The key technical points of using power trowel to handle large-span floor slabs, high-standard factories, airports, large parking lots and other projects

Using a power trowel to handle large-span and high-standard floor projects is a systematic project, and it is by no means as simple as "starting up and smoothing". It involves the meticulous management of the entire process from the initial preparation, concrete batching, laser leveling to power troweling and finishing.

The following are the key technical points of these large-scale and high-standard projects, which are elaborated at three levels: "Basic guarantee", "core control", and "advanced advancement".

Ⅰ. Basic Guarantee: Laying the Foundation for Success

These key points are the prerequisites for success or failure. If they cannot be achieved, there is no need to talk about anything else.

Foundation and bedding treatment

Density and flatness: The foundation must be uniformly compacted to prevent uneven settlement in the later stage. The flatness of the cushion layer (usually gravel or plain concrete) is of vital importance. Its elevation error should be strictly controlled (such as within ±10mm), otherwise a large amount of concrete will be wasted and the final flatness will be affected.
Waterproofing and moisture-proofing: In areas with high groundwater levels, reliable waterproof and moisture-proof layers must be applied to prevent water vapor from rising and affecting the quality and service life of concrete.

Concrete mix proportion and quality

 

Low water-binder ratio: This is the lifeline of high-strength and wear-resistant floors. The water-cement ratio is usually required to be controlled below 0.45, and the lower the better. A low water-cement ratio can reduce bleeding, enhance strength and wear resistance, and minimize shrinkage cracks.
Aggregate selection: Choose coarse and fine aggregates with good gradation and high hardness. The maximum aggregate particle size should not be too large (usually ≤25mm) to ensure the uniformity of the surface slurry.
Admixtures and additives

Mineral powder/fly ash: Reasonable use can improve workability, reduce hydration heat, and decrease temperature difference cracks.
Water reducing agent: Highly efficient water reducing agents must be used to significantly reduce water consumption while ensuring fluidity.
Fiber: In large-span floor slabs, it is strongly recommended to add polypropylene synthetic fibers, which can effectively suppress plastic shrinkage cracks in concrete.

 

The scientific pouring plan

Reasonable pouring sequence and direction: Develop a detailed pouring plan to ensure continuous supply of concrete and avoid cold joints. For large-scale construction, it is necessary to pour in separate compartments and arrange the construction joints reasonably.

Ⅱ. Core Control: Laser leveling and polishing process

This is the core operational step to achieve high flatness and high finish.

High-precision laser leveling

Equipment selection: A laser leveler with a laser emitter + laser receiver + automatic control hydraulic system must be used. This is the only way to achieve ultra-high flatness.
Reference setting: The position of the laser emitter must be stable to ensure that there is no signal obstruction throughout the entire operation area. The elevation control points need to be rechecked multiple times.
The "one-time molding" concept: The laser screed integrates scraping, vibration and leveling into one, leveling the concrete at the designed elevation in one go to form a dense and uniform base layer. This is the foundation for the subsequent work of the polishing machine.
The "golden time window" for operating a power trowel machine
The operation of the power trowel must closely follow the initial setting process of the concrete and be carried out in stages:

Phase One: Preliminary slurry extraction (before initial setting)

Timing: After the concrete pouring and laser leveling, when a person stands on it and sinks by about 3-5mm.
Equipment: Use a disc smear.
Operation: Run at low speed, press down the protruding aggregates on the surface, bring up the slurry, eliminate the slight tooth marks left by the screed, and make the surface tend to be uniform. The aim is not to smooth it out, but to compact and lift the slurry.
Phase Two: Compaction and Polishing (initial setting to final setting)

Timing: When a person stands and sinks about 1-2mm, there is no standing water on the surface, and a slight indentation appears when pressed with a finger. This is the most crucial moment.
Equipment: Replace with a blade (power trowel).
Operation

