Geopolymer based on concrete demolition waste

• It was investigated the alkaline activation of a concrete demolition waste (CDW).
• Na2SiO3 as alkaline activator contributes positively to the mechanical behavior.
• Addition of MK and OPC enhances compressive strength at ambient temperature.
• The compressive strength increased up to 46.4 MPa at 28 days of curing.
• The feasibility of using CDW as a geopolymer precursor is demonstrated.

In the present study, the synthesis of geopolymers based on alkaline activation of concrete demolition waste (CDW) was investigated using sodium hydroxide and sodium silicate as alkaline activators. To produce hybrid and binary geopolymers, Portland cement and metakaolin were added at levels up to 30% by weight with respect to the CDW. The effect on the compressive strength of Na2O/SiO2 and SiO2/Al2O3 molar ratios and type of curing (room temperature and thermal curing) was evaluated. To characterize the morphology and structure of the geopolymer pastes, techniques such as X-ray diffraction, infrared spectroscopy, and scanning electron microscopy were used. The highest compressive strength was obtained in systems activated with sodium silicate, which enabled geopolymer synthesis at room temperature. The simple geopolymer, based on 100% CDW, reached a maximum compressive strength of 25 MPa, and the hybrid geopolymer CDW + 30% OPC reached 33 MPa at 28 days with curing at room temperature. In the case of the binary geopolymer CDW + 10% MK, a significant increase in compressive strength was observed, reaching 46.4 MPa at 28 days of curing without applying thermal curing. The results obtained in the present study demonstrate the feasibility of using concrete demolition wastes as precursors to obtain geopolymer cements.

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