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Recycled aggregates

The steep growth of the construction sector resulted in massive consumption of earth resources. The using of recycled aggregates will help in preserving the environment. The construction waste amount increased rapidly in recent years. Undoubtedly, the recycling of construction waste such as concrete will help in safeguarding environments resources and ensure sustainability. Recycled aggregates can replace part of natural aggregates used in concrete. Natural aggregates can be replaced by 20% of recycled aggregates for all concrete classes, and 100% for a limited classes of concrete according to RILEM Technical recommendations. The using of recycled aggregates will produce concrete with lesser compressive strength and quality.

Figure 1

Most of the recycled aggregates produced from concrete waste. Aged concrete such as old foundation, bridges, building, and concrete pavements are the primary sources of concrete waste. Aged concrete is crushed and processed to produce recycled aggregate. Concrete used to produce recycled aggregates should not be contaminated with other materials such as gypsum, plaster, and other construction materials. Therefore concrete material should be stored in a separate pile to prevent the contamination, which will result in impairing concrete properties and reducing the quality.

Most recycling plants have primary and secondary crushers. The primary crusher handles large pieces of concrete and reduces the material size to 60-80 mm. The secondary crusher fed with the materials from a primary crusher. The crushed materials from secondary crusher are sieved. Aggregates with size bigger than 19mm are fed back to the secondary crusher. The aggregate with sizes of 7-19mm screened to use as a recycled coarse aggregate.

The using of recycled aggregates will produce concrete with higher drying shrinkage and lower concrete compressive (10-30% reduction). Recycled aggregates have a high-water absorption (up to 6%). Yet, the recycled aggregate will reduce the cost of concrete and preserve the environment by reducing the emissions and reducing the feverish consumption of earth resources.


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