City of San Jose 2021 ADA Curb Ramp Request Project #2 – Sustainable Mix Design

Location

San Jose (various)

City or County Responsible for Project

City of San Jose

Category

Roads: Efficient and Sustainable Road Maintenance, Construction and Reconstruction Projects.

Author

Irene Ding

Organization

City of San Jose

Address

1404 Mabury Rd, San Jose, CA 95133

Phone

415-816-2382

Project Description

The City of San José’s “2021 ADA Curb Ramp Request Project #2 – Sustainable Mix Design” was the City’s very first pilot project aimed at reducing the carbon footprint of its concrete construction activities. The project constructed/upgraded 94 concrete curb ramps to be ADA compliant in response to residents’ requests for improved sidewalk and street accessibility for wheelchair users and people with disabilities. The scope of work included the design and construction of curb ramps, including improving curb and gutter, and adjacent sidewalk.

The City of San José collaborated with the California Nevada Cement Association and U.S. Concrete to develop a specification for low-carbon concrete for the first time. The existing City standard required using all-Portland cement, the largest carbon-emitting component of concrete. The project specification was revised to reduce cement content and replace with lower carbon supplementary cementitious materials (SCM). Moreover, the project piloted the use of new carbon dioxide (CO2) injection technology. The technology takes post-industrial CO2 in liquid form and injects it into fresh concrete, which then undergoes a chemical reaction known as mineralization such that CO2 is permanently embedded in the concrete instead of released into the atmosphere. The CO2 has been shown to help increase the concrete’s strength, thus enabling a reduced cement content that will still achieve the required strength. The City of San José collaborated with Spencon Construction to explore three mix designs in this project: 1) 25% SCM replacement (fly ash), 2) 50% SCM replacement (slag, fly ash), and 3) 30% SCM replacement (slag) + CO2. The third mix design provided the best combination of workability and a low carbon footprint, a reduction of about 40% in global warming potential compared to an all-Portland cement mix previously used, and at a minimal or no additional cost to the City. Despite some challenges with concrete set time, all ADA curb ramps were poured successfully, allowing pedestrians and people with disabilities to cross the roads safely.

Due to the success of this project, the City of San José required contractors to use low-carbon mix designs that meet a minimum global warming potential (GWP) for all curb ramp construction beginning in 2022. The City constructs/upgrades about 2,000 curb ramps annually and with about 17,000 remaining to upgrade and construct, it will see a significant carbon savings over the next decade. The City will also consider other applications of low-carbon technologies in its construction activities and continue to meet its goals toward sustainability and carbon neutrality by 2030.