Onsite Masonry Production from Diverted Excavation
Words: Dan Kamys
Explorations in hyper-local adaptive materials reuse for real estate development
By David Easton, co-founder and president of Watershed Materials
The Kirkham Project pedestrian entry, stairs, and retaining wall along Kirkham Street provides an opportunity for installation of Watershed Materials’ blocks as both structural and decorative applications.
Watershed Materials is teaming up with Westlake Urban and Alpha Group to explore a solution to a problem that real estate developers often face—excavation that has to be moved off a construction site to make way for new buildings. Rather than haul off the excavation spoils and then import thousands of concrete masonry units (CMUs) for use at the project, the developers and Watershed Materials are working together to repurpose native excavation material right at the job site to create the structural masonry blocks used in the development. Truckloads of offhaul and truckloads of imported building materials could be eliminated by using the excavation to make the structural block, adaptively reusing waste to produce onsite building materials.
The companies are testing the feasibility of the novel adaptive reuse strategy at the Kirkham Project, an urban infill redevelopment of the Kirkham Heights Apartments in the Inner Sunset neighborhood of San Francisco.
Watershed Materials’ high compression masonry block machine produces low cement alternatives to traditional concrete masonry units (CMUs) from unwashed aggregates diverted from quarries or from onsite excavation material diverted from real estate development projects. The machine is
shown here at Watershed Materials’ pilot block factory and research lab in Napa, Calif.
Sample structural masonry block produced by Watershed Materials from soil samples
taken at the Kirkham Heights Apartments in the Inner Sunset neighborhood of San Francisco. The block achieved a final compressive strength of 2,905 psi and a density of 131 pounds per cubic foot averaged over three specimens. The appearance comes from Watershed Materials’ ultra high compression technology combined with the native site material—a medium dense reddish-brown sand with angular gravel and rock fragments. Blocks such as these are proposed to be produced onsite at the Kirhkam Project redevelopment, made from repurposed excavation and used throughout the development site as structural and decorative masonry elements.Watershed Materials, a sustainable building materials startup funded by the National Science Foundation, develops technology for the production of structural masonry using high compression, low cement technology and locally sourced, unwashed aggregates. The company has a pilot factory in Napa, Calif., where it produces masonry blocks using aggregate sourced from local quarries. Watershed Materials has created a small, portable block production machine, a sort of pop-up facility, that can be located on construction sites to produce masonry block from the excavation spoils—much in the same way it produces block from unwashed quarry aggregate.
The Watershed Materials system applies very high pressure to aggregate mixtures, mimicking the natural geological process known as lithification that creates stone from loose sedimentary material. What takes nature many millennia to accomplish is duplicated in seconds in Watershed Materials’ high compression masonry production equipment.
The company has a long history of using onsite aggregate for building structural walls using a construction method known as Rammed Earth. There’s absolutely nothing new about building masonry structures from local materials. Some of the oldest and best-known architecture in the world has been constructed from stone and clay sourced directly on site. What is new and absolutely groundbreaking is that with upgraded technology and improved material science, a construction waste product developers normally pay to dispose of can now become an asset and provides environmental benefits as well.
The Kirkham Project is a proposed redevelopment of Westlake Urban’s property located in the Inner Sunset neighborhood of San Francisco and abutting UCSF Medical Center and the Mount Sutro Open Space Reserve.The Kirkham Project proved an ideal opportunity to explore the feasibility of this novel approach. Nestled against the Mount Sutro Open Space Reserve in the Inner Sunset, the existing topography of the site requires excavation to create a new neighborhood that complies with the City of San Francisco’s Better Streets Program and will accommodate increased housing density, community open spaces, and improved accessibility. Westlake Urban’s proposed development includes realigning 5th Avenue to create a new neighborhood of up to 445 housing units. The project also will include community plazas, gardens, and stairways to view overlooks of the Pacific Ocean and Golden Gate Bridge. The project addresses the city’s dire need for additional housing near a major employer (UCSF) and public transit, but some neighbors have expressed concerns about the construction truck traffic related to the new development.
The Kirkham Project’s Development Manager, Naomi Porat of Alpha Group, connected with Watershed Materials and coordinated an in-depth feasibility analysis to determine the environmental, economic, and community advantages of onsite block fabrication as a means to reduce off-haul. She commented, “Many of our developments require trucks to haul the excess excavated material to offsite locations. As a long-time entrepreneur in the green building and prefab industries, I was on a mission to find a sustainable solution for The Kirkham Project when I met David Easton of Watershed Materials.
