CE312: Construction Materials and Testing - Concrete Preparation
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Questions and Answers

What is the standard temperature for curing concrete specimens?

23.0 + 2.0°C [73.5 + 3.5°F]

How long after removing the molds should specimens be cured with free water?

  • 30 minutes (correct)
  • 15 minutes
  • 1 hour
  • 1 day

    • Beams should be cured in water saturated with calcium hydroxide for at least 20 hours before testing.

    True

    What should be prevented between removal from water storage and completion of testing of the beams?

    <p>Drying of the surfaces</p> Signup and view all the answers

    Cylinders should be stored in or on the structure as near to the point of ______ of the concrete represented as possible.

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

    What should be done to protect the surfaces of the cylinders?

    <p>Protect all surfaces from the elements</p> Signup and view all the answers

    What is the maximum ambient temperature range allowed during curing?

    <p>20 to 30°C [68 to 86°F]</p> Signup and view all the answers

    Specimens can be left exposed to the weather during the curing period.

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

    For how long can standard curing temperatures be disregarded prior to testing?

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

    What should be done to prevent evaporation while molding specimens?

    <p>Cover the specimens immediately after finishing with a non-absorptive, non-reactive plate or impervious plastic.</p> Signup and view all the answers

    What materials should molds for specimens be made of?

    <p>Cast Iron</p> Signup and view all the answers

    Concrete used for slump tests can be reused after testing.

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

    When should molds be removed from specimens after casting?

    <p>24 ± 8 hours after casting, or 20 ± 4 hours after final set if the setting time is prolonged.</p> Signup and view all the answers

    To determine the yield of each batch of concrete, follow Test Method ___

    <p>C 138</p> Signup and view all the answers

    Match the following test methods with their corresponding purposes:

    <p>Test Method C 143/C 143M = Measure slump Test Method C 173 = Determine air content Test Method C 231 = Determine air content for lightweight aggregates Test Method C 1064 = Determine temperature of concrete</p> Signup and view all the answers

    What is the ideal curing environment temperature for specimens?

    <p>73.5 ± 3.5 °F</p> Signup and view all the answers

    The text provides instructions for making specimens from concrete not having measurable slump.

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

    What must be done if prolonged mixing is necessary during the concrete preparation?

    <p>Discard the batch and make a new batch without interruptions.</p> Signup and view all the answers

    What does the practice cover?

    <p>Procedures for making and curing test specimens of concrete in the laboratory under accurate control of materials and test conditions.</p> Signup and view all the answers

    The values stated in inch-pound units and SI units are exact equivalents.

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

    What is one of the purposes for which specimens may be used?

    <p>Mixture proportioning for project concrete</p> Signup and view all the answers

    What material should molds for concrete test specimens be made of?

    <p>Steel, cast iron, or other nonabsorbent material.</p> Signup and view all the answers

    Before mixing, the concrete materials should be brought to room temperature in the range from ___ to ___ °F.

    <p>68 to 86</p> Signup and view all the answers

    What is the weight requirement for the mallet used in concrete testing?

    <p>1.25 + 0.50 lb [0.6 + 0.20 kg]</p> Signup and view all the answers

    Which apparatus is used to measure air content in concrete?

    <p>Air Content Apparatus</p> Signup and view all the answers

    What temperature measuring device should conform to the requirements of Test Method C 1064?

    <p>Temperature Measuring Device</p> Signup and view all the answers

    What should be done with powdered admixtures that are largely insoluble?

    <p>Combine them with a portion of the cement before introduction into the batch.</p> Signup and view all the answers

    What type of aggregates should be maintained in a saturated surface-dry condition until batched?

    <p>Fine or coarse aggregates.</p> Signup and view all the answers

    What is the minimum overall length of a tamping rod?

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

    What is the maximum overall length of a tamping rod?

    <p>600 mm</p> Signup and view all the answers

    What is the acceptable diameter for an internal vibrator?

    <p>One-fourth the diameter of the cylinder mold</p> Signup and view all the answers

    What is the weight of the mallet head that should be used?

    <p>0.6 + 0.2 kg</p> Signup and view all the answers

    Placement tools should be small enough to prevent spillage during concrete placement.

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

    What type of device is used to measure air content?

    <p>Air Content Apparatus</p> Signup and view all the answers

    What size should the cylindrical specimens for compressive strength testing be?

    <p>Both a and b</p> Signup and view all the answers

    Beam specimens must be cast and hardened in a horizontal position.

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

    The supporting surface for storing specimens should be level to within _____ mm.

    <p>20</p> Signup and view all the answers

    Which of the following is NOT a method to maintain a satisfactory temperature environment during curing?

