Categories
News

The Advantages of a Concrete Laser Screed

With a cement laser screed machine, you can get the best paving results. The laser technology used in the machine makes it ideal for workshops, food materials warehouses, and medication factories. The compact design and comfortable operator seat make it an excellent choice for any business or household. You can cover up to 2400 m in just 8 hours. The unit’s automatic controls also help you achieve a level finish with an extremely high degree of precision.

laser screed

The lasers used in a laser screed system are placed in the concrete mix. They are installed at the head and receive a signal from a transmitter multiple times per second. The system is capable of controlling a distance of over 1000 feet. A single transmitter enables the unit to work to much higher tolerances, making it an excellent choice for commercial and residential projects. This machine is a great investment for any home or business.

A laser screed also allows you to control elevation. The machine has two receivers mounted on the head and sends signals from the transmitter several times per second. A single laser transmitter can control up to 1000 ft, allowing you to achieve optimum levels all over your floor area. Moreover, a single transmitter can cover a wide area, giving you the option to have a wider floor surface. With all the advantages, it is a smart choice for your business.

Compared with a mechanical screed, a laser screed is more efficient and easier to use. The device has electronic-controlling features and uses strong vibrators. This high-frequency vibration enables it to work quickly and easily. This makes it possible to get a smoother finish than ever, and allows you to get a better finished level with less work. The resulting floor will look perfect and even for years to come.

In addition to the advanced features, the concrete laser screed is much easier to use. A high-speed computer-controlled programmable machine allows you to increase productivity without sacrificing safety. Its high-precision precision can guarantee flatness and reduce construction joint spacing. Some of the models even have dry shake capabilities. You’ll never have to worry about the level of your finished floor. You’ll be assured of quality and consistency in your construction projects.

A laser screed can be a great choice for many types of projects. The process of applying a concrete laser screed can be extremely fast and easy to complete. Once installed, it will create a smooth, flat floor that will last for years. Unlike traditional screeding methods, a laser screed can save you a lot of time. By adjusting the height and depth of the concrete, the machine will achieve the desired level of perfection.

Categories
News

Planning and Pouring Large Concrete Slabs

pouring large concrete slabs
When pouring large concrete slabs, the first step is to mark the edges and doors with stakes. Then, construct two forms with side boards three inches longer than the width of the slab. Set the end form boards at a 90-degree angle to the other. Finally, attach bracing at every 2′ intervals. When the forms are completed, the concrete is moundED about two to three inches above them. After the concrete has hardened, hoe it to ensure an even distribution. Once the slab is leveled, use a two-by-four screed board to level it.


Once the slab is leveled, it’s time to begin planning the job. Drive stakes at each corner of the site and string a line level between them. Once you have this information, you can level the ground. Next, set the long side form board 3″ longer than the new slab, nailing it to the corner stakes. Continue the process by placing more stakes to mark the edges. If necessary, mark the utility lines under the slab and dig them out.


Next, mark the perimeter of the slab. You can do this by driving stakes in the four corners. After marking the perimeter, string a line level between the stakes. Now, remove any soil in the area to level it properly. Then, place long side form boards that are three inches longer than the new slab. Nail the stakes to these boards, and lay the new slab. Now, you are ready to pour the concrete.


You can now move on to the next step, planning the placement and finishing of the slab. The first step in the process is laying the form board. A long side form board should be at least three feet longer than the new slab. Then, nail the form board to the corner stakes. Once you’ve laid the long side form board, you can start the actual pour. Once it’s level, pour the concrete.


Once the forms are set, place the slab. Then, attach the kickers. Afterwards, you can finish the slab with concrete and apply a protective layer of mortar. If the slab is thicker, it may be higher in some areas than others. Then, it will be less susceptible to cracks and other types of damage. When pouring large concrete slabs, you should also consider the cost of labor. The average cost for laying and finishing a slab of this size is $0.65 per square foot, and it would cost approximately $1800.


The second step in pouring a large concrete slab is to prepare the area for the slab. The ground needs to be leveled. You will need stakes to mark the corners. Afterwards, you should dig the trench and place the forms. Then, you should fill the slab with the form. You should have a poured surface in the ground. After the fill and the slab, you should apply a waterproof coating on the top.

Categories
Uncategorized

5 Benefits of Concrete Floors for Everyday Living

When you initially think of concrete floors, you probably think ‘cold’or ‘industrial’. But with its ability to take on colour and a polished sheen, coupled with its many benefits, concrete may become your new favourite on future projects. Be prepared to have your mind blown by how beautiful, elegant and warm a concrete floor can look.

Here are just some of the benefits of concrete floors.

Sustainability
Concrete floors are a sustainable option if you use an existing concrete slab, avoiding the consumption of new materials. And they need not be relegated to basements or garages. Once the concrete is sanded down and polished or sealed, it looks perfectly refined in a traditional kitchen or living room, especially when layered with rugs and pretty furnishings and fixtures.

Easy care
The only maintenance required of concrete floors is weekly mopping with soapy water. I recommend installing a skirting board along with the concrete floor as well, even though you think you may not need it. Just imagine what a dirty mop would leave behind in the crevice where the floor meets the wall if there were no skirting. And it will make your choice look finished and intentional.

Versatile 
The cost of polishing an existing concrete slab to a satin sheen is approximately $130 per square metre, according to Caroline Kouts of Urban Concrete Floors in Victoria, though this price may vary depending on the size of the area to be polished. The concrete’s tonal differences, subtle cracks and aggregates take on a stone-like, natural feel.

More elaborate finishes can cost from$120 to $125 per square metre, including a gloss finish. Staining concrete floors has been a popular option for years, because the outcome is determined by the homeowner’s imagination – different colours and application techniques combine to create a finish that’s unique to the home, with subtle variations across the floor.

Other decorative effects can include scoring in a grid pattern to create a tiled look, or even highly decorative faux finishes, such as a marbled effect.

Longevity
A floor that has been polished and maintained can be expected to last a hundred years or more. Let’s appreciate how an aged and cracked concrete floor is not hidden under new tiles or carpet. Instead it is celebrated for the history it holds, and put on display.

Versatility
For exterior applications, silicon-based penetrating sealers can be used to avoid the wet look. We can see here how concrete is a good flooring material for indoor-outdoor transitions. Concrete also looks nice with actual stone veneer walls. It accentuates their rustic appeal. Concrete can be an economical and crafty choice in lieu of salvaged wood flooring. Stamping wet concrete with plank-like wood-grain imprints creates a lovely effect.

Categories
Uncategorized

THE BENEFITS OF CONCRETE

Concrete is so integral to our communities because it is the only building material that cost-effectively delivers:

  • the lowest carbon footprint for a structure or pavement over its lifecycle
  • unparalleled strength, durability, longevity and resilience
  • maximized energy efficiency via thermal mass
  • durability in any environment
  • a building material that doesn’t burn, rust or rot
  • safety and security
  • versatility – it can be molded into any shape, colour or pattern imaginable
  • no off-gas
  • excellent vibration and sound insulating
  • low maintenance costs
  • 100 % recyclability, plus the materials needed to make concrete are abundant in just about every locale on the planet

It is quite simply the most versatile building material on earth. Here are more details:

LOWEST CARBON FOOTPRINT

Concrete’s unparalleled durability, energy efficiency and complete recyclability, combined with industry innovations such as lower carbon Portland-limestone cement, also known as Contempra, carbonated concrete or concrete cured with CO2 rather than water, all contribute to making it the lowest carbon building material over the lifecycle of a structure or pavement. Now, a new study by Canada’s renowned International Institute for Sustainable Development finds that up to 72% of the carbon emissions from wood products may currently be omitted from wood LCAs and that when these emissions are taken into account, concrete’s embodied carbon footprint could be up to 6% less intensive than that of wood products.

STRONG, DURABLE AND LOW MAINTENANCE

Concrete lasts decades longer than alternative building materials, and actually gets stronger over time. This reduces the total cost of ownership as well as the environmental impact associated with more frequent rehabilitation or reconstruction.

