The future of concrete demolition in buildings may be seen in this robot that recently won an outstanding design award in Sweden. According to the designer this robot can demolish concrete and leave the steel reinforcement in place, while capturing the dust it creates and recycling the concrete. The link below includes more information about this innovation that may soon be seen at a concrete repair project near you
Joint sealants (caulks) are often used as a quick fix to address a problem leak, but proper attention to material selection and the joint onto which it is applied can make the difference between a long-term repair and a recurring leak. See our BLOG entry on proper sealant joint preparation, design, and application http://blog.etc-web.com/?p=854.
The most widely used commercial-grade building sealants are made of either silicone or urethane. Other materials regularly enter the marketplace, many of which are specialty products for unusual/unconventional uses. Acrylic terpolymers comprise another family of sealants (and will be a topic for a future blog entry), but silicones and urethanes are mainstays in the construction trades.
Silicones tend to be longer lasting, are resistant to ultraviolet (UV) degradation, and most commonly used on non-porous substrates like metals, window-glazing and certain masonry projects. Paint will not adhere to silicone. Urethanes are normally less expensive and are paintable . They are often used on porous or natural materials like wood, masonry, concrete, and stone repair projects.
Sealants come in a wide range of colors, single and multi-component formulations, and non-sag or self-leveling viscosities. They’re also classified by elongation characteristics. For example, a rating of 50% means that the sealant in a half-inch-wide joint can stretch or compress up to one-quarter of an inch without tearing. There is no single sealant that’s suitable for every application and product selection is key to performance.
Surface preparation is essential to achieving a long lasting bond. Many sealant manufacturers require application of a designated primer to the substrate. Pull tests should be performed on a section of cured sealant to ensure adequate adhesion. In a standard pull test, the sealant should tear before it debonds from the substrate.
Silicone and urethane sealants do not stick to each other and should never be used where such a bond would be necessary to performance. When replacing sealants in a joint, the old materials must be completely removed.
Lastly, always tool the sealant into the joint. This not only imparts a finished appearance, it helps achieve a better bond to the substrate
Clays are among the most useful and versatile materials on earth. Next to wood, it’s been the most common building material across the history of mankind. There are few households on earth that aren’t filled with products made of clay, from coffee mug to toilet bowl. It’s used in medicines and cosmetics. Industrial uses of clay include waterproofing and hazardous material containment. The slick texture of glossy paper is courtesy of a clay slurry. There’s no lead in a pencil lead, but there is clay (and graphite).
Many of the attributes that make clay so useful in those contexts also make it highly undesirable in others. Clays are hydrophilic and plastic, meaning they readily absorb water and in doing so, are easily deformed. Plasticity is necessary to form bricks and mold dinnerware, but it’s not what you want when you have to support a house or a roadbed. Clays are also expansive in the presence of water, some (such as marine clay) to an extreme degree. The expansion can be sufficient in some cases to displace overlying structures.
Because they tend to absorb rather than pass water, clays do not drain well. In construction, it’s generally advantageous to move water away from most elements. If water is held near enough to the surface to freeze, ice formation can exert enough pressure to dislodge or break overlying materials (like asphalt and concrete).
There are a number of ways to deal with clay in construction. The most effective way is to remove it entirely, but that’s not usually necessary and often impractical. In some instances (such as asphalt or concrete placement), it’s often sufficient to remove clay to a depth of several inches and replace it with a material that can be compacted and drains readily (such as gravel, stone dust, etc.). For deeper deposits that might affect foundations, underpinning by helical piers, grout injection or other methods can be successfully employed to stabilize the structure.
Clays, particularly in the Washington-Baltimore region, are inescapable. Their composition and attendant problems can vary substantially from one square yard to the next and the methods for dealing with them are equally varied. If you’ve noticed unusual movement, inexplicable cracking, displacement or similar conditions, clay might be at the root of it. In most such cases, the prudent approach is to have the condition evaluated by a qualified professional
Parking garages in this region are attacked by road salts and water throughout much of the year. The cost to repair deteriorated concrete can be quite high and the project can cause significant inconvenience to garage users. So, as part of a parking garage restoration project, we recommend and our clients tend to include, application of a vehicular-traffic-bearing membrane on the structural slabs to help protect their investment and extend the service life of the garage.
