CEMENT-FREE AND LOW-CEMENT PRESSED MATERIALS BASED ON DISPERSED CONCRETE WASTE

Abstract

Concrete waste, pressing, thermoactivation, strength, water resistance, curing.

The scientific and practical task of this study was to assess the possibility of producing pressed cement-free and low-cement materials based on dispersed concrete waste and to determine the technological factors governing their structure formation and properties. The raw material was a fine fraction of crushed concrete debris smaller than 0.14 mm, used as the main solid component for semi-dry pressing. Four systems were studied: untreated dispersed concrete waste, thermally activated waste, and compositions containing 2.5% and 5% Portland cement. The influence of moulding moisture, pressing pressure, and curing conditions on compressive strength, density, and water resistance was evaluated.

The results showed that the properties of the pressed materials are controlled by the combined effect of moisture content, compaction pressure, and curing regime. For the investigated system, rational technological parameters were a moisture content of 12-13%, a pressing pressure of 20 MPa, and air-moist curing. Under these conditions, cement-free and low-cement pressed materials with gradual strength development were obtained. It was established that both thermal activation of dispersed concrete waste at 600 °C and the introduction of small amounts of Portland cement improved compressive strength and water resistance. The highest performance was achieved for the composition with 5% cement, which reached a compressive strength of 12.8 MPa and a softening coefficient of 0.86 at 28 days. Thermal activation also proved effective, providing a 28-day strength of 11.4 MPa without a substantial increase in cement content. The obtained results confirm the prospects of using dispersed concrete waste as a structurally active component of pressed building composites.

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