Concrete Admixtures and the Environment

Concrete admixtures are liquid or powder additives. They are added to the concrete mix in small quantities to meet specific requirements as:

  • „„To fix fresh concrete behaviour
  • „„To control setting or hardening
  • „„To increase the durability

The effect of admixtures is always to improve the concrete. In quantity terms, superplasticizers (midrange and high range water reducer) and plasticizers (water reducer) as a group represents more than half of all the admixtures used today.

How much do concrete admixtures leach, biodegrade or release fumes?


Admixtures should be non-toxic, water-soluble and biodegradable.

Tests on pulverized concrete specimens show that small quantities of superplasticizer and their decomposition products are leachable in principle. However, the materials degrade well and do not cause any relevant ground water pollution. Even under the most extreme conditions, only small quantities of organic carbon leaches into the water.

How environment-friendly are superplasticizers?


Concrete admixtures are appropriate for their application and when correctly used are harmless to humans, animals and the environment.

The technical benefits of superplasticizer for clients and construction professionals outweigh the occurrence of low, controllable emissions during use. Concrete admixtures merit being rated environmentally-friendly because they create negligible air, soil or ground water pollution.

Publications:

  • „„Association of Swiss Concrete Admixtures Manufacturers (FSHBZ)
    ‘EFCA-Seal of Enviromental Quality for Concrete Admixtures: Technical Guidelines’
    Technical report
  • „„EU Project ANACAD
    ‘Analysis and Results of Concrete Admixtures in Wastewater’
    Final report BMG

EFCA Membership

Sika is a member of EFCA, the European Federation of Concrete Admixtures Associations.

Local Sika companies are working around the world together with their local Concrete and Admixtures Associations, to support and promote increasingly sustainable development through the use of concrete admixture technologies.

Powerful and Sustainable

Concrete admixtures can improve the sustainability of concrete in many different ways. Firstly, they can improve the quality and performance of the concrete significantly, which extends its service life. The addition of stabilizing and special water reducing admixtures also enables recycled aggregates to be used for the production of good quality concrete. Finally, the energy required to obtain high early strengths in precast concrete can be greatly reduced or even completely replaced by water reducing and accelerating admixtures.

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Concrete admixtures can improve the sustainability of concrete in many different ways. Firstly, they can improve the quality and performance of the concrete significantly, which extends its service life. The addition of stabilizing and special water reducing admixtures also enables recycled aggregates to be used for the production of good quality concrete. Finally, the energy required to obtain high early strengths in precast concrete can be greatly reduced or even completely replaced by water reducing and accelerating admixtures.

Efficiency

Concrete admixtures are a relevant part to achieve a significant energy reduction of the concreting process. Admixtures have an important task in prospect of sustainability.

Performance

Concrete is a building material with a remarkable product performance in case of durability and technical solutions and concrete admixtures are part of this successful concept!

Saving Resources and Reducing Waste in Concrete Production

Concrete is one of the most versatile and durable construction materials known to man, making it the most widely used construction material in the world. It is ubiquitous in our built environment, being used in schools, hospitals, homes, offices, roads, railways, dams etc.. Given the high demand for concrete, its sustainable production and application is an issue of increasing importance for the construction industry and regulators worldwide. Old concrete is being recycled more often. It is crushed and used as aggregates for production of new concrete. Material efficiency is further improved by on-site recycling of excavated material. The environmental benefits are obvious:

  • Re-using existing materials reduces extraction of new aggregate materials and
  • The pollution caused by transporting waste to landfill sites is reduced

Admixtures for quality concrete made with recycled aggregates

Recycling preserves natural resources of gravel and sand and reduces demolition waste that otherwise would be disposed in landfills. Recycled aggregates are permitted in a wide range of construction applications and must comply with the requirements of the relevant specification. Sika admixtures allow the use of recycled concrete as an aggregate in concrete production, so that concrete of good quality and workability can be produced.

Sika Solution: Admixtures for on-site recycling of excavated material

An exemplary implementation of on-site recycling was realized during the construction of the new sport stadium in Zurich. The big challenge was the production of concrete with a constant quality using aggregates produced from material excavated on the construction site. This was only possible with a continuous adjustment of the concrete formulation and Sika’s admixture know-how. In addition to saving extraction of raw materials, more than 6'000 truck runs were avoided because fewer transports were necessary.

