EFFICIENCY OF THE CONCRETE WASTE DISPERSED FRACTION ACTIVATION AS AN MINERAL ADDITIVE FOR PORTLAND CEMENT

Abstract

The article presents experimental results on the feasibility of using crushed concrete waste (dispersed particles smaller than 1 mm remaining after sieving out coarser fractions intended for use as recycled aggregate) as a complete or partial replacement for ground granulated blast furnace slag in the production of Portland cement. Experimental studies have shown that the introduction of concrete waste without additional activation may lead to a reduction in the standard compressive strength of Portland cement. Activation of the dispersed fraction of concrete waste is achieved by increasing its fineness, the combined use of active mineral additives, and alkali-fluoride salts.

A full range of standard tests was conducted on the resulting cements, including determination of granulometric characteristics, chemical composition, water demand, setting times, compressive strength, and activity index. It was shown that the composition of concrete waste, particularly the content of cement paste and calcium hydroxide formed as a result of the hydrolysis during clinker minerals hydration, plays an important role. The significance of the content of cement paste and calcium hydroxide in the dispersed fraction of concrete waste formed during hydration was confirmed.

The application of activation measures in the introduction of 15% of the dispersed fraction of concrete waste in combination with blast furnace slag made it possible to obtain Portland cement that meets standard performance requirements.