Control Joints

This project is designed to prototype subtle shifts in Market Street pavement details that expand existing opportunistic conditions of brick pavement. It also introduces visualization techniques for expressing data related to the potential impact of the Market Street’s paved surface to the San Francisco’s watershed. Market Street sidewalks represent over 100,000 sqft of brick pavement, currently designed as impervious. However, examining the finer grain of this pavement reveals opportunities for a mini urban watershed within the pattern of mortar and expansion joints. ‘Accidental permeability’ occurs where sealant at expansion joints has weathered away and opportunistic plants have taken root. These expansion joints represent gaps both in the brick paving and concrete sub-slab – designed for the pavement to adjust to expansion, contraction, and heaves. But these joints also become moments where water can divert, collect, and potentially infiltrate into the subgrade below. In addition, the existing 5/8” standard recessed mortar joint of Market Street’s brick sidewalk is an opportunity to consider water conveyance at the micro-scale. Where mortar and expansion joints have been allowed to weather, they serve as a micro-watershed within the urban dendritic pattern of Market Street’s herringbone brick pattern. Within a 12’x12’ section of Market Street sidewalk, a 5/8” mortar joint represents 31 sqft or 22% of total sidewalk surface, capable of holding 9cuft of water. Considering the total 2 mile length of Market Street, that’s nearly 30,000 sqft of control joints, equivalent to almost 5,000 cuft of potential water retention!

Given these opportunities, our project is designed to prototype installations that capitalize and express the weathering of Market Street’s paving. These installations will test opportunities to improve mortar and expansion joint capacities, install alternative materials (including lighting and plant material), and demonstrate the potential impact for community members. As a well-trafficked urban corridor with iconic streetscape elements, Market Street provides an interesting challenge to prototype alternative pavement treatment to address complex environmental concerns. The impacts to the city’s stormwater management system due to sea level rise will force the city to consider alternative methods for collecting, holding, and infiltrating rainwater from impervious surfaces. This proposal will test opportunities for improved pavement performance on Market Street and opportunities for sharing these practices and their impacts to the diverse communities of people utilizing the thoroughfare.

Collabortors: Brett Snyder, N. Claire Napawan, and Mallory Van Ness


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