Mechanical properties of alkali activated slag concrete with ultra fine dredged sand from Yangtze River

The physical and chemical properties of ultra-fine dredged sand in the lower reaches of the Yangtze River were analyzed. Five kinds of alkali activated slag concrete (AASC) mix proportions with different contents of ultra-fine dredged sand were designed. The fluidity, compressive strength, splitting tensile strength, density and water absorption were studied. The microstructure and phase composition of AASC were analyzed by SEM, XRD and mercury intrusion porosimetry (MIP). The results show that the fineness modulus of the ultra-fine dredged sand is between 0.1 and 0.5. With the increase of ultra-fine dredged sand content, the compressive strength and splitting tensile strength first increase and then decrease, while the fluidity continues to decline. When the dredged sand content (mass ratio to fine aggregate) reaches 50%, AASC obtains proper mechanical properties and workability. The results of water absorption, density test, SEM observation and MIP test show that the appropriate addition of dredged sand can increase the compactness of concrete and improve the structure of interface transition zone, but excessive dredged sand can reduce the fluidity of concrete and increase the porosity of concrete.