Ready-mixed concrete is an important construction materials obtained by mixing cement, aggregate (sand, crushed sand, pebble, crushed stone etc.), water, and some chemical and mineral additives, when needed, according to a certain production technology, that is in plastic or fluid consistency at first, can be shaped, and is hardened by time and gaining endurance.
In terms of absolute volume, an average concrete with a normal durability class is consisted of 75% aggregate, 10% cement, and 15% water. Chemical additive up to approximately 2% of the cement’s weight can be added when required.
Concrete is divided into 3 classes according to TS EN 206-1:
Normal concrete: Concrete with a unit volume mass (density) in oven dry situation of more than 2000 kg/m3 and less than 2600 kg/m3.
Heavyweight concrete: Concrete with a unit volume mass (density) in oven dry situation of more than 2600 kg/m3.
Lightweight concrete: Concrete with a unit volume mass (density) in oven dry situation of more than 800 kg/m3 and less than 2000 kg/m3. Lightweight concrete is produced by choosing some or entire aggregate used in the concrete as lightweight aggregate.
Powdered hydraulic binder obtained by mixing and grinding clinker, which is obtained by mixing ground limestone and other raw materials in certain rates and cooked in rotary furnace, with gypsum and other additives.
Cement is a ground inorganic material that can get hardened by setting with hydration reactions and processes when mixed with water, become a dough-like material, and maintaining its durability and stability after hardening even inside the water.
Function of cement within concrete is to cover the surface of aggregate grains, to fill in the spaces between the grains, and to act as a binder.
Crushed stone, sand, pebble etc. materials used in concrete and constituting approximately 60-80% of the concrete are called aggregate.
Aggregates have two different origins including natural (sand-pebble, crushed stone) and artificial (blast furnace cinder, expanded clay, perlite). But not every mineral origin material or industrial waste can be used as concrete aggregate.
Today, however, many concrete consumers have a wrong conclusion that the quality of aggregate used in concrete production only depends on the color of aggregate. There are several physical and chemical properties affecting the quality of aggregate, and these are set out in TS 706 EN 12620 standard.
Compliance of all aggregates used in production in Betonsa today to TS 706 EN 12620 standard is determined through tests, and continuity of quality is being ensured.
Aggregates have a very important role in concrete. Their granulometry, structure, hardness, and geological origin directly affects the behavior of concrete. Before being used in concrete, aggregate specification should be determined through tests.
|Agrega Tipi||Birim hacim ağırlığı (kg/m3)|
|Hafif Agrega||≤ 2000|
|Ağır Agrega||≥ 3000|
Aggregate’s maximum nominal size (Dmax) should be determined by taking the reinforcement’s concrete top layer (concrete cover), smallest size of concrete component section, and the smallest distance between the reinforcements into account.
Water is one of the basic materials constituting concrete. Mixing water used in mixing the concrete has two important missions:
– Wetting the surface of cement and aggregate grains, thus creating a lubricating effect and ensure easy mixing of concrete, placing and compacting, in brief the processability of, fresh concrete,
– Providing the chemical reactions called hydration in the cement dough arising by combining the powdered cement grains.
Any clean, drinkable, clear, and odorless water can be used for concrete production. Concrete’s mixing water does not contain acid. It should not contain chemicals like sulfate, chloride, different salts etc. that might damage the concrete.
Organic or inorganic origin chemicals added with certain rates based on the rate of cement inside the concrete for improving some properties of the concrete are called additives. Chemical additives are generally added to the concrete mixing water. Negative effects may arise if they are used more than needed, and they might also not have any effect if used less than needed. It should, however, be well known that it is not possible to improve with additives the properties of a concrete not produced according to the rules. Compliance of the concrete produced according to the rules with additives should be determined with tests performed beforehand.
Effect of chemical additives used in production in Betonsa on the fresh and hardened concrete is determined through the tests performed at fully equipped laboratories under the supervision of experienced technical experts and under the consultancy of university academicians. These additives are supplied to the facilities according to the quality analysis certificates of the supplier companies. And these additives are added to the concrete by being sensitively weighed in our computer controlled facilities featuring high technology.
Chemical additives used in concrete production are grouped as follows.
a) Water reducing / plasticizer chemical additives;
Additives falling into this group are generally used in the rate of 0,7 – 1,5% of cement’s weight. These additives increase the processability of fresh concrete, and also increase the durability of the concrete as they reduce the need for concrete mixing water.
b) Super plasticizers;
With these additives mainly used for producing high durability concrete, it is possible to reduce the water/cement rate of concrete to 0,25. Super plasticizers, however, are used 1 – 3% higher doses than normal plasticizers.
c) Chemical additives changing the setting time;
Sometimes, the hardening process of fresh concrete, also known as setting, is required to be accelerated or delayed under some conditions. Retarders are used for long transportation distances particularly during summer time, and accelerating admixtures are used during winter time.
d) Air-entraining chemical additives;
These chemical additives protect the hardened concrete against frosting-defrosting effect under cold weather conditions, and also increase the concrete’s processability.
Such kinds of additives are used for completing the setting process without exposing concrete to frosting effect at cold weathers. Adding only antifreeze additive, however, is not a final solution at cold weathers, and some special measures should be taken for protecting the concrete at the pouring place.
f) Other additives;
Different types of chemical additives providing lightweight concrete, watertight concrete, shrinkage preventer, adherence increaser, coloring agent, waterstop, water tightness etc. are also used for ready-mixed concrete production.
Fine materials used for improving some properties of concrete and for providing some special qualities to the concrete are called mineral additives. These additives provide additional durability to concrete, as well as increase the performance of concrete in terms of durability. In Turkey and in the entire world, mineral additives are used against any kind of physical, chemical, and electrochemical external effects together with portland cement or portland cement clinker for the production of reinforced structures with long service life.
Commonly used mineral additives in our country are fly ash, ground blast furnace cinder, silica fume, and truss.