    <p>Use of a blender</p> Signup and view all the answers

    What is the preferred method to maintain moisture during initial curing?

    <p>Immersion in water</p> Signup and view all the answers

    Study Notes

    Standard Practice for Making and Curing Concrete Test Specimens

    • Covers procedures for making and curing test specimens of concrete in the laboratory under accurate control of materials and test conditions
    • Uses concrete that can be consolidated by rodding or vibration

    Scope

    • This practice does not address all safety concerns associated with its use
    • Users are responsible for establishing appropriate safety and health practices and determining the applicability of regulatory limitations prior to use
    • Fresh hydraulic cementitious mixtures are caustic and may cause chemical burns to exposed skin and tissue upon prolonged exposure

    Significance and Use

    • Provides standardized requirements for preparation of materials, mixing concrete, and making and curing concrete test specimens under laboratory conditions
    • Specimens can be used to:
      • Develop mixture proportioning for project concrete
      • Evaluate different mixtures and materials
      • Correlate with nondestructive tests
      • Provide specimens for research purposes

    Apparatus

    • Molds:
      • Made of steel, cast iron, or other nonabsorbent material
      • Nonreactive with concrete containing portland or other hydraulic cements
      • Conform to dimensions and tolerances specified in the method for which the specimens are required
    • Tamping Rods:
      • Two sizes specified in ASTM methods
      • Round, straight steel rods with rounded hemispherical tips
      • Larger rod: 5/8 in. [16 mm] in diameter and approximately 24 in. [600 mm] long
      • Smaller rod: 3/8 in. [10 mm] in diameter and approximately 12 in. [300 mm] long
    • Mallets:
      • With rubber or rawhide head weighing 1.25 + 0.50 lb [0.6 + 0.20 kg]
    • Vibrators:
      • Internal vibrators: frequency of at least 7000 vibrations per minute [115 Hz]
      • External vibrators: frequency of 3600 vibrations per minute [60 Hz] or higher
    • Small Tools:
      • Shovels, pails, trowels, wood float, blunted trowels, straightedge, feeler gage, scoops, rulers, rubber gloves, and metal mixing bowls
    • Slump Apparatus:
      • No specific details mentioned
    • Sampling and Mixing Pan:
      • Flat bottom, heavy-gage metal, watertight, of convenient depth, and of sufficient capacity
    • Wet-Sieving Equipment:
      • Conforms to the requirements of Practice C 172
    • Air Content Apparatus:
      • Conforms to the requirements of either Test Methods C 231 or C 173
    • Scales:
      • Accurate within 0.3 % of the test load at any point within the range of use
    • Temperature Measuring Device:
      • Conforms to the requirements of Test Method C 1064
    • Concrete Mixer:
      • Power-driven, revolving drum, tilting mixer, or suitable revolving pan or revolving-paddle mixer### Preparation of Materials
    • Bring concrete materials to room temperature (68-86°F or 20-30°C) before mixing, unless the temperature is stipulated.
    • Store cement in a dry place, in moisture-proof containers, preferably made of metal.
    • Mix cement thoroughly to provide a uniform supply throughout the tests.
    • Pass cement through a 850-μm (No. 200) or finer sieve to remove lumps, remix on a plastic sheet, and return to sample containers.
    • Determine specific gravity and absorption of aggregates in accordance with Test Methods C 127 or C 128.
    • Determine moisture content of aggregates in accordance with Test Methods C 70 and C 566.
    • Bring aggregates to and maintain a saturated surface-dry condition until batched for use.
    • Take care to prevent drying during weighing and use.
    • Lightweight aggregates may be difficult to treat due to high absorption, affecting concrete properties.

    Admixtures

    • Mix powdered admixtures with a portion of the cement before introducing into the batch in the mixer to ensure thorough distribution.
    • Handle and add essentially insoluble materials (e.g., pozzolans) to the batch in the same manner as cement.
    • Mix powdered admixtures with hygroscopic salts with sand to prevent balling of cement.
    • Add water-soluble and liquid admixtures to the mixer in solution in the mixing water.

    Procedure for Mixing Concrete

    • Mix concrete in a suitable mixer or by hand in batches of such size as to leave about 10% excess after molding the test specimens.
    • Add coarse aggregate, some of the mixing water, and the solution of admixture to the mixer, then add fine aggregate, cement, and water with the mixer running.
    • Mix for 3 minutes, followed by a 3-minute rest, and then a 2-minute final mixing.
    • Cover the open end or top of the mixer to prevent evaporation during the rest period.
    • Take precautions to compensate for mortar retained by the mixer to ensure correct proportioning.
    • Remix by shovel or trowel to eliminate segregation and ensure uniformity.

