Benefits of Incorporating Induction Furnace Slag in Concrete as Replacement of Cement: A Case Study of Pakistan

As Pakistan along with the rest of the world continues to develop, demand for limited natural resources continues to increase also. This demand for resources and subsequent waste that is generated has driven the idea of sustainability towards the forefront of modern day research. To achieve this goal, new and innovative ways are being developed to recycle waste materials that otherwise would end up in landfill sites. Slag, a by-product of steel manufacturing is one such waste material. Pakistan as being a developing country does not have proper facilities to insure safe disposal and recycling of slag. Hence, new and innovative ways for recycling slag are a necessity for Pakistan to move towards technological advancement. Current study focuses to explore the feasibility of using local induction furnace slag as partial substitute of OPC (Ordinary Portland Cement) in concrete as well as to check its performance against chloride and sulphate damage. The test results showed that 15% or more slag replacement will make the concrete immune to chloride and sulphate damage. However, results also indicate that with increase in slag replacement percentage there is a significant drop in compressive, flexural and split tensile strength of concrete. Keeping in view the loss of strength, immunity against chloride and sulphate damage, reduction in cost of making concrete and sustainability benefits; 15% slag replacement has been deemed optimum replacement value.

Recently, attempts have been made to utilise refuse materials such as fly ash [1], silica fume [2] and recycled plastic fibre [3] etc. in concrete. The potential application of these industrial by-products as partial cement or aggregate replacement in concrete depends on their mechanical and chemical properties. Their utilization in concrete also comes from an environmental constraint i.e. safe disposal.
greatly vary from blast furnace slag.
Majority of previous researches related to using slag in concrete have been focused on incorporating blast furnace slag rather than induction furnace slag. GGBS (Ground Granulated Blast Furnace Slag) have been extensively used as fine aggregate replacement [8], coarse aggregate replacement [9] and also as partial cement replacement [10] in concrete. Other aspects of GGBS concrete like sustainability [11] as well as performance against creep and shrinkage [12] have already been evaluated also. Whereas incorporation of induction furnace slag in concrete have been mostly confined to aggregate replacement [13]. Attempts for cement replacement with induction furnaces slag have been very limited. This is due to the fact that induction furnace slag contains higher levels of iron oxide and lower levels of silica in comparison to GGBS. These factors reduce its potential of being used as cement replacement material in concrete as compared to GGBS. Therefore, current study aims to identify the benefits of partially replacing OPC content by locally available induction furnace slag in concrete.

Cement
ASTM Type-I OPC [14] cement was used throughout the study. Basic properties of the selected cement were determined using ASTM standard procedures [14][15]. Outcome of these tests are mentioned in Table 1.

Aggregates
Local quarried fine and coarse aggregates were used in the study. Their material properties were determined using ASTM standard procedure [16]. Details of fine and coarse aggregate properties are shown in Tables 2-3 respectively.

Steel Slag
Induction furnace slag was collected from a local steel mill located in Lahore. Slag Samples collected from the industry land filling site were gridded to 44 micron size (Sieve # 325 passing) as per the ASTM standard [17].
Then the powdered slag was (dry) mixed with cement as partial replacement of binder. The steel slag collection and grinding process is detailed in Fig. 1  Considering the above mentioned findings and the prospect that pollution will keep on increasing in future, current study is carried out by taking 22000 ppm or 22 g/ L of chloride concentration and 4000 ppm or 4 g/L of sulphate concentration for their respective curing mediums.
The curing guidelines mentioned in ASTM standard [21] were observed for all three mediums (water, chloride and sulphate

BULK DRY DENSITY
Bulk dry density of samples was found before they were tested for compression, flexure or splitting tensile strength.
The volumes of a cylinder and a prism are 0.  Table 6 shows the results of bulk dry density tests against each percentage steel slag replacement of concrete.
Overall increase in dry density between control (0% slag) sample and 20% slag sample is just 1.73%, which is very minute increase. The graphical representation of results in Fig. 9 shows this slight increasing trend from 0-20% slag samples. The trend indicates that each successive increase from 0-20% have very minutely increased the density of concrete.

SLUMP TEST
Slump is basically a measure of workability which is largely dependent of the value of water-cement ratio. If more free water is accessible at the time of batching then more will be the fall of slump. Review of previous researches [22][23] indicate that hydration of slag occur much slower than compared to OPC. Therefore, as the percentage of cement replacement with steel slag increases the fall of slump should also increase. This trend was also observed in results of current study as shown in Table 7. Test was conducted as per ASTM standards [24].

COMPRESSIVE STRENGTH
The compressive strength for different percentages (0,5,10,15 and 20%) of slag replaced concrete was measured after seven (7), fourteen (14) and twenty-eight (28) days. All the samples were tested using compressive strength testing machine (Fig. 10). The loading rate for testing was kept constant at 0.25  0.05 MPa/s [25]. To

SPLITTING TENSILE STRENGTH
Since This is due to the fact that slag takes longer time to hydrate as compared to OPC [27]. The delay in hydration and lack of calcining agent cause the reduction of splitting tensile strength but also provide longer duration of protection against chloride and sulphate damage.

CONCLUSIONS
Following are the conclusions drawn from experimental results: (i) Induction furnace slag can be used as partial cement replacement in concrete.

BENEFITS
The benefits of using optimum replacement (15% slag) in concrete are listed below: (i) Cost per meter cube of concrete will be reduced by 503 PKR or 13.4%.
(iii) Concrete will be immune against sulphate and chloride damage.
(iv) 31 mm slump increase will improve efficient mixing and workability of concrete mix.
(v) 1.64% increase in dry density will improve structural stability, acoustic and thermal insulation and water tightness of concrete.
(vi) Improved workability, chemical damage immunity and better water tightness will also help in reducing repair and maintenance costs.