Mechanical Properties of Steel Fiber Reinforced Concrete using Recycled Aggregate

 

Vishal Tekchandani¹, Ankit Aggarwal¹, Dr. P Rama Mohan Rao²

 

ABSTRACT:

Quickly diminishing natural resources and deteriorating environment are one of the major concerns that should be the foundation of sustainable development. Huge amount of concrete and debris produced from deteriorated and demolished structures, testing specimens are imparting severe environmental and ecological problems. To tackle this, one of the smarter way is to use this waste as recycled aggregate, henceforth utilizing the waste as well as reducing the dependency on natural resources. In the research conducted, steel fiber reinforced concrete with recycled aggregate was used in various proportions. Specimens were tested for different properties- compressive strength, split tensile strength and flexural strength. The concrete specimen tested contained recycled aggregate in various proportion of 40%, 50% and 60%, followed by addition of steel fibers- crimpled, both ends hooked and a hybrid of both the types. The flexural behavior was tested on a model beam while other behaviors on cubes and cylinders. The results reflected that the addition of steel fibers and recycled aggregate into concrete is an effective way towards the sustainable development simultaneously with effective strength. 

 

 

INTRODUCTION:

Over the last decades there is significant increase in use of concrete which makes it second largest consumed product after water on this earth. Concrete becomes the basic needs of society after industrialization. An estimated amount of 30 billion tons of concrete were consumed globally in 2006, compared to 2 billion tons in 1950¹but its other side is totally different when.We talk about sustainable development, environmental protection. There are three ways concrete waste is generated -1) Waste during construction 2) Testing labs 3) Debris coming from demolished sites and disaster site. During the construction itself a lots of waste are generated by ready mix concrete companies due to over estimation of quantities, delaying of material causes wastage and specimen test by their testing labs etc. which use to dump their waste on waste land without utilizing. In construction projects, amounts of materials used both in the cost estimating process by owners or their consultants and in the cost planning process by main contractors are determined through detailed quantity surveying studies on project drawings. However, given the current on-site practices, it is nearly inevitable that there are almost always some natural differences between planned values calculated in quantity surveying studies and real material amounts used in construction jobsites² other waste i.e. debris is one of major problem of environment. “An equivalent of nearly 11 years of waste was generated on 25^thApril 2015.it was about 750,000 houses that were destroyed or severely damaged by the tremors³. Use of recycled coarse aggregates⁴ has a wide scope for sustainability. It may be possible that the crushing strength, waterabsorptionetc. can vary from natural fresh coarse aggregate. so it is very important to optimize it, replacement with natural aggregates will tends to have less mechanical properties than concrete made of fresh coarse aggregate⁵. So the idea to add steel fibers to a concrete mixture with recycled coarse aggregate may provide stability to the concrete, increases the mechanical strength of concrete⁶.

 

AIM AND OBJECTIVE:

The main focus of presented paper was to use the concrete waste (debris waste, waste comes from Ready mix concrete companies, testing labs etc.)and extracting the recycled coarse aggregates from waste⁷ and using it in place of natural fresh aggregates. In present work the natural aggregates were replaced with 40%, 50% and 60% and mechanical properties were examined without adding any fiber. Compressive test was conducted for optimization and that percentage of replacement was used as datum. Three combination of steel fibers- 1) both end hooked fiber 2) crimpled fiber 3) hybrid were used. All the three samples has aspect ratio of 50.  Using this proportion may change material’s mechanical properties which may improve behavior and bring about new types of applications which has not been done till now⁸. Fiber reinforced concrete with recycled coarse aggregate can be considered as optimal structural concrete for various applications.

