Elsevier

Construction and Building Materials

Volume 127, 30 November 2016, Pages 144-152
Construction and Building Materials

Strength properties and micro-structural analysis of self-compacting concrete made with iron slag as partial replacement of fine aggregates

https://doi.org/10.1016/j.conbuildmat.2016.09.154Get rights and content

Highlights

  • Utilization of iron slag in self-compacting concrete (SCC).

  • Iron slag (10–40%) improved the strength properties of SCC.

  • Iron slag improves the microstructure of SCC.

Abstract

The iron and steel rolling mills are the main source of the production of iron slag. This paper presents the results on an experimental program carried to explore the possibility of use of iron slag as partial replacement of fine aggregate (sand) in self-compacting concrete (SCC). SCC mixes were designed and fine aggregates were replaced with 0, 10, 25, and 40% iron slag. Tests were performed to evaluate the fresh properties, strength properties and micro-structural analysis of SCC. Properties such as slump flow, V-funnel, U-box, L-box, compressive strength, splitting tensile strength, flexural strength and modulus of elasticity were examined. Results indicated that compressive strength, splitting tensile strength and flexural strength of self-compacting concrete improved with incorporation of iron slag at all the curing ages. SEM and XRD analysis were done to examine the microstructure, which indicated that use of iron slag made the microstructure of SCC denser.

Introduction

Concrete is compacted by vibrations in order to expel entrapped air, making it denser and homogeneous because compaction is necessary to produce durable concrete [1]. Full compaction is difficult due to heavy reinforcement, as a result self-compacting concrete (SCC) was developed in early 1980’s [2]. Self-compacting concrete (SCC) can be defined as a concrete which can be placed with its own weight with or without vibration. It facilitates and ensures proper filling and good structural performance of heavily reinforced congested members.

Natural sand (fine aggregates) is getting depleted due to increased consumption of concrete. As a result, substitutes of natural sand are being explored by using waste materials and industrial byproducts. Strength and durability properties are significantly affected by type of fine aggregates [3]. There are several types of industrial byproducts which can be used as fine aggregates in concrete. One such byproduct is iron slag (IS). During the production of iron in blast furnace, blast Furnace Slag is formed when iron ore or iron pellets, coke and a flux (either limestone or dolomite) are melted together in a blast furnace. When the metallurgical smelting process is complete, the lime in the flux has been chemically combined with the aluminates and silicates of the ore and coke ash to form a non-metallic product called blast furnace slag. During the period of cooling and hardening from its molten state, BF slag can be cooled in several ways to form any of several types of BF slag products. So, the objective of a blast furnace is to produce iron, and iron slag is a by-product in this process. Particle size ranges from fine sand to fine gravel. The appearance and particle size distribution of iron slag are similar to that of river sand. The principal constituents of iron slag are silica (SiO2), alumina (Al2O3), calcium (CaO), and magnesia (MgO), which make up 95% of the composition. Small elements entail manganese, iron, and sulfur compounds, as well as trace amounts of several others. Cooling of the slag along with its chemical composition affects its physical properties. There are three additional types of slag in blast furnace: Air-cooled blast furnace quote, Air cooled blast furnace slag rip rap, Slag cement. The rough vesicular texture of slag provides larger surface area in comparison to smoother aggregates which provides good bond with Portland cement as well as high stability in asphalt mixtures [4].

Literature survey indicates that there is no published work related to use of iron slag in self-compacting concrete. Literature review was concentrated on use of slag in concrete as well as self-compacting concrete. Few authors [5], [6], [7], [8] reported the effect of types of slags such as electric arc furnace slag [5], iron slag [6], steel slag [7], and iron filing [8] on the properties of mortar and concrete, whereas use of slags in self-compacting concrete have been reported by few authors Wang and Lin [9], Sideris et al. [10], Boukendakdji et al. [11], and Valcuende et al. [12].

Pellegrino et al. [5] concluded that strength properties of concrete made with electric arc furnace slag exhibited comparable (or even better) than conventional concrete made with natural sand. Human and Siddique [6] reported that partial replacement of fine aggregates with iron slag significantly enhanced strength properties and permeability of mortar. Maslehuddin et al. [7] reported that compressive strength of concrete made with steel slag (as coarse aggregates) is better than that of concrete made with lime stone aggregate. Moreover, the improvement in tensile strength of steel slag concrete was not significant. Alzaed [8] concluded that there was gradual increase in compressive strength with addition of iron filling. Compressive strength increased by 17% with 30% of iron filling; however, there was no significant effect on the tensile strength.