RESILIENT

Concrete doesn’t burn, rust, or rot. It is resistant to fire, wind, water, vibrations, and earthquakes, keeping people safer and reducing costs. In the aftermath of extreme weather events, concrete structures have proven to be the most resilient.

ENERGY-EFFICIENT

Concrete Buildings – Concrete’s ability to store energy (its thermal mass) helps moderate interior temperature conditions, reducing a building’s heating and cooling demands over its service life by up to 8%. Used in combination with technologies such as radiant floors and geothermal or hydronic heating and cooling systems, concrete enables energy efficiency improvements of 70% over the Model National Energy Code for Buildings. And it improves a building’ “passive survivability” in the event services such as power, heating fuel, or water are lost — increasing comfort for occupants and minimizing energy demands for the city as a whole.

Concrete Pavements are also energy-efficient in several ways. Studies show that over a 50-year period, the embodied primary energy required to construct, maintain, and rehabilitate concrete pavement is one third of that required for asphalt pavement. The rigid surface of concrete pavements helps reduce fuel consumption and related energy emissions by heavy trucks and other vehicles by up to 7%. And their light colour helps reduce the heat-island effect — which lowers cooling requirements — while also reducing exterior lighting requirements at night by up to 24%.

EMISSION-FREE

A totally inert substance when cured, concrete is literally emission-free and will not emit any gas, toxic compounds or volatile organic compounds.

VERSATILE

While strong and functional when hardened, concrete’s plasticity when freshly mixed lets designers adapt it to whatever form, shape, surface, and texture they can imagine. Innovations such as ultra-high performance concrete (UHPC), photocatalytic concrete and pervious concrete are also enabling new and creative uses — and new ways to address a host of sustainability challenges.

IDEAL FOR ADAPTIVE REUSE

Because of concrete’s strength, sound attenuation, and fire resistance, concrete buildings can easily be converted to other occupancy types during their service life. Reusing buildings in this way can help limit urban sprawl and further contributes to the conservation of our resources and preservation of the environment.

COST-EFFECTIVE

Thanks to their durability, resilience, low maintenance requirements and energy efficiency, concrete structures reduce operating costs related to operational energy consumption, maintenance, and rebuilding following disasters. Insurance costs for concrete buildings during the construction and operating phases have also been shown to be significantly lower than for buildings constructed with combustible, moisture-sensitive materials.

Concrete pavements are also cost-effective on a first cost and lifecycle cost basis, requiring only a third of the maintenance a comparable asphalt road would require over a 50-year service life. 

100% RECYCLABLE

Concrete can be recycled as aggregate — for use as sub-base material in roadbeds and parking lots, for gabion walls, as riprap to protect shorelines or in other applications — or as granular material, thereby reducing the amount of material that is landfilled and the need for virgin materials in new construction.

PRODUCED LOCALLY

Concrete is typically manufactured within 160 kilometers of a project site, using local resources. This greatly minimizes shipping and pollution and makes a significant contribution to the local economy.

Categories
Uncategorized

Which is the better building material? Concrete or steel?

Before modern engineering and the ability to manipulate concrete and steel, the world of architecture consisted of wood, adobe, thatch, and cave dwellings. We’ve come a long way. Today’s cities reveal skies punctuated by buildings so tall and austere, even architectural tour guides experience the occasional pain in the neck.

So, which material reigns supreme in the world of development today – concrete or steel?

Both provide numerous benefits. As for whether or not one is better, Buildings lets you determine which side you’re on.

1. Safety

Concrete:

The recent announcement by Ground Zero Developer Larry Silverstein regarding safety measures at the new 7 World Trade Center (WTC) building echoes what the concrete industry has been saying for years: Concrete is safer.

The building’s core (where elevators, stairs, and power systems are located) will be encased in 2-foot-thick concrete for protection in the event of a fire or terrorist attack. “Cast-in-place reinforced concrete offers outstanding resistance to explosion and/or impact. Moreover, it can endure very high temperatures from fire for a long time without loss of structural integrity,” says Alfred G. Gerosa, president, Concrete Alliance Inc., New York City.

Concrete requires no additional fireproofing treatments to meet stringent fire codes, and performs well during both natural and manmade disasters. Because of concrete’s inherent heaviness, mass, and strength, buildings constructed with cast-in-place reinforced concrete can resist winds of more than 200 miles per hour and perform well even under the impact of flying debris.

With proper design, engineering, and construction, the seemingly rigid structures built with concrete can exhibit increased ductility – a must in areas prone to seismic activity. However, according to the Skokie, IL-based Portland Cement Association (PCA), the performance of any building during an earthquake is largely a function of design rather than the material used in construction.

Steel:

While recent reports issued by the National Institute of Standards and Technology blame the reduced structural integrity of steel for the collapse of the WTC towers, the jet-fueled fires are to blame. Experts acknowledge that steel can soften and melt with exposure to extremely high temperatures.

However, with the addition of passive fire protection, such as spray-on fireproofing, buildings built of structural steel can sustain greater temperatures and, therefore, provide additional safety.

Don’t base your opinions about steel’s performance on the events of 9/11. In the October 2003 Modern Steel Construction article “Blast Resistant Design with Structural Steel,” authors Anatol Longinow and Farid Alfawakhiri recall the 1993 WTC attack.

The article indicates that the inherent redundancy of the steel frames prevented the structure’s collapse. “We’re seeing a lot of structures constructed taking into account progressive collapse for blast conditions that are designed very effectively and very economically in steel,” explains John P. Cross, vice president, marketing, American Institute of Steel Construction, Chicago.

Steel’s strength and ductility, combined with solid engineering and design, make it a safe choice in seismic zones. “Steel framing does very well under high [wind] loads because it is ductile, which means it has the ability to bend without breaking and can absorb that kind of energy,” says Larry Williams, President of the Washington, D.C.-based Steel Framing Alliance, of cold-formed steel.

2. Cost

Concrete:

It’s true: Prices of construction materials have spiked. However, the cost of ready-mix concrete remains relatively stable, and according to Ed Alsamsam, PCA’s manager of buildings and special structures, even the increase in steel has had a minimal effect on reinforced concrete building projects. “Concrete prices remain very steady despite the fluctuating and substantial increases in other building material prices,” he says.

While cast-in-place concrete construction can be pricier on the front end, the return on investment achieved can lessen the cost differential.

According to Gerosa, “Insurance companies recognize the benefits of a cast-in-place reinforced concrete office building because the aforementioned benefits – increased safety and structural integrity – reduce liability on their part. Insurance companies also report that owners and developers of a Class-A, cast-in-place reinforced concrete-framed office tower with a concrete core and wider egress stairs will save nearly 25 percent annually on the cost of property insurance.”

Steel:

The big news in development is the price of steel. And while structural steel has experienced a 50-percent increase over mill prices since November 2003, experts like Cross stress that structural steel represents less than 20 percent of all the steel used in building construction.

“If you look at the overall impact on project costs, in the past year we’ve seen project costs go up by about 10 percent as a result of increases in all types of construction materials. The increase in cost of the structural framing system represents less than 2 percent of the 10-percent increase in project costs,” Cross explains.

And despite what some concrete experts say, if you thought you’d escape the rising steel prices by opting for reinforced concrete, think again, Cross says. “The costs for a concrete framing system have gone up pretty much equivalently to the costs of a steel framing system,” he adds. To get an accurate reading on which material is most cost effective, analyze current steel and concrete framing prices on a project-by-project basis. And remember, according to Williams, “2004 was not a good year for any building material.”

3. Material Availability

Concrete:

In the fall of 2004, many states were reporting a shortage of cement, the primary binding ingredient used in concrete. The hurricanes in Florida and atypical levels of winter construction activity resulted in greater demand and shorter supply.

