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Chapter 1:Cement&Concrete B.From fresh concrete to hardened concrete 23 <br /> Table 1.4 <br /> 28-day Effect of various <br /> Change Workability compressive factors on <br /> strength workability and <br /> Smoother grading JI JI strength of <br /> More rounded aggregate J► 1► concrete <br /> More crushed(angular)aggregate <br /> More mixing water �► <br /> Higher concrete temperature �► �► <br /> Use of a superplasticizer <br /> Use of an air entrainer �► <br /> Use of a retarder J► J► <br /> *X positive influence negative influence no significant influence <br /> 2. Workability a.Slump test: <br /> The slump test is the most well-known and widely <br /> To achieve a high quality concrete structure, the used method to characterize the workability of fresh <br /> method of placing and compaction as well as the concrete.This simple test is used at the job sites to <br /> shape of the concrete element and reinforcement quickly determine whether a concrete batch should <br /> arrangement, should be considered to select the be accepted or rejected. <br /> workability of the concrete. <br /> The slump test measures the ability of concrete to <br /> The concrete workability affects the speed of flow under its own weight, without vibration. This <br /> placement and the degree of compaction of method is suitable for medium to high workability <br /> concrete. Inadequate compaction may result in the concrete with slump ranging from 10 to 210 mm <br /> reduction in both strength and durability of (EN 206). <br /> concrete. <br /> The test method is widely standardized throughout <br /> Different test methods for workability are available the world: <br /> including slump, Vebe time, flow table, etc. The TCVN 3106 <br /> choice of the test method depends on the concrete ASTM C143 <br /> workability and its application. <br /> • EN 12350-2 <br /> To get reliable results, each test method for The apparatus used in the slump test are: mold, <br /> workability should be applied within its test range tamping rod,measuring equipment(Fig 1.20): <br /> (EN206): <br /> Fig 1.20 <br /> a <br /> •Slump 2 10 mm and:5 210 mm; Apparatus to <br /> 4 determine slump <br /> •Vebe time 5 30 sec and>5 sec; <br /> • Flow diameter >340 mm and:5 620 mm. <br /> l � <br /> TCXDVN 374:2006 specifies: <br /> • For too dry concrete:the vebe time>50 second. 200_I <br /> • For dry concrete:the vebe time > 5 second and < <br /> 50 second. Slump <br /> • For plasticized concrete: The slump from 10 to 300 mm <br /> 220(mm) Du 11 <br /> • For super-plasticized concrete:the flow from 260 _ -_4 <br /> —400(mm) 100 <br />