Development of Sustainable Cement-Based Materials with Ultra-High Content of Waste Concrete Powder: Properties and Improvement

Abstract

The recycled powder (RP) of construction waste, as a kind of silica–aluminum waste, can have a certain gelling effect after alkali activation modification. Sodium silicate (water glass) and NaOH are used as composite alkali activators to stimulate RP to prepare alkali-activated mortar. The different micro and macro properties of RP are studied under the ultra-high substitution rates of 70%, 80%, 90%, and 100% of cementation-based materials. The results show that the mechanical properties of the regenerated powder mixture decrease gradually with the increase in the substitution rate. When the replacement rate of RP is 70%, the 3 d and 28 d compressive strength decreases by 73.63% and 69.46%, respectively. When the replacement rate reaches 100%, the 3 d and 28 d compressive strength decreases by 96.98% and 93.74%, respectively. The cement-based material after alkali excitation has the characteristics of early strength and the mechanical properties are greatly improved, and the mechanical properties of cement-based materials can be effectively increased by increasing the modulus of water glass. At 70%RP substitution rate, the compressive strength of 28 d increases by 3.59% and 107.71% when the modulus of sodium silicate is 1.0 M and 1.6 M, compared with the unactivated groups. At 100%RP substitution rate, the 28 d strength of the unexcited specimen is 0.92 MPa, and the 28 d compressive strength reaches 6.15 MPa and 12.86 MPa when the modulus of sodium silicate is 1.0 M and 1.6 M. The results show that the alkali-activated mortar has good application potential.