Terrazzo is a solid flooring material made with chips of marble or other stone pieces set in a cementitious or resinous binder. After the terrazzo has cured, it is ground and polished to a shiny and durable finish.The following image is a closeup shot of a terrazzo floor. Notice the zinc strip that separates the two different colors/mixes. The hot spots on the floor are from recessed down lights in the ceiling above.Types of Terrazzo - Aesthetic AppearanceStandard Terrazzo is made from relatively small stone chips and is typically ground and polished.Venetian Terrazzo is also ground and polished, however the stone chips are larger in size. The larger chips can also be infilled with smaller chips.Rustic Terrazzo is a uniformly textured finish where the binder is recessed from the chips. To accomplish this, the surface is sprayed before the binder fully sets, which slightly exposes the stone chips.Palladiana Terrazzo is more of a mosaic finish where very large chips (or slabs) of stone are set with the joints between slabs infilled with standard terrazzo.There are a number of terrazzo systems that can be used. The diagrams below show the main types of systems. While the type of terrazzo is selected for its physical appearance, the terrazzo system is selected based on construction technique and the project conditions. Thin-set Terrazzo is a 1/4" or 3/8" thick resinous topping that is directly applied over a sub-floor. Typically the sub-floor is concrete due to its stability; however, plywood floors may also be used if they are properly installed. Usually, the resin is epoxy, but polyacrylate is a common alternative. A flexible membrane may be installed between the sub-floor and the terrazzo finish so that minor cracks from the sub-floor are not translated to the finish flooring. Zinc, brass, or plastic dividers must be installed above any control joints in the sub-floor so that the terrazzo finish does not crack along the joints.Thin-set Terrazzo Composition (from bottom): Sub-floor (typically concrete or plywood) -- 1/4" or 3/8" terrazzo finish.Monolithic Terrazzo is a 1/2" thick cementitious finish applied directly over a concrete sub-floor. When the sub-floor is very smooth a bonding agent is required so the terrazzo finish properly adheres to the concrete. The flatness and general quality of the concrete sub-floor is critical in preventing the terrazzo from cracking. Monolithic terrazzo is generally recommended for slab-on-grade applications because typical above grade floors are prone to deflecting, which causes cracks in the terrazzo finish. As with thin-set systems, monolithic systems require dividers at all control joints in the concrete sub-floor.Monolithic Terrazzo Composition (from bottom): Concrete slab -- Bonding agent when required -- 1/2" terrazzo finish. Bonded Terrazzo is a 1/2" thick cementitious finish applied over a sand-cement mortar underbed, which sits on a finished concrete slab. The advantage of a bonded terrazzo system over a monolithic system is that the sand-cement underbed easily accommodates variations in the concrete slab; therefore, the quality of the slab is not as critical. However, due to the thickness of the mortar underbed, a slab depression of 1.75" to 2.5" is required. Dividers are required at all control joints in the concrete slab. Bonded terrazzo systems are acceptable for use indoors and outdoors.Bonded Terrazzo Composition (from bottom): Rough-finished concrete slab -- Mortar underbed -- 1/2" terrazzo finish. Sand Cushion Terrazzo is a 1/2" cementitious terrazzo finish that sits on a mesh reinforced mortar underbed, which is separated from the sub-floor by a isolation sheet. A sand cushion terrazzo floor is the ideal system for a floor where deflection or movement is anticipated. However, due to the thickness of the system a slab depression of 2.5" to 3" is required. Dividers at approximately 5'-0" on center are still required to help offset any expansion or contraction of the terrazzo finish. The isolation sheet and mesh reinforced mortar underbed will absorb most of the sub-floor imperfections so that they are not telegraphed to the finished terrazzo.Sand Cushion Terrazzo Composition (from bottom): Plywood or concrete sub-floor -- Thin layer of sand -- Isolation sheet -- Sand-cement underbed with mesh reinforcement -- 1/2" terrazzo finish.

