Workability Tests By: Ahmed Essam Mansour Objectives: The determination of workability of fresh concrete using three approximating methods: 1. The slump test. 2. The compaction factor test. 3. VEBE test. Standards: The slump test: ASTM : C 143 B.S. : 1882 Part II The main differences between the two methods are: In filling the cone (how many layers) ASTM: 3 layers B.S.: 4 layers From where the slump is measures ASTM: From the center B.S.: From the highest point The compaction factor test: B.S. 1881 : Part 2 1970 VEBE test: B.S. 1881 : Part II : 1970 General Discussion: When dealing with fresh concrete all we care about is its workability. Workability is defined as the amount of useful internal work that results full 1Visit www.ahm531.com for more lab reports and lecture notes!
Workability Tests By: Ahmed Essam Mansour compaction, in other words it is the ease of flow of fresh concrete and the ease of dealing with it in transporting, placing and compacting without segregation. There are many factors that affect the workability of fresh concrete, but the most important is the water content in the mix. Till now there is no perfectly acceptable method that measures the workability of fresh concrete, the methods of workability measurement gives results that are comparable only with reference to the particular method. In the concrete laboratory we did three tests on workability, mentioned below with a description of each: The Slump Test: As the name indicates, this test measure the slump in a frustum cone shaped concrete mix, the slump that occurs is classified into three classifications: Zero slumps: If the slump is equal to zero (Very stiff mixes). True slump: If the slump is between 0 to 12.5 cm. Shear slump: If the mix cone sheared into two parts; one half of the cone slides down an inclined plane. Collapse: If the slump was between 15 to 21 cm. When we get zero slump, that means that our mix is very stiff and a clear measurement for workability is not given, that s why this method is not useful for stiff mixes. Getting a true slump gives a good measure for workability, and the gained value is recorded as a measure for workability with reference to this method only. When the result is shear slump or collapse the test shall be repeated using another sample from the mix, if the same result occurs then that must be recorded and it indicates a lack of cohesion in the mix and is usually happens to lean mixes. In true slump, the higher slump value indicates higher workability. Usually the slump value required is given in the project plan, for example, for normal reinforcement the slump value is between 5 to 10 cm, and for high strength concrete the slump is given to be less than 5 cm. Compaction factor test: This method is based on using the inverse approach of the workability definition, i.e. it measures the degree of compaction done by a standard work, which results from falling through the hoppers. 2Visit www.ahm531.com for more lab reports and lecture notes!
Workability Tests By: Ahmed Essam Mansour This test is more sensitive to low workable mixes than the high workable ones. The compacting factor is measured by the density ratio, i.e. the ratio of the density of the mix obtained by the mix to the density of the mix fully compacted. In the compaction factor test we use the same volume for both densities and so the compaction factor becomes: Compaction factor = partially weight / fully compacted weight The largest value that can be obtained for the Compaction Factor Value is 1, the more workable the mix is, the nearest the compaction factor is to 1. VEBE test: It is based on measuring the time (Called VEBE time) needed to transfer the shape of a concrete mix from a frustum cone to a cylinder (these shapes are standardized by the apparatus of this test), by vibrating and compacting the mix. The more VEBE time needed the less workable the mix is. This method is very useful for stiff mixes. Comparison between the three methods and problems in each one: The method The Civil Engineering Problems Center Slump Test Not useful for stiff mixes ((Zero Slump)). Same slump Different workability. Not reliable for lean mixes with tendency to harshness. Different slumps (Types or values) same workability. There is no unique slump value for a specific workability. Same slump Different workability Different aggregates. Compaction factor test VEBE test Very stiff mixes might stick in the hoppers and so it will be needed to ease by poking with a steel rod (External effect). Stiff mixes (very low workability) the amount of work needed for full compaction depends on the richness of the mix, but the compacting factor does not depend on the richness of the mix. Same Compacting Factor Different workability. The apparatus is heavy and complicated. 1. Difficulties in establishing the end point of the test is a source of error. 3Visit www.ahm531.com for more lab reports and lecture notes!
Workability Tests By: Ahmed Essam Mansour The slump test is the more common in use because of: 1. The simplicity of the apparatus. 2. It is useful for check on day to day or hour to hour variation in the materials being fed into the mixer. The slump test is not useful for stiff mixes and lean mixes. Both Compacting factor test and VEBE test are useful for stiff mixes, but VEBE test is more useful for the following reasons: 1. The problem of sticking of concrete in the hoppers of the compacting factor apparatus. 2. The treatment of concrete during the test is comparatively closely related to the method of placing in real practice. Apparatus and Materials: Mix Materials: 1. Cement paste. 2. Aggregates (coarse, medium and fine) 3. Water. Slump test Apparatus: 1. Slump mould. Description: It has the shape of frustum cone. The internal dimensions are as follows: Bottom diameter = 203 mm Top diameter = 102 mm Height = 305 mm the thickness = 1.6 mm the internal surface is smooth, the mould is provided with foot pieces for fixing and handle for lifting the mould. 2. Tamping rod. Description: The diameter = 16 mm The length = 600 mm It should be rounded at one end (the end that we tamp the mix with) 4Visit www.ahm531.com for more lab reports and lecture notes!