According to the PCA, other factors contributing to the shortage are shipping rates and the limited availability of transport ships. With imported cement supplementing domestic supplies, skyrocketing shipping rates and limited freight transport have resulted in higher costs and unreliable supply.

Despite tight supplies of cement in some regions of the United States, the impacts have been greatest on smaller companies, builders, or contractors. “Developers are using concrete frame buildings in every building sector, and count on concrete for stable pricing and availability regionally,” says Alsamsam. Cement companies are rapidly expanding and domestic capacity was expected to increase by 2008.

Steel:

Steel availability has been the subject of more than a few conversations lately, with the blame placed on the ever-expanding construction activity in Asian countries like China. However, experts from the steel industry are eager to dispel the myth that there simply isn’t enough steel to go around.

“Over the past year, there’s been a lot of misperception out there in terms of availability of material,” says Cross. “There is no shortage. The United States’ structural steel industry has the capacity to produce 6 million tons of structural steel per year. In 2004, our usage was about 4 million tons of wide-flange structural product, which means there is certainly adequate capacity to meet any growth in the foreseeable future. Structural steel is readily available.”

4. Construction Scheduling

Concrete:

The old adage “time is money” was never more true than when talking about construction schedules. According to Gerosa, “Buildings with concrete can almost always be built faster. When compared to structural steel, sometimes twice as fast. It is not uncommon for cast-in-place reinforced concrete buildings to rise one floor every other day. Developers can finish jobs faster, earn a profit, recoup capital, and move on to the next project.”

The popular construction process Gerosa refers to is known as the 2-day cycle. Robert A. Ledwith, business manager and financial secretary-treasurer for the New York City-based Local #46 Metallic Lathers Union and Reinforcing Iron Workers, explains: “A 2-day cycle is a very labor-intensive operation. On a 2-day cycle, we can [pour] up to 20,000 square feet of floor space every 2 days.”

Completing a building faster because of the 2-day cycle offers significant benefits. “That is something that is absolutely unique for concrete construction. They have mastered it in New York City, and the cities of Chicago and Los Angeles are striving to match that, as their accessibility to downtown [with] construction cranes, equipment, and staging areas become ever smaller and more limited,” says Alsamsam.

“When those ready-mix trucks pop up on-site, they need to come in, dump, and leave very quickly.” The faster the building is completed, the sooner the owner can allow occupancy and begin collecting income from tenants.

Steel:

While concrete’s 2-day cycle may seem to give it an unarguable advantage, steel provides many construction benefits of its own.

“We believe structural steel framing systems are the way of the future,” says Cross. “We believe that they result in an accelerated schedule. We also believe that quality is enhanced because of off-site fabrication, and that the productivity opportunities that exist in construction can be best addressed in off-site fabrication with a reduction of actual on-site time and on-site construction.”

Advancements in building information modeling have integrated the design, detailing, and fabrication of steel, which have resulted in an accelerated process. Design programs and CAD packages can pass information through a CIS/2 neutral database as a 3-D model to detailing and shop floor fabrication programs.

“This is literally compressing the steel portion of the schedule of projects by 40 or 50 percent,” says Cross of the advances in interoperability. These productivity increases position steel as a viable construction material both now and in the future.

5. Design Possibilities

Concrete:

Concrete buildings are taking shape – many different shapes – everywhere. “Remember, concrete seeks the form,” says Gerosa. “You can shape anything out of concrete; that’s why the Guggenheim was built the way it was.”

In addition to the unique aesthetics achieved with concrete construction, these buildings offer some very real space advantages. “Public and private developers should also realize that using cast-in-place reinforced concrete to frame a high-rise office building would yield more rentable space because of lower floor-to-floor heights,” Gerosa explains.

This is no secret to President Donald Trump, the New York City developer building at the former Chicago Sun-Times site. Architects of the Trump Intl. Hotel & Tower switched from structural steel to concrete so that two additional stories could be added to the 1,125-foot building.

With proper engineering, concrete building can also offer uninterrupted floorplates. “A great example is the newest office building in New York City, utilizing 45-foot spans and awesome views of the park,” says Alsamsam of 505 5th Ave.

Steel:

“Steel has the highest strength-to-weight ratio of any construction material,” says Williams. And with new construction methods, steel buildings remain a popular choice for office and multifamily developers. Use of girder slab, staggered truss, and castellated beam construction enables lower floor-to-floor heights than typically expected in structural steel buildings.

Looking for long spans of column-free space? Steel delivers. “Steel can accomplish extremely long spans in structures [and] very open-bay footprints without intermediate columns. It’s a very flexible material in terms of different ways to address design requirements,” says Cross.

6. Environmental Considerations

Concrete:

Concrete is a material that is often locally sourced and thus typically requires minimal energy to transport to building sites. Rebar for concrete is often produced from recycled steel. At end of life, concrete can be crushed and recycled but the recycled material cannot be used for new building concrete.

Steel: 

According to the British publication Building, 85% of steel is recycled, a process made easier by the fact that magnets are used in the process to sort steel. New steel made from scrapped steel uses about one-third of the energy necessary for steel from virgin materials. Steel fabrication made be done at a significant distance from a building site, increasing the energy needed for transport.

If you haven’t decided which side you’re on, don’t worry. Your education on steel and concrete buildings has only just begun. To find out more, contact both local and national industry associations. Offering free information and “concrete” advice, their knowledge is a real “steel.”

At the time of this article post, Jana J. Madsen was the Managing Editor at BUILDINGS magazine.

Categories
News

Concrete in Construction: Uses, Advantages, and Types

Concrete contractors are among the most important stakeholders in most construction works. While some sustainable structures are made from pure wood and glass, most commercial and industrial buildings are still made from cement. Today, we will look into the basics, importance and advantages of different cement types used in the construction industry.

What is Concrete?

Concrete is a vital element and a vitally important thing that is used in several individual and commercial buildings. It solidifies and hardens after mixing with water and placement due to a chemical process known as hydration. It binds other building materials together. It is a material extensively used in the construction process and is made by mixing aggregate, cement, small stones, sand, gravel, and water. All the components bond together to create a stone-like material.

The Romans invented hydraulic cement-based concrete. The British improved upon it and popularized it in the modern world. The Pantheon in Rome is one of the finest examples of Roman architecture that has survived to this day and has a 42-meter-diameter dome made of poured concrete.

Uses of Cement in Construction

Cement is probably the most used man-made material. Concrete is used to make:

  •      Pavements
  •      architectural structures
  •      foundations
  •      motorways
  •      roads and bridges
  •      overpasses
  •      parking structures
  •      walls and footings for gates
  •      fences and poles

How Cement Works

The material grows together from a moldable liquid into a hard, rigid solid. In the world today, concrete has become a fact of modern life. Six billion tons of concrete are used around the world each year. The addition of sand, fine aggregates and coarse aggregates of up to a few centimeters makes concrete. It is a porous material whose properties depend on its different kinds of pore space. Air voids are entrapped in the mixing process, the capillary pores, which are spaces occupied by water from mixing.

Concrete has compressible strength related to the overall porosity of the cement paste and the amount and form of the aggregates. 

Cement in Today’s Construction

Concrete in the present infrastructure has been deteriorating at a fast pace due to the corrosion of reinforcing steel coming from the including chloride and other ions from road salts, marine areas and ground soils.

Nowadays, the focus is on the transport aspect of concrete which includes diffusivity, permeability, and absorption. Concrete is a complex composite, which needs improvement, monitoring, and control.

The amount of water in the mix is compared with the cement amount called the water/cement ratio. The lower the water-cement ratio, the stronger the concrete is. It has higher strength and less permeability. The qualities expected of it are resistant to freezing and thawing and deicing chemicals, water-tightness, low permeability, wear resistance, and formidable strength.

Admixtures are additions to the mix which are used to achieve certain goals. When Accelerating admixture-accelerators are added to concrete, they reduce the setting time of the concrete and accelerate strength. The amount of reduction in setting time varies. Retarding admixtures are often used in hot weather conditions to delay setting time. The use of Fly ash reduces the heat generated by the concrete.