Polished concrete is fast becoming the ultimate no-wax flooring material. Thanks to recent advances in polishing equipment and techniques, contractors are now grinding concrete floor surfaces, whether new or old, to a high-gloss finish that never needs waxes or coatings. Factor in the superior durability and performance of concrete, and it's no wonder why more retail, warehouse, and office facilities are opting for polished concrete flooring as an alternative to marble, granite, tile, linoleum, or coated concrete. Even homeowners are catching on to the appeal of these smooth, high-luster floors, which can be stained to replicate the look of polished stone.Because polishing is a multistep process, you can choose the level of sheen -- from satin to high-gloss -- that meets your maintenance and aesthetic requirements. This versatility makes polished concrete an ideal flooring material for a variety of applications.This section offers a complete overview of polished concrete floors, including benefits, design options, equipment requirements and maintenance needs.You'll learn the basic steps in the polishing process, the differences between wet and dry polishing, and the advantages of polished concrete compared with other flooring materials including carpeting, wood, ceramic tile, natural stone, and vinyl tile. You'll also find the average costs of polished concrete and what factors affect the final price of installing polished concrete floors.You'll learn how to prepare concrete surfaces before polishing to ensure good results, as well as why some concrete floors may not be good candidates for polishing. Also discover the difference between the various levels of shine possible with polished concrete, ranging from low gloss to reflective mirror-like finishes.Plus get popular design options for polished concrete, including coloring with stains and dyes, decorative engraving, and stenciled graphics. Find ideas for achieving interesting decorative effects by applying multiple colors of dye and using faux-finishing techniques.Finally, you'll find instructions for cleaning and maintaining polished concrete, how to improve the slip-resistance of polished concrete floors and the environmentally friendly attributes of polished concrete.Be aware that the process of polishing concrete floors requires a great deal of expertise and the use of specialized heavy-duty polishing machines equipped with diamond-impregnated disks that gradually grind down surfaces to the desired degree of shine and smoothness. Considering the investment in equipment and the skill required, it's definitely not a project for the do-it-yourselfer. You'll want to hire a professional concrete polishing contractor to do the work.Factor in the superior durability and performance of concrete, and it's no wonder why more retail, warehouse, and office facilities are opting for polished concrete flooring as an alternative to marble, granite, tile, linoleum, or coated concrete. Even homeowners are catching on to the appeal of these smooth, high-luster floors, which can be stained to replicate the look of polished stone.

In all likelihood, the condition of the floor you’ll be polishing will have more impact on the final results than any other aspect of the project. It’s the key factor influencing the type of equipment and diamond tooling to use, the time and labor required to complete the job, the grit you should start with, the amount of densifier needed, and the production rates of your equipment and crews.Determining concrete hardnessThe degree of hardness, or density, of the concrete is the chief factor determining the type and grit of diamond to use. To determine concrete hardness, use a scratch test kit based on the Mohs scale of relative mineral hardness. This easy test makes it simple for you to determine where the concrete substrate ranks on the Mohs hardness scale and help you choose the most efficient and cost-effective diamond tooling for the job.Cleaning the floorIf the concrete floor has pre-existing oil stains, you’ll need to remove them first because they will inhibit the penetration of densifiers, dyes, and stains, resulting in unwanted color variations. Degreasers and detergents are usually sufficient for removing lightly soiled areas. For heavier oil stains, try using a poultice powder-a blend of dry absorbent clay that’s effective at extracting stubborn oil and dirt stains from concrete. For light oil stains, you can also try pouring mineral spirits onto the stain and then absorbing it with kitty litter.On some projects, you may need to remove vinyl tile or asphaltic adhesive membranes from the concrete surface prior to grinding. If vinyl tile needs to be removed from a large area, the