Living concrete: Democratizing living walls

Living walls can help bring nature to urban canyons. However, contemporary living walls are cost prohibitive and made of materials with shorter life spans than their buildings. High cost often restricts their use to luxury applications promoting ecological symbolism rather than impactful propagation of urban nature. This study shows an approach to lowering living wall costs and increasing their use by integrating them into the building's structure. Existing living wall systems are hung like curtains from a building's facade; they are made as light as possible to reduce the weight they superimpose. Their lighter materials, e.g., felts and plastics, limit their life cycle. Conversely, combining the living function with the exterior envelope will match a living wall's life cycle to its building, and cost diminishes by eliminating a living wall's secondary support structure. This study focuses on concrete construction, a typology needing ecological evolution. Chosen for its ubiquity, durability, affordability, and plasticity, concrete was tested as a potential growing medium for plants. The result of the study is a new living concrete material and system aimed at advancing biophilic design in cities facing shifting climates and population densification. Presented are a new cast-in-place living wall system, a new concrete and its mechanical properties, verification of constructability, identification of plants suitable to cementitious environments, indoor germination and growth, full-scale tests of a new construction methodology, how concrete's chemical composition affects irrigation water, outdoor germination and perenniality, and a cost analysis showing a 50% reduction to the installed cost of living walls. Cost savings include plants grown from seed-insitu (eliminating raising plants in a nursery and transplantation), and not using fertilizer (eliminating chemicals and a fertigation system). This study shows how rethinking the current living wall paradigm could shift the industry toward solutions to democratize living walls via lower cost and permanence. (C) 2019 Elsevier B.V. All rights reserved.