Advantages of Using Concrete in Construction

Advantages of concrete. Among all the construction materials used in the world, concrete is most widely used due to its unique benefits compared to other materials. Ten significant advantages of concrete are explained below.

Concrete is Economical

Compared to engineered cementitious materials used for construction, the production cost of cement concrete is very low. Again, it is inexpensive and widely available around the globe when compared to steel, polymers and other construction materials. Major ingredients of concrete are cement, water, and aggregates. All of these are readily available in local markets at a low cost.

Concrete Hardens at Ambient Temperature

Concrete sets, hardens, and gains its strength at regular room temperature or ambient temperature. This is because cement is a low-temperature bonded inorganic material. Thus concrete can be used irrespective of ambient weather conditions and optimized with admixtures if required.

Ability to be Cast into Shape

Fresh concrete is flowable and is in a liquid state. Hence, concrete can be poured into various form-works or shuttering configurations to form desired shapes and sizes at the construction site. Concrete can be cast into complex shapes and configurations by adjusting the mix.

Energy Efficiency in Production

The amount of energy required for the production of concrete is low compared with steel. For plain cement concrete, only 450–750 kWh/ton energy is required and that of reinforced concrete is 800–3200 kWh/ton. Production of structural steel demands 8000 kWh/ton or more to make, which is almost 3-10 times the energy consumption.

Excellent Water Resistance Characteristics

Though chemicals in water can induce corrosion in concrete and reinforced concrete, concrete can withstand water without serious deterioration compared to wood and steel. Due to this property, concrete is ideal for underwater and submerged applications like for building structures, pipelines, dams, canals, linings and waterfront structures Pure water is not deleterious to concrete and not even to reinforced concrete, chemicals dissolved in water such as sulfates, chlorides, and carbon dioxide causes corrosion.

High-temperature resistance

Concrete can withstand high temperatures better than wood and steel. Calcium silicate hydrate, C-S-H, which is the main binder in concrete, can withstand until 910 deg C. Concrete is a bad conductor of heat; it can store a considerable amount of heat from the environment. Concrete can withstand heat for 2–6 hours, enabling sufficient time for rescue operations in case of fire. It is used to fireproof steel and used in high temperature and blast applications.

Ability to Consume and Recycle Waste

Many industrial wastes can be recycled as a substitute for cement or aggregate. This includes fly ash, slag, also known as GGBFS or ground granulated blast-furnaces slag, waste glass, and even ground vehicle tires in concrete. Thus concrete production can significantly reduce environmental impacts due to industrial waste. Using these wastes improves the properties of concrete as well; therefore, the quality of the structure is not compromised.

Application in Reinforced Concrete

Concrete has a comparable coefficient of thermal expansion to steel. “steel 1.2 × 10−5 and concrete 1.0–1.5 × 10−5”. Concrete imparts protection to steel in corrosive environments due to the existence of CH and other alkalies. Moreover, concrete contributes to the compressive strength of reinforced concrete members and structures.

Low or Zero Maintenance Required

Concrete structures do not require coating or painting for regular applications to protect weathering compared to steel or wooden structures where it is inevitable. The coating is to be replaced and redone on a routine basis making the maintenance cost for concrete much lower than that for steel or wood.

Multi-Mode Application

One of the major advantages of concrete is its ability to be used in different application methodologies. Concrete is hand applied, poured, pumped, sprayed, grouted and also used for advanced applications like shotcreting in tunnels.

Types of Concrete

In concrete technology, a variety of type-names has been used for different types of concrete. This classification is based on three factors:

  •      Type of material used in its making.
  •      Nature of stress conditions.
  •      And it’s density.

Now, here is a brief account of the different types of concrete:

Plain or Ordinary Concrete

It is one of the most commonly used types of concrete. In this type of concrete, the essential constituents are cement, sand and coarse aggregates designed and mixed with a specified quantity of water.

The ratio of essential constituents may be varied within wide limits. A very commonly used mix design, widely known as Nominal Mix Design, is 1:2:4.

Plain concrete is mostly used to construct pavements and buildings, where very high tensile strength is not required. It is also used in the construction of Dams.

Lightweight Concrete

Any type of concrete having a density of less than 1920 Kg/m3 is classed as lightweight concrete.

Various types of aggregates that are used in the manufacturing of lightweight concrete include natural materials like pumice and scoria, artificial materials like expanded shales and clays and processed materials like perlite and vermiculite.

The single important property of lightweight concrete is its very low thermal conductivity.

For example, Thermal conductivity – the k value for plain concrete may be as high as 10-12. But the thermal conductivity of Lightweight concrete is about 0.3.

Lightweight Concretes are used, depending upon their composition, for thermal insulation, for protecting steel structures, they are also used in long-span bridge decks, and even as building blocks.

High-Density Concrete

This type of concrete is also called heavyweight concrete. In this concrete type, the density varies between 3000-4000 Kg/m3.

These types of concrete are prepared by using high density crushed rocks as coarse aggregates. Among such materials, Barytes is the most commonly used material, which has a specific gravity of 4.5.

It is mostly used in atomic power plants and other similar structures because it protects all types of radiation.

Reinforced Concrete

It is also called RCC (Reinforced Cement Concrete). In this concrete type, steel in various forms is used as reinforcement to give very high tensile strength.

In fact, it is because of the combined action of plain concrete (having high compressive strength) and steel (having high tensile strength).

The steel reinforcement is cast in rods, bars, meshes, and all conceivable shapes.

Every care is taken to ensure the maximum bond between the reinforcement and the concrete during the setting and hardening process.

Thus, the resulting material (RCC) is capable of bearing all types of stress in any construction. RCC is the most crucial concrete type.

Precast Concrete

This term refers to numerous types of concrete shapes that are cast into molds either in a factory or at the site.

However, they are not used in construction until they are completely set and hardened in a controlled condition. Some of the examples of Precast Concrete are; precast poles, fence posts, concrete lintels, staircase units, concrete blocks, and cast stones, etc.

These structural and decorative members are prepared in a well-equipped place where all arrangements are made for:

  •      Perfect proportioning of the ingredients of concrete.
  •      Thorough mixing of the cement, aggregates, and water to obtain the mix of the desired design and consistency.
  •      Careful handling during transport and placement in the perfect design molds.
  •      Perfect curing, under the controlled conditions of temperature and humidity. Even steam curing is used to obtain precast products having high strength in much less time.
  •      The construction industry’s latest trend is to shift more and more to prefabricated concrete units in building construction.

Prestressed Concrete

It is a special type of reinforced concrete in which the reinforcement bars are tensioned before being embedded in the concrete.

Such tensioned wires are held firm at each end while the concrete mix is placed. The result is that when the concrete sets and hardens, the whole concrete members, so the cast is put into compression.

This arrangement makes the lower section of the reinforced concrete stronger against tension, which is the principal cause of the development of tension cracks in un-tensioned reinforced concrete.

Since pre-stressing involves jacks and tensioning equipment, the pre-stressed concrete is also cast in the factories.

Some of its advantages are the following.

  •      The potential compressive strength of concrete gets considerably increased.
  •      The risk of the development of tension cracks in the lower sections of beams is considerably reduced.
  •      The shear resistance is greatly reduced. This eliminates the necessity of stirrups to a great extent.
  •      Lighter members can be used than the un-tensioned (normal) reinforced-concrete.
  •      The prestressed concrete is greatly favored in constructing bridges, long-span roofs, and most structures with a heavy dead load.

Air Entrained Concrete

It is a specially prepared plain concrete in which air is entrained in the form of thousands of uniformly distributed particles.

The Volume of air thus, entrained may range between 3-6 percent of the concrete. The air entrainment is achieved by adding a small quantity of foaming or gas-forming agents at the mixing stage.

Fatty acids, fatty alcohols, and resins are some common air-entraining agents. Air entrained concrete is more resistant to Scaling, Deterioration due to freezing and thawing, and Abrasion.