most efficient method is to use a ride-on machine specifically designed to scrape the tile off the surface. These machines are useful for removing a wide range of materials from concrete surfaces including thick coatings (such as epoxies or urethanes), adhesives, thin-set mortars and floor coverings.If mastic or adhesive must be removed from the floor, the quickest method is to grind the material off, versus using a chemical stripping agent. Most manufacturers of grinding equipment and diamond tooling will have accessories designed specifically for this purpose.Repairing chips, spalls, and cracksWhen making repairs to the concrete before polishing, your goal is to blend the fix as closely to the surrounding concrete as possible. To get the best results, you must use specific products for specific repairs. For chips left behind from carpet tack strips, small divots and spalls, you can choose from a variety of different cement-based patching compounds, depending on the depth and severity of the affected area. Keep in mind, though, that even the best patch may not be an identical match to the rest of the polished floor. If you are repairing colored concrete, use a patching product that can be tinted to match the desired color.For minor flaws no deeper than 1/8 inch, try using a traditional skim-coat material used for overlaying concrete floors. For deeper flaws (1/4 inch or greater), use anchoring, or hydraulic, cement as a patching compound or even a self-leveling overlay if the flaws cover a large area.When dealing with cracks, you first need to determine if they are static or moving cracks. Static cracks (sometimes called “craze cracks”) are hairline flaws that only affect the surface of the concrete. Generally, this type of crack requires little if any attention and can actually add decorative interest once the floor is colored and polished. If you want to disguise the cracks, an effective method is to apply a tinted urethane as a skim coat.Moving cracks, also called “active cracks,” are more serious and typically must be repaired before you start polishing by crack chasing, cleaning, and filling. Crack chasing involves using a V-grooved diamond blade attached to an angle grinder or a walk-behind machine specifically designed to route out the crack. Next, thoroughly clean out the crack by removing all debris with a shop vac and then blow away any remaining dust with compressed air. To fill the routed crack, use a semi-rigid polyurea, which you can have color-matched to the floor, or apply a grind-and-fill repair material before polishing. Cleaning and filling jointsFilling contraction, isolation and construction joints is just as important as successfully polishing the floor-not only for aesthetic reasons, but also to greatly reduce the chance of the joint edges chipping and spalling, especially in commercial settings subject to heavy forklift and other vehicle traffic. Filling the joints will also make the floor easier to clean by preventing dirt from collecting in the gaps.The best method for the job is to fill the joints with a polyurea or semi-rigid epoxy at the beginning stages of the project. By cleaning the joints out first and then filling and ultimately grinding and polishing, any residual filler that flows out and isn’t scraped off will easily be removed during the coarse grinding step. Also, by filling the joint early, you’ll reduce the chance of chipping the joint edges during coarse grinding with aggressive metal-bond diamonds.

Stamped concrete, often called textured or imprinted concrete, is concrete that replicates stones such as slate and flagstone, tile, brick and even wood. Ideal for beautifying pool decks, driveways, entries, courtyards, and patios, stamped concrete is the perfect outdoor paving choice.Recently, stamped concrete has become a popular choice for many homeowners because it offers a wide array of options when it comes to concrete pattern and concrete colors. Another factor contributing to its popularity is its price. The cost of stamped or imprinted concrete is often considerably lower than the materials it is a substitute for.Concrete is the perfect canvas for creating a cost-effective replica of more expensive materials, without giving up a natural, authentic look. When choosing colors and patterns for your stamped cement, make sure they blend with other stone, tile or textured concrete elements at your residence. Even in complex designs with steps and fountains, patterns can be still be pressed into the concrete. Stamped concrete can also be used in conjunction with other decorative concrete elements such as exposed aggregate or acid staining. Popular patterns include running bond brick, hexagonal tile, worn rock or stone.