 

MATERIALS AND METHODOLOGY:

Coarse aggregate occupies a large proportion of concrete and its shape, size, strength play an important role in strength of concrete. Recycled aggregates was obtained after crushing the waste in stone crusher. Various tests were conducted on aggregates for both fresh and recycled aggregate whereas results are shown in Table 1 which is under IS code provision. Ordinary Portland cement of grade 53(compressive strength not less than 53MPa) was taken as binding material, fine aggregate (River sand) of zone II was used. Crushed granite of size in the range of 10 to 20mm was considered towards coarse aggregate, while steel fibers of different type (Crimpled, Both ends hooked and Hybrid mix) and aspect ratio 50 were used in various proportions and combinations

 

Mix Design:

In the experiment conducted, IS Code for Mix Design were referred for obtaining the designated proportion of each material for characteristic strength of 25 N/mm². Ordinary Portland cement of 53 grade (compressive strength not less than 53 N/mm2) was used in the study. The cement was selected as per IS-12269⁹.The following table, Table 2 depicts the amount of materials required per m³ of concrete for a grade of M25. The quantity of cement, water and sand were kept constant throughout the experiment whereas amount of coarse aggregate was varied. Table 3 shows material composition for optimization of RCA proportion. After the optimization of RCA, the resulted proportion was used further along with 1% steel fiber for further improving other mechanical properties like tensile strength, flexural strength. Table 4 shows the material composition for SFRC with RCA. Adding fibers to the concrete resulted in decreased workability of the mix prepared so far. Further, tests were conducted, exhibiting results of specimen with RCA along with steel fiber also called SFRC. To check for compressive strength, split tensile strength and flexural strength, numerous cubes, cylinders and beams were casted of 100 mm x 500mm for flexural strength, leading to the casting of 15 cubes (6 + 9), 6 cylinders and 6 beams. Out of which, 6 cubes accounted for optimization of RCA, corresponding to 2 cubes each with 40%, 50% and 60% RCA. With the observed result of 40% RCA as optimized proportion, 3 cubes, 2 cylinders and 2 beams each were casted with steel fibers- crimpled, both ends hooked and hybrid (both mixed) for 28 days strength. The specimens were remolded after 24 hours of casting and kept in water for a curing period of 28 days.

 

Table 1. Properties of coarse aggregate.

Property	Fresh coarse aggregate	Recycled aggregate
Specific gravity	2.66	2.62
Water absorption (%)	2	2.6
Fineness modulus	7	7.12

 

Table 2: Quantities of required material per m³.

%RCA Kg/m3	Cement Kg/m3	Water Kg/m3	Fine Agg. Kg/m3	Fresh Coarse Agg. Kg/m3	Recycled Coarse Agg. Kg/m3
0%	415	200	575	1225	0
40%	415	200	575	735	490
50%	415	200	575	612.5	612.5
60%	415	200	575	490	735

 

Experiment execution:

Different specimens were casted to observe the influence of recycled coarse aggregates into concrete mix, followed by addition of different types and proportions of steel fibers (constant by weight). In present work, we took the square mould of size 100mm x 100mm for compressive strength. Whereas cylindrical mould of 100 mm x 200mm for split tensile strength and a rectangular beam section mould of 100 mm x 500 mm were casted

 

Table 3: Quantities of required material with steel fibresTable

Type of steel fiber	Cement Kg/m3	Water Kg/m3	FA. Kg/m3	Fresh CA. Kg/m3	RCA Kg/m3	Fiber (1% by weight)Kg/m3
Both end hooked	415	200	575	735	490	24.15
Crimpled	415	200	575	735	490	24.15
hybrid	415	200	575	735	490	24.15

 

Table 4: Optimized coarse aggregate

%RCA	Compressive strength(N/mm2)
0%	36.6
40%	34.8
50%	28.3
60%	21.2

 

 

 

RESULT AND DISCUSSION:

The results for the first phase of the experiment, i.e., optimization of RCA is given in Table 5, showing compressive strength of specimens kept under curing for 14 days for M30 grade of concrete. The results were quite evident and depicting the ideal proportion of RCA to be 40% over 50% and 60% of RCA. It was observed that the compressive strength decreased with the increase in percentage of RCA replacing natural aggregate. Further

 

Optimization of Recycled Aggregate:

From the table 1 we can conclude that compressive strength of specimen decreases when we increase the percentage  of recycled coarse aggregate. Fig 1 shows that there is more compressive strength for 0% replacement while for 40%, 50%, 60% are 34.8 N/mm², 28.3 N/mm², and 21.2 N/mm² respectively, hence rendering 40% of coarse aggregate to be RCA as an optimum replacement.

