How to deal with water reducing agent in concrete

Most of the water reducers are anionic surfactants. At present, polycarboxylate water reducers and naphthalene water reducers are commonly used in the market. Under the condition of maintaining the slump of the concrete, it can greatly reduce the water consumption for mixing and improve the quality of the concrete. It plays an important role in the adjustment of concrete performance by increasing the strength of concrete and reducing the generation of cracks.

However, due to the influence of multiple factors such as the decline in the quality of raw materials and the lack of professionalism of the staff, various phenomena will appear in the concrete mixture mixed with water reducing agent. The following will analyze and solve them one by one.

01 sticking phenomenon

Part of the cement mortar sticks to the barrel wall of the mixer, resulting in uneven concrete, less ash, and sticky concrete.

Reason: 

Concrete is sticky, which often occurs after mixing retarder superplasticizers, or in drum mixers with close shaft-to-diameter ratios.

Solution:

(1) Pay attention to cleaning and removing the remaining concrete in time;

(2) First add aggregate and some water and stir, then add cement, residual water and water reducing agent;

(3) Use a large shaft-to-diameter ratio or a forced mixer.

02 Pseudocoagulation

(1) Insufficient content of calcium sulfate and gypsum in cement leads to excessive hydration of calcium aluminate;

(2) The water reducing agent has poor adaptability to this kind of cement.

(3) The amount of triethanolamine exceeds 0.05-0.1%. At this time, the initial setting is very fast but not the final setting.

Solution:

(1) Change the cement type;

(2) Appropriately adjust the admixture and carry out reasonable compounding;

(3) Add Na2SO4 component in the admixture.

03 non-condensation phenomenon

After adding water reducing agent, the concrete has not solidified for a long time, even a whole day and night; or the surface is bleeding and turns yellowish brown.

reason:

(1) The amount of superplasticizer is too large;

(2) Excessive use of retarder.

Solution:

(1) Do not exceed the recommended dosage by 2-3 times. Although the strength is slightly reduced, the 28d strength is less reduced, and the long-term strength is reduced even less;

(2) Properly increase the curing temperature after final setting, and strengthen watering and curing;

(3) Remove the formed part and pour it again.

04 Low intensity phenomenon

The strength is much lower than the test results of the same age, or the concrete has set, but the strength is extremely low.

reason:

(1) The amount of air-entraining water reducer is too large, so that the air content in the concrete is too large;

(2) The vibration is not enough after the air-entraining water reducer is mixed;

(3) The water-cement ratio was not reduced or instead increased.

(4) The quality of the water reducing agent does not meet the requirements, such as the content of active ingredients is too low.

Solution:

(1) Adopt other reinforcement measures or re-pour;

(2) Strengthen the vibration after pouring;

(3) Take measures against the aforementioned reasons;

(4) Identify this batch of water reducer.

05 Slump loss too fast

The concrete loses its workability quickly, and the slump decreases by 1-50mm every 2-3 minutes after being out of the tank, and there is obvious bottoming phenomenon. Concrete with large slump is more prone to this phenomenon.

reason:

(1) The water reducing agent has poor adaptability to the cement used;

(2) The air bubbles introduced into the concrete continue to overflow, and the water evaporates, especially when the air-entraining water reducer is used;

(3) Concrete mixing temperature or high ambient temperature;

(4) The concrete slump is very large.

Solution:

(1) Find out the reason and take measures against the reason;

(2) The post-mixing method is adopted, and the water reducing agent is mixed after mixing the concrete for 1-3 minutes or even before pouring, and then mixed again;

(3) Be careful not to add water alone.

06 Settlement joint

There will be some short, straight, wide and shallow cracks in the poured concrete before and after the initial setting.

Reason: 

The concrete is more viscous after being mixed with water reducing agent, it does not bleed and is not easy to sink completely, and it mostly appears on the top of the steel bar;

Solution: 

Apply pressure to the cracks before and after the initial setting of the concrete until the cracks disappear.