Case Studies in Construction Materials (Dec 2023)
Determining the content of steel furnace slag in asphalt concrete
Abstract
Steel furnace slag containing heavy metal components is covered by asphalt cement when it is used to replace natural aggregates in road paving. When such a pavement deteriorates as a result of wear by people and vehicles as well as washing by rain, the aggregates are worn away and the heavy metal components within can overflow on the road’s surface, forming rust spots. This phenomenon has been observed on many roads, leading the general public to question the validity of using steel furnace slag and whether this is in violation of a contract with the contractor. However, it is known from literature that such rust spots on a road surface may also be caused by natural minerals such as pyrite that are contained in natural aggregates. Unlike cement concrete, the slag cannot be separated from the mixture after hardening; however, the asphalt cement can be separated from the aggregates by using a solvent. In this study, separated aggregates are tested for pH value, magnetic attraction, and elemental composition in order to assess the usability of slag. Based on the findings and the characteristics of steel furnace slag, this paper proposes a method for detection of steel furnace slag in asphalt concrete, which is divided into two stages. In the first stage, core samples of asphalt concrete are obtained from the road site. The asphalt cement is separated from the aggregates according to AASHTO T164 and then the separated aggregates are analyzed in pH value and magnetic attraction tests. When one or both of the tests indicate steel furnace slag characteristics, that is, alkalinity or magnetism, then it is possible that the asphalt concrete sample contains steel furnace slag, and should be tested in the second stage for further confirmation. In the second stage, the separated aggregates are grinded to less than 0.075 mm (No. 200) and their elemental composition is analyzed. Based on the composition of steel furnace slag, when the analysis results indicate ≥30 % CaO and ≥10 % Fe2O3, it can be regarded that steel furnace slag has been used in the asphalt concrete.
