Frequently Asked Questions

WHAT IS CHEMICAL ADMIXTURE?

  • They are organic and inorganic substances other than cement, aggregate and water added at a rate of maximum 5% of the cement dosage. They are chemical substances applied by added to the concrete mixing water for such purposes as improving the workability of fresh concrete, changing setting times, affecting the properties of hardened concrete and improving its strength.
  • Liquid concrete admixture added at rates predetermined by experimental studies in low-consistency concrete in the construction yard in order to be able to pump fresh concrete and facilitate its placement is called “redosing”.
  • As the specific gravities and sizes of the materials comprising the concrete are different, fresh concrete is a mixture which is close to segregation. Aggregates are apt to move below the mixture and water above it.
  • Absence of segregation in concrete is dependent on the fact that the paste viscosity shall be so high as not to allow aggregates to move down the cross-section within the paste under the effect of gravity.
  • Structural components may be deformed, slap may deflect and collapse and stress and transform which will be permanent during the lifetime of the building may occur in the course of early form stripping. Time for the concrete to get strong may vary depending on the thickness of concrete, structural component, concrete class used, concrete admixtures, weather conditions and concrete maintenance.
  • They have purposes of use different from the properties used in industrial facilities, warehouses, highways, car parks and other facilities in which surface preparation varies by the type of concrete. Designs must be made in consideration of concrete thickness, type of concrete, quantity of iron reinforcement it contains and slopes.

FREQUENTLY ASKED QUESTIONS

WHAT IS CONCRETE?

  • ‘Concrete’ is a building material obtained by mixing aggregates, cement, water, chemical admixtures and, when necessary, some building materials complying with production standards together.

WHAT IS FRESH CONCRETE?

  • We may call the easily mixable, movable, placeable, compactible and burnishable form of concrete remaining soft and formable for a while once concrete materials have been mixed together “fresh concrete”.

WHAT IS WORKABILITY IN CONCRETE?

  • Fresh concrete’s being easily mixed, handled without segregation, placed, compacted and its surface being smoothed shows how workable concrete is.

PLACEMENT OF CONCRETE AND WHAT SHOULD BE DONE BEFORE PLACEMENT?

  • Placement method and casting time should be predetermined.
  • Before casting unreinforced and ground concrete, the section to which it is to be applied should be humidified and compacted, thus making it ready for casting.
  • Formwork should be made ready to use by applying clean, durable and standard form oil.
  • The product delivered to the construction yard should be received by checking its properties on the delivery ticket before casting concrete.

PLACEMENT OF CONCRETE AND WHAT SHOULD BE DONE AT THE TIME OF PLACEMENT?

  • Concrete should be cast into the formworks that have been previously made suitable for casting at a height and angle not to cause any segregation.
  • In order to prevent any placement problems arising from reinforcements in vertical structural components, the casting should be carried out so that casting should fill the formwork at three stages.
  • Concrete should be cast into the formwork in the form of horizontal layers.
  • Except such special products as self-compacting concrete and prescribed concrete, all concrete types should be cast by compacting with vibration.

WHAT ARE THE ISSUES REQUIRING ATTENTION IN APPLYING VIBRATION?

  • Vibrator must not definitely contact the concrete formwork. 
  • It should be dropped into the concrete rigorously from a height and slowly taken out in order to ensure placement.
  • Vibration should be carried out to ensure the concrete to merge into the previous layer each time in order to ensure the concrete layer to merge with one another.
  • Vibrator should be dipped into the fresh concrete in a vertical position.
  • It should be used to place the concrete but not to move it.
  • A vibrator suitable for the structural component should be selected and kept in the concrete for a period of time suitable for the structural component.
  • Incorrect vibrator application has an adverse impact on the rheological properties of the concrete, thus reducing its performance.

WHAT SHOULD BE PAID ATTENTION IN FINISHING CONCRETE SURFACE OPERATION?

  • In case of slap concretes, surface finishing operations are predominantly carried out by means of steel or wooden floating rules and trowels. And in cases requiring trimming, bevelling and aluming operations, border finishing operations should be first carried out. A bristle broom may be applied in a certain direction in order to provide the required roughness after floating rule and trowel operation.

WHAT IS MAINTENANCE OF CONCRETE?

  • The process of keeping the concrete at proper humidity and temperature conditions for a sufficient period of time immediately after the processes of placing, compacting and floating the concrete so that any properties expected of the concrete may develop is called maintenance.  Objective of the maintenance process is to fill the capillary pores initially filled with water with hydration products as much as possible.

WHAT ARE CONCRETE MAINTENANCE METHODS?

