What is the meaning of slump and slump loss of fresh concrete? Write out its trial steps

Slump is to characterize the workability (workability) of concrete: including fluidity, the performance of filling the mold under the action of its own weight, the greater the slump, the greater the fluidity; Reaction cohesiveness and water retention.

Slump loss is the concept of a decrease in slump over time.

Slump Experiment:

1. Main instruments and equipment.

1.Slump cylinder A round table-shaped cylinder made of thin steel plate or other metal materials, and the inner wall should be smooth. The dimensions of the cylinder are shown in Fig

2.Pounding sticks. 3.Square-toed small shovels, rulers, etc.

2. Experimental Procedures.

Before the test, the amount of various materials required for the sample should be calculated according to the preliminary calculation mix ratio of the concrete.

1.Accurately weigh the various materials required on different scales.

2.When using manual mixing, the inside and outside of the slump cylinder should be cleaned first, moistened with water, and the cylinder should be placed on a rigid plate that is moistened with water and does not absorb water, and other utensils should also be moistened with water.

3.Mix cement and sand evenly on the steel plate, add a part of the water and stir into a mortar, then add stones and the rest of the water, stir and mix on the board, shovel and cut, until it is uniform, if you mix it with a mixer, you should first wet the inner wall of the mixer barrel with water, pour in the stones, sand and cement for 1min, and then slowly add water and mix for about 2min.

4.Put the cement on the slump cylinder, step on the pedal under the cylinder with both feet, divide the concrete into three layers with a small shovel, evenly load it into the cylinder, and the height of each layer is about one-third of the cylinder height after tamping. Each layer is inserted 25 times with a tamper, the ramming should be carried out along the spiral direction from the outside to the center, each time the ramming is evenly distributed on the cross-section, when inserting the concrete on the edge of the tamper, the tamper can be slightly inclined, when inserting the formation, the tamper should run through the entire depth, and when inserting the first layer and the top layer, the tamper should penetrate the surface of this layer to the next layer.

When pouring the top layer, the concrete should be poured high above the cylinder opening, and the slump cylinder should be lifted vertically and smoothly. The lifting process of the slump cylinder should be completed within 5 10s.

The whole process from the start of the charge to the slump cylinder should be carried out uninterruptedly and should be completed within 150s.

3. Experimental results.

1.After lifting the slump cylinder, measure the height difference between the height of the cylinder and the highest point of the concrete test body after the slump. That is, the slump value of the concrete mixture (expressed in mm to 5mm).

2.Observe the cohesion and water retention of the concrete specimen after slump. The method of checking for cohesion is to gently tap the side of the collapsed concrete cone with a tamper.

At this time, if the cone gradually sinks, it means that the cohesion is good, and if the cone collapses, partially cracks, or segregation, it means that the cohesion is not good.

The water retention is evaluated by the degree of slurry precipitation in the concrete mixture. If more slurry is precipitated from the bottom after the slump cylinder is lifted, the concrete of the cone part also loses slurry and the aggregate is exposed, which indicates that the concrete mixture has good water retention.

Slump refers to the workability of concrete, specifically to ensure the normal progress of construction, including the water retention, fluidity and cohesion of concrete. Workability refers to whether concrete is easy to construct and operate, and the performance of uniform and dense is a very comprehensive property, which includes fluidity, cohesion and water retention. The effects and workability mainly include water consumption, water-cement ratio, sand rate, including cement variety, aggregate conditions, time and temperature, admixtures and other aspects.

Test method of slump: use a 100mm upper mouth, 200mm lower mouth, 300mm high trumpet-shaped collapse bucket, pour into the concrete and then tamp it, and then pull up the barrel, the concrete collapses due to its own weight, and subtracts the height of the highest point of the concrete after the collapse with the barrel height (300mm), which is called the collapse. If the difference is 10mm, the slump is 10.

The slump of concrete should be determined according to the structural section of the building, the content of reinforcement, the transportation distance, the pouring method, the mode of transportation, the vibration capacity and the climate.

It is how big the flow of the freshly finished concrete is, and how much it can flow after an hour, and the less it is, the greater the loss.

According to the standard of the concrete mixture slump test, the measured value of 187 mm should be expressed as: 187 mm, abbreviated as 187 mm or 187 m should not be expressed as 187 m. Because according to the standard, the unit of slump should be millimeters (mm), not meters (m).

