetic quality.