Experimental Study on the Effects of Recycled Concrete Powder on Properties of Self-Compacting Concrete

Although hundreds million tons of concrete wastes have been generated annually in China, the use of recycled aggregate for concrete is limited because of low density and high absorption due to adhered cement paste and mortar.

A new method to produce high quality recycled aggregate by heating and grinding concrete rubbles to separate cement portions adhering to aggregate was developed recently. In this process by-product powder with the fineness of 400m²/kg is generated. By-product recycled fine powder consists of fine particles of hydrated cement and crushed aggregate. To use the recycled fine powder as concrete additives two series of experiments were performed to make clear of the effect of recycled fine powder.

Self-compacting concrete with recycled fine powder, granulated blast furnace slag and granulated limestone were tested for slump flow, compressive strength, modulus of elasticity and drying shrinkage. Reduction in super plasticizing effect of high range water reducer was found for concrete with recycled powder. Compressive strength of concrete with recycled fine powder was the same as those with granulated limestone, and lower than those with granulated blast furnace slag. Concrete with recycled fine powder showed lower elastic modulus and higher drying shrinkage than those with granulated blast furnace slag and granulated limestone. The recycled fine powder is usable for self-compacting concrete without further processing, despite the possible increase in dosage of high range water reducer for a given slump flow and in drying shrinkage. The addition of granulated blast furnace slag together with recycled powder to self-compacting concrete improved super plasticizing effect of high range water reducer and properties of concrete.