Cement Americas

WIN 2018

Cement Americas provides comprehensive coverage of the North and South American cement markets from raw material extraction to delivery and tranportation to end user.

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www.cementamericas.com • Winter 2018 • CEMENT AMERICAS 21 FEATURE Construction Inspection Repair www.mariettasilos.com ( 740 ) 373-2822 Silo/Bin Cleaning Roof Coating Vacuum Truck Service Air Pad Maintenance www.usasilos.com ( 740 ) 749-3329 pacted sample of cement at ro o m te m p e rat u re between 18 and 22 C by measuring the time tak- en for a fixed quantity of air to flow through the cement sample, and this recorded time is a mea- sure for the specific sur- face area. The method is a comparative test between a known and unknown material, therefore a reference sample with a known surface area is used for calibration. By measuring the time taken for air to flow through the reference mate- rial, the user can establish a correlation of the surface area based on the time taken on the test cement. The Blaine Apparatus is employed for this test and consists of a permeability test cell, a perforated disk, a plunger, filter paper, a manometer U-tube, manometer liquid, reference cement and a timer. The applicable standards are EN 196-6, ASTM C204 and AASHTO T153. Consistency, Setting Time and Flow The consistency of a mixture plays an important role in the performance of the mix when poured through reinforcing bars within a form, and in the time taken for the mortar or concrete to set. The consistency test is performed to esti- mate the amount of water needed to form a paste of nor- mal consistency, defined as the percentage water require- ment of the cement paste. When water is added to cement, the resulting paste will begin to harden and gain compressive strength, and the Vicat needle test measures the time taken for the cement-water mixture to harden (or set). Consistency is measured by the Vicat test that provides both initial and final setting times – measurements that can be regarded as the two stiffening states of the cement. The beginning of solidification, or the initial set, marks the point in time when the paste has become unworkable, and the time taken to completely solidify marks the final set. This should not be too long so that construction activity can be resumed within a reasonable time after the place- ment of concrete. The Vicat plunger has a specified weight, dimensions and drop height, and the resistance to penetration by the plung- er is determined by the viscosity of the cement paste in a mold. The initial setting time is defined as the time taken for the Vicat needle to be able to penetrate the paste in the mold to a depth of 5 mm. The final setting time is the time taken for the cement paste to harden sufficiently such that the Vicat needle can- not penetrate the cement paste in the mold and leaves no mark on the surface of the specimen. The required equip- ment includes a Vicat frame, Vicat needles and mold (EN or ASTM), glass graduates and mixing tools. Alternatively, ELE manufactures an automatic Vicat apparatus. Applicable standards include: EN 196-3, EN 480-2, EN 13454-2, ASTM C187, ASTM C191, AASHTO T129 and AASHTO T131. Determination of consistency can also be carried out by using a Flow Table Test Apparatus. While flow is not usually included in hydraulic cement specifications, it is common- ly used in standard tests that require the mortar to have a water content that provides a specified flow level. Cement paste acts as a separator for aggregates in mortar, and a lack of sufficient mortar results in a mixture of limited flow, which is prone to segregation and difficulty of finishing. A cement paste or mortar mix is placed in a mold of defined volume and dimensions, and the mold is placed on top and in the center of a flow table apparatus, where the sample is formed and compact- e d . T h e m o l d i s t h e n removed, leaving behind the formed sample of mortar, which is then raised and dropped from a height of 12.5 mm, 15 times in approximately 15 seconds. Briquette mold. Flexural tensile machine.

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