The working pressure of the concrete pump causes the concrete to be transported along the pipeline and concreted at the entrance and exit of the pipeline.Concrete pumping takes into account not only the requirements of compressive strength, service performance and cohesiveness of concrete design scheme, but also the limitations of pipeline transportation on concrete.So usually choose to add admixture to improve the pumpability of concrete.Adding water reducing agent in concrete pumping can improve the workability of concrete, it has a great impact on the pumping engineering construction, usually the admixture has the effect of retarder, reducing water, etc., considering the effect of the admixture on concrete pumping engineering, so the key consideration in the use of water reducing agent multiple levels.
1. The water reducing rate
Water reduction rate of additives is an important index value to consider. Reducing water demand and concrete water-cement ratio are the key ways to improve the strength of concrete, usually reducing water demand by 15% or so.
2. Air content
After adding concrete, most of the superplasticizers have the actual effect of air entrainment, resulting in the necessary proportion of bubbles.If the air content is too low, it will endanger the fluidity and pumpability of concrete, so it should be controlled within the effective value range. In addition, water-reducing agent can also increase or decrease the compressive strength grade of concrete.
3. Time hazard
Because increased slightly when manufacturing impermeable concrete expansion agent such as UEA - 3 water reducing agent, the concrete into the first 30 min slump concrete tank damage only 1 cm from top to bottom, but in the 30 min after the slump dramatically damage condition, cause original concrete slump is very good and transportation to the construction site after don't can pump.
4. Harm of average temperature
After the application of some water-reducing agents, concrete's slump damage per hour at the beginning of 30-35℃ is 2-3cm; when the average temperature is higher than 36℃, concrete's slump damage per hour at the beginning is more than 5-6cm. Therefore, it is necessary to select water-reducing agents with small slump damage in summer construction.
5. Reasonable collapse range
General pumping height below 30cm when the concrete slump can be selected 14-16cm, 30m above when the slump 16-18cm, 60m above when the choice 18-20cm, more than 100m, compared to the pumping, not only to ensure a reasonable pumpable concrete slump, but also to the size of stone, sand rate, cement dosage and additives should be appropriately adjusted.
