Experimental Behavior of Reinforced Concrete

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Experimental Behavior of Reinforced Concrete Beams with Electric Arc Furnace Slag as Recycled Aggregate Article in Aci Materials Journal · March 2013 DOI: 10.14359/51685534

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Carlo Pellegrino

University of Padova

University of Padova

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ACI MATERIALS JOURNAL

TECHNICAL PAPER

Title no. 110-M19

Experimental Behavior of Reinforced Concrete Beams with Electric Arc Furnace Slag as Recycled Aggregate by Carlo Pellegrino and Flora Faleschini The aim of this study is to investigate the possibility of partially substituting natural aggregates with black/oxidizing electric arc furnace (EAF) slag for reinforced concrete (RC) structural elements. International research has been mainly focused on experimental tests on small specimens rather than investigating the behavior of RC structural elements. In this study, the experimental behavior of RC beams made with EAF slag as aggregate was studied showing that these beams have both ultimate flexural and shear capacity higher than the corresponding traditional beams. Some comparisons between experimental results and analytical predictions according to the European and U.S. recommendations were also shown. The main result of this study is that the use of steel slag as aggregate in RC structural elements is, in principle, possible, and the rate of substitution could reach the entire part of coarse aggregates, obtaining benefits both from an economical and environmental point of view. Keywords: beams; bending; electric arc furnace slag; reinforced concrete; shear; sustainable development.

INTRODUCTION In recent years, problems linked to industrial material landfill disposal has become more and more relevant to society, with cost increases for environment and municipalities. Directive 2008/98/EC of European Parliament and Council established the legislative framework for handling of waste in Europe—the first objective was the minimization of negative impact of waste management on human health and environment, applying waste hierarchy, and supporting reduction of natural resources. As a consequence, waste reutilization becomes attractive to reduce economical costs and potential pollution problems, and preserve natural raw resources. In this context, construction materials are very significant because they represent the 3 to 4% of the total product in Europe,1 and their environmental impact related to the use of natural aggregates in traditional concrete could be limited using a series of alternative solutions. Nowadays, there are, among others, two significant possibilities: the use of recycled concrete from construction and demolition waste,2-4 and the use of slag from metallurgical industrial production.5-8 Steel production takes place in two types of plants: basic oxygen furnace (BOF) and electric arc furnace (EAF) plants. The latter ones produce more than 40% of global steel and, differently from the others, they are used for scrap metal recycling, aiming to a more sustainable production. Black/ oxidizing slag (also called EAF slag) production in Europe is approximately 10 million tons every year9 and is destined to grow because of the increase in the use of this technology. In 2009, steel production in Italy represented approximately 14% of the total European steel industry, yielding a considerable quantity of EAF slag during the production cycle.10 EAF slag is the main by-product of steel production, and it could be classified into two types: black basic slag, with ACI Materials Journal/March-April 2013

a lime content less than 40%, resulting from the cold loading of scrap; and white basic slag, with a lime content higher than 40%, generated during grinding, when more lime is added to remove sulfur and phosphorus from the produced steel.11 Chemical composition, microstructure, texture, and morphology of slag mainly depend on slag origin, affecting the further behavior of the material. The main compounds in EAF slag are oxides: approximately 85% is a set of iron, calcium, aluminum and silicon oxides, plus minor amounts of manganese and magnesium. Chemical stability of the material could be a problem affecting the use of slag as concrete aggregate: disintegration or expansive compounds should be in small quantities to allow a further use in concrete production. Free CaO, MgO, or sulfide oxides could hydrate, increasing their molecular volume and then modifying crystalline lattice. A proper pretreatment, aimed to stabilize slag by exposing them to outdoor weather and regular spraying for at least 90 days, may strongly reduce subsequent expansive phenomenon.12 In the aforementioned general context, the scientific research on investigating the possibility of partially substituting natural aggregates with black/oxidizing EAF slag for reinforced concrete (RC) structural elements has been mainly focused on experimental tests on small specimens (for example, cubic or cylindrical specimens specifically designed to study mechanical properties and durability of the concrete) rather than investigating the behavior of RC structural elements. Because very little research is available on structural elements (for example, beams) made with recycled concrete, and these are mainly related to the use of aggregates derived from building demolition waste, this experimental study aims to investigate the opportunity of partially substituting natural aggregates of concrete with EAF slag. The main purpose of this research is to test a new, sustainable building material allowing to save raw materials, reduce energy consumption, and recycle industrial by-products; and contribute to the existing knowledge on flexural and shear behavior of RC structural elements made with concrete containing EAF slag as a partial substitution of natural aggregates. This experimental study first shows the physical/mechanical and chemical characterization of traditional and recycled concrete, according to Fuller’s ideal grading curve. Structural behavior was then investigated by means of four-point bending tests on RC beams made with traditional and recycled aggregates, subjected to both flexural and shear failure. Maximum load, deflections, crack patterns, and crack widths ACI Materials Journal, V. 110, No. 2, March-April 2013. MS No. M-2011-350.R1 received June 3, 2012, and reviewed under Institute publication policies. Copyright © 2013, American Concrete Institute. All rights reserved, including the making of copies unless permission is obtained from the copyright proprietors. Pertinent discussion including author’s closure, if any, will be published in the January-February 2014 ACI Materials Journal if the discussion is received by October 1, 2013.

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Carlo Pellegrino is Assistant Professor in the Department of Civil, Environmental, and Architectural Engineering, University of Padova, Padova, Italy. He received his PhD in structural mechanics at the University of Bologna, Bologna, Italy. His research interests include bridge design and management, structural behavior of recycled concrete, and fiber-reinforced polymer strengthening of reinforced concrete and steel structures. Flora Faleschini is a PhD student at the University of Padova, where she received her master’s degree. Her research interests include structural behavior of recycled concrete, and mechanical and durability characteristics of recycled materials.

Table 1—Physical properties of slag Diameter range, mm

4 to 22

Apparent specific gravity, kg/m3

3876 to 3900

Water absorption, %

0.4 to 0.5%

Shape

Sharp-pointed

Fineness modulus

6.59 to 7.78

Shape index (4 to 8 mm), %

2.2


2.7


1.5

Flakiness index (4 to 8 mm), %

4.4


6.1


3.6

focused on experimental tests on small specimens rather than investigating the behavior of RC structural elements. For these reasons, this experimental study aims to increase the knowledge of flexural and shear behavior of RC structural elements made with concrete containing EAF slag as a partial substitution of natural aggregates.

Note: 1 mm = 0.0394 in.; 1 kg/m3 = 0.0624 lb/ft3.

Table 2—Leaching tests results Element

Concentration, mg/L

Limits

Nitrates