February** Dynamic Incentive Program
The concrete mixture is a mixture made by measuring and stirring cementitious materials, coarse and fine aggregates, water, admixtures and other components, and the difference in the density of each substance and the sedimentation rate under the action of gravity are also different, which will inevitably produce the phenomenon of delamination. When the viscosity of the slurry is not enough to prevent the coarse aggregate from sinking, the aggregate will sink and the slurry will float, and in serious cases, a large amount of water will be leaked above, the middle is the mortar layer, and the bottom layer is the aggregate. Water leakage, slurry leakage, and segregation are all undesirable phenomena of concrete mixture, which are all required to be avoided by concrete companies, because this phenomenon causes pipe blockage in the construction pumping process, separation of mixture after pouring, cracks and other undesirable quality problems, such as cavities.
(1) Raw materials
Raw materials are the necessary components of concrete, and the change of their quality will inevitably cause fluctuations in the amount of concrete mixture, and the violent fluctuation of raw materials is an important factor that causes water leakage, slurry and segregation of concrete mixture. The influencing factors of raw materials are concentrated in the following aspects, which are listed below for your reference:
1) The cement changes. For example, the aging time of cement in the cement plant is different, the aging time of cement is short, and the fresh cement adsorbs more admixtures, with the extension of aging time, the activity of cement decreases, and the adsorption capacity of admixtures decreases. When it is suddenly transformed into cement that has been aged for a long time in the cement plant, the amount of admixture is not adjusted in time during the concrete production process, which can easily cause concrete segregation and delamination. For example, during the Spring Festival holiday, cement will be aged for a long time in cement plants or in concrete production line tanks. In addition, the temperature of cement aging time is long, the charge on the surface of cement particles is neutralized, and the cement gypsum changes, such as anhydrous gypsum in contact with air part into dihydrate gypsum, all cause the adsorption capacity of admixtures to decrease.
2) Changes in mineral admixtures. It is mainly manifested in the obvious reduction of the water demand of the mineral admixture compared with the original production and use, resulting in the untimely adjustment of admixtures in the concrete production process, water leakage and segregation. The fineness of mineral powder is different from the fineness of cement clinker, the fineness of clinker is coarse, the specific surface area is small, and it is easy to lag and leak water. In addition, mineral powder made from water residue that has been aged for a long time is prone to water leakage.
3) Aggregates. The coarse aggregate gradation is single, the particle size is large, and the needle flake content is more, which is easy to cause the poor state of the concrete mixture and easy to leak water. During the production process, the mud content of the sand suddenly decreases, resulting in the reduction of admixture adsorption, resulting in water leakage and segregation. In addition, the use of machine-made sand containing flocculants is generally high, and the sudden use of part of the machine-made sand without flocculants causes segregation and water leakage, which is often difficult to prevent and difficult to prevent.
4) Admixtures. The use of polycarboxylic acid superplasticizer and the dosage is too large, and it is easy to cause water secretion and segregation if the saturation dosage is exceeded. The retarding components in the admixture are excessive, especially the use of phosphate, sodium gluconate and other retarding components that are easy to secrete, and sugars are easy to produce hysteresis and water secretion. Aliphatic superplasticizer and sulfamate superplasticizer are easy to produce water secretion, so it is appropriate to increase water retention and thickening components when used.
(2) Mix ratio
1) In the design of the mix ratio, the one-sided pursuit of low water consumption results in low dosage of cementitious materials, less slurry, and poor wrapping of mixture, such as: the slurry volume is less than 280L m3.
2) The fineness modulus of machine-made sand is large, the particle shape is poor, and the gradation is unreasonable, which is manifested as "large at both ends and less in the middle", 0315mm～1.18mm particles are few, have poor fluidity, and are prone to water leakage.
3) Sand 0The particle content of 315mm is less than 15%, and the amount of cementitious material is low, resulting in the total amount of the two being less than 400kg m3, coupled with the low sand rate and poor water retention.
4) The particle size of coarse aggregate is single, the particle content of 5 10mm is insufficient, and the gradation is unreasonable.
5) The mud content of the aggregate is significantly reduced, or the moisture content suddenly increases significantly, and the concrete segregation is caused by improper adjustment in the production process.
(3) Control of water consumption in the production process
1) During the production process, improper control by the operator causes serious segregation of the factory concrete.
2) The concrete production equipment is not regularly overhauled, and the measurement error of admixture or water consumption is large, and the overuse causes concrete segregation. The measurement of the equipment is not accurate, and the powder or fine aggregate is insufficient, resulting in a small sand rate and poor water retention, resulting in segregation.
3) During the production process, the tank truck driver did not pour the water before loading, resulting in the segregation of the concrete mixture.
(4) Add water during the construction process
Adding water during construction is a common and unavoidable problem. On the one hand, the secondary water addition is unevenly stirred and directly leaks water, and on the other hand, the secondary water addition makes the concrete slurry thinner, the cohesiveness and cohesion worse, and the mixture produces stratification and segregation. Overcoming the secondary water addition can avoid a large amount of concrete water leakage.
(5) Prevention and handling measures
First of all, it is necessary to find the causes of water leakage and segregation of concrete mixture, so as to take targeted measures to avoid and solve them. When the cause is unclear and it is difficult to determine the cause, consider a solution.
1) Reduce water consumption or reduce the amount of admixtures.
2) Adjust the mix ratio, appropriately increase the sand rate, increase the cementitious material, and increase the amount of fine sand ......In short, improve the water retention of concrete.
3) When conditions permit, the admixture formula can be adjusted, such as reducing the water reduction component, increasing the water retention and thickening components, or adding an appropriate amount of sulfate.
4) Adjust the initial slump of concrete, and try to avoid secondary water addition by construction workers.
5) The site is returned, adjusted according to the amount, an appropriate amount of thick mortar with the same ratio or high strength grade is added, or powder is added to stir, and the strength grade is reduced according to the situation, and it is used in non-load-bearing parts.
6) When the water stratification occurs after the concrete is poured, it should be stopped according to the actual situation, and the second plastering should be carried out after the settlement is completed, covering the film, and when the stratification is serious, it can be considered to sprinkle fine stones and then wipe the pressure to prevent the settlement cracks along the rib.
7) "fast plugging and slow pulling" during vibrating, and vibrating evenly according to the state of concrete to prevent over-vibration from causing coagulation stratification and segregation.