There are two basic classes of products commonly used to protect garage slabs, one of which is penetrating sealers. Penetrating sealers include materials such as silanes and siloxanes, which are silicone-based water repellants. These compounds penetrate into the concrete and react with the silica to create a water repellant barrier that also retards chloride migration.
Penetrating sealers are breathable so they do not create a vapor barrier and are relatively inexpensive. However, they do not seal cracks and require frequent reapplication as their effectiveness decreases with wear and time. These materials usually need to be renewed on a three to five year schedule.
The other class is traffic-bearing membranes, which are liquid-applied materials in several layers of cementitious, epoxy, or urethane compounds. These systems are all relatively thick (up to about 90 mils) and are designed with the properties needed to withstand the destructive forces imposed by vehicles tires.
Cementitious products are generally robust, breathable, and well suited for on-grade or elevated slabs, especially those with steel decking supports.
Epoxies are very durable and offer outstanding abrasion resistance, but are not breathable and are less flexible. So they are prone to cracking when slabs move/crack over time. They are well suited for on-grade slabs and areas where chemical and/or extreme wear resistance is needed.
Urethanes are softer, non-breathable, and more flexible so they have the ability to bridge cracks, which makes them ideal for elevated, reinforced concrete slabs. Some systems include an epoxy primer so that the urethane can be applied to on-grade slabs. Systems from reputable manufacturers are generally warranted for five to ten years and can remain serviceable longer, if properly maintained. Most membrane systems offer fast-cure and low-odor formulations, if the project has special requirements.
Consult your trusted restoration engineer before embarking on a garage coating project, as picking the right coating system can make the difference between a successful and not-so successful result.
Three-dimensional Ground Penetrating Radar (3D GPR) allows us to peer inside visually impenetrable building elements. We most often use it locate embedded steel reinforcement,tendons, pipes etc., in concrete slabs. There are other technologies that can perform such tasks, but they have a number of shortcomings.
1. Radiography can produce reliable, high-resolution images, but the process requires a potentially hazardous radioactive source and access to both sides of the scanned item. It’s also tedious and time consuming.
2. Magnetometers can detect ferrous metal (iron and steel), but cannot determine depth or dimensions. Deeply embedded materials can be elusive to most hand-held magnetometers and non-ferrous materials (aluminum, plastic, copper, etc.) are undetectable.
3. Two-dimensional GPR will locate embedded items and gross anomalies in the scanned materials, but depth cannot be accurately determined. It also produces a lower resolution image compared to 3D.
The system we use can scan extremely dense materials (such as concrete) to depths of up to 20 inches in any plane. The three-dimensional aspect reliably depicts the scanned items in context. Please do not hesitate to ask us for a free demonstration of our 3D GPR.
If scientists from South Korea have created a product that works as well as its advertisement says it does (and not many do), a new self-healing concrete coating may be on the market soon. They claim that it can automatically seal cracks and prevent water from entering concrete pavement. The new, high-tech coating is intended for roadway use and claims to be inexpensive and environmentally friendly.
The secret of this new self-healing concrete protective coating is that it contains microcapsules that are filled with a material that can seal cracks. So when a crack occurs, the microcapsules are ruptured, and the integral sealant is released. When sunlight hits the material it becomes solidified, and thereby completes the sealing process. The new material promises to reduce the need to frequently repave roads, however, it is not clear what might happen on shady streets.
The scientists claim to have created the first self-healing protective coating for concrete, as well as the first to use capsule-type, photo-induced, materials that are catalyst-free, environment-friendly, and inexpensive, We will keep you abreast of any future developments
Moisture problems in concrete cause about $1 billion dollars in flooring failures every year. Prevention of such failures requires strict adherence to product specifications and ASTM procedures. Below are some key points to consider.
- The concrete slab needs proper curing time, and all lighting, heating, and cooling conditions need to be stabilized.
- Any curing compounds used on the slab must be removed.
- Regarding the concrete itself, it should have a water-cement ratio of less than 0.50 and a vapor retarder should be installed at a minimum thickness of 10 mils.
