Posted on October 29, 2020
With today’s innovative concretes, designers have more latitude. At the same time, these new formulations promote sustainability in ever more effective ways. Updated building codes and corporate mission statements demand more sustainable construction as never before. Consumers and investors consider a company’s commitment to sustainable practices.
Many of today’s innovative formulations tackle common challenges. Bendable concrete resists cracking under stress. Others have self-healing capabilities. Some lightweight concrete is as strong as its traditional counterpart. Some ultra-high performance formulations offer extremely long lifespans.
Fiber-reinforced, Bendable Concrete
The inspiration for bendable concrete is nacre, a coating on the inside of abalone shells. It includes platelets that can slide from side to side when stressed. A New York Times article explored nacre’s special qualities. It suggests that “A microscopic cross-section looks like brickwork, with flat, hexagonal tablets of a crystalline, calcium carbonate mineral stacked in neat layers. Mortaring them is a flexible protein-rich gum originally secreted by the shellfish.”
University of Michigan researchers used tiny, randomly dispersed fibers to achieve the “nacre effect” in fiber-reinforced concrete (FRC). Michigan’s Dr. Victor Li says the bendable concrete “can deform up to 3 to 5 percent in tension before it fails." He calculates that it has 300 to 500 times more tensile strain capacity than normal concrete.
It is possible to use different kinds of fiber in FRC. Examples include steel, jute, sisal, polypropylene, glass and carbon fiber. Some fibers are very eco-friendly. For example, it is possible to produce carbon fiber from lignin extracted from paper waste.
Case study — Carbonhaus
In 2020, a $5.6 million, two-story structure at Germany’s Technical University Dresden becomes the “world’s first building made entirely of carbon-fiber-reinforced concrete.” The innovative concrete formula introduces impressive design flexibility. For example, the building features a seamless stretch of bendable concrete more than 78 feet long.
Case study — Seisho Bypass Viaduct
Bendable concrete has also proven itself in transportation projects. For example, it is used in link slabs on bridges. It was used to retrofit the Seisho Bypass Viaduct, a 28-km-long toll road in Japan.
Self-healing concrete is also attractive in colder climates. There, road salt and freeze-thaw cycles otherwise exploit cracks in roadways. Concrete that bends under stress and self-heals is more sustainable. It lasts longer and requires less maintenance. Its ductility also makes it attractive for use in earthquake-resistant buildings.
Ultra-high Performance Concrete (UHPC)
UHPC contains high levels of cementitious materials and low water-to-binder ratios. A refined microstructure delivers impressive strength and durability. Lifespans can exceed 200 years, even in saltwater and deicing environments. A dense matrix minimizes disconnected pores, resulting in low permeability. High flow rates make it self-compacting.
Ultra-fine materials like silica fume yield a smooth, dense surface that is at once beautiful and durable. UHPC resists freeze-thaw cycles, salt-scaling, abrasion and oxygen permeability per ASTM C1856/1856M. Some UHPC construction does not require reinforcing steel. This eliminates concerns over corrosion.
Case study — Shawnessy LRT Station
Calgary’s Shawnessy Light Rail Transit (LRT) Station features a boarding area protected by 24 thin UHPC canopies. They achieve the specified 19,000 psi strength, despite the fact that the shells are just 0.79-in thick.
Self-consolidating Concrete (SCC)
There are multiple reasons to consider the use of SCC. Thanks to slump flows of 18 - 26 inches, SCC spreads into congested formwork with ease. Mechanical vibration is not required. Formwork can be more detailed. Self-leveling SCC reduces the labor needed to place and finish the concrete. Tackle cosmetic repairs in less time. Reduce wear and tear on equipment.
With SCC, it is possible to use eco-friendly pozzolans like fly ash and GGBF slag.
Geopolymer concrete uses a sodium-based activator to react with silicate and aluminate. Recently, researchers at Rice University developed a geopolymer concrete requiring far less activator. A precise mixture of calcium oxide, nano-silica and calcium-rich fly ash reduces the amount of activator by 90 percent. This makes it possible to replace Portland cement with fly ash.
Graphene concrete is the product of sophisticated nanotechnology. Tiny shards of graphene are suspended in the mixing water. The result is a much stronger and water-resistant concrete. It is estimated that weight reductions made possible by graphene reduce carbon emissions by 446 kg per ton.
Self-cleaning (TiO2) Concrete
Titanium dioxide is a white pigment. It is in everything from paint and porcelain enamels to cosmetics and sunscreens. In self-cleaning concrete, TiO2 acts as a photocatalyst. It accelerates the chemical reaction between UV light and airborne pollutants. UV light activates the TiO2, generating a charge that disperses across the surface of the concrete. This aids in the decomposition of soot, bacteria, mold spores and nitrogen dioxide. TiO2 concrete depollutes the air while keeping concrete surfaces looking new longer.
The NRMCA’s Lionel and Brian Lemay discuss the problem of nitrogen dioxide. They suggest that "it is one of the compounds responsible for acid rain, smog, respiratory problems and staining of buildings and pavements.” A team at the University of Pittsburgh notes the advantages of TiO2 concrete in greater detail.
Workers typically add TiO2 to cement during production. It is also possible to apply nano-liquid TiO2 to hardened concrete surfaces.
The substance is eco-friendly in other ways. Since it is a white pigment, TiO2 increases concrete’s reflectance. This limits the heat that ages components and often increases cooling costs.
The Pennsylvania Aggregates and Concrete Association (PACA) highlights the latest industry developments at SpecifyConcrete.org. For further information, please contact us.