Environment Impact

Q: What are the environmental and social impacts of cement industries?

A: Cement manufacture causes environmental impacts at all stages of the process. These include emissions of airborne pollution in the form of dust, gases, noise and vibration when operating machinery and during blasting in quarries and damage to countryside from quarrying. Equipment to reduce dust emissions during quarrying and manufacture of cement is widely used and equipment to trap and separate exhaust gases are coming into increased use. Environmental protection also includes the re-integration of quarries into the countryside after returning them to nature or re-cultivating them has closed them down.

Climate

Cement manufacture contributes greenhouse gases both, directly through the production of carbon dioxide when calcium carbonate is heated, producing lime and carbon dioxide and indirectly through the use of energy, particularly if the energy is sourced from fossil fuels. The cement industry produces about 5% of global man-made CO2 emissions, of which 50% is from the chemical process, and 40% from burning fuel. The amount of CO2 emitted by the cement industry is nearly 900kg of CO2 for every 1000kg of cement produced.
Newly developed cement types from Novacem and Eco-cement can absorb carbon dioxide from ambient air during hardening.
Fuels and raw materials
A cement plant consumes 3–6GJ of fuel per tonne of clinker produced, depending on the raw materials and the process used. Most cement kilns today use coal and petroleum coke as primary fuels and, to a lesser extent, natural gas and fuel oil. Selected waste and by-products with recoverable calorific value can be used as fuels in a cement kiln, replacing a portion of conventional fossil fuels, like coal, if they meet strict specifications. Selected waste and by-products containing useful minerals such as calcium, silica, alumina and iron can be used as raw materials in the kiln, replacing raw materials such as clay, shale and limestone. Because some materials have both useful mineral content and recoverable calorific value, the distinction between alternative fuels and raw materials is not always clear. For example, sewage sludge has a low but significant calorific value and burns to give ash-containing minerals useful in the clinker matrix.

Local impacts

Producing cement has significant positive and negative impacts at a local level. On the positive side, the cement industry may create employment and business opportunities for local people, particularly in remote locations in developing countries where there are few other opportunities for economic development. Negative impacts include disturbance to the landscape, dust and noise and disruption to local biodiversity from quarrying limestone (the raw material for cement).

 

Q: Is precast concrete a green building material?

A: Precast concrete contributes to green building practices in significant ways. The low water-cement ratios possible with precast concrete are -0.36–0.38, which mean it can be extremely durable. The thermal mass of concrete allows shifting of heating and cooling loads in a structure to help reduce mechanical-system requirements. Because precast concrete is factory-made, there is little waste created in the plant (most plants employ exact-batching technologies) and it reduces construction waste and debris on site, reducing construction IAQ concerns. The load-carrying capacities, optimised cross sections and long spans possible with precast concrete members help eliminate redundant members and concrete readily accommodates recycled content.


Q: Is precast concrete energy-efficient?

A: The thermal mass of precast concrete absorbs and releases heat slowly, shifting air conditioning and heating loads to allow smaller, more efficient heating, ventilating and air conditioning (HVAC) systems. Insulation is often used in architectural panels and sandwich wall panels to increase thermal efficiency, with continuous insulation (ci) in walls being possible. The resulting savings are significant up to 25% on heating and cooling costs.


Q: Does precast concrete contain recycled materials?

A: Precast concrete’s fresh and in-place performance can improve when several common industrial by-products are added. Fly ash, slag and silica fume, which would otherwise go to landfills, can be incorporated into concrete as supplementary materials. These by-products can also reduce the amount of cement that is used in concrete.
Reinforcement is typically made from recycled steel. (Steel is one of the most recycled building materials and can be reused repeatedly) Insulation and connections within the precast concrete also contain recycled content.


Q: Can precast concrete members be reused?

A: Precast concrete members are unique in that they are individually engineered products that can be disassembled. Designers can easily plan future additions to buildings, because the precast concrete components can be rearranged. Once removed, precast concrete members may be reused in other applications.
Precast concrete is also friendly to downcycling, in which building materials are broken down, because it comes apart with a minimum amount of energy and retains its original qualities. An example of downcycling would be the use of crushed precast concrete as aggregate in new concrete or as base materials for roads, sidewalks, or concrete slabs.


Q: How does precast concrete contribute to LEED-NC rating points?

