Effect of steel slag and steel sludge on concrete properties

Abstract

The wastes generated from steel industries are known to be as sludge and slag. The problem with some of these by-products is they contain large amount of heavy metals that can be leached out to the environment and cause pollution. Several studies have been conducted on steel slag as a replacement for cement in concrete but it is still not sufficient and well established. However, there is no significant research carried out using steel sludge in concrete. This study represents the results of electric arc furnace steel slag and steel sludge for replacing cement materials. Both materials were investigated for their pozzolanic properties, strength, and durability. Initially, the steel slag and steel sludge were screened for pozzolanic properties using pozzolanic activity test based on ASTM C618 and thermogravity method. Then they were incorporated in concrete mixes by replacing cement from 5% to 20%. The specimens were tested at its fresh and hardened state. The fresh concrete was also tested for slump and concrete grade 25 for its strength and durability at 7, 28 and 90 days. For durability performance, the specimens were tested for their initial surface absorption, water absorption and leaching test. The morphology testing of the concrete was also carried out. It was found that steel slag and steel sludge showed positive pozzolanic activity based on pozzolanic activity test. In addition, it was found that the compressive strength for concrete containing steel slag and steel sludge increased up to 10% replacement and started to decrease in strength beyond the replacement level. It clearly shows that 10% replacement of steel slag and steel sludge is the optimal percentage that is required for the replacement. In case of durability, both replacement of cement by steel slag and steel sludge can be categorised as low permeability. Denser structure, less pores and rougher surface were seen in the morphology of 10% steel slag. The heavy metals are found to be effectively solidified and stabilized in the cement-based matrix. In conclusion, steel slag and steel sludge showed good potential to be used in the replacement of cement materials. Moreover, the use of steel slag and steel sludge in concrete can certainly help in preserving the environment.