Ready-mixed concrete

The ready-mixed concrete industry uses by-products from other industries such as fly ash, ground granulated blastfurnace slag (GGBS) and silica fume to reduce its environmental burden where product performance can be retained or enhanced. At present the use of these alternative materials is running at between 10 and 15%.
 
A very high proportion of ready-mixed plants have a silo containing one of these additions. Adding additions at the concrete mixer allows a concrete producer to satisfy a range of customer needs by combining Portland cement and additions in different proportions.
 
Typically 30% of Portland cement can be replaced with fly ash, or 40 to 50% with GGBS in the concrete mix. In conditions that require sulfate-resisting cement (for example, foundations in soil with a high sulphate content), the proportion of GGBS can be increased to 70%.
 
The use of recycled water is common but not yet universal amongst ready-mixed concrete manufacturers. A recent survey of a limited number of companies found that about 40 to 50% of plants use recycled water.
 
Recovered returned concrete is obtained by washing the cement paste out of fresh concrete, returning the aggregates to the aggregate stockpile and storing the cement paste in a separate storage basin from which it can be recycled into further batches of concrete.
 
Recycled aggregates comprise crushed, graded, inorganic fragments processed from materials that have been previously used in construction, e.g. crushed concrete and masonry. The rules for the use of recycled materials in concrete in BS 8500 has overcome technical barriers to their use.
 
A number of companies are setting up recycling operations, and the new concrete standard allows all potentially available materials to be reused. It is clear that recycling activities will reduce waste and conserve natural resources. Whether or not they improve the total environmental performance of the concrete depends on other factors such as location of construction site, type of aggregate and the supply of primary aggregates in the locality. As a rule of thumb, using recycled aggregates is an environmentally-sound option so long as they do not travel more than 30 miles by road from their point of source.
 
The majority of the larger ready-mixed companies are introducing environmental management systems: either aiming for ISO 14001 certification or following these principles without formal recognition and certification. These companies account for approximately 95% of UK production. Although some of the smaller companies may not currently have formal environmental management policies they still have to operate within strict environmental standards.