Concrete Pumping Technology
This technology utilizes concrete pumps or pump trucks to efficiently transport concrete mix through delivery pipes to the pouring site. Not only is it fast and labor-saving, but it is also the ideal choice for transporting and pouring concrete in large-volume projects and high-rise buildings.
Concrete pumps, as the key equipment for efficient concrete transport, are categorized into extrusion-type and piston-type, with the latter being more commonly used. Based on mobility, concrete pumps can be further classified into stationary, trailer-mounted, and truck-mounted types. Among these, truck-mounted concrete pumps are self-propelled, facilitating easy transfer between construction sites. Equipped with a three-stage telescopic or articulated placing boom, they enable direct delivery of concrete to the pouring location, significantly streamlining the construction process.
Piston pumps primarily consist of a hopper, hydraulic cylinders and pistons, a concrete cylinder, and a distribution valve. The distribution valve, a critical component, comes in various types such as gate-type and pipe-type, both offering superior performance and widespread application. Conveying pipes can be selected from steel pipes, rubber hoses, or plastic hoses as needed. Steel pipes are typically 3 meters long per section, with common specifications of φ100, 125, and 150mm. They are complemented by elbows of various angles and variable-section tapered pipes to optimize pipe layout and minimize flow resistance within the pipes.
For pumped concrete, slump should not be less than 100mm, with good flowability and appropriately sized aggregate. To prevent segregation and blockages during pumping, specialized pumping agents such as water-reducing agents and plasticizers must be added to ensure smooth passage of the concrete mixture under pump pressure. Additionally, incorporating appropriate admixtures like fly ash helps mitigate issues such as segregation, bleeding, and pipeline blockages during concrete placement.
However, current practices in some regions exhibit imprecise mix design for pumped concrete, with inflexible formulations for special conditions, leading to frequent construction accidents. Furthermore, the performance of pumping agents may alter under specific environmental conditions-all issues demanding urgent research and resolution.
The maximum aggregate size must maintain a specific ratio relative to the pump pipe diameter. For pumping heights below 50 meters, this ratio should not exceed 1:2.3 for crushed stone and 1:2.5 for rounded aggregate. For pumping ranges between 50 and 100 meters, the appropriate ratio range is 1:3 to 1:4. When the pumping height exceeds 100 meters, a ratio of 1:4 to 1:5 is recommended. Additionally, both coarse and fine aggregates must comply with the provisions of the current national standard "Standard Specification for Quality and Test Methods of Sand and Stone for Ordinary Concrete" (JGJ 52-2006). Coarse aggregate should be continuously graded, with the content of needle-shaped and flake-shaped particles not exceeding 10%. Fine aggregate should preferably be medium sand, with the sand passing through a 0.315 mm sieve not less than 15%.
When mixing pumped concrete, the water used must comply with the current national standard "Standard for Water Used in Concrete" (JGJ 63-2006). Additionally, admixtures incorporated into pumped concrete must comply with a series of national standards, including "Admixtures for Concrete" (GB 8076-2008). Furthermore, the appropriate addition of fly ash benefits pumped concrete, but its quality must meet current national standards such as "Fly Ash for Cement and Concrete" (GB/T 1596-2005). Finally, the concrete mix design is a critical factor, requiring a reasonable proportion of all components to meet pumping and construction requirements.
Cement content should be moderate
For concrete with strength grades ranging from C20 to C60, cement content should be controlled between 350 and 550 kg/m³.
Admixtures optimize performance
To enhance concrete properties, conserve cement, and reduce costs, admixtures like fly ash, slag, or zeolite powder are commonly added. Note that the total cement and mineral admixture content must not fall below 300 kg/m³.
Sand Ratio Adjustment Ensures Workability
To ensure concrete's flowability, cohesion, and water retention during transportation, pumping, and placement, the sand ratio for pumped concrete is typically 6% higher than for standard flowable concrete, ranging from approximately 38% to 45%.
Aggregate Gradation Must Meet Pumping and Strength Requirements
The aggregate size-to-pipe-diameter ratio is generally controlled within the following ranges: 1:2.5 (cobbles), 1:3 (crushed stone) to 1:4, and 1:5.
Water-cement ratio impacts pumping resistance
The water-cement ratio should be controlled between 0.4 and 0.6. If the ratio falls below 0.4, pumping resistance increases significantly. Conversely, ratios exceeding 0.6 cause bleeding, segregation, and layering, similarly impairing pumpability.
Exercise Caution When Selecting Pumping Agents
High-efficiency water-reducing agents combined with retarders, air-entraining agents, and similar additives are commonly used as pumping agents. These agents significantly impact both the workability of concrete and its hardened properties, necessitating careful selection.