A: Precast concrete:
Minimally disrupts the site (area and time)
Reduces damage to drainage paths and natural habitats
Increases open area when multi-level parking structures are used
Reduces the heat-island effect because of concrete's light colour
Improves energy efficiency and thermal comfort
Reuses and recycles formwork, keeping materials out of the landfill
Uses recyclable concrete and steel
Can be reused or recycled
Can use waste and recycled materials such as slag, fly ash and silica fume
Is generally made from materials that are extracted and manufactured regionally
Does not off-gas and does not need to be sealed or painted


Q: What LEED-NC points does precast concrete contribute toward?

A: Precast concrete and other materials contribute to LEED points by providing performance and properties that are measured by the LEED program. At this time, PCI endorses potential precast concrete contributions for up to 20 LEED points (see LEED Project Checklist) and possibly more, depending on the project.

 

Q: How can precast concrete reduce the heat-island effect described in the LEED Sustainable Sites credit (SSc7.1)?
A: Sustainable Sites credit 7.1 is intended to reduce heat islands, meaning the thermal gradient difference between developed and undeveloped areas. The heat-island effect is partially attributed to the dark surfaces of roofing and paving and the additional heat in developed areas increases HVAC loads and contributes to the creation of smog. Reducing heat islands minimises impact on microclimate and human and wildlife habitat.
Precast concrete parking structures that place at least 50% of the spaces under cover (for example, underground, under a building, or under a deck or roof) can reduce this effect. Any roof used to shade or cover parking must have a solar reflective index (SRI or albedo) of at least 29. In addition, high-albedo vertical precast concrete wall surfaces reduce the heat-island effect.


Q: How can precast concrete contribute to Innovation and Design in LEED?

A: Projects earn Innovation and Design credits when they demonstrate exemplary performance in a recognised LEED credit area, or bring new approaches and technologies such as carbon-fibre reinforcing that reduce weight and embedded energy and advance sustainable design. Because of its significant contributions to LEED and its inherent green characteristics, precast concrete offers an excellent platform on which creative project teams can base their sustainable design plans.

 

Q: How does precast concrete contribute to the underlying sustainability concept of “Reduce, Reuse, Recycle”?
A: By reducing the amount of materials and the toxicity of waste materials
Precast concrete can be designed to optimise (lessen) the amount of concrete used in a structure or element
As one example, the use of carbon-fibre reinforcement or insulation can reduce:
Amount of concrete needed in a precast concrete panel
Weight of a precast concrete panel
Transportation cost of precast concrete panel
Amount of energy used to erect a precast concrete panel
Precast concrete generates low amounts of waste with low toxicity
2% of the concrete at a precast plant is waste
95% of the waste is used to manufacture new panels

 

By reusing products and containers and repairing what can be reused
Precast concrete panels can be reused when buildings are expanded or dismantled
Concrete pieces from demolished structures can be reused to protect shorelines
Wood or fibreglass formwork used to make precast concrete products is generally reused 40 or more times
Concrete and steel have practically unlimited service lives

 

By recycling as much as possible, including buying products with recycled content
Industrial wastes (fly ash, slag and silica fume) can be used as partial replacements for cement
Wood and steel forms are recycled when they become worn or obsolete
Virtually, all reinforcing steel is made from recycled steel
Insulation contains partially recycled material
Concrete in most urban areas is recycled as fill or road base


Q: What steps are precast operations taking toward sustainability?

A: PCI Producer Members meet local and state ordinances and emissions requirements. Initiatives within the industry include:
Use of local materials in all mixtures; local aggregate resources
Water reclamation and recycling
Reducing cement requirements by lowering watercement ratios
Admixtures such as hardening accelerators to eliminate applied heat in curing
Use of self-consolidating concrete (SCC) for quicker placement, no vibration and reduced surface defects
Use of environmentally friendly thin brick in place of conventional brick in precast concrete systems
Carbon-fibre reinforcement that allows lighter and larger concrete sections with less embedded energy and no corrosion
Use of supplemental cementitious materials (SCMs) to reduce cement consumption; participation in Cool Climate Concrete
Enclosed sandblasting facilities with 100% process-waste control
Standardising wood form parts for multiple reuse; recycling discarded forms into mulch or fuel
Recycling all scrap steel and reinforcement
Reducing and reusing product packaging received in facilities

 

Q: What is being done about CO2 emissions during the cement-manufacturing process?
A: Since 1975, the cement industry has reduced CO2 emissions by 33%. Today, cement production accounts for less than 1.5% of U.S. carbon dioxide emissions, well below other sources such as electric generation plants for heating and cooling the homes and buildings we live in (33%) and transportation (27%).
In 2000, the cement industry created a new way to measure CO2 emissions. Recently introduced guidelines will allow for greater use of limestone as a raw material in cement, ultimately reducing CO2 by more than 2.5 million tons per year. By the year 2020, plans call for further reduction of CO2 emissions to 10% below the 1990 baseline through investments in equipment, improvements in formulations and development of new applications for cements and concretes that improve energy efficiency and durability.