The Canadian government is considering tariffs and quotas on steel after global exporters were looking for countries where they could divert steel originally meant for the United States.This is just part of the movement that resulted in the fallout from U.S. President Donald Trump's trade war.Canadian counter-tariffs on U.S. steel, aluminum and other products will go into effect on July 1.The Canadian government is taking measures to thwart a potential flood of steel imports as a result of global exporters trying to avoid U.S. tariffs, according to a Bloomberg News story.Citing "people familiar with the plan," the story says those proposed measures include quotas and tariffs aimed at certain countries, including China. The potential move follows in the footsteps of the European Union's decision to ward off dumping of steel that would have been sent to the U.S. Although not finalized, the announcement could come as early as next week, Bloomberg said.This is just part of the fallout from U.S. President Donald Trump's trade war. The U.S. has levied tariffs of 25 percent on steel and 10 percent on aluminum on Canada, the EU and other nations. As a result, some of the U.S.' biggest trading partners have retaliated with counter-tariffs.Canadian counter-tariffs on U.S. steel, aluminum and other products will go into effect on July 1.The U.S. accounted for 55 percent of Canada's steel imports in 2017, with the remainder coming from China, South Korea, Brazil and Turkey.U.S. tariffs could open the door to cheaper steel imports from abroad, said Sean Donnelly, chief executive officer of ArcelorMittal Dofasco, the Canadian unit of ArcelorMittal of Luxembourg. With steel being diverted to Canada, Canadian steel groups have been pressing for safeguard measures.“We must be able to operate in an un-distorted, market-based competitive environment,” Donnelly said. “Canada’s response to past and future threats from unfairly traded and diverted offshore imports is critical.”Additional tariffs could negatively affect the Canadian housing market. Only a handful of companies produce steel in the country, making construction companies and steel fabricators heavily reliant on imports.Canada's Office of the Minister of Finance had no comment.

In 2009, the American Society of Civil Engineers (ASCE) assigned a grade of “D” to the overall quality of infrastructure in the United States, saying that ongoing evaluation and maintenance of structures was necessary to improve that grade. Since then, federal stimulus funds have made it possible for communities to repair some infrastructure, but high-tech, affordable methods for continual monitoring remain in their infancy. Instead, most evaluation of bridges, dams, schools and other structures is still done by visual inspection, which is slow, expensive, cumbersome and in some cases, dangerous.Civil engineers at MIT, working with physicists at the University of Potsdam in Germany, recently proposed a new method for continual electronic monitoring of structures. In papers appearing in the journals Structural Control Health Monitoring and Journal of Materials Chemistry, the researchers describe a flexible fabric with electrical properties that could adhere to areas prone to cracking — such as the undersides of bridges — and detect cracks almost immediately when they occur.Installing this “sensing skin” would be as simple as unrolling it and gluing it to the surface of a structure. The rectangular patches on the skin that detect changes in its electrical charge could be tailored in a geometric design appropriate for the type of crack likeliest to form in a particular part of a structure: for example, diagonal square patches to detect cracks caused by shear, or horizontal patches to detect the cracks caused by a sagging horizontal beam.The formation of a crack would cause a tiny movement in the concrete under the patch, changing the capacitance, or stored energy, of the sensing skin. Once a day, a computer system attached to the sensing skin would send a current to measure the capacitance of each patch and detect any difference among neighboring patches. In this way, it could detect a flaw and its exact location within 24 hours — a task that has proved difficult for other types of sensors proposed or already in use, which tend to rely on detecting global changes in the entire structure using a few strategically placed sensors.“The sensing skin has the remarkable advantage of being able to both sense a change in the general performance of the structure and also know the damage location at a pre-defined level of precision,” says Simon Laflamme PhD ’11, who did this research as a graduate student in MIT’s Department of Civil and Environmental Engineering. “Such automation in the health-monitoring process could result in great cost savings and more sustainable infrastructures.” Laflamme worked with Jerome Connor, professor of civil and environmental engineering at MIT, and University of Potsdam researchers Guggi Kofod and Matthias Kollosche.The researchers originally tested their idea using a commercially available, inexpensive stretchy silicon fabric with silver electrodes. While this worked in some lab experiments performed on both small and large concrete beams under stress, the material ultimately proved too thin and flexible for this application. The researchers have now developed a prototype sensing skin made of soft stretchy thermoplastic elastomer mixed with titanium dioxide that is highly sensitive to cracks; painted patches of black carbon measure changes in the electrical charge of the skin. A patent for the sensing method has been filed.“The innovation of this proposed sensor design is in its use of a material that provides mechanical flexibility and serves as a capacitor,” says Professor Tzu-yang Yu of the University of Massachusetts at Lowell, a structural engineer who specializes in the mechanical analysis of structures and the design of nondestructive methods for testing infrastructure. “This design allows the sensor to overcome the difficulties associated with conventional piezoelectric sensors which have strict contact conditions between the sensor and the structure’s surface. The proposed sensor is also superior to conventional fiber-optic sensors in the way that two-dimensional readings can be collected from one sensor.“Like all innovations in the development stage, there are additional issues this sensor needs to address, such as instrumentation, packaging and environmental vulnerability. Naturally, the next step would be to perform a small field test in order to investigate the field performance of the sensor,” Yu says.“Many of the types of infrastructures graded by the ASCE are made of concrete and could benefit from a new monitoring system like the sensing skin — including bridges, which received a ‘C’ grade, and dams and schools, which earned ‘Ds,’” Connor says. “The safety of civil infrastructures would be greatly improved by having more detailed real-time information on structural health.”The work of Kofod and Kollosche was funded by the German Ministry of Education and Research.