“I suggested the idea of an onsite pop-up plant as a possible solution,” Porat continued. “The concept resonated with David Easton as a way to bring this innovative technology to construction sites. Our preliminary feasibility analysis at The Kirkham Project was extremely promising and we are now engaged in further analyses to prove the concept and confirm that the methods and technology will work for the project.”
The Kirkham Project development team is evaluating the feasibility of using Watershed Materials’ blocks for the structural elements of sub-grade parking structures below these residential buildings.
The feasibility analysis involves the following steps:
- Soil Testing: excavate 1’ - 5’ deep boring depth for Watershed Materials to test in its Napa lab then produce sample blocks and a report summarizing mix designs, compressive strength, and density. The Kirkham Project site’s excavation proved ideal for producing masonry units using this high-compression manufacturing process. Sample blocks were produced with a compressive strength of 2,905 psi, significantly greater than conventional CMU blocks.
- Identification of Site Elements for Block Utilization: The development team identified the site elements that could incorporate masonry blocks as the primary building material, including landscape pavers, pedestrian pavers, retaining walls, foundation, and garages.
- Take-Offs & Total Block Estimate: The architect, engineer, and landscape architect prepared rough take-offs of the elements for block material. The development’s contractor is providing detailed square footage estimates for Watershed Materials to determine the total block utilization potential at the site.
- Cost Estimates & Business Case: The final step in the feasibility analysis is to estimate the total cost of purchasing and installing the blocks as an alternative to conventional building materials for each of these estimates. In addition, the cost of setting up the pop-up facility and producing on site is incorporated into the total cost of the project, and compared to the cost of off-hauling and trucking new materials to the site.
David Easton of Watershed Materials and Gaye Quinn of Westlake Urban at Watershed Materials’ lab in Napa, Calif., discussing the viability of making structural masonry units from repurposed excavation from the Kirkham Project in San Francisco.
David Easton of Watershed Materials and Gaye Quinn of Westlake Urban at Watershed Materials’ lab in Napa, Calif., discussing the viability of making structural masonry units from repurposed excavation from the Kirkham Project in San Francisco.The Kirkham Project Community Plaza, a one-quarter acre accessible open space in the center of the development, provides excellent opportunities for installation of Watershed Materials’ blocks as pavers and landscaping features.
The Kirkham Project development team, in collaboration with Watershed Materials, summarized the compelling advantages and potential challenges of the onsite fabrication facility and block integration in the project:
- Reduces off-haul. Kirkham Heights is an infill redevelopment project in an existing neighborhood. Producing block onsite allows for a reduction in the number of truckloads of off-haul needed to remove excavation. Reducing off-haul reduces costs, reduces diesel emissions, and importantly reduces impact on the neighborhood.
- Aesthetic, indigenous sustainability. Watershed Blocks are a beautiful building material that helps to tell the story of more sustainable development practices.
- Reuse of site material provides an excellent demonstration of an important and cost-effective innovation in the real estate industry.
- Noise. The pop-up block machine is no louder than the excavation machinery or typical construction equipment and it is only on the site for a limited period of time.
Watershed Materials’ high compression masonry block machine imparts 500,000 pounds of compressive force to produce low cement alternatives to traditional concrete masonry units (CMUs). The process is similar to the way nature produces rock from loose sedimentary materials under intense geologic pressure. Watershed Materials reproduces this effect in seconds rather than millenia.Gaye Quinn of Westlake Urban succinctly summarizes the advantages of this approach: “Real estate developers like us are always looking for creative, sustainable solutions to problems we face as we develop our properties. David Easton and his team at Watershed Materials created both a product and a process that solves a number of problems for us. First, it creates a product that is both useful and beautiful. And equally important, it reduces the environmental impacts of truck traffic that would be required to take the material off site. We were thrilled to see that the excavation at our Kirkham Project in the Inner Sunset in San Francisco create absolutely gorgeous, structurally strong, building blocks that can be created onsite, and we are optimistic about the possibility of incorporating the blocks in our proposed project. We would have been happy simply to use the material in places where it would be unseen as a utilitarian material, but after seeing the sample blocks, we are pushing our designers to find as many ways as possible to put them on display.”
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