Q: What is Self-Cleaning Concrete

A: Self-cleaning buildings and pollution-reducing roadways: These may sound like futuristic ideas, but they are realities of some of today’s concrete. Recently introduced formulations of cement are able to neutralise pollution. Harmful smog can be turned into harmless compounds and washed away. Anything made out of concrete is a potential application, because these cements are used in the same manner as regular Portland cements. These products provide value through unique architectural and environmental performance capabilities.
Proprietary technology (based on particles of titanium dioxide) is what makes this cement special—capable of breaking down smog or other pollution that has attached itself to the concrete substrate, in a process known as photocatalysis.

Q: What steps are being taken to make concrete environment friendly?
A: Recently, the use of recycled materials as concrete ingredients is gaining popularity because of increasingly stringent environmental legislation. The most conspicuous of these is fly ash, a by-product of coal-fired power plants. This has a significant impact by reducing the amount of quarrying and landfill space required and, as it acts as a cement replacement, reduces the amount of cement required to produce a solid concrete.

Q: What is concrete recycling?
A: It is a method of disposing of concrete structures. Concrete debris was once routinely shipped to landfills for disposal, but recycling is increasing due to improved environmental awareness, governmental laws and economic benefits.
Concrete, which must be free of trash, wood, paper and other such materials, is collected from demolition sites and put through a crushing machine, often along with asphalt, bricks and rocks.
Reinforced concrete contains rebar and other metallic reinforcements, which are removed with magnets and recycled elsewhere. The remaining aggregate chunks are sorted by size. Larger chunks may go through the crusher again. Smaller pieces of concrete are used as gravel for new construction projects. Aggregate base gravel is laid down as the lowest layer in a road, with fresh concrete or asphalt placed over it. Crushed recycled concrete can sometimes be used as the dry aggregate for brand new concrete if it is free of contaminants, though the use of recycled concrete limits strength and is not allowed in many jurisdictions. On 3 March 1983, a government funded research team (the VIRL research.codep) approximated that almost 17% of worldwide landfill was by-products of concrete based waste.
Recycling concrete provides environmental benefits, conserving landfill space and use as aggregate reduces the need for gravel mining.

Q: How does concrete contribute to Urban heat
A: Concrete and asphalt are the primary contributors to what is known as the Urban heat island effect.
Using light-coloured concrete has proven effective in reflecting up to 50% more light than asphalt and reducing ambient temperature. A low albedo value, characteristic of black asphalt, absorbs a large percentage of solar heat and contributes to the warming of cities. By paving with light coloured concrete, in addition to replacing asphalt with light-coloured concrete, communities can lower their average temperature.
Many U.S. cities show that pavement comprise approximately 30-40% of their surface area. This directly impacts the temperature of the city, as demonstrated by the urban heat island effect. In addition to decreasing the overall temperature of parking lots and large paved areas by paving with light-coloured concrete, there are supplemental benefits. One example is 10–30% improved night time visibility. The potential of energy saving within an area is also high. With lower temperatures, the demand for air conditioning decreases, saving vast amounts of energy.
Atlanta has tried to mitigate the heat-island effect. City officials noted that when using heat-reflecting concrete, their average city temperature decreased by 6°F. New York City offers another example. The Design Trust for Public Space in New York City found that by slightly raising the albedo value in their city, beneficial effects such as energy savings could be achieved. It was concluded that this could be accomplished by the replacement of black asphalt with light-coloured concrete.

Q: Does concrete create air pollution?
A: Building demolition and natural disasters such as earthquakes often release a large amount of concrete dust into the local atmosphere. Concrete dust was concluded to be the major source of dangerous air pollution following the Great Hanshin earthquake.

