Studies on Processed Granulated Blast Furnace Slag as Fine Aggregate in Mortars and Concrete
Fine aggregate is essential for the preparation of mortar and concrete. There are attempts to find alternatives to the river sand as the natural sources for fine aggregates are dwindling. Currently, sand mining from river bed has been banned in several countries including India. Different industrial by-products and non-organic solid wastes are being explored to meet the growing need for fine aggregates. The steel industries produce huge quantities of slag, especially blast furnace and steel slag. The main focus of the investigations was on exploring the feasibility of using the granulated blast furnace slag (GBS) as a substitute for river sand in the mortars and the concrete. The GBS sourced from a local steel industry caused difficulty in handling (sharp edges and flaky/needle-shaped particles) and leading to poor workability for the mortar and the concrete. Therefore, the processed GBS designated as PGBS was used in the experimental investigations. The experimental investigations were focused on (i) characterising the properties of PGBS (ii) exploring the characteristics of the mortar and the masonry using PGBS as fine aggregate, and (iii) investigating the influence of PGBS on mechanical and durability characteristics of the concrete. The characteristics of the mortars (using PGBS aggregates) investigated include workability, water retentivity, strength, and stress-strain characteristics. The hydration products in the mortars with PGBS and river sand were quantified using thermogravimetric techniques (TGA). The impact of PGBS inclusion in mortars on the masonry flexure bond strength and compressive strength were investigated. Similarly, the characteristics of the concrete (in the fresh and hardened state) were investigated by replacing the river sand with PGBS (25, 50, 75 and 100%). The workability, shrinkage, compressive strength, tensile strength, rebar bond strength, stress-strain characteristics and the durability of the concrete were examined. The X-Ray diffraction and TGA techniques were employed to identify and quantify the hydration products in the concrete. The durability tests on concrete were aimed at determining the chloride penetration, the initial rate of absorption, water penetration and absorption. The permeable porosity and the pore area fraction of the concrete with and without PGBS were investigated to supplement the durability experimental results. The results revealed that (i) the PGBS showed mild pozzolanic activity which increased the long-term strength of the mortars and the concrete, and (ii) both the mortar and the concrete with PGBS showed lower workability than the workability of corresponding river sand based mortar and concrete. A marginal increment in the water-binder ratio of mortars and the use of suitable super-plasticisers resolved the workability issues. The TGA and XRD analysis on the mortar and the concrete confirmed the pozzolanic reactivity of PGBS particles. The limiting values from the durability statutes and the values from the literature indicate that the durability performance of PGBS based concrete was analogous to the concrete with natural aggregates. The major findings of the research work showed that the mortar and the concrete can be prepared using PGBS alone as fine aggregate, with no detrimental effects on the mechanical and durability characteristics of the concrete as well as the mortars used for the masonry construction.