Life Cycle Assessment for Concrete Admixtures

Megatrends are identified which will change also the needs for building materials as concrete. The selected megatrends are:

  • „„Energy and resource efficiency
  • „„Climate change
  • „„Water scarcity
  • „„Rising need for efficient infrastructure
  • „„Rising need for hazard-free and safe products

Life Cycle Assessment (LCA) provides a method to quantify and evaluate potential environmental impacts throughout a product’s life cycle from raw material purchase through production, use, end-of-life treatment, recycling to final disposal, commonly called cradle to grave (ISO, 2006). LCA assists evaluating products and activities within the megatrend framework, namely by providing a quantitative assessment of their environmental profile. This enables to improve and differentiate products.

Cradle to gate approach:
In a "Cradle to Gate" approach, the LCA investigates the potential environmental impact of a product from raw material extraction to finished production.

For concrete admixtures four impact categories and resource indicators below are considered to be the most relevant:

  • „„Cumulative Energy Demand (net calorific value)
  • „„Global Warming Potential (GWP 100 years)
  • „„Eco Indicator 99
  • „„Input of Net Freshwater

MJ
kg CO2-eq.
points

Life cycle analysis of an ecologically optimized concrete mix design          
Parameters of comparison Concrete mix design reference Optimized concrete mix design
Mix design comparison Cement: 350 kg/m³
Additive: 0 kg/m³
Water content: (0.52) 182 L/m³
Sand: 857 kg/m³
Gravel: 1'007 kg/m³
Cement: 280 kg/m³
Additive: (Limestone) 40 kg/m³
Water content: (0.52) 145.6 L/m³
Sand: 926 kg/m³
Gravel: 1'087 kg/m³
Superplasticizer: 3.36 kg/m³
Concrete technology comparison

Fresh concrete
Flow table spread (FTS): 44 cm

Compressive strenght
1-day: 22.3 N/mm²
28-day: 40.0 N/mm²
Porosity: 4.8%

Fresh concrete
Flow table spread (FTS): 42 cm


Compressive strenght

1-day: 22.4 N/mm²
28-day: 41.2 N/mm²
Porosity: 2.8%

Economic comparison Costs / m³: 80.75 €/m³
Additional costs: more cement and water
Costs / m³: 80.25 €/m³
Additional costs: more admixture, limestone, gravel and sand
Life Cycle Impact Assessment
Cradle-to-gate (Method: CML2001 – Nov.09)
   
Input net freshwater [m³] 182 L/m³
146 L/m³
Global warming potential [kg CO2-eq.] 286 kg CO2-Equiv./m³
230 kg CO2-Equiv./m³
Cumulative energy demand [MJ] 1'196 MJ/m³
982 MJ/m³
Eco imdicator 99 [points] 4.5 points 3.7 points

Example: Ethylene Concrete Buffer Tank

A one million tons ethylene concrete buffer tank was built in Belgium. The total concrete volume is 3'461 m³. To show the benefits of using Sika® ViscoCrete® superplasticizer technology in this specific project, a Life Cycle Assessment (LCA) of two concrete systems with the same performance (w/c-ratio of 0.46) was made. The concrete system contains a superplasticizer in its recipe, while the alternative concrete system was designed to provide the same performance without the addition of a superplasticizer. The LCA is from cradle-to-gate, which includes all life cycle stages from raw material extraction and logistics to manufacturing and packaging.

Results and conclusion
To assess the gains from using the superplasticizer in terms of water and cement reduction, the input of net freshwater use, Cumulative Energy Demand and Global Warming Potential (GWP) for both concrete systems are shown below. The input of net freshwater accounts for the consumption of fresh water (e.g. feed water, ground water, lake water, river water, surface water). The GWP measures the potential contribution to climate change, focusing on emissions of greenhouse gases (e.g. CO2, CH4), which enhance the heat radiation absorption of the atmosphere, causing the temperature at the earth’s surface to rise.