- Adhesives used for the flooring installation must be allowed their proper cure time, after the concrete has cured.
Finally, it’s critical that the slab be tested for moisture by a certified concrete slab moisture testing technician, according to ASTM guidelines. If you have experienced a flooring failure or require moisture testing before flooring installation, give us a call! We have an ICRI certified testing technician on staff to help you.
If you are contemplating laying a new concrete driveway or replacing an old asphalt parking lot, consider an environmentally friendly and potentially cost-saving option: permeable pavement. Traditional concrete and asphalt hardscapes are impervious, which means that storm water collects on the surface and runs to the storm drainage system. Standard hardscapes often lead to increased costs to install and maintain storm water management systems. They also create runoff which contributes to flooding and erosion. A green option such as permeable pavement allows a large portion of the rain water to drain through the material and filter into the ground below.
You may have heard of permeable pavement referred to by different name, including pervious pavement, porous pavement, or even popcorn pavement. Some of these pavements feature porous concrete or asphalt which literally allows water to drain through it via an interconnected system of voids. Other pavements feature a system of permeable pavers which allow water to travel through the material, as well as between the pavers. All these permeable hardscapes accomplish the same goals: helping the environment by reducing storm water runoff and helping your wallet by eliminating or reducing the need for retention ponds, underground retention tanks, swales, and other storm water management mechanisms.
There are just as many applications of permeable pavements as there are design considerations and limitations, so be sure to have a qualified professional discuss with you which options are best suited for your specific goals!
After the extensive power outages caused by Hurricane Sandy and the freak derecho storm in late June and with predictions of a rough winter, many people have purchased portable generators to keep the lights on and the beer cold in anticipation of the next big storm.
Although generators are a great way to provide some temporary creature comforts, they don’t come without hazards. Most people are aware exhaust fumes from gasoline-powered equipment are toxic and running a generator within or too close to your home can be lethal. Nonetheless, people continue to be hospitalized or killed by carbon monoxide poisoning due to generator misuse.
Exhaust isn’t the only danger. The method by which a generator’s power is utilized can also be deadly. Often people attempt to power the entire house by “back feeding” the generator output into an electrical outlet (such as a dryer receptacle). Not only is this illegal in most jurisdictions, it could potentially electrocute linemen working to restore electrical service.
If you feel the need to use a portable generator during the next power outage it’s best to be prepared and have the generator properly wired to a transfer switch by a qualified electrician. With a properly wired generator installed a safe distance from the house, you can relax in anticipation of the next power outage.
A common way to protect steel against corrosion is to galvanize it. The term refers to the original process that entailed deposition of zinc by an electrical process, using a galvanic cell (battery). Electroplating is still used but coating raw steel with molten zinc (hot-dipping) is the more common practice. “Hot-dipped galvanized” is technically a misnomer, but a commonly accepted one. Our language is rife with them.
Not all hot-dipped treatments are equal. Sheet steel is usually coated with a thin layer, producing a uniformly smooth texture and is generally termed a G-90 coating. While certainly a “hot-dipped” process, G-90 differs substantially from what is customarily called hot-dipped, which usually refers to a G-185 coating that can be four to six times thicker than G-90. It also usually produces a rough texture that is advantageous in certain applications. For example, wood fasteners benefit from a rough texture by introducing a mechanical advantage and enhanced resistance to back-out.
G-90 can also be employed for fasteners; however, corrosion resistance is minimal and not generally recommended for exterior use. In some applications, G-90 treated fasteners should never be used. The latest generation of pressure-treated lumber utilizes preservatives rich in copper salts, presenting an environment corrosive to steel. Some dissimilar metals (like steel and copper) immersed in an electrolyte (such as various chemicals in preservatives) produce an electrochemical (galvanic) reaction.
The anode in a galvanic couple (in this case the steel fastener) dissolves over time and migrates to the cathode. The zinc on a galvanized fastener is more reactive with copper and acts as a sacrificial anode to protect the steel; however, a G-90 coating is rapidly depleted in the aggressive reaction. A G-185 coating is considered acceptable for use in treated lumber. Stainless steel is preferable, since the electrical activity between it and copper is minimal.