Wang and Lin [9] indicated that fresh concrete properties and compressive strength of self-compacting high strength concrete (SCHSC) made with 15% furnace slag is higher than control mix. Sideris et al. [10] concluded that use of ladle furnace slag improved fresh concrete properties and as well as compressive strength of SCC. Boukendakdji et al. [11] described that use of ground granulated blast furnace slag in replacement with cement is good for fresh and strength properties of SCC. Valcuende et al. [12] concluded that at early ages the compressive strength of SCC using granulated blast furnace slag as fine aggregates is similar to the SCC made with fine aggregates, but at 90 and 365 days, the strength is higher.

As there has not been published work on the use of iron slag in self-compacting concrete, he aim of the present research work was to ascertain the suitability of iron slag as a partial replacement of sand in self-compacting concrete.

Section snippets

Cement

Ordinary Portland cement 43 grade conforming to BIS: 8112-1989 [13]. SEM morphology and EDS spectrum of cement are shown in Fig. 1, Fig. 2, respectively. Physical and chemical properties of cement are given in Table 1.

Fine aggregates

River sand (Tokka sand name commonly used in Punjab, India) was used as fine aggregates. They were collected from Chandigarh, Punjab, near Ghaggar River. The specific gravity and fineness modulus of river sand were 2.57 and 2.62 respectively. Sand used for SCC complied with

Mixture proportions

The mixture proportion of SCC was selected by trial mixes. Control mixture achieved strength of 36.25 MPa at the age of 28 days. Sand was replaced with iron slag by mass in SCC and 10% of fly ash replaced by cement. Fixed quantities of cement, fly ash and coarse aggregates i.e., 455 kg/m3, 45 kg/m3, 760 kg/m3 respectively were used in concrete samples. Fixed water powder ratio of 0.44 and admixture of 1.2% by weight of powder were applied in all SCC mixes. Mix proportions of self-compacting concrete

Testing procedures

Before casting, the entire test molds were cleaned and oiled properly. These were firmly tightened to correct dimensions before casting. Care was taken that there is no gap left from where there is any possibility of escape of slurry. The ingredients of concrete were mixed in 0.08 cu-m capacity mixer. Testing for SCC involved four mixture compositions using 228 samples (108 cubes of 15 × 15 × 15 cm size, 72 cylinders of 15 cm diameter and 30 cm height, and 36 beams of 50 × 10 × 10 cm size and 12 cylinders

Fresh concrete properties

The properties of SCC at fresh stage were evaluated by flow ability, passing ability and consistency of SCC incorporating different percentages of iron slag. The evaluation of fresh concrete properties is done by slump flow test, L-box test, U-box test and V-funnel test. It was perceived that inclusion of iron slag in self compacting concrete mixture decreased the workability. All fresh concrete properties are in good quality resemblance as per European procedure, ENFNARC [15].

Mixtures were

Compressive strength

Compressive strength test results presented in Fig. 7 show that the strength development pattern of iron slag at all levels of sand replacement with iron slag is similar to the control mixes. It is observed that compressive strength increase in increase with iron slag content. At 7 days, SCC mixtures containing 10, 25, 40% iron slag as fine aggregates gained 3, 8, and 16% respectively more compressive strength as compared to 7 days SCC mixture without iron slag. At the curing age of 28 days, SCC

Microstructure

The hardened property of concrete depends on its intrinsic microstructure. The concrete structure is principally affected by the hydration period, water cement ratio, addition of mineral admixture and type of cement used in the production of concrete. Scanning electron micrograph (SEM) can provide both topographic and compositional analysis of material. In this research broken pieces of concrete generated by crushing were mounted on the SEM stub and images were obtained using SE image mode. SEM

X-ray diffraction

X-ray diffraction is one of the most powerful tools for identifying unknown crystalline phases. By comparing the positions and intensities of the diffraction peaks against a library of known crystalline phases, the target material can be recognized. In addition, multiple phases in sample can be identified and quantified. XRD analyses were conducted to identify the components of SCC mixtures and material used. The X-ray diffraction technique was used to analyze the SCC Control mixture without

Conclusions

The present experimental study was carried out to investigate the factibility of using iron slag as a replacement of fine aggregates in SCC. Experiments were conducted by replacing fine aggregates with iron slag in varying percentages in SCC. Test result indicates that iron slag is a good candidate to be used in partial replacement of fine aggregates in production of structural self compacting concrete of grade between M30 and M40. Based on the analysis of test results, the following

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