Civil Engineering: Concrete Technology I Chapter 4
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What is the primary reason why the quality of water is important in concrete?

  • It affects the mixing and curing purposes
  • It determines the appearance of the concrete
  • It affects the strength of the concrete
  • It participates in the chemical reaction with cement (correct)

    • What is the recommended pH range for water to be used in concrete mixing?

  • 6 to 8 (correct)
  • 8 to 10
  • 5 to 7
  • 7 to 9

    • Why should sea water not be used in concrete mixing?

  • It reduces the risk of corrosion
  • It increases the strength of the concrete
  • It causes persistent dampness and efflorescence (correct)
  • It affects the appearance of the concrete

    • What is the definition of an additive in concrete?

    <p>A material added at the time of grinding cement clinker at the cement factory</p> Signup and view all the answers

    What is the primary purpose of using chemical admixtures in concrete?

    <p>To achieve certain properties in concrete more effectively than by other means</p> Signup and view all the answers

    What is the effect of using sea water in reinforced concrete?

    <p>It increases the risk of corrosion</p> Signup and view all the answers

    What is the significance of water in concrete mixing?

    <p>It participates in the chemical reaction with cement</p> Signup and view all the answers

    What is the term used to describe a material used as an ingredient of concrete, other than cement, water, and aggregates?

    <p>Admixture</p> Signup and view all the answers

    Why should tap water be considered suitable for mixing concrete?

    <p>It is fit for drinking</p> Signup and view all the answers

    What is the primary function of accelerating admixtures in concrete?

    <p>To accelerate the early strength development of concrete</p> Signup and view all the answers

    What is the maximum percentage of admixtures that can be added to the concrete mix by mass of cement?

    <p>5 per cent</p> Signup and view all the answers

    What is the primary benefit of using accelerating admixtures in precast concrete manufacture?

    <p>Rapid removal of formwork</p> Signup and view all the answers

    What is the classification of admixtures that exhibit both water-reducing and accelerating properties?

    <p>Type E</p> Signup and view all the answers

    Why may accelerators result in shrinkage cracking at high temperatures?

    <p>Due to too high a rate of development of heat of hydration</p> Signup and view all the answers

    What is the primary function of Type A admixtures?

    <p>To reduce the water content in the concrete mix</p> Signup and view all the answers

    What is the benefit of using accelerating admixtures in urgent repair work?

    <p>Earlier finishing of the concrete surface</p> Signup and view all the answers

    What is the common accelerator used over many decades?

    <p>Calcium chloride</p> Signup and view all the answers

    What is the purpose of using admixtures in concrete, especially in adverse weather conditions or intricate placements?

    <p>To maintain the quality of concrete during the stages of mixing, transporting, placing, and curing</p> Signup and view all the answers

    Why should calcium chloride not be used in reinforced concrete?

    <p>It contributes significantly to the corrosion of steel reinforcement</p> Signup and view all the answers

    What is the primary purpose of using a water-reducing admixture in a concrete mix?

    <p>To allow a reduction in the water/cement ratio while retaining the desired workability</p> Signup and view all the answers

    What is the primary function of retarding admixtures?

    <p>To prolong the time during which concrete can be transported, placed, and compacted</p> Signup and view all the answers

    What factors affect the effectiveness of a water-reducing admixture?

    <p>Cement content, water content, type of aggregate used, and presence of air-entraining agents or pozzolanas</p> Signup and view all the answers

    What is the minimum duration of retardation required for Type B admixtures according to ASTM C 494-10?

    <p>1 hour</p> Signup and view all the answers

    What is the approximate percentage of sugar added to cement to act as a retarder?

    <p>0.05 per cent</p> Signup and view all the answers

    What is the maximum percentage reduction in water content possible with the use of superplasticizers?

    <p>30%</p> Signup and view all the answers

    What is the maximum duration of retardation allowed for Type B admixtures according to ASTM C 494-10?

    <p>3 hours</p> Signup and view all the answers

    What is the primary mechanism of action of superplasticizers?

    <p>They wrap themselves around the cement particles and give them a highly negative charge</p> Signup and view all the answers

    What is the primary function of water-reducing admixtures?

    <p>To reduce the water content of the mix</p> Signup and view all the answers

    What is the typical increase in slump value achieved with the use of superplasticizers?

    <p>75 mm to 200 mm</p> Signup and view all the answers

    What is the primary advantage of using superplasticizers over traditional plasticizers?

    <p>They can reduce the water content up to 30%</p> Signup and view all the answers

    How much water can be reduced from the mix by using water-reducing admixtures?

    <p>10 per cent</p> Signup and view all the answers

    What type of admixture is classified as Type A according to ASTM C 494-10?

    <p>Water-reducing admixture</p> Signup and view all the answers

    What is the primary reason why superplasticizers are more expensive than traditional plasticizers?

    <p>They are synthesized using a complex polymerization process</p> Signup and view all the answers

    What is the primary benefit of using superplasticizers in concrete mixes?

    <p>They improve the workability of the concrete</p> Signup and view all the answers

    What is the probable mechanism of sugar's retarding action?

