1. What should we do when the raw materials cannot be stopped immediately and the supply of concrete cannot be interrupted?

At the same time of contacting the raw material supplier, special personnel must be assigned to control the mixing water consumption and on-site concrete curing monitoring to prevent the construction site from adding water by itself. If necessary, the water binder ratio shall be kept unchanged, and the amount of cement shall be appropriately increased to increase the fluidity of concrete. Generally, 1.5%~2.5% of the cement slurry volume shall be increased for every 1m3 of concrete when the slump is increased by 1cm.

2. What kind of fly ash can be used in ready mixed concrete?

According to its fineness, water demand ratio and carbon content, fly ash is divided into Class I, II and III, and Class I and II fly ash can be used in ready mixed concrete.

3. Under what circumstances should fly ash not be used?

During winter construction, especially at the temperature of~10 ℃ and below, due to the low early strength of fly ash concrete, it needs a long time of pre curing at positive temperature to reach the critical strength of frost resistance, and the site insulation is poor, so it is easy to be frozen, so fly ash should not be mixed. In addition, fly ash shall not be added to the concrete ground that is polished with compaction and the concrete that has deicing salt requirements.

4. Can the acceptance age of fly ash concrete be extended?

Yes, as fly ash has contributed to the late strength of concrete, the age of design strength grade of fly ash concrete is specified in the Technical Code for the Application of Fly Ash Concrete (GB J146). 28 days for ground works; The ground works should be 28 days or 60 days; 60 days or 90 days for underground works; Mass concrete should be 90 days or 180 days.

5. Under what conditions is silica fume used?

Silica fume is mainly used to prepare high-strength concrete, sulfate resistant concrete, chloride corrosion resistant concrete, underwater concrete, deicing salt concrete, and high wear resistance pavement concrete.

6. When is zeolite powder used?

Zeolite powder can be used as active admixture of cement.

Zeolite powder can replace part of the cement in concrete to improve the water retention of concrete. Especially when the polycarboxylic acid superplasticizer is used to prepare large flow and ultra-high strength concrete, the proper amount of zeolite powder can effectively improve the water retention of concrete and prevent concrete bleeding.

When preparing lightweight aggregate concrete, the structural viscosity of cement slurry will be increased due to its incorporation, which can greatly improve the floating problem of lightweight aggregate in vibration molding.

Zeolite powder concrete is also suitable for underwater concrete and concrete cured in underground humid environment, with good frost resistance and impermeability. When using zeolite powder to prepare high-performance concrete, it is better to replace 10% of cement.

7. What is the reason why there are so many bubbles on the concrete surface after the formwork removal of the concrete produced with naphthalene superplasticizer? What should we do?

Some additive manufacturers purchase cheap crude sodium hydroxide (normal sodium hydroxide is white and yellow in appearance, and sodium hydroxide containing impurities is pink and red brick in appearance) and mixed sodium hydroxide. These chemical components are impure. The phenol content is high and the purity is low, which will bring many bubbles in the superplasticizer (inferior sodium will bring 3% bubbles in the concrete). The bubbles are large and the defoaming time is long, which directly affects the concrete strength. At this time, contact the admixture factory in time to suspend the use to prevent affecting the concrete strength.

8. How will the quality of concrete be affected if the waiting time of concrete on site is too long?

The concrete is mixed with retarder, but the retarding time is limited. After 2h, the cement starts to hydrate, and the slump starts to decline, so the concrete strength will lose some. Some enterprises have conducted tests in this regard, and the test results show that the concrete strength starts to decline when the on-site waiting time exceeds 2h. Therefore, the waiting time of concrete on site shall not exceed 2h.

9. What are the consequences of adding water to the concrete truck?

The normal water binder ratio of concrete ensures that it has a certain fluidity and strength. In addition, adding water later will reduce the concrete strength (excess water will form voids after evaporation, weakening the concrete section). According to the test data of some concrete enterprises, the 28 day strength of concrete will decrease by 3.7Mpa for every 10kg of water added in the concrete. Therefore, the construction site shall be strictly controlled and no water shall be added to the transport vehicle.

10. How long is the initial and final setting time after concrete pouring? How to judge?

The initial setting time of concrete under normal temperature is 6-8 hours. Press the concrete surface gently without sticking. The concrete surface collects water. The initial setting is when there is a layer of shiny film; When the color of the concrete surface turns white and there is no mark when pressing, it is final setting. The final setting time is about 8-10 hours. Depending on the temperature in summer and winter, the initial and final setting time will be shortened or extended.