In the face of limited funding to address massive infrastructure needs, and with climate action at top of mind, it is more important than ever for engineers, designers, and policy makers to understand the full economic and environmental costs of infrastructure project decisions — and not just impacts relating to material choice or from initial construction, but the impacts of choices across the entire life cycle of a project.“As we develop strategies to reach sustainability goals, it is vital that we adopt methodologies that use a life-cycle perspective to evaluate impacts and use that knowledge to create a strategic path moving forward,” says Jeremy Gregory, research scientist in the MIT Department of Civil and Environmental Engineering and executive director of the MIT Concrete Sustainability Hub (CSHub).Life-cycle analysis methodologies exist for both environmental and economic impacts: Life cycle assessment (LCA) examines environmental impacts, while life cycle cost analysis (LCCA) examines economic impacts. LCA and LCCA enable engineers, designers, and decision-makers to better understand opportunities that exist to reduce environmental and economic impacts, but CSHub research has found that these tools are rarely used at a point in the decision-making process when they can have the greatest impact. The CSHub team recently released several new papers and materials discussing research designed to improve life cycle thinking for buildings and pavements. “For buildings, placing too much emphasis on minimizing initial costs and not paying enough attention to the use phase can lead to higher costs, both environmentally and economically,” says Gregory. “Construction projects that focus on first costs fail to account for costs associated with lifetime energy use, and the stakeholders who aren’t typically involved in early planning stages, such as future homeowners, insurance agencies, and taxpayers, are the ones left holding the bill.”The environmental impacts are significant; in the United States, the heating, cooling, and operation of buildings and homes accounts for more than 40 percent of carbon dioxide emissions each year. The CSHub has several projects underway that quantify the full life cycle impacts of buildings, from initial construction to demolition, and has developed building LCA tools that allow impacts to be quantified earlier in the design process than is allowed by traditional methodologies. Researchers have published several recent papers on the topic. All five papers can be found on the CSHub website in a section dedicated to building LCA.“LCA and LCCA approaches work best when they accompany each other, by providing the necessary economic context to implement solutions into the marketplace,” explains Gregory. “Poorly insulated and leaky residential construction leads to high annual energy costs, which can result in substantially higher life-cycle costs. Likewise, roadway closures cause traffic congestion, which leads to higher costs for road users.”For pavements, CSHub LCA work considers all life-cycle phases from initial construction to demolition, including operation, maintenance, and end-of-life phases, and factors such as traffic delay, lighting demand, and future maintenance, while LCCA research considers life cycle, context, and future, and also incorporates risk.The team recently released a pavements LCCA and LCA info sheet, which highlights key concepts and statistics from CSHub studies. CSHub tools use probabilistic price projections compatible with existing software tools used by pavement designers, such as the Federal Highway Administration’s RealCost tool. One of the studies highlighted noted a 32 percent improvement on 20-year cost estimates and LCCA results for roadway projects in Colorado when using CSHub models.CSHub research is supported by the Portland Cement Association and the Ready Mixed Concrete Research and Education Foundation.