  • Concrete surface should be ensured to be damp at all times. Water is usually sprayed by means of such auxiliary materials as hoses and the like and allowed to accumulate to form a pond. .
  • Concrete surface is covered with watertight covers.
  • Water losses which may occur on the concrete surface are overcome by the use of chemical curing admixtures.

WHAT IS A WARM WEATHER CONDITION?

  • TS 1248 ‘Concrete making, casting and maintaining rules’ standard defines a weather condition in which air temperature is above 30°C for three consecutive days as ‘warm weather’.

WHAT ARE THE ACTIONS TO BE TAKEN IN A READY-MIXED CONCRETE PLANT IN WARM WEATHER CONDITIONS?

  • Using 100% cold water at those plants with cold water units, supplying ice bars from ice making facilities close to the plants without chiller units, cutting water suitable for prescribed amount and adding it to the mixers.
  • Supplying  fly ash stocks because the use of fly ash in concrete reduces consistency losses and increases workability time and carrying out production with recipes containing fly ash. 
  • Carrying out production not to allow the explant consistencies of the concrete to be lower than the limits permitted by the standards as redosing needs will increase at construction yard. 
  • Wrapping the tanks of truck mixers with curing blankets and wetting the same after filling and then carrying to the construction yard Not casting concrete without admixtures (encouraging recipes with reduced admixtures especially in field concretes).
  • Not casting particularly C30 and higher concrete classes in the heat of noon.
  • Turning on the spray systems at the plants and causing the aggregates stored in the outdoor storage areas to be saturated surface dry.
  • Shortening the concrete casting time and carrying out controlled shipments, thus preventing any strength losses which may occur due to excessive storage of the concrete.
  • Turning on the aggregate sprinkling systems (particularly wetting the #1 and #2 aggregates stored in outdoor areas to get water-saturated).

WHAT SHOULD BE DONE IN A CONCRETE CASTING SITE IN WARM WEATHER CONDITIONS?

  • Using 100% cold water at those plants with cold water units, supplying ice bars from ice making facilities close to the plants without chiller units, cutting water suitable for prescribed amount and adding it to the mixers.
  • Supplying volatile ash stocks because the use of volatile ash in concrete reduces consistency losses and increases workability time and carrying out production with recipes containing volatile ash.
  • Carrying out production not to allow the explant consistencies of the concrete to be lower than the limits permitted by the standards as redosing needs will increase at construction yard 
  • Wrapping the tanks of truck mixers with curing blankets and wetting the same after filling and then handling to the construction yard.
  • Not casting concrete without admixtures (encouraging recipes with reduced admixtures especially in field concretes).
  • Not casting particularly C30 and higher concrete classes in the heat of noon.
  • Turning on the spray systems at the plants and causing the aggregates stored in the outdoor storage areas to be saturated surface dry.
  • Shortening the concrete casting time and carrying out controlled shipments, thus preventing any strength losses which may occur due to excessive storage of the concrete.
  • Turning on the aggregate sprinkling systems (particularly wetting the #1 and #2 aggregates stored in outdoor areas to get water-saturated).

WHAT IS A COLD WEATHER CONDITION?

  • TS 1248 ‘Concrete making, casting and maintaining rules’ standard considers a condition in which the average air temperature is lower than 5°C for three consecutive days to be ‘cold weather’. Daily average air temperature is the average of the lowest and highest air temperature recorded during the period of time elapsing from one midnight to the next midnight.

WHAT ARE THE MEASURES REQUIRED TO TAKE IN COLD WEATHER CONDITIONS?

  • Using 100% cold water at those plants with cold water units, supplying ice bars from ice making facilities close to the plants without chiller units, cutting water suitable for prescribed amount and adding it to the mixers.
  • Supplying volatile ash stocks because the use of volatile ash in concrete reduces consistency losses and increases workability time and carrying out production with recipes containing volatile ash.
  • Carrying out production not to allow the ex-plant consistencies of the concrete to be lower than the limits permitted by the standards as redosing needs will increase at construction yards.
  • Wrapping the tanks of truckmixers with curing blankets and wetting the same after filling and then handling to the construction yard.
  • Not casting concrete without admixtures (encouraging recipes with reduced admixtures especially in field concretes).
  • Not casting particularly C30 and higher concrete classes in the heat of noon.
  • Turning on the spray systems at the plants and causing the aggregates stored in the outdoor storage areas to be saturated surface dry.
  • Shortening the concrete casting time and carrying out controlled shipments, thus preventing any strength losses which may occur due to excessive storage of the concrete.
  • Turning on the aggregate sprinkling systems (particularly wetting the #1 and #2 aggregates stored in outdoor areas to get water-saturated).

WHAT DOES ADDITIONAL WATER CAUSE AT A CONSTRUCTION YARD?

