AIM OF THE EXPERIMENT: Determining concrete consistency by the help of a Vee-Bee Consistometer as this identifies the needed time for the process of transforming.
THEORY
Green concrete or fresh one behavior that appears after mixing up to compaction is based on the concrete workability as this is a term that consists of four concrete partial properties which are Compactiability, Mouldability, Transportability and Mixability. This can also be explained in general way which is the workability is that factor expressing the work amount that is needed to be made for compacting the specific concrete in a certain given mould. When there is a particular mix and there should be a particular workability for it; the compaction type that is followed can identify this along with the reinforcement complicated nature related to the used reinforcement in the concrete that is reinforced. Regarding the workable mix, it mustn't segregate. Regarding the workability partial properties they can be explained as follows: Mixability: mixability is the mix's ability to produce specific concrete that is homogeneous and green made from the constituent materials. Transportability: Transportability is the concrete mix ability to keep the concrete mix that is homogenous from segregation process in the concrete transportation time that is limited as this can occur as a result of the limited nature of handling. Mouldability: is the fresh concrete mix's ability of complete filling of moulds and forms prepared for it keeping its homogeneity and continuity during the process of concrete placing using different techniques available for this process. Compactibility: it is the concrete mix ability for being compacted into specific dense with certain minimum void and under conditions of existence of the compaction means in the site.
It is suggested that the best mix based on the compactibility is that mix that close the voids. Regarding the workable concrete, it is that concrete which is of very low internal friction between its different particles and that is able to overcome the offered frictional resistance presented by the reinforcement or the formwork surface which are found in the concrete with a specific amount of forthcoming compacting works.
. A . KAIKADE, J. (2005).
APPARATUS: there should be the following: A pot made of metal, a vibrator table, a sheet metal cone that is open at its two ends with a high that is 30 cm and a diameter of bottom is 20 cm and a top diameter that is 10cm. A standard iron rod that is 20 mm in the diameter and in length it is 500mm. there should be trowels and a Stop watch and at the base there should be a cylinder, there should be containers and balance as shown in figure 2.1
MATERIALS: Sample of concrete that is fresh.
EXPERIMENT METHOD: 1.Prepare the needed mix of concrete with specific proportions that are 1:2:4 for (Cement : Sand: Coarse Aggregate) for getting an amount of concrete mix of nearly 16.7 kg and 0.6 w/c ratio.
2. Place the slump cone in the consistometer cylindrical container. Fill the slump cone as being with four layers and each layer should nearly be one quarter of the cone height. Each layer should be tamp with about twenty-five strokes of the end of the tamping rod that is rounded. Distribution of the strokes is in uniformally over the cone's cross-section and for the second as well as the subsequent layers, the tamping bar has to go into the underlying layer. After tamping the top layer, use a trowel for strucking off level the concrete in order to make the cone properly filled. There should be a slump test to be performed in the consistometer sheet metal cylindrical pot.
3. The glass disc that is connected to the swivel arm has to be moved and put into the pot on the slump cone top and before the cone is gone up, the concrete cone position has to be monitored through adjusting the glass disc that is connected to the swivel arm.
4. The cone needs to be lifted up and the slump needs to be noted on the graduated rod through lowering the glass disc on the concrete cone top.
5. Then switch on the electrical vibrator and allow the concrete to go out into the pot.
6. The vibration then has to be continuous till the total concrete surface completely adheres to the glass disc, the stop watch has to be used for monitoring time needed for this process.
7.Recording time shall be based on seconds.
DATA AND THE EXPERIMENT RESULTS: Time for remoulding completion equals 5.75 seconds
| Description of workability |
Vee-Bee Time (in Second)
|
| Extremely dry | From 32 to 18 |
| Very stiff | From 18 to 10 |
| Stiff | From 10 to 5 |
| Stiff plastic | From 5 to 3 |
| Plastic | From 3 to zero |
| Flowing |
Figure 2.3 the used data in the experiment
ρ = concrete density 2400 kg/m3
ρ =m/υ
m = ρ . υ
m = 2400× 0.00549= 13.188kilograms
The dimensions of the cone are:
1. diameter of the bottom -20cm
2. diameter of the top-10cm
3. Height is-30cm
3
3
100³
25% wastage = 13.188+ 25%
=13.188+3.0825
=16.47 kilograms
* percentage :- 1:2:4 related to cement to fine agg to coarse agg 1 + 2 + 4 = 7 respectively
*the cement = 1/7 × mass = 1/7 × 16.47 = 2.35kg
*the fine agg = 2/7 × mass = 2/7× 16.47 =4.71 kg
*the coarse agg = 4/7 × mass = 4/7 × 16.47 =9.41 kg
w/c =0.6 w = c ×0.6 = 2.35 × 0.6 = 1.4 liters.
DISCUSSION: The result gained from this experiment is 5 seconds which shows that the concrete type Stiff Plastic is that type that has the appropriate usages in proceses of construction. Cullen, D. (1998).
CONCLUSION: the current experiment shows that because results based on seconds range from zero to 35; this means that each type of concrete can be defined by time and that consistency time of concrete is very important to identify the Vee-Bee consistency time of the concrete mix.
1 comment:
very useful article
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