Glass Concrete

When the recycled glass is used as an aggregate in the concrete, this type of concrete is known as Glass Concrete.

They provide better thermal insulation and also have a great appealing look as compared to other types.

Rapid Hardening Concrete

This type of concrete is mostly used in underwater construction and in repairing roads. Because its hardening time is significantly less, it can be hardened in just a few hours.

They are also used in building construction, where the work should be done fast.

Asphalt Concrete

Asphalt concrete is a combination of aggregates and asphalt. It is also known as Asphalt. They are vastly used in the highways, airports, as well as in the embankments.

They can be hardened in just an hour. That is the reason for its vast usage inroads.

Lime Concrete

In this type of concrete, lime is used as a binding material with the aggregates. Before the invention of cement, the most used concrete was lime concrete.

In today’s age, Lime concrete is also used in floors, domes, and so on.

Roller Compacted Concrete

This concrete is mostly used as a filling material. They don’t have a better strength value. They are lean concrete and are compacted with the help of heavy means, like rollers.

A significantly less amount of cement is used in this type of concrete.

Stamped Concrete

They are ordinary concrete with some little differences and are mostly used for architectural purposes.

A stamp of different shape and design placed on the concrete structures when they are in their plastic state to acquire an appealing look design.

Pigments are used for color purposes of different types to give it a more realistic and appealing look.

Pumped Concrete

Pumped concrete is used for high rise buildings where concrete conveyance other than the pump is not an easy task.

They are made workable enough for an easy conveyance. Fines materials are used for a better supply. The finer the material is, the easier the discharge will be.

The pump used for conveyance purposes is made from rigid or flexible materials to discharge the concrete easily.

Vacuum Concrete

In this type, more quantity of water is added to the concrete mix, and then the mixture is poured into the form-work.

The excess water is then removed from the concrete with the help of a vacuum pump. That is why it is called vacuum concrete.

This technique is used to attain the strength of concrete early. It will attain the compressive strength within 10 days compared to 28 days of ordinary concrete.

Permeable Concrete

Permeable concrete is prepared in such a manner that the water can be passed in it. They have about 15 to 20% voids so that the water can pass in it.

They are used in those areas where stormwater issues persist.

Shotcrete

Shotcrete is concrete prepared in the same manner as ordinary, but the difference is that they are placed differently.

They are placed with the help of higher air pressure through nozzles. The benefit of this technique is that the compaction and placing of concrete will be done simultaneously.

Ready-mix Concrete

This concrete type is prepared in concrete plants and or transported with the help of truck-mounted transit mixtures.

Once they are reached at the site then, there is no further treatment necessary.

The plant location will be at an adjustable location so that the concrete can be supplied before the setting time can be started.

Self-Consolidated Concrete

These types of concrete are compacted by their weight, mean by the process of consolidation. There is no need to use a vibrator or doing manual compaction.

The workability of concrete is always high in this type. That is the reason it is also known as flowing concrete.

Fiber Reinforced Concrete

The type of concrete in which steel fibers 10 to 20 microns in diameter and 10 to 50 mm in length is used.

Fiber increases resilience, tensile strength, flexibility, and other qualities.

The fibers may be of different materials like steel, polymer, glass, carbon, or even natural fibers like coconut fiber.

Some types of fibers react with the cement; special care should be taken while using them. It has been used mostly as overlays for pavements in bridges, airports, and industrial floors.

Fiber reinforced concrete can also be used in places where increased resistance to cracking is required.

Fly Ash Concrete

Concrete using fly ash is called fly ash concrete. Fly ash is obtained from coals. Fly ash can be used to replace fine aggregates or cement or to replace partially both.

Up to 30 percent replacement of fine aggregates and 20 percent replacement of cement have been reported.

Fly ash improves workability in the fresh concrete and durability and strength in hardened concrete.

The particles of fly ash should be finer than cement particles.

High Strength Concrete

High-strength concrete is concrete with a strength over 40 N/mm2. It is also known as High-performance concrete (HPC).

High-performance concrete is used to achieve some special concrete properties like high strength, low shrinkage, self-compaction, high fire resistance, etc.

Normally, such concrete’s strength should be over 60 N/mm2 (Strengths up to 80 N/mm2 have been reported).

The materials used in the HPC are the following:

  •      Cement
  •      Coarse and fine aggregates of the required quality
  •      Water
  •      Supplementary cementing materials like silica fume, fly ash, blast furnace slag, etc.
  •      Superplasticizers (high water reducing agents)
  •      Air entraining agents (optional)

Silica Fume Concrete

Silica fume is a byproduct of silica, which is very finely divided in the industry. Concrete in which silica fume is used is called “silica fume concrete.”

The typical concrete with a normal water-cement ratio always has micro-pores, which limits the strength of regular concrete.

Silica fumes consist of very fine particles (actually, six times finer than cement particles).

Hence, if it is added to the concrete mix, the minute pore spaces can be reduced, resulting in high-strength concrete.

Polymer Concrete

Polymerization is a process of conversion of monomers into polymers. In typical concrete, you should have seen that micro-pores cannot be avoided.

The impregnation of monomer into these pores and subsequent polymerization is the technique that has been developed recently to reduce the porosity of the concrete and to improve its strength and other properties.

The following are the four types of polymer concrete materials available at present:

  •      Polymer impregnated concrete (PIC)
  •      Polymer Portland cement concrete (PPCC)
  •      Polymer concrete (PC)
  •      Partially-impregnated and surface-coated polymer concrete

Ferro Cement Concrete

Ferro cement concrete should not be confused with fiber concrete. Ferro cement consists of closely spaced wire-meshes which are impregnated with a rich mix of cement mortar.

Usually, 0.5 to 1.0 mm diameter steel wires are formed into meshes.

Mortar 1:2 to 1:3 with a water-cement ratio of 0.4 to 0.45 is poured into the form-work with fabricated steel by using layers of the wire mesh.

The steel content of this concrete will be as high as 300 to 500 kg/m3 of mortar. As the material consists of a large percentage of steel, it has high ductility and tensile strength.

The material was developed in 1940 by the Italian architect P. L. Nervi to build a large number of pleasing structural forms.

Pre-packed Concrete

Generally, concrete is prepared by mixing different ingredients.

However, it is also possible to pack some of the ingredients (coarse aggregate) in the form-work and then fill the pores with specially prepared cement-sand grout so that it will fill all the pores and form a concrete mass.

Pre-packed concrete is used in special situations, such as where a large volume of concrete (like a large machine block foundation) has to be concreted without construction joints.

One of the advantages of pre-packed concrete is that it has very little shrinkage.

Conclusion

Concrete is an essential part of any construction project. But you don’t even need a professional to tell you that concrete forms a crucial part of any building or structure. Just take a look at the buildings surrounding you, the pavements you walk on, and other various structures around. Concrete is everywhere. 

To make the most of its properties, you just need to realize which concrete type is best for a particular project.

Categories
News

How Safe Are Concrete Buildings? 5 Benefits of Using Concrete

Are you looking for a construction material that will meet your needs today without compromising the ability of the future generation to meet the needs of the future?

How you ever wondered why there are so many concrete buildings?

Concrete is the most widely used building material in the world because of the many benefits it offers the building and the environment.

Not only is concrete the best building material for your wallet and the environment, but it’s also the safest. Keep reading to learn more about the benefits of building with concrete.

Concrete construction building

THE BENEFITS OF CONCRETE BUILDINGS

We mentioned that concrete is the most widely used material in the world. Everywhere you look you see concrete. This is because concrete delivers a wide array of benefits while being cost-effective and sustainable.

Concrete is incredibly durable and extremely versatile. There’s a reason it’s so widely used. Not only is concrete used in building construction, but it’s also superior to asphalt when it comes to pavement.

Concrete pavement is more cost-effective than asphalt and requires much less maintenance over time. Concrete is built to last.