  • Addition of water to the concrete for any reason whatsoever by intervening the mix design at the concrete casting site causes the water-cement ratio which is determined by concrete classes and which is the main source of strength to reduce and thereby fail to provide the strength as required by the concrete class. It further prevents the chemical admixture applied at the determined percentage so that workability of concrete may be at optimum level from working and the water delivered so that the concrete may be worked makes an adverse effect as a result of segregation, thus making the concrete unworkable.

WHAT IS  CHEMICAL ADMIXTURE?

  • They are organic and inorganic substances other than cement, aggregate and water added at a rate of maximum 5% of the cement dosage. They are chemical substances applied by adding to the concrete mixing water for such purposes as improving the workability of fresh concrete, changing setting times, affecting the properties of hardened concrete and improving its strength.

WHAT ARE THE CHEMICAL ADMIXTURE TYPES?

  • Water reducer
  • Highly water reducer
  • Water stopper
  • Air entrainer
  • Set accelerator
  • Set retarder
  • Viscosity improver

WHAT IS REDOSING?

  • It is the liquid concrete admixture added at rates predetermined by experimental studies in low-consistency concrete in the construction yard in order to be able to pump fresh concrete and facilitate its placement.

WHAT IS CONCRETE SEGREGATION?

  • As the specific gravities and sizes of the materials comprising the concrete are different, fresh concrete is a mixture which is close to segregation. Aggregates are apt to move below the mixture and water above it. Absence of segregation in concrete is dependent on the fact that the paste viscosity shall be so high as not to allow aggregates to move down the cross-section within the paste under the effect of gravity. Segregation in concrete may be prevented by using proper gradation and control of the paste viscosity. Segregation not only leads to deviation in the reinforced concrete structural component but reduces the cross-section performance to a great extent as well. However, segregation may occur as a consequence of the mistakes made in the mixing, handling, placing and compacting processes of fresh concrete.

TYPES OF CRACKS AND CAUSES THEREOF

  • Plastic settlement
  • Plastic shrinkage
  • Early thermal shrinkage
  • Long-term drying shrinkage
  • Surficial fine cracks
  • Corrosion of reinforcement
  • Alkali silica reaction
  • Early freezing damage
  • Freeze-thaw damage

WHAT SHOULD BE PAID ATTENTION AT THE TIME OF ORDERING CONCRETE

  • Delivery date and time and quantity of concrete to be delivered at unit time
  • Causing a survey to be carried out for suitable team and equipment in the vicinity of the construction yard
  • Special carrying method, if any
  • Special placement method, if any
  • Environmental exposure class
  • Consistence class
  • Maximum nominal upper aggregate size (Dmax)
  • Compressive strength classes
  • Chloride content

WHAT ARE THE ENVIRONMENTAL EXPOSURE CLASSES?

WHAT IS EXPOSED CONCRETE? WHERE IS IT USED?

  • Dmax is determined as per TS 500 and thus aggregate is selected.  
  • Maximum grain size as per TS 500 should not be larger than
  • 1/5 of the formwork width;
  • 1/3 of the slap thickness; and
  • 3/4 of the distance between two reinforcement bars. Ratios should be determined by the building properties to be identified prior to concrete casting and thus proper concrete should be required.

EARLY FORM STRIPPING

Structural components may be distorted, floor may deflect and collapse and stresses and transformations which will be permanent during the lifetime of the building may occur in the course of early form stripping. Time for the concrete to get strong may vary depending on the thickness of concrete, structural component, concrete class used, concrete admixtures, weather conditions and concrete maintenance. For instance, each day when the air temperature is below +5°C should be added to form stripping time. Proper concrete maintenances determined for the structural component should be carried out in order to strike the form at the desired time (see ‘What Is Concrete Maintenance?’)

WHAT IS FIELD CONCRETE? WHAT SHOULD PAID ATTENTION IN THE APPLICATION THEREOF?

  • They have purposes of use different from the properties used in industrial facilities, warehouses, highways, car parks and other facilities in which surface preparation varies by the type of concrete. Designs must be made in consideration of concrete thickness, type of concrete, quantity of iron reinforcement it contains and inclinations. Sub-filler of the field concrete is compacted and brought to the proper elevation in increments with proper filling material prior to application. And in case of concrete castings to rest on dirt surface, the surface should be covered with proper material which will break the connection of the ground with the concrete prior to concrete casting so that the water in the concrete will not be lost by being absorbed by the soil. And in case of field concrete to rest on concrete surface, attention should be paid that the surface should be cleaned of such materials as dirt, dust, grease, etc. and made suitable for casting. Before starting concrete casting, moulding locations should be determined and steel formworks installed according to the projected elevation. Arrangements required for structural joints and iron reinforcement should be made. And in cases where two layers will be laid, concrete cover should be checked by a trestle and then placed.