 

Fig 1:Compressive strength of various % of RCA                                             Fig 2. Compressive strength of SFRC samples.

 

Steel Fibers Reinforced Concrete (SFRC):

In table 5 we observe that there is sudden increment of compressive strength as compared to specimen without steel fibers. Fig 2 shows that hybrid mix account a compressive strength of 45.03N/ mm² while other are less than specimen with both end hooked and crimpled. It is evident that for hybrid specimen, compressive strength attained was commendable while split tensile and flexural strength were quite satisfactory, more than 0.7, as per IS 456-2000 ¹⁰. Fig 1, Fig 2 and Fig 3 depicts the ideal comparison between different types and proportions of fibers. Although hooked fibers performed better than crimpled ones, but the hybrid fibers emerged to be the best in class option with very satisfactory strengths in all aspects (compressive, split tensile and flexural strengths).                    

Fig 3. Split tensile strength of SFRC samples                               Fig 4. Flexural strength of SFRC samples.

 

Table 5: Mechanical properties of SFRC

Steel Fiber Type	Compressive Strength(N/mm2)	Split tensile Strength(N/mm2)	Flexural Strength(N/mm2)
Both End Hooked	41.13	2.6	3.37
Crimpled	35.9	2.765	3.14
Hybrid	45.03	3.22	3.88

 

CONCLUSION:

After successfully executing the experiment and obtaining the output, the results were critically analyzed which brings us the following conclusions:

·        The tests conducted on concrete with RCA proves that wastes from various construction and building can be used in the structures.

·        RCA could be obtained from various source like- Testing specimens used for lab testing, under construction site waste, waste from demolished buildings.

·        Using RCA ensures proper disposal of waste, revenue generation out of the waste which was earlier a liability now turned into an asset.

·        This experiments gives a way out towards sustainable development by finding an effective replacement for natural resources, without exploiting the nature and its resources.

·        Concrete with 0% RCA had more strength than concrete with RCA (all proportions) without steel fiber.

·        The compressive strength, tensile strength and flexural strength of concrete with RCA were improved substantially by using steel fibers.

·        Although hooked steel fibers proved to be superior over crimpled ones, but hybrid steel fibers (mix of both-hooked and crimpled) proved out to be the most effective one.

 

REFERENCE:

1.       Concrete Recycling, Cement Sustainability Initiative

2.       Aynur Kazaza, Serdar Ulubeylib , Bayram Era , Volkan Arslanb , Ahmet Arslana , Murat Aticia, Fresh ready-mixed concrete waste in construction projects: a planning approach

3.       James Daniell, BijanKhazai, Trevor Girard, Nepal Earthquake – Report No-1 , CEDIM Forensic Disaster Analysis Group and CATDAT and Earthquake-Report.com

4.       Eguchi, K., Teranishi, K., Nakagome, A., Kishimoto, H., Shinozaki, K., Narikawa, M. 2007. Application of recycled coarse aggregate by mixture to concrete construction. Construction and Building Materials, 21, 1542–1551.

5.       Hendriks Ch.F. and Janssen G.M.T., Use of recycled materials in construction, Materials and Structures Constructions

6.       R.F. Zollo, Fiber-reinforced concrete> an overview after 30 years of development, Cement Concrete Composite, p. 1357-64, 34, 2004,

7.       Marta Kosior-Kazberuk, Mateusz Grzywa, Recycled Aggregate Concrete as Material for Reinforced Concrete Structures

8.       J. Krátký, K. Trtík, J. Vodička, Fiber reinforced concrete structures, Prague, 1999-36, 604, (2003).

9.       Indian Standard Code IS: 12269, Specifications for 53 Grade Ordinary Portland Cement.

10.     IS: 516–1956, Indian Standard Methods of Tests for Strength of Concrete (1999)

 

Received on 16.11.2015            Accepted on 23.12.2015            © EnggResearch.net All Right Reserved Int. J. Tech. 5(2): July-Dec., 2015; Page 215-218 DOI: 10.5958/2231-3915.2015.00023.1