An experimental investigation on self-compacting alkali activated slag concrete mixes

In present work, an attempt has been made to develop self-compacting, alkali activated slag concrete mixes, using steel slag sand as fine aggregate and EAF (Electric Arc Furnace) slag as coarse aggregate. The study investigates the properties such as compressive strength, splitting tensile strength and water absorption of these mixes. Development of Self-Compacting Alkali Activated Slag Concrete mixes (hereafter referred to as SCAASC mixes) was made with GGBFS (Ground Granulated Blast Furnace Slag) as the binder, with its content varying between 700 kg/m3 and 900 kg/m3 of fresh concrete. The net W/B (water to binder) ratio of the mixes was varied between a narrow 0.47 - 0.48 range. The alkaline solutions had Na2O percentages in the range 7 - 9%, but a constant activator modulus was maintained at 1.0 in all the mixes. In order to optimise the number of trial mixes to be tested, Taguchi's design of experiments methodology was adopted. A total of nine mixes were formulated using Taguchi orthogonal L9 array. Results showed the slump flow values for the mixes greater than 700 mm, with their L-Box ratios and V-Funnel values ranging between 0.90 and 0.95 and 9 - 11 s respectively, satisfying the EFNARC guidelines. Results also showed good compressive strengths (65-80 MPa), split-tensile strengths (2-4 MPa) and low water absorption values in the range of (2%-3%). The microstructural studies such as SEM, EDX and XRD analysis were also carried out, showing denser morphologies clearly indicating effective activation of slag by the alkaline solution.