Workability Tests By: Ahmed Essam Mansour 3. Trowel. 4. Smooth, rigid and not absorbent plate. Compacting Factor Apparatus: 1. The compacting factor apparatus. Description: It consists mainly of two hoppers frustum cone shaped and one cylinder, all fixed on the vertical rigid frame. The dimensions: Upper hopper: Top diameter = 254 mm Bottom diameter = 127 mm Height = 279 mm Lower hopper: Top diameter = 229 mm Bottom diameter = 127 mm Height = 229 mm the distance between the two hoppers and between the lower hopper and the cylinder = 203 mm the hoppers and the cylinder shall be smooth at the internal surface. The lower ends of the hoppers shall be closed tightly fitting hinged trap doors having quick release catches. 2. Two trowels. 3. Tamping rod. 4. Weighing machine. VEBE test Apparatus: 1. VEBE consistometer. Description: It consists of: Cylindrical container with diameter = 240 mm, and height = 200 mm. Mould: the same mould used in the slump test. Disc: A transparent horizontal disc attached to a rod which slides vertically. Vibrating Table: 380*260 mm, supported by four rubber shock absorbers. 2. Tamping rod. 3. Stop watch. 5Visit www.ahm531.com for more lab reports and lecture notes!
Workability Tests By: Ahmed Essam Mansour Procedures: Mix Design: The concrete mix we tested had the following specifications: Cement aggregate ratio = 1:6 Coarse: Medium: Fine ratio = 2:2:2 Fine aggregate ratio = 1 Sweileh: 1 normal fine Water/Cement ratio = 50%. 1. Calculating the EA of each type of Aggregates. Coarse 480gm Medium 200gm Fine 40gm Calculating the quantities of materials when taking 2kg of cement: Water requirement = Water in the W\C + EA = 1720gm 4 kg coarse aggregates. 4 kg Medium aggregates. 2 kg Sweileh fine aggregate. 2 kg Normal fine aggregate. 2. Mixing these materials within 4:25 minutes Slump test: 1. We cleaned the internal surface of the slump mould. 2. We placed the mould on the plate and press by the legs on the foot pieces to fix it. 3. We filled the mold with the concrete mix we made previously, in three layers (each consisted the third of the mould). And we tamped each layer 25 times by the rounded end of the tamping rod. 4. The last layer is leveled then with the upper part of the mould. 5. The mould was removed gently then by holding it from the handles and moving it vertically. 6. The mould was placed next to the frustum cone shaped mix, and the slump value was measured then by measuring the difference between the difference in heights of the mould and the center of the concrete mix. 6Visit www.ahm531.com for more lab reports and lecture notes!
Workability Tests By: Ahmed Essam Mansour Compaction value test: 1. We cleaned the hoppers and the cylinders from the inside. 2. Weighing the empty cylinder. (W 1 ) 3. We placed the concrete mix gently in the upper hopper till it was filled. 4. The upper hopper s trap door was then opened and the concrete mix filled the lower hopper. 5. The lower hopper s trap door was then opened so that the concrete mix filled the cylinder. 6. The upper surface of the cylinder is then leveled using two trowels, but no compaction shall be done. 7. The weight of the cylinder with the partially compacted concrete mix was taken. (W 2 ) 8. The cylinder is emptied then and filled with the concrete mix on six layers with tamping 25 times for each layer. 9. The weight of the cylinder with the fully compacted concrete mix was taken. (W 3 ) VEBE test: 1. We placed the mould concentrically in the container. 2. It was filled with the concrete mix on four layers with tamping 25 times each layer. 3. The mould then is left up, and the slump value was calculated. 4. The transparent disk was placed on the concrete cone. 5. The vibrator was started as the timing did. 6. The timing shall stop when the transparent disc is totally covered with concrete and all the cavities in the mix are disappeared. 7Visit www.ahm531.com for more lab reports and lecture notes!
Workability Tests By: Ahmed Essam Mansour Results and Calculations: Conclusion: According the test results we obtained, concrete mix we used can be judged as follows: 8Visit www.ahm531.com for more lab reports and lecture notes!
Workability Tests By: Ahmed Essam Mansour Slump test: The mix has a medium workability. Compacted factor test: The mix has medium workability. VEBE test: The mix has low workability. This variation in the workability between the first 2 tests and the last one (VEBE test) can be a result to losing the workability with time, the time between making the mix and doing the VEBE time test was larger than it to the other two tests. Other reason for that might be an error resulted from the determination of the end of the test. 9Visit www.ahm531.com for more lab reports and lecture notes!