Let’s dive into some of the biggest benefits of using concrete in your construction.

1. DURABILITY

Concrete construction lasts longer than any other building material. This is because concrete actually becomes stronger over time.

When you build with concrete you don’t have to worry about long term costs or the environment as a result of maintenance and upkeep. The fact that you won’t have to fund regular repairs also reduces the cost of ownership.

Concrete is resistant to burns, rust, and rot. It can also stand up to vibrations, water, wind, fire, and even earthquakes.

Not only does this reduce costs, but it keeps people safe. Concrete has proven to be the most durable building material when it comes to natural disasters and extreme weather events.

2. SUSTAINABILITY

Concrete is produced locally and is highly sustainable. It’s usually produced near the construction site using local resources. This reduces pollution and shipping costs and also boosts the local economy.

Concrete is also recyclable. It’s recycled as both an aggregate and as granular material.

Aggregate concrete is used in parking lots, gabion walls, roadbeds, and to protect shorelines. Granular material is recycled to reduce the amount of material that ends up in landfills and the amount of new material needed for new construction.

3. VERSATILITY

While concrete is strong and formidable when it has hardened, it has plasticity when it’s freshly made which makes it very versatile. Designers and builders can mold freshly mixed concrete to any shape, surface, form, or texture they desire.

There are also many different kinds of concrete that serve specific functions for applications. Concrete is continually being adapted in new and creative ways to make it more sustainable.

Buildings constructed with concrete are easy to repurpose and adapt to new uses. This is because concrete is strong and fire-resistant. When buildings are repurposed instead of abandoned, resources are conserved and the environment is preserved.

4. ENVIRONMENTALLY FRIENDLY

Concrete is the lowest carbon building material over the lifetime of a structure. This is because of its durability, recyclability, efficiency, and thanks to innovations in the industry to address sustainability concerns.

This recent study found that concrete buildings have a significantly smaller carbon footprint than those made using wood materials. Concrete is also highly energy efficient.

This is because of its ability to store energy, also called its thermal mass. Concrete’s thermal mass allows it to reduce the heating and cooling demands of the building.

When concrete is used in conjunction with other green construction technologies, significant energy-efficient improvements are seen. Occupants of concrete buildings are more comfortable and concrete buildings reduce energy demands on cities as a whole.

Concrete is also completely inert, meaning it won’t emit any toxic compounds, gas, or harmful organic compounds.

5. SAFETY

You might be wondering, “Is concrete safe?” The answer is yes.

Concrete is very safe for building occupants and the environment. Because concrete is inert, it doesn’t burn. It also won’t experience rot or mildew.

Air quality in concrete buildings is excellent. When constructed properly, concrete won’t allow the entry of airborne pollutants like dust or pollen. You can rest assured that concrete is safe because of how long it has been used and studied.

Designers, builders, and engineers understand concrete and have refined construction techniques over time. The same can’t be said about newer materials.

Because concrete walls are so solid, building occupants will experience a sense of security and privacy., Because concrete has such strong integrity, it can protect its occupants from severe weather and earthquakes.

It’s high thermal mass also protects against temperature swings and keeps the interior of the building consistently comfortable and free of drafts.

CHOOSE CONCRETE FOR YOUR NEXT BUILDING PROJECT

As you can see, there are a number of reasons why concrete buildings outperform their competition. Concrete is the most widely used construction material on the planet for many good reasons.

Not only is concrete safe, but it’s by far the best choice to protect a building’s inhabitants and the environment. Concrete is a tried and true construction material that only gets better with time.

If you’re considering material for a new building or pavement project, we recommend using concrete.

Categories
News

How Climate Affects Concrete

While working with concrete may come as second nature to many contractors, it is one of the trickiest substances to work with due to how quickly it can change when exposed to different temperatures, humidity, and wind rates.

According to the ACI, concrete may be affected by, “…one or a combination of the following conditions that tends to impair the quality of freshly mixed or hardened concrete by accelerating the rate of moisture loss and rate of cement hydration, or otherwise causing detrimental results: high ambient temperature; high concrete temperature; low relative humidity; and high wind speed.” Under fair weather conditions, concrete can take anywhere from 8 to 48 hours to set properly. While concrete can reach its full strength in as little time as a week, it also takes nearly a month for it to cure properly.

However, anyone who has worked in construction before knows that weather conditions are seldom ideal.

While working with concrete may come as second nature to many contractors, it is one of the trickiest substances to work with due to how quickly it can change when exposed to different temperatures, humidity, and wind rates. The American Concrete Institute’s (ACI) technical publications are an excellent resource that provide insights regarding the plethora of effects of environmental factors on concrete. The ACI covers a variety of subtopics, ranging from extreme temperatures, humidity levels, wind velocity, natural disasters, saltwater, and freshwater’s effects on concrete in order to give contractors and concrete industry professionals accurate and up-to-date information.  

Heat

The ACI’s (305.1 – 14 Hot Weather Concreting) specifications for setting and mixing concrete in hot weather suggests contractors should try to limit the maximum concrete temperature to 95º F. Contractors should ideally aim to work with, or pour, concrete when it is anywhere from 50-60º F. Under fair weather conditions, concrete can take anywhere from 8 to 48 hours to set properly. While concrete can reach its full strength in as little time as a week, it also takes nearly a month for it to cure properly.

However, anyone who has worked in construction before knows that weather conditions are seldom ideal, which is why contractors must have a firm understanding of the effects of hot weather on concrete structures and how to use weather to their advantage. For example, concrete is known to set quicker in hot weather when compared to cold weather. This is because moisture found in freshly poured concrete evaporates at a quicker rate in hot weather and subsequently allows for a faster setting time. 

Due to the rapid evaporation of moisture, concrete that is poured during warm weather conditions is also more likely to experience cracks. Concrete will also be prone to more cracks if it is poured in a location where the weather cools down quickly during the night. Because of these effects, concrete that is poured and cured in 75º F weather will likely outperform concrete that is poured and cured in 100º F weather. Simply put, timing and background knowledge are absolutely crucial when it comes to working with concrete in warm weather.

Cold

Cold weather, according to the ACI 306 – “Guide to Cold Weather Concreting”, is defined as three continuous days of low temperatures, specifically below 40º F. Additionally, the ACI also considers air temperatures below 50º F for more than 12 hours as “cold weather.” 

Unlike working with concrete in hot weather, where certain warm temperatures can be used to a contractor’s advantage, colder temperatures can be detrimental to newly poured concrete. 

When a concrete powder is mixed with water, an immediate chemical reaction will occur which results in an internal crystallization of the concrete. These crystals make it possible for concrete to withstand additional pressure that may be caused by frozen water molecules within the concrete. Crystals will continue to grow for an extended period of time, even in cold weather. However, if temperatures drop below 15º they will no longer grow and the concrete will not cure at its full compressive strength. 

Under ideal weather conditions, concrete can attain a minimum compressive strength of roughly 500 lbs. per square inch in as little as 24 hours. This is much harder to achieve in colder climates, so contractors have learned industry tricks to “fool” the concrete into thinking it’s in warmer conditions so it will ultimately cure faster.

The ultimate contractor rule when working with concrete in cold weather: Never pour concrete directly onto frozen or thawed ground space. The frozen ground will actually settle as it thaws. Because of this, concrete that is poured in very cold temperatures could also be susceptible to cracking, similar to working with concrete in warmer climates. 

Wind

The ACI also states that wind velocity can affect freshly poured concrete by allowing too much water or moisture to evaporate from the concrete’s surface at a fast rate. In fact, the ACI technically classifies high wind velocity under hot weather due to the similar excessive loss of moisture concrete can experience when poured in warmer temperatures. 

When concrete is poured during extremely windy weather, the rapid velocity of air will only contribute to excess moisture evaporating from the slab of concrete. Because of this, the abrasion resistance and curing condition of concrete will subsequently suffer. 

