Effect of electric arc furnace dust on the properties of OPC and blended cement concretes

Abstract

This paper presents results of a study conducted to evaluate the mechanical properties and durability characteristics of ordinary Portland cement (OPC) and blended cement (silica fume and fly ash) concrete specimens prepared with electric arc furnace dust (EAFD). Concrete specimens were prepared with and without EAFD. In the silica fume cement concrete, silica fume constituted 8% of the total cementitious material while fly ash cement concrete contained 30% fly ash. EAFD was added as 2% replacement of cement in the OPC concrete and 2% replacement of the total cementitious content in the blended cement concretes. Mechanical properties, such as compressive strength, drying shrinkage, initial and final setting time, and slump retention were determined. The durability characteristics were evaluated by measuring water absorption, chloride permeability, and reinforcement corrosion. The initial and final setting time and slump retention increased due to the incorporation of EAFD in both OPC and blended cement concretes. The drying shrinkage of EAFD cement concrete specimens was more than that of concrete specimens without EAFD. The incorporation of EAFD was beneficial to OPC concrete in terms of strength gain while such a gain was not noted in the blended cement concretes. However, the strength differential between the blended cement concretes with EAFD and the corresponding concretes without EAFD was not that significant. The water absorption and chloride permeability, however, decreased due to the incorporation of EAFD in both the OPC and blended cement concretes. The corrosion resistance of OPC and blended cement concrete specimens increased due to the addition of EAFD.

Introduction

Electric Arc Furnace Dust or EAFD is generated as a by-product during Electric Arc Furnace steel making process. It is in the form of very fine powder forming major part of the smoke or fume from the furnace. The powder from the furnace is drawn through cooling pipes and collected by specially designed bag filters. EAFD consists mostly of iron oxide (approx. 50%) and zinc oxide (approx. 21%). Other constituents include: oxides of calcium, magnesium, silicon, nickel, chromium, etc. The quantity of EAFD generated is about 1% of the steel produced. Worldwide approximately, 70% of EAFD is sent for land fill, the remaining 30% is processed for Zn recovery and other purposes. Due to the leachability of heavy metals, such as zinc, chromium and nickel, EAFD is termed as hazardous material by World Environmental Protection Agency (EPA) and therefore, needs to be disposed off after its stabilization. Earlier studies were focused on the chemical fixation of EAFD, such that its leachability is reduced. Some of the methods involved solidifying the EAFD using proprietary processes that may require the addition of cement or other cementitious materials. The world steel industry spends approximately $50–250 per ton to stabilize EAFD for landfill or process it for Zn recovery. In the plant under study, nearly 70% of EAFD generated is being utilized for the past couple of years as feed material for cement manufacture, while the remaining quantity is stockpiled.

Earlier studies conducted on the use of EAFD in concrete have indicated that it improves the properties of both fresh and hardened concrete [1], [2]. The initial and final setting time of cement concrete incorporating up to 2% EAFD was reported to be more than that of concrete without EAFD [1], [2]. However, the slump retention of EAFD cement concrete was reported to be superior to that of normal and plasticized cement concrete mixtures. A 15–30% increase in the 7 and 28 days compressive strength of concrete was also reported due to the addition of EAFD [1], [2].

Sikaldis and Mitrakas [3] investigated the properties of extruded clay-based ceramic building products fired at various temperatures (850–1050 °C), as well as dolomite-concrete products with up to 20 wt.% EAFD. The chemical, mineralogical and particle size distribution were performed in order to characterize the EAFD used in that study [3]. The water absorption, firing shrinkage, apparent density, mechanical strength, color, and leaching behavior of the ceramic specimens was reported to be within the acceptable limits. Addition of 7.5–15 wt.% EAFD was reported to improve the properties, while 20 wt.% EAFD was not beneficial. Dolomite-concrete specimens were prepared by vibration and press-forming of mixtures containing cement, sand, dolomite aggregate, EAFD and water. The modulus of rupture of the concrete was reported to increase significantly due to the addition of EAFD. It was reported that leaching tests showed stabilization of all toxic metals within the sintered ceramic structure, while they indicated that leaching behavior of lead in dolomite-concrete products needs further detailed study [3].

Xuefeng and Yuhong [4] evaluated the chemical composition and physical properties of EAFD for its possible application in the cement production. It was reported that the quality of cement produced with EAFD meets the Chinese specifications for cement. Further, it was reported that the use of EAFD in cement is more economical that the use of iron ore [4].

Sorlini et al. [5] investigated the potential reuse of Waelz slag (modified EAFD) as a partial substitution of the natural aggregate in concrete production. The Waelz process was utilized to convert EAF dust (with zinc concentration of 18–35%) into an impure zinc oxide, called Waelz oxide (with zinc concentration of 55–65%), that can be reprocessed in metallurgical plants. During the Waelz process, EAFD and pellets are mixed with coke breeze (reducing agent) and other additives (lime or gypsum) and are continuously fed into the rotary kiln. The furnace temperature, 700–800 °C, allows a reduction and vaporization of zinc (and other volatile metals like lead and cadmium), and a consequent oxidation/condensation that generates an impure zinc oxide, called Waelz oxide [5]. It was reported that Waelz slag can be successfully reused as aggregates for concrete mixtures [5]. The environmental compatibility of the Waelz slag aggregate was confirmed by leaching tests, which show a similar behavior between the reference and the waste-containing concrete.

Previous studies were concentrated on utilizing EAFD in ordinary Portland cement concrete [1], [2], [3], [4], [5]. However, there is a need to investigate the compatibility of EAFD with blended cements. Since supplementary cementing materials, such as fly ash and silica fume, are invariably used in the present day concrete it is recommended to evaluate the compatibility between EAFD and blended cements. Further, the importance of such studies emanates from the fact that there is an increasing awareness worldwide to utilize waste materials in concrete with the aim of reducing the consumption of cement thereby decreasing the green house gas emissions.