Civil Engineering: Building Materials & Testing
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Questions and Answers

What is the primary use of concrete blocks in construction?

  • Wall construction (correct)
  • Pavement
  • Roof construction
  • Flooring

    • What is another name for a concrete block?

  • Cement brick
  • Building material
  • Concrete masonry unit (correct)
  • Wall material

    • What does the term 'precast' refer to in concrete blocks?

  • The blocks are designed for heavy loads
  • The blocks are made of special cement
  • The blocks are cast on site
  • The blocks are formed and hardened before being brought to the job site (correct)

    • What is the typical feature of most concrete blocks?

    <p>They have one or more hollow cavities</p> Signup and view all the answers

    Who designed the first hollow concrete block?

    <p>Harmon S. Palmer</p> Signup and view all the answers

    In what year did Palmer patent his concrete block design?

    <p>1900</p> Signup and view all the answers

    What is the typical color of concrete blocks?

    <p>Light gray</p> Signup and view all the answers

    What determines the classification of concrete masonry units?

    <p>Their density</p> Signup and view all the answers

    What is the main ingredient in the concrete mixture used to make concrete blocks?

    <p>Portland cement</p> Signup and view all the answers

    What type of materials are used to manufacture normal-weight units?

    <p>Well-graded sand, gravel, and crushed stone</p> Signup and view all the answers

    What is the purpose of the weigh batcher in the manufacturing process?

    <p>To measure the proper amounts of each material</p> Signup and view all the answers

    How long are the dry materials blended together in the stationary mixer?

    <p>Several minutes</p> Signup and view all the answers

    What is added to the mixer after the dry materials are blended?

    <p>Admixture chemicals and coloring pigments</p> Signup and view all the answers

    What is the purpose of the rotating brush in some operations?

    <p>To remove loose material from the top of the blocks</p> Signup and view all the answers

    How are the pallets of blocks arranged in the curing kiln?

    <p>On a set of rails</p> Signup and view all the answers

    What type of curing kiln is most commonly used?

    <p>Low-pressure steam kiln</p> Signup and view all the answers

    How long are the blocks held in the low-pressure steam kiln?

    <p>One to three hours</p> Signup and view all the answers

    What is an advantage of lightweight units compared to normal-weight units?

    <p>Higher thermal and fire resistance</p> Signup and view all the answers

    At what rate is steam introduced to raise the temperature of concrete blocks?

    <p>60°F per hour (16°C per hour)</p> Signup and view all the answers

    What is the purpose of introducing steam to raise the temperature of concrete blocks?

    <p>To control the rate of temperature increase</p> Signup and view all the answers

    What are the three basic forms of concrete block?

    <p>Solid, cellular, and hollow</p> Signup and view all the answers

    What is the difference between the nominal dimension and the specified dimension of a concrete block?

    <p>The thickness of the mortar joint</p> Signup and view all the answers

    What is the typical range for the dry density of concrete blocks?

    <p>500-2100 kg/m3</p> Signup and view all the answers

    What is the main factor that affects the compressive strength of concrete blocks?

    <p>Mix composition</p> Signup and view all the answers

    What is the classification of concrete masonry units based on compressive strength?

    <p>Load-bearing and non-load-bearing</p> Signup and view all the answers

    What is the relationship between the strength and density of concrete blocks?

    <p>The strength increases with an increase in density</p> Signup and view all the answers

    What is the purpose of specifying the nominal dimension of a concrete block?

    <p>To allow for the thickness of the mortar joint</p> Signup and view all the answers

    What is the direction of the load applied to determine the compressive strength of individual concrete masonry units?

    <p>In the direction of the height of the unit</p> Signup and view all the answers

    What is the purpose of controlling water absorption in concrete masonry units?

    <p>To reduce the effect of weathering and limit moisture loss after construction</p> Signup and view all the answers

    How is the absorption of concrete masonry units determined?

    <p>By immersing the unit in water for 24 hours</p> Signup and view all the answers

    What is the main factor that influences the magnitude of dimensional changes in concrete blocks?

    <p>The constituent materials and mix proportions</p> Signup and view all the answers

    What is the most important type of shrinkage in normal applications of concrete blocks?

    <p>Drying shrinkage</p> Signup and view all the answers

    What is the recommended strength of concrete blocks for use in extreme conditions of pollution and weather?

