Modification And Properties Of Alkali Activated Slag Under Simulated Ocean Environment

Alkali-activated slag (AAS) is a new type cementitious material which is mixed by ground granulated blast furnace slag and alkaline solutions. AAS, as one of the most potential substitutes for PC binder, has been found to have lower hydration heat, quicker development of mechanical properties and better durability than PC. However, the application of AAS so far is very limited because of its high drying shrinkage and high rate of carbonation.Besides, the use of sea water (the percentage is 97% from the total water on Earth) as the mixing and curing water of concrete is absolutely necessary. Research about the properties of sea water mixing AAS is very important to enhance the application of AAS.In this research, the effects of the modulus of alkali activator on workability and mechanical properties of AAS to identify the optimum mix proportion. The optimum mix proportion was chosen that Ms is 1.2. Based on this mixing proportion, several inverstigation was done as follow:Firstly, the effect of Metakaolin (MK), MgO and the Multi Wall Carbon nanotubes (MWCNTs) on the mechanical strengths and shrinkage properties of AAS mortar was investigated. The results showed that the addition of MK substantially increased the mechanical properties of AAS and decreased the drying shrinkage. The replacement of MK decreased the early strength of AAS, while the 10%,20% MK replacement of Slag increased the later strength and decrease the drying shrinkage. Compared to the addition of MK, the addition of MgO showed less effect on the modification of AAS. The addition of 2.5% MgO showed the best modification on AAS. Two surfactants were employed as the dispersants to evaluate the dispersion of MWCNTs. NAA/MWCNTs showed the best modification on AAS with the dosage of 0.1%.Secondly, the effect of artificial sea water (ASW) and tap water(TW) on the properties, hydration products and pore structure of alkali-activated slag was studied. The results showed that ASW decreased the early mechanical strength and had little effect on later strength. Furthermore, the addition of some salty content increased the amount of crystalline phase and changed the morphology of gel particle and pore structure.The mechanical strength development of three types of mortars (ASW mixing alkali activated slag (SAAS) mortar, TW mixing alkali activated slag mortar (TAAS) and cement slag blended (CS) mortar) after wet-dry cycle was investigated. The corrosion behavior of two types of steel bars, low carbon steel bar (LC) and low alloy steel bar (LA), in three types of mortars were tested via corrosion potential, polarization resistance (Rp), and electrochemical impedance spectroscopy measurements (Rct). During the wet-dry cycle, SAAS and TAAS mortars showed higher compressive strength than CS mortar. The Rp results showed little difference between the reinforced SAAS and the reinforced TAAS mortar. All the Rp and Rct values of the 6 mortar specimens demonstrated that corrosion rate was low.