    Hand Mixing

    • Mix cement, powdered insoluble admixture (if used), and fine aggregate without adding water until thoroughly blended.
    • Add coarse aggregate and mix without adding water until uniformly distributed throughout the batch.
    • Add water and admixture solution (if used) and mix until the concrete is homogeneous in appearance and has the desired consistency.

    Making Specimens

    • Mold specimens as near as practicable to the place where they will be stored during the first 24 hours.
    • Avoid jarring, striking, tilting, or scarring of the surface of the specimens when moving them to the storage place.
    • Use a scoop, blunted trowel, or shovel to place the concrete in the molds, ensuring each portion is representative of the batch.
    • Remix the concrete in the mixing pan with a shovel or trowel to prevent segregation during molding.
    • Distribute the concrete by use of a tamping rod prior to consolidation.

    Consolidation

    • Use rodding, internal, or external vibration methods of consolidation, depending on the slump.
    • Rod or vibrate concrete with a slump greater than or equal to 1 in. (25 mm).
    • Vibrate concrete with a slump less than 1 in.
    • Do not use internal vibration for cylinders with a diameter less than 4 in. (100 mm), and for beams or prisms with a breadth or depth less than 4 in.

    Rodding

    • Place the concrete in the mold in the required number of layers of approximately equal volume.
    • Rod each layer with the rounded end of the rod, using the specified number of strokes and size of rod.
    • Rod the bottom layer throughout its depth.
    • Distribute the strokes uniformly over the cross section of the mold and for each upper layer, allowing the rod to penetrate through the layer being rodded and into the layer below approximately 1 in. (25 mm).
    • Tap the outsides of the mold lightly 10 to 15 times with the mallet to close any holes left by rodding and to release any large air bubbles that may have been trapped.### Consolidation
    • Use an open hand to tap light-gage single-use molds to avoid damage
    • Tap the outside of the mold at least 10 times with a mallet to close holes and release entrapped air voids after each layer is vibrated
    • Use internal vibration to compact the specimen, inserting the vibrator slowly and withdrawing it slowly to avoid large air pockets
    • For cylinders, insert the vibrator at intervals not exceeding 6 in. along the center line of the long dimension of the specimen
    • For beams, prisms, and horizontal creep cylinders, insert the vibrator at intervals not exceeding 6 in. along the center line of the long dimension of the specimen, or along both sides but not in contact with the strain gage
    • Allow the shaft of the vibrator to penetrate into the layer below approximately 1 in.

    Finishing

    • Strike off the surface of the concrete and float or trowel it in accordance with the method concerned
    • Finish the surface with a wood or magnesium float, performing all finishing with the minimum manipulation necessary to produce a flat, even surface
    • For cylinders, finish the top surfaces by striking them off with the tamping rod or a wood float or trowel
    • For horizontally cast creep cylinders, strike off the specimen with a trowel or float, then trowel the minimum amount required to form the concrete in the opening concentrically with the rest of the specimen

    Curing

    • Cover the specimens immediately after finishing to prevent evaporation of water from unhardened concrete
    • Use a non-absorptive, non-reactive plate or a sheet of tough, durable impervious plastic to cover the specimens
    • Store the specimens immediately after finishing until the removal of the molds to prevent loss of moisture from the specimens
    • Record the maximum and minimum ambient temperatures during the initial curing

    Removal from Molds

    • Remove the specimens from the molds 24 ± 8 h after casting
    • For concrete with prolonged setting time, molds shall not be removed until 20 ± 4 h after final set

    Curing Environment

    • Moist cure all specimens at 73.5 ± 3.5 °F (23.0 ± 2.0 °C) from the time of molding until the moment of test
    • Store specimens in a vibration-free environment during the first 48 h of curing
    • Cure flexural strength test specimens in accordance with Initial Curing and Removal from Molds, and then immerse them in water saturated with calcium hydroxide at 73 ± 3 °F (23 ± 2 °C) for a minimum period of 20 h immediately prior to testing

    Scope

    • This practice covers procedures for making and curing cylinder and beam specimens from representative samples of fresh concrete for a construction project
    • The concrete used to make the molded specimens shall be sampled after all on-site adjustments have been made to the mixture proportions, including the addition of mix water and admixtures

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    Construction Materials and Testing CE312 PDF

    Description

    This quiz covers the preparation and curing of concrete test specimens in the laboratory, following standard practices. It's a part of the Construction Materials and Testing course, CE312. Engr. Vera Karla Caingles presents this topic.

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