    <p>In excess of 7 Mpa</p> Signup and view all the answers

    Why are open-texture blocks more susceptible to frost attack?

    <p>Because water can move freely within the block on freezing</p> Signup and view all the answers

    What is the typical application of concrete blocks with adequate durability?

    <p>Most normal applications</p> Signup and view all the answers

    What is the standard used to determine the strength requirements of load-bearing and non-load-bearing concrete masonry units?

    <p>ASTM C90</p> Signup and view all the answers

    What is the primary cause of efflorescence in concrete blocks?

    <p>Reaction between atmospheric carbon dioxide and calcium hydroxides</p> Signup and view all the answers

    What is the main factor that controls the fire-endurance of concrete blocks?

    <p>Numerous factors</p> Signup and view all the answers

    What is the typical thickness of concrete blocks that can provide an adequate resistance to fire for up to 2 hours?

    <p>100 mm</p> Signup and view all the answers

    What is the relationship between the thermal conductivity of a concrete block and its block density?

    <p>Thermal conductivity increases as block density increases</p> Signup and view all the answers

    What is the effect of increasing moisture content on the thermal conductivity of a concrete block?

    <p>It increases the thermal conductivity</p> Signup and view all the answers

    What type of concrete blocks have relatively low thermal conductivities?

    <p>Autoclaved aerated concrete blocks</p> Signup and view all the answers

    What is the effect of increasing the block density of a concrete block on its thermal conductivity?

    <p>It increases the thermal conductivity</p> Signup and view all the answers

    What is the typical duration of fire resistance for non-load-bearing concrete blocks of 100 mm thickness?

    <p>4 hours</p> Signup and view all the answers

    What is the primary component of efflorescence in concrete blocks?

    <p>Sodium carbonates</p> Signup and view all the answers

    Study Notes

    Blocks

    • A concrete block is a building material used in wall construction, also known as a concrete masonry unit.
    • The first hollow concrete block was designed by Harmon S. Palmer in the United States in 1890.
    • By 1905, around 1,500 companies were manufacturing concrete blocks in the United States.

    Raw Materials

    • Concrete blocks are made from a mixture of powdered portland cement, water, sand, and gravel.
    • The mixture produces a light gray block with a fine surface texture and high compressive strength.
    • Concrete masonry units are manufactured in three classes: lightweight, medium-weight, and normal-weight units, based on their density.

    Manufacturing Process

    • The process involves mixing, molding, and curing.
    • Mixing involves blending dry materials (sand, gravel, and cement) with water and admixture chemicals.
    • Molding involves compacting the mixed concrete into blocks, which are then pushed out of molds onto a flat steel pallet.
    • Curing involves conveying the blocks to an automated stacker or loader, which places them in a curing rack.

    Form and Size

    • There are three basic forms of concrete blocks: solid, cellular, and hollow.
    • Concrete masonry units are specified by their nominal dimensions, which are greater than their actual dimensions by the thickness of the mortar joint.
    • Different types of concrete blocks include solid, cellular, hollow, common, facing, normal, insulating, lintel, quoin, cavity closure, and multipurpose blocks.

    Properties

    • The properties of concrete blocks depend on the type and proportions of constituent materials, manufacturing process, mode and duration of curing, and form and size of the block.
    • Density ranges from 500-2100 kg/m3, depending on aggregate density, size, and grading, degree of compaction, and block form.
    • Compressive strength is the basic requirement of concrete blocks, and is dependent on mix composition, degree of compaction, and aggregate type.
    • Water absorption is controlled by ASTM standards to reduce weathering effects and limit shrinkage due to moisture loss.
    • Dimensional changes occur due to variations in ambient moisture and temperature conditions, influenced by constituent materials, mix proportions, and manufacturing process.
    • Durability is generally adequate for most normal applications, but may be affected by extreme conditions of pollution and weather.
    • Efflorescence is rarely a problem with concrete blocks, but may occur as a result of a reaction between free hydroxides and atmospheric carbon dioxide.
    • Fire resistance is good, with most concrete blocks providing adequate resistance to fire for up to 2 hours if load-bearing or up to 4 hours if non-load-bearing.
    • Thermal conductivity is largely dependent on block density, with autoclaved aerated concrete and lightweight concrete blocks having relatively low thermal conductivities.

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    Description

    This quiz is for 1st year Civil Engineering students at the University of Halabja, covering topics related to building materials and testing.

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