Lucideon announce that it is has published a new white paper, ‘The Concreting Process and Petrographic Examination’.Free-to-download, the white paper is aimed at a broad range of targets, including engineering firms, contractors, ready-mix suppliers, architects, municipalities and owners (residential and industrial firms).The paper provides an overview of the concreting process and discusses how petrographic examination identifies the root cause of common deficiencies and degradation mechanisms in hardened concrete; low compressive strength, surface scaling and spalling, cracking, alkali-aggregate reactions, and effects of chemical reaction.The paper is primarily for cast-in-place concrete, however much of the content is also applicable to precast concrete.A petrographic examination usually begins with a detailed visual examination followed by a combination of analytical techniques, including surface and chemical analysis and microscopy. Within the concrete, the features of interest are examined: aggregates, cement paste matrix, crack surfaces, air void distribution and filling, and embedded reinforcement.Using petrographic analysis to examine concrete can provide many benefits, from assessing the entrained air content and determining the present condition of previously placed concrete, to establishing the water/cement ratio and defining cracks by type and uncovering crack mechanisms.Author of the paper, Dale L. Purvis, leader of special projects at Lucideon, said:“At Lucideon, our timely petrographic examinations provide clients with in-depth, detailed reports focused on the specific attributes in question. We are able to provide answers to a whole host of questions, from has it cured correctly, to establishing the geological provenance of the stone, through to examining the corrosion of reinforced concrete.“Ultimately, petrographic analysis can help confirm whether the defects will affect the concrete performance or if they are just surface flaws.”Lucideon provides petrographic analysis of concrete, mortars, building stone and other geological materials to evaluate the integrity of concrete and understand the mineralogy of materials.Petrographic analysis at Lucideon is carried out in accordance with both American and European standards: ASTM C295, ASTM C856, ASTM C457 and BS 1881-211:2016.

Cement materials, including cement paste, mortar, and concrete, are the most widely manufactured materials in the world. Their carbon footprint is similarly hefty: The processes involved in making cement contribute almost 6 percent of global carbon emissions.The demand for these materials is unlikely to decline any time soon. In the United States, the majority of concrete bridges, buildings, and pavement-lined streets, erected in the 1960s and 1970s, were designed in an era with fewer environmental stresses to infrastructure and built to last 50 years at most.Now, MIT researchers have discovered the beginnings of a new approach to producing concrete that is inspired by the hierarchical arrangements of simple building blocks in natural materials. The findings could lead to new ways to make concrete stronger and to use more sustainable, local materials as additives, to offset concrete’s greenhouse gas emissions.In the new study, Oral Buyukozturk, a professor of civil and environmental engineering, and his colleagues analyzed a key property in concrete, at the level of individual atoms, that contributes to its overall strength and durability. The group developed a computer model to simulate the behavior of individual atoms which arrange to form molecular building blocks within a hardening material.These simulations revealed that an interface within the molecular structure exhibited a “frictional” resistance under sliding deformation. The team then developed a cohesive-frictional force field, or model, that incorporates these atom-to-atom interactions within larger-scale particles, each containing thousands of atoms. The researchers say that accurately describing the forces within these assemblies is critical to understanding the way strength develops in concrete materials.The team is now examining ways in which the cohesive and frictional forces of groups of atoms, or colloids in cement, are improved by mixing in certain additives such as volcanic ash, refinery slag, and other materials. The team’s computer model may help designers choose local additives based on the molecular interactions of the resulting mixtures. Through careful design at the microscopic level, he says, designers and engineers can ultimately build stronger, more environmentally sustainable structures.“The conditions of the world are changing,” Buyukozturk says. “There are increased environmental demands, including from earthquakes and floods, and stresses on infrastructure. We need to come up with materials that are sustainable, with much longer design life and better durability. That is a big challenge.”Buyukozturk and his colleagues, graduate student Steven Palkovic and Sidney Yip, professor emeritus in MIT’s Department of Nuclear Engineering, have published their results in the Journal of the Mechanics and Physics of Solids.Strength from frictionBuyukozturk’s vision for revamped, locally sourced concrete is inspired, in part, by Roman construction. During the empire’s peak, the Romans erected temples, bath buildings, and amphiteaters in Pompeii, Ostia, and through Spain and the Middle East, including towns in Turkey, Libya, and Morocco. In each far-flung location, archaeologists have found that the Romans constructed their buildings from local materials — a technique that has helped preserve these structures for more than 2,000 years.