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Ground levelness and levelness in modern buildings

If you have ever sat at the dining table wobbly, spilling wine out of the glass and causing you to spill cherry tomatoes on the other side of the room, you will know how inconvenient the wavy floor is.
But in high-bay warehouses, factories, and industrial facilities, floor flatness and levelness (FF/FL) can be a success or failure problem, affecting the performance of the building’s intended use. Even in ordinary residential and commercial buildings, uneven floors can affect performance, cause problems with floor coverings and potentially dangerous situations.
Levelness, the closeness of the floor to the specified slope, and the flatness, the degree of deviation of the surface from the two-dimensional plane, have become important specifications in construction. Fortunately, modern measurement methods can detect levelness and flatness issues more accurately than the human eye. The latest methods allow us to do it almost immediately; for example, when the concrete is still usable and can be fixed before hardening. Flatter floors are now easier, faster, and easier to achieve than ever before. It is achieved through the unlikely combination of concrete and computers.
That dining table may have been “fixed” by cushioning a leg with a matchbox, effectively filling a low point on the floor, which is a plane problem. If your breadstick rolls off the table by itself, you may also be dealing with floor level issues.
But the impact of flatness and levelness goes far beyond convenience. Back in the high-bay warehouse, the uneven floor cannot properly support a 20-foot-high rack unit with tons of things on it. It may pose a fatal danger to those who use it or pass by it. The latest development of warehouses, pneumatic pallet trucks, rely even more on flat, level floors. These hand-driven devices can lift up to 750 pounds of pallet loads and use compressed air cushions to support all the weight so that one person can push it by hand. It needs a very flat, flat floor to work properly.
Flatness is also essential for any board that will be covered by a hard floor covering material such as stone or ceramic tiles. Even flexible coverings such as vinyl composite tiles (VCT) have the problem of uneven floors, which tend to be completely lifted or separated, which may cause tripping hazards, squeaks or voids below, and moisture generated by floor washing Gather and support the growth of mold and bacteria. Old or new, flat floors are better.
The waves in the concrete slab can be flattened by grinding away the high points, but the ghost of the waves may continue to linger on the floor. You will sometimes see it in a warehouse store: the floor is very flat, but it looks wavy under high-pressure sodium lamps.
If the concrete floor is intended to be exposed-for example, designed for staining and polishing, a continuous surface with the same concrete material is essential. Filling the low spots with toppings is not an option because it will not match. The only other option is to wear off the high points.
But grinding into a board can change the way it captures and reflects light. The surface of the concrete is composed of sand (fine aggregate), rock (coarse aggregate) and cement slurry. When the wet plate is placed, the trowel process pushes the coarser aggregate to a deeper place on the surface, and the fine aggregate, cement slurry and laitance are concentrated on the top. This happens regardless of whether the surface is absolutely flat or quite curved.
When you grind 1/8 inch from the top, you will remove fine powder and laitance, powdered materials, and begin to expose the sand to the cement paste matrix. Grind further, and you will expose the cross-section of the rock and the larger aggregate. If you only grind to the high points, sand and rock will appear in these areas, and the exposed aggregate streaks make these high points immortal, alternating with the unground smooth grout streaks where the low points are located.
The color of the original surface is different from layers 1/8 inch or less, and they may reflect light differently. The light colored stripes look like high points, and the dark stripes between them look like troughs, which are the visual “ghosts” of the waves removed with a grinder. Ground concrete is usually more porous than the original trowel surface, so the stripes may react differently to dyes and stains, so it is difficult to end the trouble by coloring. If you do not flatten the waves during the concrete finishing process, they may bother you again.
For decades, the standard method for checking FF/FL has been the 10-foot straight-edge method. The ruler is placed on the floor, and if there are any gaps under it, the height of them will be measured. The typical tolerance is 1/8 inch.
This completely manual measurement system is slow and can be very inaccurate, because two people usually measure the same height in different ways. But this is the established method, and the result must be accepted as “good enough.” By the 1970s, this was no longer good enough.
For example, the emergence of high-bay warehouses has made FF/FL accuracy even more important. In 1979, Allen Face developed a numerical method for evaluating the characteristics of these floors. This system is commonly referred to as the floor flatness number, or more formally as the “surface floor profile numbering system.”
Face has also developed an instrument to measure floor characteristics, a “floor profiler”, whose trade name is The Dipstick.
The digital system and measurement method are the basis of ASTM E1155, which was developed in cooperation with the American Concrete Institute (ACI), to determine the standard test method for FF floor flatness and FL floor flatness numbers.
The profiler is a manual tool that allows the operator to walk on the floor and acquire a data point every 12 inches. In theory, it can depict infinite floors (if you have infinite time waiting for your FF/FL numbers). It is more accurate than the ruler method and represents the beginning of modern flatness measurement.