Colder winds can produce what’s called a “wind chill,” which can strip excess heat from concrete. Additionally, plastic shrinkage cracking can occur when the surface of concrete dries before it has fully cured. To combat wind chill, it isn’t uncommon for contractors to turn to heaters to aid the curing process. Contractors can also use sealers to protect concrete from climates below 50º F. 

Concrete is a delicate material. Unbeknownst to many people, it is not only affected by extreme temperatures, but also by humidity levels, as well as the velocity and intensity of the wind. Working with concrete demands skill and patience. It requires both the expertise of those working with concrete, as well as the cooperation of environmental factors in order to produce a smooth, strong, properly cured structure.

Categories
News

TRENDS IN RETAIL FLOORING

The science of construction of large retail space floor slabs continues to develop at a fast pace.
The science of construction of large retail space floor slabs continues to develop at a fast pace.

Within the past six years, advancements in concrete construction have come about more quickly than for any other construction material. This is especially true for commercial and industrial slab-on-ground floor construction. It’s the result of the owners’ willingness to look beyond the initial cost of construction and focus on durability and maintenance over time; the specifiers and consultants who study how to improve the performance of floors; the contractors who revisit their projects over time to improve their concrete mixes and craft skills; and the manufacturers who develop new equipment able to produce higher quality floors. For contractors, the added incentive lies in the reality that they sometimes are held liable for making repairs on poorly designed floors.

Today green and sustainable construction is becoming the norm. Owners such as Wal-Mart want the public to know that they are doing their part to help reduce emissions of greenhouse gases into the atmosphere by using recycled materials, reducing energy costs, and spending less money on maintenance. Sometimes this results in higher initial construction costs, such as paying for very hard-troweled finishes. Even developers, who build and own structures briefly, are beginning to understand the marketing benefits of more durable and sustainable construction.

Of all the building elements, floors take the most abuse and cause the greatest disruption when problems arise. As a result, floors have become a focus for improvement and changes are occurring.

Owners influence floor construction

The trend toward exposed concrete floor surfaces replaces products such as carpet, vinyl tile, and quarry tile that add to the cost of construction, increase maintenance costs, and can increase insurance liabilities. Sometimes owners include decorative finishes, such as integral concrete coloring, chemical staining, and diamond polishing. They also are specifying gloss numbers to quantify levels of reflectance that can reduce lighting costs and ensure customer appeal. As always, they want floors without cracks and curled joints that cause problems for forklifts and store fixtures, and result in wavy appearances. Some of these expectations are unrealistic—all concrete cracks and all joints curl. Joe Neuber, president of Neuber Concrete, Kimberton, Pa., says he’s noticing a trend toward buildings with less square footage and higher volumes. This means that aisle widths are decreasing while storage racks are getting taller, this problem.” When additional products aren’t used for a floor surface, the material and the energy to produce them is saved.

The concrete shown here is a well-graded mix with top size aggregate of 1-1/2inches. These mixes make it possible to reduce the portland cement content, also resulting in less shrinkage and curling at the edges of a panel.
Neuber ConcreteThe concrete shown here is a well-graded mix with top size aggregate of 1-1/2inches. These mixes make it possible to reduce the portland cement content, also resulting in less shrinkage and curling at the edges of a panel.

Owners of retail stores want to reduce their lighting costs and floors with glossy surfaces offer that opportunity. Some retail facilities save as much as 40% on lighting bills.

It’s widely known that a fair amount of carbon dioxide (a greenhouse gas) is produced in the kilning of portland cement. Wal-Mart and some other owners are specifying replacements of portland cement with as much as 20% fly ash or slag for concrete floors. These pozzolans are waste products from other industries so the only energy commitment is the trucking needed to bring them to ready-mix producers. Properties of the concrete also are enhanced when using fly ash or slag in the process.

Neuber says that crushed recycled concrete from 1-inch top-size aggregate down to finings is being used more often as compactable subgrade material. He uses it wherever he can because unhydrated material in the aggregate sets and provides a more stable working platform during concrete placement. But he stresses the need to properly compact it.

The nature of floor finishes

Owners want flatter floors, harder troweled, and more durable floor finishes. Thanks to the increased abilities of contractors and the constant development of tools and equipment to perform the work, these goals are being accomplished without significantly changing installation costs.

With concrete as the wearing surface, there’s a trend to color floors using integral color, chemical stains, and water-based stains. Diamond polished finishes are standard as well. Owners know that customers like shiny floors so this becomes part of the building’s aesthetics.

Wet curing for seven days is becoming more standard for retail stores. The slab is saturated with water and covered with plastic cover materials that hold water uniformly in position during the curing cycle. Floors develop much better resistance to abrasion as a result.
PNA Construction TechnologiesWet curing for seven days is becoming more standard for retail stores. The slab is saturated with water and covered with plastic cover materials that hold water uniformly in position during the curing cycle. Floors develop much better resistance to abrasion as a result.

Some owners are willing to pay extra for very hard-troweled floors because they are more abrasion resistant and last longer. In order to preserve the finish during the polishing process, some owner specs avoid using diamond grinders and instead require the use of floor maintenance machines with diamond-embedded strip pads to attain the proper gloss. Afterward, owners maintain the floors with the same equipment—polishing the floor as abrasive foot traffic wears the surface and reduces the gloss.

Building owners also are hiring expert consultants to train crews and be onsite during concrete placements. More specifications require a percentage of finishers on a crew to complete the American Concrete Institute finisher certification program to ensure they understand concrete basics and have the needed skills to properly finish concrete.

The ability of concrete contractors to routinely increase floor flatness and levelness has changed dramatically in the past five years. This is in large part due to the development of equipment, especially riding trowels. So owners now specify more floors with FF requirements between 50 and 60.

Equipment and tool developments

Many developments in the past five years make work easier and better. Here are some examples.

Laser screeds. Their ability to screed very high FF floors continues to improve. Neuber waits to start finishing operations until the concrete is almost too hard to work before the first pass with pan floats in order to preserve flatness.

Finishing machines. Lampasona and Neuber agree that ride-on trowels make a big difference. Ride-ons are getting bigger (up to 3050 pounds) and better. Popular models currently have 4-foot or 5-foot-diameter rotors with up to 2 feet of space between rotors to prevent “ridges” or “windrows” from doubling up. They currently feature five or six blades per rotor to provide better support for pan floats and to achieve flatter finishes. Hydraulic steering provides longer life for the machine and less operator fatigue. They are powered by diesel or gasoline engines up to 100 hp. Look for them to get even bigger because they produce flatter floors.

Plastic blades. Installing burned finishes with steel blades darkens floors, causes problems for colored finishes, and reduces the reflectivity of plain concrete floors. At first contractors installing colored floors switched to plastic blades after the first few passes with steel blades but now contractors are using them on plain concrete as well; and some owners are specifying that they be used. The recent introduction of composite plastic pan floats allows contractors to start the finishing process earlier and achieve flatter finishes.

Vacuums for control joint cutting saws. Without a vacuum, early-entry saws collect dust between the saw’s skid plate and the concrete, scratching the fresh concrete 4 inches on either side of the cut. This blemish compromises the appearance of finished work. Vacuuming the dust away as it’s created solves the problem.

Placing equipment. Using laser-guided placing equipment to provide the right amount of concrete for a laser screed to strike the final grade improves FF numbers.

Laser-controlled grading. Machine control systems that pick up signals from laser levels provide much more accurate subgrade elevation control under floor slabs, which in turn ensures even thickness floors. Contractors increasingly are adding controllers to their machines. Grade is being rechecked with laser-guided equipment during placement or to remove ruts left from concrete trucks and laser screeds.

