What are the methods for determining the workability of concrete?

Hello, the workability of concrete is a big aspect, which includes fluidity, water retention, and cohesion.

Fluidity: refers to the performance of fresh concrete under the action of self-weight or mechanical vibration, which can produce flow and evenly and densely fill the formwork. The fluidity reflects the thickness of the mixture.

If the concrete mixture is too dry and thick, the fluidity is poor, and it is difficult to vibrate and compact; If the mixture is too thin, it has good fluidity, but it is easy to appear stratified and segregated. The main influencing factor is the water consumption of concrete.

Cohesiveness: refers to the performance that there is a certain degree of cohesion between the constituent materials of the fresh concrete, and the delamination and segregation will not occur during the construction process. Cohesiveness reflects the uniformity of the concrete mixture.

If the cohesion of the concrete mixture is not good, the aggregate and the cement slurry in the concrete are easy to separate, resulting in uneven concrete, and honeycomb and cavities will appear after vibration. The main influencing factor is the glue-to-sand ratio.

Water retention: refers to the performance that the fresh concrete has a certain water retention capacity and will not produce serious water leakage during the construction process. Water retention reflects the stability of the concrete mixture.

Permeable channels are easy to form inside the concrete with poor water retention, which affects the compactness of the concrete and reduces the strength and durability of the concrete. The main influencing factors are cement variety, dosage and fineness.

However, we usually talk about workability is only the wrapping of concrete, that is, the cohesiveness, and the way to judge is to see whether the mortar of the concrete is wrapped around the stone, and the overall feeling is whether there are many stones. If you have any questions, you can continue to ask!

The workability of concrete is a comprehensive technical index.

The measurement method is slump determination method. The specific determination method is as follows:

The concrete mixture is loaded into the slump cylinder in three times according to the regulations, each time the vibrating rod is inserted 25 times from the center of the cylinder to the surrounding in the clockwise direction, the excess concrete is scraped flat after the three times are inserted, the slump cylinder is lifted vertically upwards and moved to the side, the concrete mixture will produce a slump phenomenon due to its own weight, and then the size of the concrete slump is measured with a ruler, that is, the slump.

Subtract the height of the barrel (300mm) from the height of the concrete at the highest point after the collapse, which is called slump. If the difference is 100mm, the slump is 100. The greater the slump, the better the liquidity.

The slump test was performed to determine the fluidity of the mixture, supplemented by intuitive empirical evaluation of cohesion and water retention. According to the different slumps, the concrete mixture can be divided into 4 grades: low-plastic concrete (10 40mm), plastic concrete (50 90mm), fluidity concrete (100 150mm), and high-fluidity concrete (greater than 160mm).

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How to evaluate the workability of concrete mixture is as follows: The workability of concrete mixture refers to the fact that the concrete mixture is easy to construct and operate, and can obtain the properties of uniform quality and dense molding. The workability of concrete mixture is a comprehensive property, which includes three aspects: fluidity, cohesion and water retention.

The workability of concrete mixture is a comprehensive concept, which can be comprehensively and appropriately expressed by a simple evaluation method, usually by using a certain method to determine the fluidity of concrete mixture, and then paving to evaluate the cohesion and water retention by intuitive experience. There are many factors affecting the workability of concrete mixture, mainly including: (1) the nature and quality of raw materials

For example, the variety and fineness of cement, the variety, specification and quality of aggregates, admixtures and other additives (2) the dosage relationship of raw materials: such as the amount of cement slurry and water-cement ratio, sand rate, etc. (3) environmental conditions. Construction conditions and time, etc.

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Concrete is made of each component material in a certain proportion of the combination and mixing. The workability of concrete mixture is a comprehensive index, which includes three properties: fluidity, cohesion and water retention. Due to its complex connotation, according to the current standards in China, "slump" and "dimensional neck consistency" are used to determine the fluidity of concrete mixture.

Here we start with the "slump" test. (This test is applicable to the slump value of the banquet fiber is not less than mm, and the aggregate particle size is not greater than mm concrete concomitant). 2. The standard slump cylinder and warhead rammer made of metal materials for experimental equipment and instruments (Fig. 4-1), shovels, rulers, trowels, scales, etc.

3. Experimental step 1, according to the proportion of the mixing material, (such as cement: ..)kg；Sand:

kg；Stone: .

7kg；Water: ...2kg。

Pour them onto a mixing plate and mix well with a shovel, then take a dimple in the middle and mix while adding water until they are evenly mixed. 2. Use a damp cloth to wipe and lubricate the inside and outside of the mixing plate and the slump cylinder, and add a funnel to the top of the cylinder and put it on the mixing plate. Press the pedal firmly with both feet so that it is in a fixed position.

3. Use a small shovel to evenly load the mixed mixture into three layers into the cylinder, and the loading height of each layer is roughly one-third of the cylinder height after insertion. When the top layer is charged, the mixture should be high and vertical out of the top of the cylinder. During the insertion process, if the specimen settles below the barrel mouth, it should be added at any time so that it remains higher than the top of the cylinder from beginning to end.

Each layer is inserted 25 times with a tamper, and the tamper should be carried out on the entire area, along the spiral line from the edge to the center. When inserting the pound on the edge of the barrel, the tamper should be slightly tilted, and then the center part should be inserted vertically. Each layer should be pounded until the surface of the lower layer is smashed.

4. After the insertion is completed, remove the funnel, scrape off the excess mixture with a trowel to make it flush with the top surface of the cylinder, and the debris on the mixing plate around the cylinder must be scraped and removed. 5. Lift the slump cylinder carefully and smoothly vertically upward, without skewing, and complete the lifting process within about 5 10s, put the cylinder on the side of the mixture test body, measure the height difference between the highest point of the mixture test body and the cylinder after the collapse (in mm, the reading is accurate to 5mm), and the hole is the slump of the mixture (as shown in Figure 4-2). The entire process from the start of the charge to the lifting of the slump cylinder was completed in 150s.

6. When the slump cylinder is lifted, if the specimen collapses or is sheared on one side, the sample should be re-sampled for testing. If this phenomenon still occurs for the second time, it means that the workability of the mixture is not good and should be recorded. 7. After measuring the slump, observe the following properties of the mixture and record it.

Cohesiveness: Gently tap on the side of the collapsed mixture cone with a tamper, if the cone gradually sinks, it means that the cohesiveness is good; If it collapses suddenly, partially cracks or segregates stones, it is a sign of poor cohesion.

Water retention: If more slurry is precipitated from the bottom after lifting the slump cylinder, and the mixture in the cone part is also exposed due to the loss of pulp, it indicates that the water retention is not good. If this phenomenon is absent, it indicates good water retention.