Physico-chemical, mechanical, microstructure and durability characteristics of alkali activated Egyptian slag

• Alkali activator contents affected the location and intensities of the conductivity maximum.
• Mix S5 shows the higher values of compressive strength at all curing ages up to 90 days.
• Mix S1 shows higher values of strength in 5% MgSO4 or MgCl2 solution upto 180 days.
• Alkali activated GBFS improves the durability and the resistance to chemical attack.
• The total chloride and total sulphate contents decrease with alkali activated GBFS.

The aim of the present work is to study the characteristics of alkali activated Egyptian slag (GBFS) mixed with different contents of Na2O and SiO2. The rate of the kinetic of activation of GBFS has been studied by electrical conductivity, FTIR, DTA/TGA, XRD and SEM techniques. Electrical conductivity of alkali activated slag systems depends mainly on the binder composition, the activator type and its concentration. The increase in alkali activator contents affected the location and intensities of the conductivity maximum. As the hydration time increases the amount of hydration products increase, hence the chemically combined water and combined slag contents increase. SEM images showed the presence of (N,C)ASH gel with low porosity. With the increase of the content of Na2O leads to form a denser closed microstructure, leading to higher compressive strength values. The activated GBFS showed good durability in 5% MgSO4 or 5% MgCl2 solution, i.e., the compressive strength increased gradually with immersing time up to 180 days. The total chloride and total sulphate contents decrease with alkali activated GBFS due to the forming hydrated products that fill some available open pores, thereby inhibiting Cl− or SO42− ions penetration; this effect leads to a decreased accessibility of Cl− or SO42− ions towards the more dense with low capillary pore structure. It can be concluded that alkali activated GBFS are more durable in 5% MgSO4 or 5% MgCl2 than OPC pastes.