“They probably did this through intuition,” Buyukozturk says. “Ours is an effort to hopefully implement that kind of philosophy of using materials that are locally available, by understanding the underlying scientific principles within those materials.”In their new paper, the scientists describe a computer model that is part of a computational framework that they have developed to analyze how the atomic structure of concrete affects engineering properties. These models simulate the sliding and movement of clusters of particles at molecular scales within concrete.The researchers used their atomistic model to simulate mixtures containing Portland cement, the most common type of cement used in the world. Specifically, they simulated the mechanical response of the gel-like substance called calcium-silicate-hydrate (C-S-H), the main phase that forms when water reacts with Portland cement. The group modeled the movements of thousands of atoms in a C-S-H molecular building block, noting the influence of cohesive forces that cause particles to stick together, and the presence of a shear resistance as clusters of atoms slide past each other along a water-filled interface.They then simulated how these molecular-scale properties control larger particles containing thousands of atoms, or colloids, at what they call the “mesoscale.” They discovered that the degree to which frictional properties resist the movement and separation of colloids at the mesoscale was the strongest factor in determining the strength of concrete at the centimeter scale.Designers often use the properties of cement at the centimeter scale to predict the strength of a final, much larger-scale structure. The researchers thus implemented the results of their atoms-to-colloids simulations within computer models of the hardened microstructure, to allow for comparison with actual, centimeter-sized laboratory experiments. Buyukozturk found the team’s predictions matched with experimental outcomes better than predictions made with simulations that neglect frictional interactions.“The material science of cement strength is still in its infancy regarding molecular-level descriptions and an ability to perform quantitative predictions,” Yip says.  “The issue of frictional force, addressed in our work, pertains to the mechanical behavior of cement that varies over time. This rate sensitivity is an aspect of the scientific challenges at the mesoscale, which is the research frontier where microscale concepts and models developed in several physical science disciplines are linked to macroscale properties for technological applications.” Buyukozturk adds, “We are confident that our new framework is opening a new era in concrete science.”Additives in the mixThe group is now working on integrating various additives into their model, to investigate the effect of such materials on the atom-to-atom behavior of cement, and the resulting strength of the final, solidified concrete. From preliminary studies, they have observed that there is a chemical dependence of the friction value, or degree to which colloids resist sliding against each other. Future work will investigate how additives influence the chemical composition of these colloidal phases. This information could be used as part of a database to design and optimize new concrete materials with improved strength and deformation behavior.“We know relatively little of what happens when additives are used in concrete,” Palkovic says. “We would not expect volcanic ash from Saudi Arabia to give the same performance as volcanic ash from Hawaii. So we need this greater understanding of the material, that starts at the atomistic scale and accounts for the chemistry of the material. That can give us greater control and understanding of how we can use additives to create a better material.”This research was supported, in part, by the Kuwait Foundation for the Advancement of Sciences, as part of the MIT-Kuwait signature project on sustainability of Kuwait’s built environment.

SAN DIEGO, Calif. (September 6, 2017) – Westcoat Specialty Coating Systems is proud to announce that the ALX Pro System, in both Standard and Custom finishes, has been independently tested to meet the Acceptance Criteria for Walking Decks (AC39) and has received certification through ICC. It joins ALX Standard and Custom on the updated ICC-ES Evaluation Report ESR-2201. Long known for its Class A and One-Hour Fire Ratings, Westcoat’s ALX received the ICC-ES Class I Vapor Retarder (0.1 perm or less) listing in June 2017 with ALX Pro receiving its listing in September 2017. This certification comes at a crucial time when building code standards for waterproofing decks are becoming more stringent. Some cities and counties in California are already enforcing the need for this E96 testing certification prior to any statewide change. All Westcoat ALX and ALX Pro systems provide a Class A Roof Covering Classification (ASTM E108) and One-Hour Fire Rating (ASTM E119). In addition to these certifications, when WP-40 Sheet Membrane is applied over the entire plywood substrate, both ALX and ALX Pro in Standard and Custom finishes meet classification for a Class I Vapor Retarder (ASTM E96). The full listings can be found on the ALX page of westcoat.com. What is ALX Pro? The ALX Pro system features all the proven attributes and benefits of the existing ALX system, but features an additional Fiberlath Resin Membrane layer. This additional layer provides greater waterproofing and helps protect against cracking, especially on larger spans or cantilever decks. ALX is the clear choice when choosing a waterproofing system for elevated decks and walkways. It is the ultimate protection for the end user, applicator and specifier. When installed by a Westcoat QCA, these systems are eligible for up to a 15-year warranty. Contact Westcoat for a referral to a QCA or more information on the ALX systems.

