Can Concrete Really be Bent?

As with many other products and processes, biomimicry (learning and imitating the processes of nature) is transforming the world of concrete. Although in the early stages of being applied, concrete that is bendable without fracturing is now a reality. Concrete is the most ubiquitous building material on the planet, but it contributes between 6-7 percent of greenhouse gases and is thus a major contributor to climate change. It has great compressive strength but, when it cures, it becomes a hard, brittle material.

The idea for bendable concrete is borrowed from nacre (mother of pearl), the material that lines the inside of abalone shells. The main material in nacre--small, hard bits derived from calcium carbonate--is made flexible by the natural elastic polymer that surrounds and ties these small chunks together. This combination makes nacre both strong and bendable.

A number of universities around the world, including the University of California at Irvine, Stanford and the University of Michigan have been investigating the nacre model for concrete. By eliminating the coarse aggregate from the mix (gravel, sand and cement) and adding microfibers of silica, glass, steel and/or polyvinyl, they approximate the flexibility of nacre. The interfaces between these tiny fibers and the cement recreate the controlled slippage in nacre. Bendable concrete, technically called engineered cementitious composite (ECC) is not a single design mix but a broad range of design mixes. The precision of these formulae comes from the application of micromechanics theory.

Essentially, the microfibers create many pre-calculated microcracks. This contrasts with conventional concrete that develops a few large cracks that permit water intrusion, degradation of the reinforcing steel and, consequently, early rupture and failure under stress. The fibers and accompanying microcracks allow ECC to deform without catastrophic failure.

The advantages of ECC concrete are numerous: lighter weight (40 percent less); 300 times more flexible; superior seismic performance; less frequent maintenance and repairs, thus saving on costs; no need for expansion/contraction joints (e.g., on roads and bridges); and faster curing (7 days compared to 28 days).

The disadvantages are higher cost, the need for more skilled labor, and getting structural engineers to specify it when they have been taught that concrete cannot be flexible.

There are recently built bridges in Japan, Korea and the US using ECC. A 60-story skyscraper using flexible concrete for superior seismic performance is currently under construction in Japan. When our roads and bridges, which badly need fixing, get rebuilt, they can have a much longer projected life by using bendable concrete. The significantly greater durability of flexible concrete is the biggest sustainable improvement. Less frequent rebuilding of concrete’s failures also means big reductions of greenhouse gases.

Using Crushed Rock to Tackle Climate Change

A previous article focused on the need for large scale carbon sequestration with a look at a project in northern British Columbia that shows promise for meeting this challenge. Its approach takes biodiverse seed packets enveloped in biochar for nutrients and moisture retention and uses drones to spread these casings over wide areas to regenerate forests. This method of reseeding forests works especially well in remote, inaccessible terrain where replanting by hand is impossible.

Forests, or more specifically, the growing of trees, have been scientifically proven to pull carbon dioxide from the atmosphere. The calculations of some scientists, however, suggest that this natural process cannot achieve the scale of carbon drawdown required to offset our ever-growing carbon emissions. They cite the availability of land for forest restoration being the limiting factor. Consequently, another natural process is being considered to enhance and accelerate the storing of carbon not only in forests but on farms as well.  This process occurs when rain dissolves the carbon dioxide that is present in air creating a weak carbonic acid. If this acid falls on basalt rock, it reacts to form a carbonic mineral (calcium carbonate) that locks up the dissolved carbon for hundreds of thousands of years.

Basalt is the most common rock found on Earth’s surface. It is formed primarily from volcanic eruptions. Various forms of basalt are widely used in construction as aggregate in asphalt and concrete mixes and as base layers for highways and railroads. Although dense, this igneous rock crushes easily. Once pulverized into dust it can be spread relatively inexpensively on forest and farmland, making it readily available for rain to wash carbon out of the air and accelerate the process of sequestration. The understanding of this process, called “enhanced weathering” is not new, but because it speeds up a natural process it has only recently been explored for its potential to offset human-made emissions that are causing climate change.

The Future Forest Company, a recent start-up company, is conducting a trial of this speeded up weathering approach on a large birch and oak forest on the Isle of Mull in Scotland. Results of the trial will be known soon. If the data show the expected increase in carbon sequestering, then this accelerated weathering process could potentially capture gigatons of carbon dioxide when applied to forests and on farms around the world. Reseeding of forests is still needed, but enhanced weathering can supplement forest restoration and be applied to farmland as well.

