Concrete

Environmental Impact Rating

Harvesting — Moderate to High

Portland cement and aggregate ingredients are non-renewable but abundant resources that are widely available. They are quarried or dug from geological deposits. Most limestone quarries have been long established, so are not responsible for the disturbance of untouched ecosystems. Impact at existing quarries tends to be low, and can include interference with and silting of ground and surface water and the creation of airborne dust. Little to no contaminated effluent is created and no chemicals are used in obtaining these materials. Pressure for ever-increasing quantities of aggregate means new pits are being opened, usually close to urban centers and often on or near prime agricultural lands, resulting in serious impacts including loss of arable land, natural habitat disturbance and contamination of ground and surface water.

The balance of materials required for concrete are mainly mined or quarried (including gypsum, calcium sulfate and bauxite, among others), and make up a very small percentage of the mix. These will all have harvesting impacts similar to other quarried materials.

Mining ore to make steel for reinforcement bars or mesh is a high-intensity activity, resulting in serious impacts including habitat destruction and air and water pollution. Depending on the specifications for the slab, the amount of steel used can be low to high.

Manufacturing — High

Portland cement is by crushing the raw limestone and heating it in a kiln to a high temperature (1300–1500 °C / 2350–2750 °F). This is an energy-intensive process and uses fuels such as natural gas, oil, coal and landfill waste, with resulting air and water pollution and habitat destruction. During the heating process, the limestone releases a large amount of carbon dioxide, contributing significantly to greenhouse gas emissions.

Aggregate is relatively low in manufacturing energy inputs and resulting effects.

Admixtures for concrete are often industrial by-products, like blast furnace slag (from ore smelting) and fly ash (from coal burning). While these activities have high impacts, the by-products are not typically attributed with the effects.

The making of steel for reinforcement bars and mesh is a high-intensity activity, including high-energy inputs for melting ore. Impacts include significant air and water pollution.

Transportation — Moderate to High

Sample building uses 5,664 – 14,047 kg of concrete flooring:

5.3 – 21.3 MJ per km by 35 ton truck

Most of the processes involved in making concrete happen relatively close to the source of raw materials, to minimize transportation costs for these heavy materials. Distances from point of harvesting to batching plant may be small or large, depending on the region.

Steel for reinforcement will have varying transportation impacts, depending on the origin of the steel and the number of steps it takes from manufacture to site delivery.

Installation — Moderate to High

The mixing and delivery of cement involves mechanical mixing equipment, with the delivery truck typically doing the mixing as it travels to the site. Some installations require the use of pumper trucks, adding to the impacts. Finishing equipment is often gasoline-powered, further adding to impacts.

Waste: Low

Compostable — Excess concrete. Can be left in the environment if crushed into aggregate. Quantities can vary depending on the accuracy of the material take-off for ordering.

Landfill — Excess concrete. Bags from site-mixed concrete ingredients. Quantities can vary from low to high.

Chart of Embodied energy & carbon

Energy Efficiency

A concrete floor will have little impact on energy efficiency. When used as a slab floor on grade, an adequate amount of insulation must be used to isolate the slab from cold ground temperatures and in particular any edges of the slab that are exposed to the cold exterior. A concrete floor is very conductive, and feet in contact with concrete may feel colder than the actual temperature indicates, resulting in higher thermostat settings to maintain comfort levels.

Material costs: moderate

Labour Input: moderate

Pouring a concrete slab is a labor-intensive activity, and includes the construction and bracing of formwork, laying of reinforcement bars and/or mesh, mixing/pouring/leveling of concrete and multiple steps of finishing.

Pouring a thin finished floor will not usually require any formwork to be constructed, eliminating one labor-intensive step.

Skill level required for homeowners

Preparation of sub-floor — Moderate to Difficult

If formwork is needed, carpentry skills will be required. An aggregate base must be laid, leveled and tamped, then a grid work of reinforcing steel laid. The perimeter of the formwork must be leveled, and all required drains, water lines and electrical conduits installed, braced and leveled.

Skim coat floors will not require as much preparation in terms of formwork, but reinforcement and floor penetrations must still be handled.

Installation of floor — Moderate to Difficult

The placement and leveling of wet concrete is a skill that requires some experience to master, and as the size of the pour increases so does the level of difficulty. Creating a level floor requires careful preparation and screeding and troweling skills. Finishing concrete requires an understanding of the stages of the curing process and troweling or power-troweling experience. Concrete has a limited working time due to its chemical curing process, so there is no time for mistakes or slow work.

Finishing of floor — Easy to Difficult

If a homeowner is intending to trowel off the finished surface, it can be difficult to achieve a smooth, even floor. Particular finishes (stamping, pigmenting, high gloss) are very difficult to achieve without prior experience. If a fairly level, fairly smooth surface is acceptable, this can be achieved with a moderate level of difficulty. If the homeowner is only applying a finish treatment to the surface of the concrete, then it is a relatively simple process that typically involves brushing or rolling a product onto the floor surface as per manufacturer’s instructions.

Sourcing & availability: Easy

Concrete and concrete finishing are available in every region. Premixed concrete is ordered from a local batching plant, or ingredients can be ordered from building supply outlets or masonry supply stores. Concrete finishing is a common trade, and competitive quotes should be obtainable in most regions.

Durability: Very High

A concrete floor can last for at least a hundred years, and possibly longer.

Code compliance

A concrete slab must be designed and installed to meet the structural requirements of local codes, which all recognize this type of floor. If the concrete floor is only a finish, the sub-floor will have to be designed to meet the loads imposed by the concrete.

Indoor air quality: high

Cured concrete is quite benign, and will have little effect on IAQ. Some products used to color and seal concrete can be extremely toxic. Acid stains will carry warnings for cancer, reproductive system damage and miscarriages for pregnant women. Sealants are often petrochemical based, and many off-gas dangerously in the short and/or long term. Using third-party certified finishes will help to ensure minimal impacts on IAQ.

Resources for further research

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Future development

There is a lot of R&D work into making more environmentally friendly concrete. Currently, concrete manufacturers tout the long lifespan of concrete as an adequate offset for its high environmental impacts, but this is difficult to support in any balanced analysis. Before concrete becomes a sustainable choice, the high energy inputs and high greenhouse gas emissions must be addressed. While it is likely that developments in these regards will occur, for now the best argument for concrete is in its combined use as a structural floor material and a finished floor. By reducing the need for additional flooring materials, some of its impacts may be balanced. Should it become feasible to create a concrete with much lower impacts that can still serve the double functions of structure and finish, it would be a revolutionary development.