What IS Concrete?

Concrete is one of the most widely used construction materials in the world. It is produced to be used in many ways, some of its uses are depicted to the right.

Concrete is made up of five main components: Cement, aggregate, concrete admixtures, concrete additions and supplementary cementitious materials (SCM), and water.

Click the icons below to learn more about each component.

Cement is a hydraulic binder, meaning it hardens when combined with water. It can be made different ways, but typically with similar materials. Portland cement, for example, consists of limestone, marl, and clay. These are mixed in defined proportions, heated, and ground to the fine powder we know as cement.

Aggregates make up 80% of the weight and 70% of the volume of concrete. Aggregates primarily consist of sand and gravel. Their size and quality can improve the outcome of concrete. They should have a strong bond with the hardened cement paste, should not interfere with cement hardening, and not have a negative effect on durability.

Admixtures are liquids or powders that are added to the concrete during mixing in small, specific quantities. Dosage is usually determined by cement content. Admixtures have significant impact on the fresh and/or hardened concrete properties and can act chemically and/or physically. Sika has been developing admixtures since it was founded - in 1910!

See Our Admixtures

Concrete additions are defined as finely divided materials used in concrete in order to improve or to obtain desired fresh and hardened concrete properties. There are two types. Materials such as lime fillers, quartz dust, and color pigments are known to be nearly latent additions. Pozzolanic additions, or latent hydraulic additions, include pozzolans, fly ash, silica dust, and ground, granulated blast furnace slag.

Arguably the most important component, water needs to be perfectly rationed into a concrete mix. The suitability of water for concrete production also depends on its origin. Potable and non-potable water may be used as mixing water, however, it must always be tested. Concrete performance requirements for mixing water include compressive strength and time of set. Density of water should also be tested or monitored with a hydrometer.

How is Concrete Prepared?

There are many important factors to consider when preparing a concrete mix. Be it project specifications, weather conditions, transportation, or other unexpected interferences, it is important to prepare the concrete for anything it might encounter. This preparation starts long before the concrete is even made.

Click the images below to learn more about each step.

Defining the Parameters

Specific project requirements should be considered when preparing concrete designs. These might include:

  • Strength requirements
  • Durability requirements
  • Aesthetic requirements
  • Maximum aggregate diameter
  • Method of placement
  • Placing rate
  • Concrete consistency
  • General boundary conditions (temperature, etc.)
  • Delivery method and time
  • Curing/waiting time
  • Definition of test requirements
  • Mix design and specification
  • Preliminary testing
  • Mix design adjustment, if necessary
Production

Production is a critical factor for the resulting concrete and involves dosing and mixing the components. The following parameters can have an effect when producing concrete:

  • Concrete mix design
  • Type and dosage of admixture
  • Type and size of mixer
  • Mixing intensity and mixing time
  • Concrete mixer operator
  • Cleaning/maintenance of mixer
  • Addition of raw materials
  • Plant quality control
Preparation On-Site

Site preparation is of essence when placing concrete. Typical steps to prepare a site might include the following:

  • Installation of the concrete handling/placing systems
  • Preparation of the formwork (including release agent application)
  • Reinforcement check
  • Formwork check (fixing, integrity, form pressure)
  • Supply of tools for compacting (vibrators, etc.) and finishing (beams and trowels, etc.)
Delivery

Getting the concrete from point A to B is a factor that is often overlooked. When the concrete is supplied, the following additional criteria must be considered:

  • Delivery time (traffic conditions, potential hold-ups, etc.)
  • Define the necessary drum revolutions during the journey
  • Do not leave the ready-mix truck standing in the sun during waiting periods
  • For a fluid consistency (SCC), define the maximum capacity to be carried
  • Do not add water or extra doses of admixture (unless specified)
  • Mix again thoroughly before unloading
Learn about SCC
Placement

The concrete is generally placed within a limited and defined time period. The following factors contribute to the success of this operation, which is critical for the concrete quality:

  • Delivery note check
  • Use of the right equipment (vibrators, etc.)
  • Avoid over-handling the concrete
  • Continuous placing and compacting
  • Re-compaction on large pours
  • Take the appropriate measures during interruptions
  • Carry out the necessary finishing (final inspection)
Curing

To achieve constant and consistent concrete quality, appropriate and correct curing is essential. The following curing measures contribute to this:

  • Generally protect from adverse climactic influences (direct sun, wind, rain, frost, etc.)
  • Prevent vibration
  • Use a curing agent
  • Cover with sheets or frost blankets
  • Keep damp/mist or spray if necessary
  • Maintain the curing time relevant to temperature