Up to 80 percent of the mass of concrete in sidewalks, foundations, and walls is made up of sand and gravel. Building a single detached home requires close to 400 tonnes of aggregate; a low-rise condominium could use 20 to 50 times that much. Asphalt used in roads and parking lots is 94 percent sand and gravel: two kilometers of a four-lane highway requires over 40,000 tonnes of aggregate. As historian Vaclav Smil, author of the 2013 book Making the Modern World: Materials and Dematerialization, put it, “The most important material in terms of sheer mass in our civilization, is cement made into concrete.”
The global consumption statistics bear this out—and quickly get astronomical. After water, concrete is the second-most consumed substance on Earth. One 2016 estimate of the global aggregate industry for that year—called “a wild guess” by Jason Christopher Willett, Mineral Commodity Specialist with the US Geological Survey, since most countries don’t track data on aggregate sales—was 43 billion tonnes. That’s about the same weight as 130,000 Empire State Buildings, and worth an estimated US $350-billion.
In 2012, the world used enough concrete to wrap a 27 meter by 27 meter band around the equator; in that same year, China alone built 146,000 kilometers of roads. Increasing and rapid urbanization, particularly in countries like China and India, are causing demand to spike. For Smil, the most “stunning” fact he uncovered in his research was learning that in only three years—from 2011 to 2013—China used more cement powder than the United States used over the last century.
The Earth’s crust is made of rock, so finding aggregate is relatively easy; finding it in places where local residents won’t object to the noise of a quarry operation—and to a gaping hole in the landscape—is much more difficult. The equally challenging problem is transportation: getting it from the quarry to the worksite.
Rocks are heavy. Their upside and value is that—more so than wood, clay, or metal, at least—they last. As a result, humans have been enduring, or finding ways to overcome, the hernia-inducing labor involved in quarrying and moving stone for a long, long time. Around 4,500 years ago, Stonehenge’s large, 25-tonne sandstone blocks were transported 30 kilometers to their famed circle; the smaller “bluestones” (rhyolite or dolerite stones, up to two tonnes each) were quarried in Wales, 225 kilometers away, and transported either overland or by sea. That’s a long way to move rock using prehistoric technology. While it’s not certain that the builders of Stonehenge used rafts or boats, long-distance shipping of quarried rock has been around since at least 600 BCE, when the Greeks were importing marble from the island of Naxos to the temples at Delphi, just under 300 kilometers away. That was centuries before the Romans pockmarked Europe with quarries to build out their imperium. Shipping rock, whether slabs or gravel, is therefore an ancient workaround.
For Polaris’s Romero, the inspiration to join this long tradition of aggregate transport first struck in 1999. Romero lives in Vancouver, British Columbia, where Polaris Materials is headquartered. In the 1980s and ’90s, he oversaw projects at other Vancouver-based mining firms—Eldorado Gold and Ivanhoe Mines, among others. He started to explore the possibilities of aggregate mining only after hearing about a British company shipping aggregate from Sechelt, British Columbia, to California.
“When I heard that I did an about-face and thought, ‘This is surprising! How can you move such a low-value product so far and still have a business?’”
Romero researched the industry. At one point he flew to San Francisco and pulled up in his rental car at ready-mix concrete plants. “I told them, ‘Hey, we’re thinking about shipping in sand from Mexico. How can we help you?’ That was the initial idea.”
Sourcing Mexican aggregate didn’t work out, but from these meetings with concrete producers, Romero learned that sand and gravel sources close to San Francisco were depleting rapidly. To keep searching the west coast for an aggregate source made sense: while California has ample reserves of sand and gravel, the problem is moving it around, especially over land: aggregate is so heavy it can only be cost-effectively transported by trucks within a range of about 40 kilometers.
“Aggregate is a relatively low-value product that is extremely sensitive to transportation and logistics costs,” says Romero. “There is plenty of it around. What is much harder to find are resources that are near the urban centers where it is mostly consumed.”
Paradoxically, proximity of aggregate resources to urban areas is part of the problem, says Polaris CEO Kenneth Palko. Natural aggregate usually shows up as deltas and around floodplains. “These are generally flat areas where it’s best to build your houses. California has all kinds of sand and gravel, but they’ve built on top of a lot of it, or nearby. And nobody wants a quarry in their backyard.”
