Basic Mechanical Properties and Microscopic Characteristics of Alkali-Activated Slag/Fly Ash Concrete Incorporating Dredged Sand

To improve the utilization efficiency of dredged sand and alleviate the depletion of natural aggregate resources, ultrafine dredged sand (DS) was used as a fine aggregate replacement to prepare alkali-activated slag/fly ash concrete. The effects of DS and fly ash (FA) replacement rates on the workability and mechanical properties of the concrete were investigated. XRD, SEM, and MIP tests were conducted to analyze the hydration products, micromorphology, and pore structure, and the underlying modification mechanism of DS for alkali-activated concrete was clarified. The results show that, compared with the group without dredged sand, the 3 d, 28 d, and 90 d cubic compressive strengths of the group with 30% dredged sand increased by 8.35%, 9.3%, and 9.8%, respectively. Appropriate incorporation of dredged sand can optimize the pore distribution and microstructure, improve the compactness of the concrete matrix, and significantly enhance both the early and later strength of alkali-activated concrete. The 28 d compressive strength and splitting tensile strength of AASC both increase first and then decrease with the rising FA dosage. Moreover, the incorporation of fly ash exerts a remarkable enhancement effect on its later strength.