Concrete in the actual mixing process, due to the environment, weather, raw materials and other factors, will appear slow set, false set and rapid set phenomenon, and then affect the performance of concrete, delay construction. What causes the abnormal setting time of concrete? How to take emergency measures?

First, concrete retardation
The combination of slurry and aggregate forms the weak zone, which leads to the reduction of the bonding force between cement paste and aggregate, and then affects the strength of concrete. If the mud content mixing is not uniform and the formation of mud, concrete strength deterioration will be more serious.
why
01, retarder overmixing
Summer to meet the construction requirements, pumping concrete, concrete products, often mixed with retarder, but the content is too large, easily lead to serious more than design and the concrete setting time is expected to the setting time, and even concrete not setting for a long time, not only cause the strength greatly reduce and delay the construction period, and even bring engineering serious quality problems.

02, water reducer and cement, admixture compatibility problem
The main influencing factors are the chemical properties, molecular weight, crosslinking degree, sulfonation degree and equilibrium ions of water reducing agent, as well as the content of SO3 and C3A in cement, cement fineness and alkali content. If the compatibility is poor, the concrete will be delayed over time.

03, cement admixture
In order to reduce the cost and improve some properties of cement, a certain amount of mineral admixture is often added in the process of cement production. But admixture variety or dosage is not when, can cause concrete abnormal set. If the dosage is too high, it may cause timeout retardation.

04, inappropriate construction technology or measures
In the process of concrete production and construction, inappropriate construction technology may also cause the delay of concrete. Such as concrete in the production of mixing water containing oil, acid, sugar, etc., mixing in the condition of retarding agent will cause concrete serious retarding phenomenon.
preventive measure
1, regular school, prevent measurement is not allowed to cause admixture overmixing;
2, before construction, the first test to determine the use of admixture and cement, admixture and other raw materials between the adaptability and appropriate dosage.
3. Reserve samples for each batch of cement at the station, and trace any abnormalities found;
4. Correctly guide the construction units to use commercial concrete, and put an end to inappropriate construction technology affecting the use effect.

Two. Concrete false coagulation phenomenon
The combination of slurry and aggregate forms the weak zone, which leads to the reduction of the bonding force between cement paste and aggregate, and then affects the strength of concrete. If the mud content mixing is not uniform and the formation of mud, concrete strength deterioration will be more serious.

Concrete pseudosetting refers to an abnormal early solidification or early hardening of cement. After the machine, short time to achieve the initial set, after re-mixing plasticity, this phenomenon calls concrete false set.

The factor that causes concrete false coagulate is very MUCH, basically BE BECAUSE OF CEMENT POWDER WHEN GRIND grind inside TEMPERATURE IS higher, make 2 WATER gypsum dehydrates the reason of half water gypsum.
When cement mixed with water, hemihydrate gypsum quickly into dihydrate gypsum, forming a needle-like crystal network structure, thus causing slurry solidification.

Additional, certain contain alkali higher cement, sulphate potassium and 2 water gesso generation potassium gesso grows quickly, also can cause concrete false set.

preventive measure
1, the selection of appropriate cement, generally mixed with mixed materials of cement rarely produce concrete false set phenomenon
2, add the right amount of admixture, such as concrete water reducer or retarding agent
3, vigorous mixing, in the preparation of concrete to prolong the mixing time can also eliminate the concrete false coagulation phenomenon

Three, concrete setting time too fast
The combination of slurry and aggregate forms the weak zone, which leads to the reduction of the bonding force between cement paste and aggregate, and then affects the strength of concrete. If the mud content mixing is not uniform and the formation of mud, concrete strength deterioration will be more serious.

01. Hemihydrate gypsum
Cement clinker and gypsum grinding together fine, mill temperature is too high, diwater gypsum dehydrated into half water gypsum, this half water gypsum will cause concrete rapid setting.

02. Anhydrous gypsum
In cement production, anhydrous gypsum is used. After the admixture is added, the dissolution rate of calcium sulfate is greatly reduced. C3A in cement cannot fully hydrate with calcium sulfate to form ettringite, but directly hydrate with water to form calcium aluminate hydrate, which causes rapid setting.

03, the cement temperature is too high
In the cement supply is tight period, cement has just been ground on the direct shipment use, resulting in the high temperature of mixing concrete out of the machine, if do not use other measures to deal with, concrete will also appear quick setting phenomenon.

04, overmixing of accelerating agent
When the temperature is low, the concrete is difficult to set, and the accelerating agent is often added. Still have is concrete production company to shorten disassemble mold time, raise template turnover rate, and join accelerating agent. But if the accelerating agent is added too much, the setting time will be too fast.

preventive measure
1, mixing station should be prior to the cement production of raw materials to investigate, can not use anhydrous gypsum, hemihydrous gypsum, phosphogypso prepared cement.
2, for the ground cement, need to wait for thorough cooling before use. Alternatively, add appropriate admixture or use ice water mix.