One of the worst natural disasters in U.S. history took place early on a January morning in 1994, when a 6.7 magnitude earthquake occurred 20 miles north of downtown Los Angeles.Fifty-seven people were killed, and almost 9,000 others injured. Property damage was estimated at up to $50 billion.The Northridge earthquake, as it came to be known, gained worldwide attention because of the extensive damage it caused to the region’s freeway network.Surface roads were clogged for three months while the freeways were repaired.“The 1994 Northridge earthquake is one of the most important ground motions in North America,” said Mohammad Javad Tolou Kian, who is researching high-performance reinforced concrete walls that possess improved damage properties that protect them when an earthquake strikes.“Because even well-designed structures suffer permanent deformations and concrete damage when withstanding strong ground motions (such as seismic events and earthquakes), a structure which suffers limited damage will be of great benefit,” he said.Tolou Kian, who is a PhD candidate in structural engineering at the University of Alberta, says that, since Northridge, there have been numerous studies on the different types of damage that was sustained by structures during the earthquake.“The studies have led to significant changes in the construction of earthquake-resistant buildings since then,” he said.Tolou Kian describes his PhD research project, in a nutshell, as looking at high-performance reinforced concrete walls which have improved damage properties.“Concrete walls are used in reinforced concrete structures to provide them with enough stiffness to withstand lateral forces,” he said. “The goal of my project is to study the residual displacements of concrete walls that have fibre reinforcement and innovative steel reinforcements, to see if they suffer less damage from ground motion.”To replicate in the university laboratory what happens when concrete walls are shaken by ground motion, wall specimens were anchored to the laboratory floor, and then were hit with the same back-and-forth motion of an actual earthquake.The response of the test walls was captured by sensors and a digital imaging system that measured the extent of the walls’ deformation caused by the experimental ground motion.The concrete walls used in the tests contained two types of fibres: PVA (Poly vinyl alcohol) fibres 12 mm long, and hooked-end steel fibres 50 mm long.“In general, fibre reinforcement increases the resistance of concrete, because it limits the opening and propagation of cracks,” said Tolou Kian. “In the study, fibre reinforcement mitigated concrete damage, including cover spalling (peeling and flaking, due to moisture in the concrete])and cracking, in the test walls.”Three types of advanced concrete reinforcement were used in the study: 1. Shape-memory alloy, an alloy of nickle and titanium; 2. glass-fibre reinforced polymer, a composite material made of glass-fibres held together by a polymeric binder, and 3. high-strength steel, about three times stronger than conventional steel.“The distinctive property of these types of advanced reinforcement, compared to conventional steel, is their tendency to return to their original lengths after being unloaded (from ground motion),” said Tolou Kian. “This means that if you stretch them, they will return to their initial shape when released.“This property of the advanced reinforcements helps reinforced concrete walls return to their original position after resisting an earthquake. They will suffer less damage, can be repaired sooner, and require less retrofit funding.”Tolou Kian’s PhD is being supervised by Professor Carlos Cruz-Noguez, a specialist in masonry systems.The experimental part of the study and preliminary numerical modeling of the sample walls was completed in 2017.“The next step of the study, to begin this summer (2018) to numerically simulate the response of four full-scale reinforced concrete structures, with and without high-performance walls, under different ground motions, in order to measure the effectiveness of test innovations in the design and construction of reinforced concrete structures,” said Tolou Kian.