However, the profiler has obvious limitations. On the one hand, they can only be used for hardened concrete. This means that any deviation from the specification must be fixed as a callback. High places can be ground off, low places can be filled with toppings, but this is all remedial work, it will cost the concrete contractor’s money, and will take the project time. In addition, the measurement itself is a slow process, adding more time, and is usually performed by third-party experts, adding more costs.
Laser scanning has changed the pursuit of flatness and levelness of the floor. Although the laser itself dates back to the 1960s, its adaptation to scanning on construction sites is relatively new.
The laser scanner uses a tightly focused beam to measure the position of all reflective surfaces around it, not only the floor, but also the nearly 360º data point dome around and below the instrument. It locates each point in three-dimensional space. If the position of the scanner is associated with an absolute position (such as GPS data), these points can be positioned as specific positions on our planet.
Scanner data can be integrated into a building information model (BIM). It can be used for a variety of needs, such as measuring a room or even creating an as-built computer model of it. For FF/FL compliance, laser scanning has several advantages over mechanical measurement. One of the biggest advantages is that it can be done while the concrete is still fresh and usable.
The scanner records 300,000 to 2,000,000 data points per second and usually runs for 1 to 10 minutes, depending on the information density. Its working speed is very fast, flatness and levelness problems can be located immediately after leveling, and can be corrected before the slab solidifies. Usually: leveling, scanning, re-leveling if necessary, re-scanning, re-leveling if necessary, it only takes a few minutes. No more grinding and filling, no more callbacks. It enables the concrete finishing machine to produce a level ground on the first day. The time and cost savings are significant.
From rulers to profilers to laser scanners, the science of measuring floor flatness has now entered the third generation; we call it flatness 3.0. Compared with the 10-foot ruler, the invention of the profiler represents a huge leap in the accuracy and detail of the floor data. Laser scanners not only further improve accuracy and detail, but also represent a different type of leap.
Both profilers and laser scanners can achieve the accuracy required by today’s floor specifications. However, compared with profilers, laser scanning raises the bar in terms of measurement speed, information details, and the timeliness and practicality of results. The profiler uses an inclinometer to measure elevation, which is a device that measures the angle relative to the horizontal plane. The profiler is a box with two feet at the bottom, exactly 12 inches apart, and a long handle that the operator can hold while standing. The speed of the profiler is limited to the speed of the hand tool.
The operator walks along the board in a straight line, moving the device 12 inches at a time, usually the distance of each travel is approximately equal to the width of the room. It takes multiple runs in both directions to accumulate statistically significant samples that meet the minimum data requirements of the ASTM standard. The device measures vertical angles at every step and converts these angles into elevation angle changes. The profiler also has a time limit: it can only be used after the concrete has hardened.
Analyzing the floor is usually done by a third-party service. They walk on the floor and submit a report the next day or later. If the report shows any elevation issues that are out of specification, they need to be fixed. Of course, for hardened concrete, the fixing options are limited to grinding or filling the top, assuming it is not decorative exposed concrete. Both of these processes can cause a delay of several days. Then, the floor must be profiled again to document compliance.
Laser scanners work faster. They measure at the speed of light. The laser scanner uses the reflection of the laser to locate all visible surfaces around it. It requires data points in the range of 0.1-0.5 inches (much higher information density than the profiler’s limited series of 12-inch samples).
Each scanner data point represents a position in 3D space and can be displayed on a computer, much like a 3D model. Laser scanning collects so much data that the visualization looks almost like a photo. If needed, this data can not only create an elevation map of the floor, but also a detailed representation of the entire room.
Unlike photos, it can be rotated to show space from any angle. It can be used to make precise measurements of the space, or to compare as-built conditions with drawings or architectural models. However, despite the huge information density, the scanner is very fast, recording up to 2 million points per second. The entire scan usually only takes a few minutes.
Time can beat money. When pouring and finishing wet concrete, time is everything. It will affect the permanent quality of the slab. The time required for the floor to be completed and ready for passage may change the time of many other processes on the job site.
When placing a new floor, the near real-time aspect of the laser scanning information has a huge impact on the process of achieving flatness. FF/FL can be evaluated and fixed at the best point in floor construction: before the floor hardens. This has a series of beneficial effects. First, it eliminates waiting for the floor to complete remedial work, which means that the floor will not take up the rest of the construction.
If you want to use the profiler to verify the floor, you must first wait for the floor to harden, then arrange the profile service to the site for measurement, and then wait for the ASTM E1155 report. You must then wait for any flatness issues to be fixed, then schedule the analysis again, and wait for a new report.
Laser scanning occurs when the slab is placed, and the problem is solved during the concrete finishing process. The slab can be scanned immediately after it is hardened to ensure its compliance, and the report can be completed on the same day. Construction can continue.
