A Study into the Use of Recycle Iron and Steel Slag as an Alternative Aggregate in Concrete Production

Abstract

The study researches into the use of recycle iron and steel slag as an alternative aggregate to granite in concrete production. X-ray diffract meter (XRD) and scanning electron microscopic (SEM) were implored to assess the mineral composition and morphology of the aggregate; mechanical properties of the aggregates that were assessed includes sieve analysis, water absorption, bulk specific gravity and Los Angeles abrasion value. In this study the workability of fresh concrete was assessed using slump and compacting factor tests and the strength of the concrete was assessed using the uniaxial compressive strength test to establish the suitability of recycle iron and steel slag aggregate as alternative aggregate in concrete production. Concrete of M20 grade was considered for a water cement ratio of 0.60 using 1:2:4 mix ratio, slag aggregate replacements were observed from 0 to 100% at interval of 10%.  The results of experimental investigations carried out to evaluate the fresh and hardened concrete properties showed that the slump value at 100% granite was 17mm (true slump) while at 100% slag was 28mm (shear slump); while the compacting factor are 0.79 at 0% slag replacement and 0.87at100% slag replacement; which confirms that concrete casted with granite is more workable than concrete casted with slag aggregate. The compressive strength at 7,14, 21 and 28days for the control cubes of 0%, 50% and 100% slag content are; 23.11, 21.78, 24.44 and 27.79N/mm²;  13.78, 20.00, 20.67 and 29.89N/mm² ; and 19.56, 22.67, 24.00 and 23.33N/mm² respectively. The results showed that maximum strength is obtained at 50% slag replacement; though all the results met the requirement of 20N/mm² by standard BS 5328: part 1: 1997. The results of mineral composition and morphology showed that granite and slag aggregates contained (70.2, 11.56, 1.19, 1.12, 0.96, 0.75, 3.26, 3.41, 0.00, 0.08 and 0.05) % and (13.7, 1.68, 10.32, 24.08, 45.16, 7.31, 0.19, 0.04, 0.03, 0.81 and 5.89) % of minerals composition respectively. The water absorption, abrasion value and specific gravity of granite and slag aggregate are (0.12%, 20.0 and2.20) and (0.82%, 23.0, and3.54) respectively. The result showed that the slag aggregate is more porous and absorbed water than granite aggregate and great care must be taken when using slag aggregate in concrete production as reduced water-cement ratio as compared to granite aggregate is required for better performance ; adequate stalking is also required prior to usage.  Based on overall observations it could be recommended that slag could be utilized as coarse aggregate in concrete production either as partial or full replacement of granite aggregate.

Keywords: granite, iron and steel slag, X-ray diffract meter (XRD), scanning electron microscopic (SEM), mineral composition and morphology.