Cement is one of the oldest building materials cooked up by humans, but it’s so misunderstood. It’s not what paves your cement sidewalk, that’s concrete. And it’s not concrete, although cement is a main ingredient. Modern advances in production and ingredient mix are reinventing this “everywhere” substance as a sustainable champ. The material itself is fairly green but fails miserably in whole lifecycle assessment. Cement relies on fossil fuels for processing its raw materials. Resultant emissions mean that making basic cement causes about 5 percent of all manmade carbon dioxide.
Think of it as glue. The ancients discovered that finely ground lime or silicates, mixed with water, will react at ordinary temperatures to form a sludgy ooze with superior binding powers. Recent advances in chemical mix and production technologies are not only making concrete carbon-neutral, it’s actually achieving carbon-negativity.
Concrete’s made of three ingredients: water, aggregates (sand and rock rubble), and cement. Conjuring up their inner Iron Chefs, early builders played with the recipe. Grabbing nearby ingredients (volcanic ash, pumicite, and fly ash, as example), they cooked up new types of cements, each with specific characteristics. Some worked best as mortar for bricks, others as binders for formed rubble structures.
The type of cement used will influence the ultimate functionality of that specific concrete. It’s a wonder product.
Rapid urbanization outpaced supply of quarried stone in many places; others areas were stone-starved.
Cement allowed builders to create stone-like structures using locally sourced water and aggregates, easily acquired and transportable materials found virtually everywhere.
Ancient Minoans and Greeks and Romans slathered it on most everything they built. It lasts. A famous example is the dome of the Roman Parthenon. By the 18th Century, it’s no longer batched up on jobsites: mass production’s required to meet global demand. And the sustainability inherent in its ingredient list, clean manufacture and ease of transport disappears.
Fast forward the world’s clock, watch builders better control cements’ properties. Concrete becomes malleable, formable, increasingly strong and durable. It’s the preferred building material for post-industrial-age civil works and large buildings. And on the way, concrete became the world’s third-largest source of man-made carbon dioxide. It doesn’t have to be that way.
Cement chemists and process engineers get creative.
A company called Novacem has developed a cement based on magnesium oxide that can make a significant contribution to a low carbon world.
Their “carbon negative” cement absorbs more carbon dioxide (CO2) during production than it emits: they’ve replaced the calcium carbonates used in typical cement with magnesium silicates, and use a lower temp production process that’s fueled by biomass.
Novacem engineer Danial Bowden told Architect magazine that in developmental trials the cement is already achieving strengths up to 80Mpa. If implemented, this material would take care of most of construction’s attempts at carbon reductions in one fell swoop. Commercial rollout is planned for 2014-2015.
Calera is a company that uses the carbon in industrial flue emissions (the stuff collected in smokestacks) as ingredients in concrete and asphalt. Their process, called Carbonate Mineralization by Aqueous Precipitation (CMAP), involves running flue gases through pH-adjusted seawater or alkaline brine water.
Water chemistry works to convert CO2 to calcium and/or magnesium carbonate, which is then extracted from the water and dried, recycling the heat already being released from the flue. CMAP removes 70-90% of CO2 from the gases, and every ton of the resultant building materials holds half a ton of captured carbon.
CMAP captures 95-98% of sulfur dioxide in flue gases, and neutralizes pollutants such as mercury, trace metals, nitrogen and ammonia. Combined with a desalination plant, it could also economically produce drinking water (desalination made cheaper since seawater would already be getting pumped in, and have its calcium and magnesium removed as part of the CMAP “mining”). Calera’s process could also use the leftover brine slurry from desalination to extract CO2 from flue gas. As with the green miner who is pulling minerals from brine, this process would clean post-slurry wastewater – the toxic waste from a stand-alone desalination plant. Milking revenue from desalination waste brine makes CMAP cost-effective.
Calera’s process is being used in a pilot project at the Moss Landing power plant in California. Similar technologies are being pursued by companies such as America’s Carbon Sciences and Canada’s Carbon Sense.
Then there’s Syndecrete, developed by architect David Hertz as an eco-friendly concrete alternative made from recycled materials that include everything from broken glass to old vinyl LPs. Syndecrete can be used indoors and out, and formed in limitless sizes and shapes for big projects like a walls and floors, or tiny jobs like a bathroom countertop. In addition to looking fabulous, this composite has half the weight and twice the compressive strength of regular concrete.
Its high volume of reclaimed post-consumer and post-industrial materials make it a green no-brainer.
Image of cementing bricks from Shutterstock