    <p>Prevention of the formation of C-S-H</p> Signup and view all the answers

    What type of concrete can be achieved with the use of superplasticizers?

    <p>All of the above</p> Signup and view all the answers

    What is the primary advantage of using flowing concrete?

    <p>It is suitable for placing in very heavily reinforced sections.</p> Signup and view all the answers

    What is the typical dosage range of superplasticizers to increase the workability of the mix?

    <p>1 to 3 litres per cubic metre of concrete</p> Signup and view all the answers

    What type of admixture is used to prevent excessive bleeding and segregation?

    <p>Workability Admixtures</p> Signup and view all the answers

    What is the primary function of Air-detraining Admixtures?

    <p>To remove air from the concrete</p> Signup and view all the answers

    What type of admixture is used to prevent fungal growth in concrete?

    <p>Fungicidal, Germicidal, Insecticidal Admixtures</p> Signup and view all the answers

    What is the purpose of Bonding Admixtures in concrete?

    <p>To enhance the bonding between old and new concrete</p> Signup and view all the answers

    What type of admixture is used to improve the curing of concrete?

    <p>Concrete Curing Compounds</p> Signup and view all the answers

    What is the primary function of Gas forming Admixtures?

    <p>To generate air bubbles in the concrete</p> Signup and view all the answers

    What type of admixture is used to improve the decorative appearance of concrete?

    <p>Colouring Admixtures</p> Signup and view all the answers

    Study Notes

    Water in Concrete

    • Water is an essential ingredient in concrete, participating in the chemical reaction with cement.
    • The quality of water is crucial, as impurities can interfere with cement setting, affect concrete strength, or cause surface staining and reinforcement corrosion.
    • Suitable water for mixing and curing purposes should be considered, including tap water with a pH between 6 and 8 that doesn't taste saline or brackish.
    • Sea water or water with high chloride content should not be used, especially when appearance is important or a plaster finish is applied, as it can cause corrosion of the reinforcement.

    Chemical Admixtures

    • Admixtures are materials added to concrete, excluding cement, water, and aggregates, to achieve specific properties.
    • Major reasons for using chemical admixtures include:
      • Achieving certain properties effectively
      • Maintaining quality during mixing, transporting, placing, and curing
      • Overcoming emergencies during concreting operations
      • Economy
    • Admixtures are added in quantities no larger than 5% by mass of cement.

    Types of Admixtures

    • Admixtures can be classified into various types based on their function in concrete, including:
      • Type A: Water-reducing
      • Type B: Retarding
      • Type C: Accelerating
      • Type D: Water-reducing and retarding
      • Type E: Water-reducing and accelerating
      • Type F: High-range water-reducing or superplasticizing
      • Type G: High-range water-reducing and retarding, or superplasticizing and retarding

    Accelerating Admixtures

    • Accelerating admixtures accelerate early strength development in concrete.
    • They are useful in low-temperature placements, precast concrete, or urgent repair work.
    • However, they can cause excessive heat of hydration and shrinkage cracking at high temperatures.

    Retarding Admixtures

    • Retarding admixtures delay the setting of cement paste.
    • They are useful in hot weather concreting, preventing cold joints, and prolonging the time for transportation, placement, and compaction.
    • Retarders include sugar, carbohydrate derivatives, soluble zinc salts, and soluble borates.

    Water-Reducing Admixtures

    • Water-reducing admixtures reduce the water content of the mix, usually by 5-10%, up to 15% in high-workability concretes.
    • They allow for a reduction in the water-cement ratio while maintaining workability or improving it.
    • Water-reducing admixtures can be used in pumped concrete or concrete placed by a tremie.

    Superplasticizers (High-Range Water Reducers)

    • Superplasticizers permit a reduction of water up to 30% without reducing workability.
    • They are water-soluble organic polymers synthesized through a complex process, making them relatively expensive.
    • Superplasticizers wrap themselves around cement particles, giving them a highly negative charge, resulting in deflocculation and dispersion of cement particles.
    • They increase workability, allowing for flowing concrete with a high slump, which is useful for heavily reinforced sections, inaccessible areas, and rapid placement.

    Other Types of Admixtures

    • Air-entraining admixtures
    • Pozzolanic or mineral admixtures
    • Damp-proofing and waterproofing admixtures
    • Gas-forming admixtures
    • Air-detraining admixtures
    • Alkali-aggregate expansion-inhibiting admixtures
    • Workability admixtures
    • Corrosion-inhibiting admixtures
    • Bonding admixtures
    • Fungicidal, germicidal, insecticidal admixtures
    • Colouring admixtures
    • Concrete curing compounds
    • Polymer bonding agents
    • Polymer-modified mortar for repair and maintenance
    • Mould-releasing agents
    • Protective and decorative coatings
    • Installation aids
    • Floor hardeners and dust-proofers
    • Non-shrink high-strength grout

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    Description

    This quiz covers the fourth chapter of Concrete Technology I, focusing on water and admixtures in concrete. It explores the quality of water and its importance in concrete production.

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