Greening a Bathroom

Bathrooms, along with kitchens, are the most expensive spaces to construct in a home, because of the plumbing needed, the greater density of lighting and numerous appliances. To create a sustainable bathroom, it must be energy efficient, use minimal water, be comfortable, non-toxic, quiet and basically maintenance free.

California codes keep nudging all new and remodel construction to be more sustainable. Consequently, any remodel project today triggers upgrading ALL plumbing fixtures throughout the home or business. The most recent State standards are: 1.8 gallons per flush for toilets; 1.2 gallons per minute (gpm) for bathroom faucets and 1.8 gpm for showerheads, giving California the toughest standards of any US state. For comparison, these flows are about a quarter or less of what was standard 3-4 decades ago.

Not only are these standards saving hundreds of billions of gallons of water each year, but also lots of energy and greenhouse gas emissions, since 19 percent of energy consumed in California is used to pump, transport, treat and heat or cool water.

Selecting an efficient and effective showerhead has become easier in the last decade, due to the Federal WaterSense program. To carry the WaterSense label, a showerhead must list its flow rate, which must be below the maximum allowable federal standard, and meet strict user satisfaction standards. A popular WaterSense model by Niagara, rated at 1.5 gpm and receiving stellar customer reviews, costs only about $8.

A promising development that cuts water consumption even more is the atomizer mist technology. Showerheads using this approach disperse water through millions of microscopic droplets into an effective wet area while saving 70 percent of water. Similarly, with sink faucets, the fine mist produced is a 98 percent reduction in water use, with no loss in functionality.

Controlling humidity in bathrooms is key to promoting health. Good natural ventilation (operable windows) as well as effective air-moving equipment avoids mold, mildew and rot. A good bathroom fan needs to move about 150 cubic feet of air per minute while having a noise rating of 1 sone or less, making it virtually unnoticeable.

The leading green-building thinking today emphasizes all electric homes, where the loads are minimal, and the power needed is produced on-or-off-site by the sun or wind. LED lighting and super-efficient equipment keeps loads to a minimum without sacrificing performance. Hot water can also be heated by solar electric panels or directly by solar thermal panels. Water and heat can be additionally saved by on-demand hot water delivery. At the push of a button, a pump turns on, rapidly bringing hot water to faucets while pushing the cold in-line water out into the cold-water lines rather than wasting it down the drain.

Good insulation, high performance windows, using only non-toxic materials and avoiding carpeting are additional strategies to improve sustainability in bathrooms and are even more important for the entire house. Savings on water and electricity are often easily calculable. Putting a price on good health is not easy but for most of us it is priceless.

An Option to Replacing Old Windows

Swapping out old single glazed windows with high performance dual or triple pane units is costly. Moreover, it is often not allowed in historic buildings. Architectural historians insist on maintaining the appearance and character of windows in classic old buildings, irrespective of their performance.

According to the US Department of Energy, around 30% of the energy used to heat and cool our homes is lost through inefficient windows, even though windows often make up less than 10 percent of the surface area of a house.

A less costly possibility, rather than replacing inefficient windows, is to install an insulating window film. Glazing films have been around for more than 50 years, but high performance films only in the past decade. They have evolved along with the great gains in window technologies. Coatings and films have become standard in high quality windows. The large choice of offerings can yield greater or lesser heat gain, visual clarity, ultraviolet blocking and insulating values, to name a few of the available options.

The cost of replacing residential windows can easily be $125 per square foot or more. Window films such as 3M’s Thinsulate Climate Control film offers good performance for a fraction of the cost. This type of low emissivity or “low-E” film improves the insulation value of a typical single pane window to approximate a double pane unit (up to about 92 percent). The emissivity rating can be as low as 7 percent, meaning that 93 percent of a room’s heat is reflected back into the space and doesn’t escape outside. Low-E coatings reduce heat loss in winter and heat gain in summer. As a result, the initial installed cost of $5-$15 per square foot (depending on film type and size of the job), is a 2-5 year return-on-investment (ROI). The comparable ROI for replacing old windows with high performance units is 30-50 years.

Some of the recently introduced low-E films have high visible light transmission (VT of 70 percent), meaning they have basically no impact on views-no darkening and no distortion. Furthermore, these coatings block 99 percent of ultraviolet rays to fully protect furniture, rugs, upholstery and artwork from fading. Window film application does not require a professional installer. Professional installation, however, is highly recommended for quality purposes and to have the 20-30 year warrantee apply. Installation by professionals takes only minutes per window. Full curing of the film takes a few days to a month.

For reasons of energy savings, modest cost, comfort and fade protection, low-E window films are important to know about.