Concrete mix design trends

Using top aggregate sizes of 1½ inches for floor slabs 5 inches thick and greater has become the norm. But Neuber says he now uses top aggregate sizes of 2½ inches whenever projects allow because shrinkage is reduced further. When 2½-inch sizes are added to a well-graded aggregate concrete mix, aggregate surface areas are minimized and therefore the amount of cement paste to coat the surfaces. Neuber says mixes using 520 pounds of cementitious material are common and more specifiers are replacing some of that with fly ash or slag. Lampasona adds that water-cement (w/c) ratios tend to range from 0.47 to 0.55 with 0.52 being the trend. The goal is to minimize shrinkage and curling over time. When combined with a close joint spacing—no more than 15 feet in a 6-inch slab-load transfer devices in low shrinkage concrete mixes minimize joint deterioration, resulting in more durable floors. Contractors are in a good position to know how their mixes perform because they can return to their projects years later to see the long-term results.

Figure 1, Materials distribution.
Neuber ConcreteFigure 1, Materials distribution.

Good concrete is compromised when improperly cured. The old curing method for floors involved covering it with plastic sheeting to help retain moisture. This process is being replaced with wet curing for the first seven days after placement. Contractors flood water on newly finished floors and place wet curing covers made from plastic fabric with a polyethylene backing over the water to ensure a saturated environment. When the covers are removed, floors are scrubbed and cleaned immediately to remove hydration byproducts that could leave markings and stains. The resulting floors have more durable surfaces and abrasion resistance, and are aesthetically pleasing.

What owners receive

The owners of retail facilities are thinking more about how to achieve longer life and durability in their floors now. They want to save more on energy costs and maintenance as well. Through the combined efforts of contractors and engineers, owners are receiving floors they can be proud of—flatter than ever, elegant decorative finishes, gloss numbers that reduce lighting costs, and with minimal shrinkage, less cracking, and reduced curling.

Categories
News

CREATING FLAT AND LEVEL FLOORS

Flat and level concrete floors are vital for warehouses. 

The forklifts and material handling equipment traversing many warehouses and distribution centers at times may rival a big city’s rush hour traffic. These vehicles are most effective when the facility’s concrete floor is perfectly flat and level.

The best way for a building owner who needs a concrete floor to meet flatness and levelness requirements for this equipment is to specify the floor tolerance requirements at the very beginning, at the conception phase of the project.

In fast-track construction of new big box facilities, floors sometimes are placed and finished in pours of 50,000 to 80,000 square feet or more with laser screeds and large riding trowels with pans. Then, the surface is remediated to a specific tolerance by grinding the material handling equipment wheel paths only or simply the width of the aisles between the racks to increase throughput or material handling efficiency. Both depend on the owners’ necessary F-min tolerance.

For example, a FF 50/FF 35 floor is specified in a building which sits empty for six months or more before it is occupied. Depending on how the facility is proposed to be laid out by the new tenant/owner and depending on the amount of slab curling and settling that occurred while it was vacant, it will likely require remediation to meet F-min tolerances of at least F-min 50 to F-min 100 or higher if required by forklift manufacturers’ recommendations or the architect/engineers’ tolerances. (See ACI 360-10, Guide to Design of Slabs-on-Ground.)

In lieu of Type II concrete, Type K shrinkage compensating concrete is placed and finished in large square pours by experienced contractors. Construction joints or form boundaries are set about 100 feet apart. These methods may allow for quicker installation of the floor and could reduce the amount of grinding at joints due to the lack of curling because of the expansive properties of Type K cement.

Strip pour

Some owners and contractors prefer to get high-tolerance F-min floors using the “strip pour” method. This placing and finishing method uses forms set to rigid tolerances of plus or minus 1/16-inch, milled wood form tops or thin steel edge forms, and vibrating truss screeds with hand tools (check rods and bump cutters) used for strike-off. Some contractors prefer laser screeds instead of truss screeds. Floors installed this way usually require little or no remediation, as tolerances are more stringently controlled with the narrow strips.

What if owners want to expand or move, and must buy or lease an existing facility? What if they have an existing facility and want to upgrade, move, or reconfigure the current material handling equipment, racking layout and conveyors, but the floor isn’t up to par?

There are usually three options. But first, they should hire a qualified firm to measure the existing slab with the proper floor flatness and levelness equipment to assess its current condition. This could save time and money if deciding to lease a nearby facility that could be better than the one the owner is seeking to rent.

The strip pour method uses forms to set rigid tolerances, milled wood form tops or thin steel edge forms, and vibrating truss-screeds with hand tools used for strike-off.
AllflatThe strip pour method uses forms to set rigid tolerances, milled wood form tops or thin steel edge forms, and vibrating truss-screeds with hand tools used for strike-off.

There are three common methods for upgrading:

1. Remove and replace, which is expensive, invasive, and time consuming in an operational facility or one that must be operational soon.

2. Apply a self-leveling or epoxy topping, which often requires scabbling or scarifying the existing surface for an underlying mastic layer. If not applied by an experienced contractor, this can be challenging, time consuming, and have a high probability of failure (blister or delaminate) due to moisture content of the subgrade and high alkalinity at the surface.

3. Usually the most cost-effective fix entails grinding, but don’t be afraid, read on.

Grinding might have its pitfalls. People immediately think of loud noises (engines and blades), dust (silicosis), and downtime. However, relatively quiet and dust-free concrete floor resurfacing equipment capable of creating superflat F-min tolerances for very narrow aisle (VNA) applications does exist and is used every day with great success.

Some grinding equipment was designed to work in operational VNA buildings, order picker paths, crane rows, or even wide open areas while the facility continues to operate with little or no interruption. Hundreds of building owners that had their floors ground as long as 25 years ago are currently operating today with great success.

Planing, skimming

What is the F-min System?

The most effective vehicle material handling system for warehouse and distribution centers is based on floors that have superior flatness and levelness.

F-min is a floor industry standard measuring system for very narrow aisle (VNA) traffic floors. It is expressed as a unitless number for both the longitudinal and transverse axis for the exact wheelbase configuration of a VNA forklift or truck or order picker crane in high-stack warehouses. The higher the number, the more flat and level the floor. As an example, it may be expressed at F-min L 85/F-min T 100 (L = longitudinal; T = transverse).

The primary reason for developing the F-min system was to quantify the threshold of mast sway for preventing lift truck payload racking strikes and analyze the bumpiness of VNA floors. The system allowed contractors to expedite floor repairs and ultimately paved the way for development of construction techniques to manufacture this type of floor.

Because a VNA lift truck’s wheel path does not vary in its movement down an aisle from side to side, it is important to measure the exact path that the truck will travel. F-min measurements are taken by a vehicle lift truck simulator that tracks the exact wheel paths the actual lift truck follows in the aisle.

ALLFLAT’s proprietary measuring device, the F-min Profiler, is a digital, semi-continuous recording dual-axis differential profileograph. The data from the profileograph is used in the F-min calculations to provide a certification of compliance or to report any noncompliance, which then indicates the location of any required remedial activity or grinding.

Instead of grinding, it should be called planing or skimming, which does not sound so harsh. Think of it this way: If the American Concrete Institute says an F-min 100 floor is approximately plus or minus 1/16-inch in any one location and a floor is currently plus or minus 1/8-inch, then only 1/16-inch needs to be removed.

It does not take much to throw off the performance or longevity of material handling equipment in warehouses. That is true for the amount of concrete that must be removed to make an ordinary Random-Traffic FF/FL floor a Defined-Traffic Superflat Floor. (See ASTM E 1155, Standard Test Method for Determining FF Floor Flatness and FL Floor Levelness Numbers.)

However, the key to this is doing it planar or kept to a high degree of levelness. That’s the tricky part, but there is equipment that can do the job. Many concrete grinders are on the market, but they are usually manually operated (although there are a few laser-guided models.)

The problem is one will almost always encounter an area that needs 1/2 to 3/4 inches removed. That is a lot of concrete to remove, but some equipment can move right through it with a single pass with results well above F-min 100.

In conclusion, there are different ways to design a high-tolerance concrete floor with a specific use, and there are several qualified architects, engineers, and consultants who can assist owners and developers with their projects. There are many experienced contractors who can install these types of floors every day.