Laser scanning allows you to get to the ground as quickly as possible. It also creates a concrete surface with greater consistency and integrity. A flat and level plate will have a more uniform surface when it is still usable than a plate that must be flattened or leveled by filling. It will have a more consistent appearance. It will have a more uniform porosity across the surface, which may affect the response to coatings, adhesives, and other surface treatments. If the surface is sanded for staining and polishing, it will expose aggregate more evenly across the floor, and the surface may respond more consistently and predictably to staining and polishing operations.
Laser scanners collect millions of data points, but nothing more, points in three-dimensional space. To use them, you need a software that can process them and present them. The scanner software combines the data into a variety of useful forms and can be presented on a laptop computer on the job site. It provides a way for the construction team to visualize the floor, pinpoint any problems, correlate it with the actual location on the floor, and tell how much height must be lowered or increased. Near real time.
Software packages like ClearEdge3D’s Rithm for Navisworks provide several different ways to view floor data. Rithm for Navisworks can present a “heat map” that displays the height of the floor in different colors. It can display contour maps, similar to topographic maps made by surveyors, in which a series of curves describe continuous elevations. It can also provide ASTM E1155-compliant documents in minutes instead of days.
With these features in the software, the scanner can be used well for various tasks, not just the level of the floor. It provides a measurable model of as-built conditions that can be exported to other applications. For refurbishment projects, the as-built drawings can be compared with historical design documents to help determine if there are any changes. It can be superimposed on the new design to help visualize the changes. In new buildings, it can be used to verify the consistency with the design intent.
About 40 years ago, a new challenge entered the homes of many people. Since then, this challenge has become a symbol of modern life. Programmable video recorders (VCR) force ordinary citizens to learn to interact with digital logic systems. The blinking “12:00, 12:00, 12:00″ of millions of unprogrammed video recorders proves the difficulty of learning this interface.
Every new software package has a learning curve. If you do it at home, you can tear your hair and curse as needed, and the new software education will take you the most time in an idle afternoon. If you learn the new interface at work, it will slow down many other tasks and can lead to costly errors. The ideal situation for introducing a new software package is to use an interface that is already widely used.
What is the fastest interface for learning a new computer application? The one you already know. It took more than ten years for building information modeling to be firmly established among architects and engineers, but it has now arrived. Moreover, by becoming a standard format for distributing construction documents, it has become a top priority for contractors on site.
The existing BIM platform on the construction site provides a ready-made channel for the introduction of new applications (such as scanner software). The learning curve has become quite flat because the main participants are already familiar with the platform. They only need to learn the new features that can be extracted from it, and they can start using the new information provided by the application faster, such as scanner data. ClearEdge3D saw an opportunity to make the highly regarded scanner application Rith available to more construction sites by making it compatible with Navisworks. As one of the most widely used project coordination packages, Autodesk Navisworks has become the de facto industry standard. It is on construction sites across the country. Now, it can display scanner information and has a wide range of uses.
When the scanner collects millions of data points, they are all the points in 3D space. Scanner software like Rithm for Navisworks is responsible for presenting this data in a way you can use. It can display rooms as data points, not only scanning their location, but also the intensity (brightness) of reflections and the color of the surface, so the view looks like a photo.
However, you can rotate the view and view the space from any angle, wander around it like a 3D model, and even measure it. For FF/FL, one of the most popular and useful visualizations is the heat map, which displays the floor in a plan view. High points and low points are presented in different colors (sometimes called false color images), for example, red represents high points and blue represents low points.
You can make precise measurements from the heat map to accurately locate the corresponding position on the actual floor. If the scan shows flatness issues, the heat map is a quick way to find them and fix them, and it is the preferred view for on-site FF/FL analysis.
The software can also create contour maps, a series of lines representing different floor heights, similar to topographic maps used by surveyors and hikers. Contour maps are suitable for exporting to CAD programs, which are often very friendly to drawing type data. This is particularly useful in the renovation or transformation of existing spaces. Rithm for Navisworks can also analyze data and give answers. For example, the Cut-and-Fill function can tell you how much material (such as cement surface layer) is needed to fill the low end of the existing uneven floor and make it level. With the correct scanner software, the information can be presented in the way you need.
Of all the ways to waste time on construction projects, perhaps the most painful is waiting. Introducing floor quality assurance internally can eliminate scheduling problems, waiting for third-party consultants to analyze the floor, waiting while analyzing the floor, and waiting for additional reports to be submitted. And, of course, waiting for the floor can prevent many other construction operations.
Having your quality assurance process can eliminate this pain. When you need it, you can scan the floor in minutes. You know when it will be checked, and you know when you will get the ASTM E1155 report (about one minute later). Owning this process, rather than relying on 3rd party consultants, means owning your time.
Using a laser to scan the flatness and levelness of new concrete is a simple and straightforward workflow.
2. Install the scanner near the newly placed slice and scan. This step usually only requires one placement. For a typical slice size, the scan usually takes 3-5 minutes.
4. Load the “heat map” display of the floor data to identify areas that are out of specification and need to be leveled or leveled.


Post time: Aug-29-2021