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?
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?
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Cylinders should be stored in or on the structure as near to the point of ______ of the concrete represented as possible.
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What should be done to protect the surfaces of the cylinders?
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What is the maximum ambient temperature range allowed during curing?
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Specimens can be left exposed to the weather during the curing period.
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For how long can standard curing temperatures be disregarded prior to testing?
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What should be done to prevent evaporation while molding specimens?
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What materials should molds for specimens be made of?
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Concrete used for slump tests can be reused after testing.
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When should molds be removed from specimens after casting?
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To determine the yield of each batch of concrete, follow Test Method ___
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Match the following test methods with their corresponding purposes:
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What is the ideal curing environment temperature for specimens?
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The text provides instructions for making specimens from concrete not having measurable slump.
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What must be done if prolonged mixing is necessary during the concrete preparation?
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What does the practice cover?
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The values stated in inch-pound units and SI units are exact equivalents.
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What is one of the purposes for which specimens may be used?
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What material should molds for concrete test specimens be made of?
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Before mixing, the concrete materials should be brought to room temperature in the range from ___ to ___ °F.
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What is the weight requirement for the mallet used in concrete testing?
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Which apparatus is used to measure air content in concrete?
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What temperature measuring device should conform to the requirements of Test Method C 1064?
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What should be done with powdered admixtures that are largely insoluble?
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What type of aggregates should be maintained in a saturated surface-dry condition until batched?
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What is the minimum overall length of a tamping rod?
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What is the maximum overall length of a tamping rod?
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What is the acceptable diameter for an internal vibrator?
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What is the weight of the mallet head that should be used?
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Placement tools should be small enough to prevent spillage during concrete placement.
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What type of device is used to measure air content?
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What size should the cylindrical specimens for compressive strength testing be?
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Beam specimens must be cast and hardened in a horizontal position.
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The supporting surface for storing specimens should be level to within _____ mm.
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Which of the following is NOT a method to maintain a satisfactory temperature environment during curing?
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What is the preferred method to maintain moisture during initial curing?
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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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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.