The slump test is one of the important tests to test the fluidity and engineering applicability of concrete mixtures. The higher the number, the better the flow of the concrete, which is suitable for pouring and construction. If the measured value of 187 mm is expressed in meters, it will produce a 10-fold error, resulting in a large misjudgment of the spike liquid, which is not conducive to the evaluation and application of concrete properties.

Therefore, the unit of slump should be unified into millimeters (mm) when recording direct readings from the instrument, as well as when recording experimental reports and result calculations. If there is an error of recording millimeters as meters, there will also be a large error in the calculation and evaluation of the results, which is not conducive to the accuracy and quality control of the concrete mix design. In the performance test of ordinary concrete, millimeters are the most commonly used size class in the unit of measurement.

In addition to the slump test, in the measurement of the size of the test block and the determination of cohesion, the millimeter will be used as the unit of measurement. Therefore, when selecting and expressing units, both operators and experimenters need to pay attention to distinguishing and correctly using the two units of millimeter and meter.

Reason: The adaptability of the admixture and cement is not good, causing rapid slump loss; The amount of admixture is not enough, and the effect of retarding and plastic preservation is not ideal; In hot weather, the admixture fails at high temperature, the water evaporates quickly, and the bubble overflow causes rapid slump loss; The initial slump is too small, and the unit water consumption is too small, resulting in insufficient gypsum solubility during cement hydration; The coordination between the construction site and the mixing plant is not good, and the pressing and traffic jam time is too long, resulting in excessive slump loss. Workaround:

Adjust the admixture formulation to suit the cement. Before construction, be sure to do the admixture and cement adaptability test; Add an appropriate amount of fly ash to replace part of the cement; Increase the amount of admixtures appropriately to prevent water evaporation too quickly and bubble overflow too quickly; Improve the water retention and cooling devices of transport vehicles.

Reason: The adaptability of the admixture and cement is not good, causing rapid slump loss; The amount of admixture is not enough, and the effect of retarding and plastic preservation is not ideal; In hot weather, the admixture fails at high temperature, the water evaporates quickly, and the bubble overflow causes rapid slump loss; The initial slump of Tanzi is too small, and the unit water consumption is too small, resulting in insufficient gypsum solubility during cement hydration; The coordination between the construction site and the mixing plant is not good, and the time of pressing and traffic jamming is too long, resulting in excessive slump loss. Workaround:

Adjust the admixture formulation to suit the cement. Before construction, be sure to do the adaptability test of the external nuclear agent and cement; Add an appropriate amount of fly ash to replace part of the cement; Increase the amount of admixtures appropriately to prevent water evaporation too quickly and bubble overflow too quickly; Improve the water retention and cooling devices of transport vehicles.

The slump test is mainly used to detect and determine the working performance of the concrete mixture, that is, the fluidity and plasticity of the concrete.

Through the slump test, the pumpability, pourability, and formability of the concrete can be evaluated to ensure the smoothness and suitability of the concrete during construction. The slump test mainly detects and determines the working performance of the concrete mixture to ensure the fluidity, plasticity and adaptability of the concrete during the construction process. This is essential to ensure the quality and safety of concrete construction.

The characteristics of the slump test are ingenious

1. Fluidity: The slump test can measure the degree of deformation of the concrete after being stressed, so as to evaluate the fluidity of the concrete. Different construction needs may require different concrete fluidity, and slump testing can help determine the suitability of concrete.

2. Plasticity: The slump test can reflect the plasticity of concrete, that is, its plastic deformation ability in the process of vibration or molding. By evaluating the slump, it can be determined whether the concrete is malleable enough to meet the construction requirements.

3. Mixture mix adjustment: The slump test can be used to evaluate the slump change of concrete under different mix ratios. By testing concrete with different mix ratios, the optimal mix mix can be determined to obtain the desired concrete working performance.

Specific requirements for concrete slump:

In high-temperature construction, the slump of concrete should not be less than 70mm, the general on-site construction concrete slump is 100 20mm, and the construction slump can be increased to 160mm in high temperature and harsh environment.

Concrete slump is used in the actual construction to judge the concrete construction and workability of a wide bridge brother standard, if the slump is large is easy to cause the segregation of the mixture, if it is too small to bring difficulty to the construction, you can change the amount of aggregate without changing the water-cement ratio, or add cement slurry to reduce the height to change.