Green concrete roof

A green or vegetated roof provides the function of a conventional roof, while allowing plants to grow on the surface. A vegetated roof includes water proofing, a drainage system, filter layer, a lightweight growing medium and plants.

An ‘extensive’ green roof has a relatively shallow soil profile (25 to 125 mm) and is planted with ground cover plants that are adapted to the harsh conditions of the rooftop microclimate. ‘Intensive’ green roofs refer to more substantial roof gardens with deeper soil (150 mm or more) and are often planted with shrubs, and trees as well as ground cover.

Vegetated roofs are ideal for any place where people spend their day, including residential communities, office buildings, hospitals, day care centers, schools, recreational facilities, shopping centers and airports.

Concrete is the structural system of choice for vegetated roofs because it provides a continuous load-bearing surface for the potentially moist growing medium and plants. In addition, cast-in-place concrete provides a uniform surface. Projects constructed using waterproof concrete made with proprietary admixtures allow for the elimination of membranes and therefore simplify design, construction and maintenance processes. Lightweight concrete topping can be used to create the sloping deck of a vegetated roof system. In addition, structural lightweight aggregate can be used as a lightweight, absorptive portion of the growing medium. Lightweight applications reduce the dead load on the roof structure.

Read more on the subject in the application note by Portland Cement Association (PCA)

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Reducing carbon footprint of concrete

As I understand on date, there is no carbon neutral or carbon negative concrete mix design available, as all concrete contains cement. The production of one tonne of cement emits nearly the same amount of carbon dioxide in the atmosphere. It is interesting to know that fresh concrete absorbs some of that CO2 back during carbonation which takes place during the setting and hardening process. One effective way to reduce the carbon footprint of concrete is to minimise the use of cement, partially replacing it with the mineral admixtures like fly ash, blast furnace slag, rice husk ash, which are industrial and agricultural wastes. These admixtures, besides giving long term strength to concrete also enhance its durability.

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