Q: Does concrete have any effect on the health of the people in the building?
The presence of some substances in concrete, including useful and unwanted additives, can cause health concerns. Natural radioactive elements (K, U and Th) can be present in various concentrations in concrete dwellings, depending on the source of the raw materials used. Toxic substances may also be added to the mixture for making concrete by unscrupulous makers. Dust from rubble or broken concrete upon demolition or crumbling may cause serious health concerns depending also on what had been incorporated in the concrete.

Q: How much CO2 is associated with the manufacture of cement?

A: For each tonne of cement produced by BCA member companies 822kg (0.822t) of CO2 emissions are released. About 40% of these emissions come from fuel combustion at cement manufacturing operations and 60% originate from the manufacturing process that converts limestone (CaCO3) to calcium oxide (CaO), the primary precursor to cement. It is chemically impossible to convert CaCO3 to CaO and then cement clinker, without generating CO2. Additionally, indirect CO2 during the transport of raw materials, fuels and products, as well as electricity generation, would account for around 7% of the total emissions from cement manufacture.

 

In 2002, global cement production was responsible for around 3.8% of man-made CO2 emissions.

 

In 2004, the UK (and Crown dependencies) cement industry produced 1.74% of UK CO2 emissions (source: data from the BCA and National GHG Inventory).

 

Q: Is concrete combustible?
A: No. Concrete is an inert inorganic conglomerate. It does not burn, melt, warp, lose structural strength or drip molten material in a fire.

 

Q: How does concrete compare to steel in fire?
A: It is known that structural steel begins to soften around 425°C and loses about half of its strength at 650°C. This is why steel is stress-relieved in this temperature range. But even a 50% loss of strength is still insufficient, by itself, to explain the World Trade Centre collapse. It was noted above that the wind load controlled the design allowables. The World Trade Center, on this low-wind day, was likely not stressed more than a third of the design allowable, which is roughly one-fifth of the yield strength of the steel. Even with its strength halved, the steel could still support two to three times the stresses imposed by a 650°C fire.

The additional problem was distortion of the steel in the fire. The temperature of the fire was not uniform everywhere and the temperature on the outside of the box columns was clearly lower than on the side facing the fire. The temperature along the 18m-long joists was certainly not uniform. Given the thermal expansion of steel, a 150°C temperature difference from one location to another will produce yield-level residual stresses. This produced distortions in the slender structural steel, which resulted in buckling failures. Thus, the failure of the steel was due to two factors: loss of strength due to the temperature of the fire and loss of structural integrity due to distortion of the steel from the non-uniform temperatures in the fire.


Q: What is the effect of concrete on acoustics?

A: The issue of sound insulation and acoustic performance of homes has grown in importance, primarily due to the growing demand from government for increased density of urban dwellings. The number of complaints about noise has risen due both to this closer proximity and the new demands placed on housing (e.g. entertainment systems). For this reason, the UK Building Regulations Part E now requires improved sound insulation.

 

 

In general, increasing the mass of a wall or floor improves the sound insulation of a room; hence concrete and masonry offer a good barrier to airborne sounds, while impact sound is easily controlled with appropriate floor and ceiling finishes. A range of 'Robust Details' (RD) for both masonry and concrete walls and concrete floors have been agreed by the Building Regulations Advisory Committee. These offer approved construction choices for both party walls and separating floors and include aspects of the external wall in controlling sound between dwellings.

 

Good acoustic properties can also be achieved for multi-occupancy residences using a range of concrete options. One example is tunnel form construction (in which the walls, floors and ceilings are made from cast in-situ concrete using specialist reusable formwork) that was used for a residential block at the University of East Anglia. Two separating floors in the new block, consisting of 250mm of concrete with a stuck-down carpet and no ceiling finish beneath, were tested. They both exceeded the regulations by more than 5dB for both airborne and impact sound insulation and therefore met the levels required by Robust Details.

 

Concrete walls provide a buffer between:
Outdoor noise and the indoor environment in a building.
Road noise and residential areas with a sound barrier.
Indoor noise between adjoining apartments or other spaces as a separating wall.

 

A study in America reported in the PCA bulletin No. 15434 proved that:


"...The greater mass of concrete walls can reduce sound penetrating through a wall by over 80% compared with wood or steel frame construction. Although some sound will penetrate the windows, a concrete building can be two-thirds quieter than a wood or steel frame building. Concrete panels also provide effective sound barriers separating buildings from highways or industrial areas from residential areas..."