Angle control: At the beginning, the Angle between the power trowel blade and the ground should be small (almost parallel) to perform low-speed and large-area finishing.
Multiple cross-operation: Cross the light at least 2 to 3 times along both the longitudinal and transverse directions. Each time, increase the blade Angle appropriately compared to the previous time and raise the rotational speed.
Objective: Eliminate the marks left by the disc, fully compact the surface slurry, and achieve a dense and bright effect.
Phase Three: Final Calendering (before final setting)

Timing: When standing on it, there is almost no sinking. Only by pressing hard with fingers can marks be left.
Operation: The blade is at the maximum Angle to the ground and runs at high speed. This polishing is done to achieve an extremely high degree of smoothness and eliminate all spatula marks.
Note: All operations must be completed before the concrete loses its plasticity. It is strictly prohibited to sprinkle water or cement for finishing.

Ⅲ. Advanced: Addressing Special Requirements and Enhancing Durability

 

For airports, high-standard factories, etc., the following key points also need to be considered:
Seam treatment technology

Precise joint cutting: Cutting should be carried out immediately when the concrete reaches a certain strength (usually 6 to 12 hours after pouring, when it can be cut with a toothless saw without chipping). The depth of the cut seam should be 1/3 to 1/4 of the plate thickness, aiming to induce shrinkage cracks to occur at the predetermined position.
Grouting material: Use high-quality and durable grouting glue to protect the seam edge from being damaged by hard objects such as forklifts.
A complete maintenance system

Timeliness: Start curing immediately after the final finishing is completed and the concrete surface is about to dry.
Method selection

Spray curing agent: Most suitable for large-scale construction, it can form a film to prevent water evaporation. It is necessary to ensure that the spraying is uniform and full coverage.
Covering and water retention maintenance: If geotextiles, films, etc. are used for covering and continuous watering for moisture retention, the effect is the best but the cost is relatively high.
Curing period: At least 7 days. For high-grade concrete with crack resistance requirements, it is recommended to cure for 14 days.
Construction of special functional layers (if necessary)

Wear-resistant aggregates (quartz sand, metal, alloy) :

The timing of spreading: It should be carried out after laser leveling and before initial setting when the base concrete reaches a state "sufficient to bear the weight of people and spreader".
Spread in several portions: Spread at least twice (60%/40% of the total amount) to ensure even distribution.
Integrated finishing: After spreading, the wear-resistant aggregate is completely pressed into the surface layer of the concrete through the disc and blade operation of the power trowel machine and integrates with it.
Sealant curing agentConstruction should be carried out after the curing period has expired and the floor is completely dry.
Through effective penetration and chemical reactions with the components in concrete, it can significantly enhance surface hardness, wear resistance and impermeability, making it a powerful tool for creating ultra-long-life floors.

Summary: List of key technical points

Stage	Key points	Objectives and Descriptions
Preparatory work	The foundation cushion layer is flat and dense	Provide a stable foundation for the floor
	Low water-cement ratio concrete + fiber	Ensure the material's own strength and crack resistance
Core construction	High-precision laser leveling	The foundation for achieving ultra-high flatness (FF/FL value)
	Master the "Three Stages" of polishing	The initial setting involves extracting the slurry, finishing before the final setting, and finally calendering to achieve a smooth finish
Post-processing	Cut the seams accurately and promptly	Guide and control shrinkage cracks
	Maintain with sufficient time and materials	Ensure the development of concrete strength and prevent cracking
Function improvement	Wear-resistant aggregates are evenly spread and integrated	Enhance the surface wear resistance and impact resistance
	Penetrating sealant curing agent	Significantly enhance hardness, density and chemical resistance

The key to success lies in integrating all the above points into a seamless and controlled process. Any oversight in any link may lead to all previous efforts being wasted. Therefore, a high-quality construction team, advanced equipment and strict on-site management are all indispensable.

 

Note: The parameters provided in this document are for reference only and are not mandatory. Due to differences in technical characteristics between different brands and models of laser levelers, please consult the manufacturer for a suitable solution before actual operation. This reference document assumes no responsibility for any issues arising from failure to follow the manufacturer's instructions.

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