Designation: c 157/C 157M – 08 Standard Test Method for Length Change of Hardened Hydraulic-Cement Mortar and Concrete 1
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- 10. Procedure for Curing of Specimens
| 9. Procedure for Molding Specimens
9.1 Mortar Specimens—Place the mortar in the mold in two approximately equal layers. Compact each layer with the tamper. Work the mortar into the corners, around the gage studs, and along the surfaces of the mold with the tamper until a homogeneous specimen is obtained. After the top layer has been compacted, strike off the mortar flush with the top of the mold, and smooth the surface with a few strokes of a trowel. Immediately after completion of molding, loosen the device by holding the gage studs in position at each end of the mold in order to prevent any restraint of the gage studs during initial shrinkage of the specimen. 9.2 Concrete Specimens—Place the concrete in the mold in two approximately equal layers in accordance with the general instructions for placing concrete in specimens given in Practice C 192/C 192M . Consolidate each layer by rodding, except use external vibration if the slump is less than 3 in. [75 mm] in accordance with the instructions for consolidation of flexure test specimens given in Practice C 192/C 192M . The same method of consolidation is to be used for all specimens to be compared. In addition, as the top layer is being placed, work the concrete thoroughly around each gage stud with the fingers. The top layer shall slightly overfill the mold. After consolida- tion is complete, strike off the excess material with a straight- edge. Immediately after completion of molding, loosen the device by holding the gage studs in position at each end of the mold in order to prevent any restraint of the gage studs before the test specimens are demolded. 10. Procedure for Curing of Specimens 10.1 Cure the test specimens in the molds in a moist cabinet or room in accordance with Specification C 511 . Protect specimens from dripping water. 10.2 Remove specimens from the molds at an age of 23 1 ⁄ 2 6 1 ⁄ 2 h after the addition of water to the cement during the mixing operation. In order to avoid damage during removal from the molds, it is not permitted, especially in the case of certain slow-hardening cements, to allow specimens to remain in the molds for more than 24 h. When this is found necessary the moist curing schedule shall be extended, but all specimens that are to be directly compared with each other shall be subjected to the same conditions of moist-curing and shall have their initial comparator reading made within 6 1 ⁄ 2 h of the same age. It is permitted to use the demolding device to remove speci- mens without striking or jarring and with particular care not to exert pressure directly against the gage studs. The gage stud holder shall remain attached to the stud during this operation. Marks placed on the specimens for identification or positioning are only to be made by graphite applied either by a soft pencil or as a liquid that deposits essentially graphite without binder or made with waterproof indelible ink. Upon removal of the specimens from the molds, place them in lime-saturated water maintained at 73 6 1 °F [23 6 0.5 °C] for a minimum of 15 min in the case of 1-in. [25-mm] square cross-section speci- mens, and for a minimum of 30 min in the case of 3-in. [75-mm] or 4-in. [100-mm] square cross section specimens before being measured for length. This is to minimize variation in length due to variation in temperature. At an age of 24 6 1 ⁄ 2 h after the addition of water to the cement during the mixing operation, remove the specimens from water storage one at a time, wipe with a damp cloth, and immediately take the initial comparator reading. 10.3 After the initial comparator reading, store the speci- mens in lime-saturated water at 73 6 3 °F [23 6 2 °C] until they have reached an age of 28 days, including the period in the molds. At the end of the curing period, take a second comparator reading after the specimens have been brought to a tải về 128.58 Kb. Chia sẻ với bạn bè của bạn:
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