Analysis of common problems with admixtures and concrete and countermeasures

Common problems with mixing admixtures and fresh concrete

Concrete segregation and bleeding

Problem:

1 Slump test management center There are stone deposits and water folded out from the edges;

2. Water layer is visible on the surface during transportation, especially when using dump trucks and hand trucks;

3. Dissolved water on the surface after forming layer.

Reasons:

1. The slump is large and the sand preparation rate is slightly low; 2. The amount of concrete used is small;

3. The application of admixtures or the type is not suitable;

4. Add retarder, especially if there is too much carboxylate, phosphate or glycogen;

5. Excessive water release or water release again.

Countermeasures:

1 Adjust the mortar mix ratio and increase the sand rate and concrete usage;

2 Moderately reduce the amount of admixtures such as coal ash;

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　3 Increase or adjust the amount of admixture used and reduce the water flow;

　4Replace the retarder with a retarder admixture;

　5 Apply emulsifier.

The main manifestations and reasons of insufficient concrete rebound

The main manifestations of insufficient compressive strength: Insufficient concrete rebound will eventually be accompanied by a reduction in the working ability of the impermeability grade and a reduction in performance. , more importantly, it will affect the bearing capacity of the structure. Specifically manifested in three aspects:

1. Reduce structural strength and rigidity.

2. Poor cohesion, resulting in many wide gaps.

3 Prefabricated components deform, and the deformation is so large that it affects normal use

Reasons for insufficient strength:

Poor quality of raw materials:

　(1) Poor quality of concrete: 1. The actual specificity of concrete is low; 2. The stability of concrete is not satisfactory;

　(2) Poor quality of stone (sand, stone): 1. Strength of gravel Low; 2. The volume of the gravel is poor; 3. The appearance and surface condition of the gravel are not good; 4. The organic chemical residues in the sand and stone have high moisture content, the soot moisture content is high, and the mica moisture content in the sand is high;

(3) The quality of the mixing water is not up to standard:

(4) The quality of the admixture is not up to standard or the composition is not properly formulated

2. The concrete mix ratio is not good:

Concrete mix ratio is one of the four important factors that determines strength. At least the water-cement ratio of concrete directly affects the rebound of concrete. In addition, the amount of water, sand rate, urn ratio, etc. also affect various properties of concrete. , which in turn leads to safety accidents with insufficient compressive strength.

(1) Increase in water demand: The more commonly used ones include the prohibition of metering and verification of water discharge equipment on mixers; the water content in sand and stones is not deducted; and water is discharged at the irrigation location at will.

(2) Inserting the mortar mix proportions at will;

(3) The dosage of admixtures is prohibited.

(4) Wrong operation of admixtures;

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(5) Sand and gravel measurement verification is prohibited and the amount of concrete used is insufficient.

Three Wrong Construction Techniques

(1) Poor mixing, too short or too long time leading to uneven mixing.

(2) The leakage of cement mortar during concrete pouring is relatively serious; the concrete is falsely set and initially set; and the vibration is false.

(3) Poor maintenance; such as lack of water and dryness in the early stage, cold exposure, etc.

The four test blocks were not maintained as required or were not manufactured as required

In order to save and solve the problem of insufficient concrete rebound, the actual compressive strength is usually measured and the medium and late compressive strength is used. Strength, reducing structural loads, structural reinforcement, analytical column calculation, to disassembly and reconstruction, etc.

Common problems with mixing admixtures and fresh concrete

False setting (rapid setting)

Problem:

1 Out of mixing The concrete in the container loses its fluidity and hardens in 5-12 minutes;

It completely loses its fluidity within 30 minutes and is barely formed. After removing the formwork this year, a lot of honeycomb pockmarks were found;

3. The compressive strength is low after hard menstruation.

Reasons:

1. The solubilities of reducing sugars and polyols to dihydrate plaster of paris and fluorogypsum of paris are different. Reducing sugars and polyols will significantly reduce the solubility of anhydrite in water, resulting in insufficient soluble SO3 in the aqueous solution, which cannot be converted into any ettringite to inhibit the hydration of C3A. The extremely rapid initial hydration of C3A causes the problem of false setting of concrete (especially cement paste). If the moisture content of C3A is very low in the concrete, the problem of false setting is unlikely to occur. Using anhydrite or fluorinated plaster of paris as a concrete setting agent, or when machine grinding concrete, the local temperature is high so that part of the pure natural plaster of paris is dehydrated into semi-hydrated plaster of paris or anhydrous gypsum, which will cause the concrete to be mixed with reducing sugar and False coagulation occurs after polyol. In cement slurry, false setting occurs within 12 minutes, and the concrete hardens after 16 minutes. It hardens quickly when fluorinated plaster of paris is used.

2. The amount of triethanolamine used exceeds the standard, causing the initial setting to be too short;

3. The initial setting of concrete is not satisfactory;

4. The mixing temperature is too high;

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5. Too much quick-setting agent is added.

Countermeasures:

1. For concrete that often causes false setting, retarder such as hydroxycarboxylate, ether and diethylene glycol can be used. This type of retarder is not easy to set. Causes the solubility of anhydrite and other materials to decrease, which will increase the relative increase (fluorine plaster is limited to);

2. Use the strategy of first adding water to mix the concrete material, and then adding the retarder after 1-2 minutes. , can prevent the occurrence of false coagulation.

3 Change the type of composite admixture or ask the manufacturer to adjust the multi-component; 4 Add 1-2% anhydrous sodium sulfate to the concrete usage;

5 Change the concrete type or production batch number;

6 Reduce the mixing temperature.�;

7 The formed concrete has been wet and cooled for up to 13 days.

Common problems with mixing admixtures and fresh concrete

Foundation settlement (grabbing the bottom)

Problem:

1 Mixture It is sticky and difficult to cut and mix manually;

2. The mixture is grasped by the stainless steel plate, ground and bucket, and the surface becomes dry after being scooped up.

Reasons:

1. Too much high-efficiency water reducing agent;

2. Too little air entrainment;

3. Excessive amount of concrete used High

Countermeasures:

1. Reduce the usage of high-efficiency water-reducing admixture;

2. Use two single multi-component high-efficiency composite blends;

　3Add appropriate air-entraining agent;

　4Add coal ash or mineral powder to reduce the amount of concrete used.

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