Concrete pumping is usually composed of six multi-components including concrete, water, sand, stone, water reducing agent and mineral admixtures. Usually it is mainly used for water reducing agent and pumping agent.
The working pressure of the concrete pump prompts the concrete to be transported along the pipeline and concrete is poured at the entrance and exit of the pipeline. Concrete pumping not only considers the requirements for strength, performance, and cohesion required by the concrete design, but also considers the restrictions on concrete caused by pipeline transportation. Therefore, admixtures are usually added to improve the pumpability of concrete. Adding water-reducing admixtures during concrete pumping can improve the workability of concrete. It has a great impact on the construction of pumping projects. Usually admixtures have the functions of retarding and reducing water. Considering the impact of admixtures on concrete pumping projects, , so it is important to consider multiple aspects when using water reducing agents.
1. Water reduction rate
The water reduction rate of admixtures is an important indicator to consider. Reducing water demand and reducing the water-cement ratio of concrete are important ways to improve the strength of concrete. Generally, the water demand is reduced by about 15%.
2. Air content
Most of the water-reducing agents added to concrete It has an air entrainment effect and creates a certain proportion of bubbles. If the air content is too low, it will affect the flowability and pumpability of the concrete, so it should be controlled within the effective range. At the same time, the water-reducing agent will also increase or decrease the compressive strength level of the concrete.
3. Time Hazards
When producing impermeable concrete, due to the addition of micro-expansion agents such as UEA-3 and other water-reducing agents, the concrete enters concrete tank trucks. The slump loss was only about 1cm in the first 30 minutes, but a significant slump loss occurred in the last 30 minutes. This caused the concrete to have a very good slump at the original factory but could not be pumped after being transported to the construction site. Condition.
4. Temperature hazards
After some water-reducing agents are used, the concrete will be damaged at 30 The initial slump loss per hour is 2-3cm at -35°C, and the initial slump loss per hour exceeds 5-6cm when the temperature is higher than 36°C. Therefore, slump loss must be selected during summer construction. Smaller superplasticizer.
5. Reasonable slump range
General pump When the delivery height is less than 30cm, the slump of concrete can be 14-16cm. When the height is more than 30m, the slump can be 16-18cm. When the height is more than 60m, the slump can be 18-20cm. When it exceeds 100m, compared with pumping, it is necessary not only to ensure reasonable pumpability According to the slump of the concrete delivered, the size of the stone, sand rate, cement dosage and additives must be appropriately adjusted. </p
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