Napa company developing greener concrete blocks

A Napa company is working to significantly reduce greenhouse gas emissions by making an alternate to the most common construction material on the planet: concrete.

Watershed Materials recently received a $743,000 grant from the National Science Foundation to make concrete blocks without cement. Already, in an earlier grant phase, the company demonstrated the scientific feasibility of its proposal and produced a masonry block made with only half the regular amount of cement.

Under the grant, the company now seeks to develop both the cement-less blocks and the machinery needed to mass produce them.

“Cement is a really, really good glue,” said Watershed President David Easton. “But what we’ve discovered is it’s expensive and hard on the environment.”

Portland cement, which binds together sand and gravel to form concrete, is made in kilns using intense heat, a process that releases carbon dioxide from the limestone and other ingredients in the mixture. Its production is deemed responsible for more than 5 percent of the world’s greenhouse emissions.

“The making of cement is second only to automobiles and coal-fired electrical plants in the amount of CO2 it generates,” said Robert Courland, author of the book “Concrete Planet.” Courland hasn’t studied Watershed’s operation, but he said other businesses and researchers also are seeking “the Holy Grail” - a material that would be both more permanent and environmentally friendly than today’s concrete.

Easton brings more than four decades of construction experience as the founder of Rammed Earth Works. The Napa company builds homes and other structures from rammed earth, a mixture of clay-like, mineral-laden subsoils and a little cement that is tamped down in forms to build thick, sturdy walls. The process relies on techniques developed by ancient cultures.

“We are completely committed to earth as a sustainable building material,” he said.

The company already has developed its Watershed Block, which contain 5 percent Portland cement, about half that of a typical concrete block. The company’s website says at times the blocks are made with such “supplemental cementitious materials” as fly ash, slag, silica fume and rice hull ash.

Now Watershed is seeking both the right ingredients and the right process to further reduce the need for cement. To that end, it is working to build a press that can apply “compressive forces so great as to actually lithify mineral grains, turning loose sediment into stone,” according to its news release.

“The machine that we’re developing is key to the overall success of the business and the product that we’re developing,” Easton said.

The science foundation earlier provided a $150,000 grant for the project’s first phase, he said. The second phase is expected to last two years.

The Roman Empire mastered cement making, and some of that culture’s masonry bridges still stand 2,000 years later, author Courland said. In fact, he said, Roman structures that rely on the arch for strength can far outlast modern concrete buildings that rely on steel reinforcement bars, which eventually corrode.

It remains to be seen whether Watershed can succeed in its efforts to build concrete blocks without cement, Courland suggested. But he expressed hope that researchers and business people will continue to develop greener ways to build.

“I would love to see a new form of concrete that doesn’t involve spewing huge amounts of CO2 in the atmosphere,” Courland said.