Experimental Investigation on the use of Light Experimental Investigation on the use of Light Concrete Mix

Experimental Investigation on the use of Light Experimental Investigation on the use of Light Concrete Mix

Geethu S,

M.Tech Scholar, Dept. of Civil Engineering,

Sree Buddha College of Engineering, Pattoor, Nooranad, Alappuzha Dist,

Kerala, India.

Renjith R,

Assistant Professor, Dept. of Civil Engineering

Sree Buddha College of Engineering, Pattoor, Nooranad, Alappuzha Dist,

Kerala, India.

Abstract Glass fibre reinforced gypsum (GFRG) panels are new building materials made essentially of gypsum plaster reinforced with glass fibre . GFRG panels can be unfilled when used as partition walls, but when used as external walls, it is filled with M20 grade concrete (reinforced concrete filling) in order to resist the Lateral loads. M20 grade is adopted in order to satisfy the durability requirements stipulated in the code IS 456:2000 rather than for strength. In the present scenario,the experiment was conducted in two stages: In the first stage, a study was conducted on normal concrete by replacing cement with phosphogypsum and fine aggregate with EPS beads, to formulate a trial mix with optimum percentage which can be used as an alternative to M20 grade concrete (and is lighter than the same). In the second stage, the trial mix developed in first stage is used for a comparative study between GFRG filled with M20 grade concrete and with the alternative trial mix. The results of the first stage are presented in this paper.

Keywords: Green product, Low cost, Prefabricated, hollow panels, Phosphogypsum, Expanded Polystyrene (EPS) Beads, Light weight.

1. INTRODUCTION

   Building materials form the backbone of civil engineering construction. Of all the modern building materials, concrete is one of the oldest and the most versatile building material used in any type of civil engineering structure. The advantages of using concrete include relatively good compressive strength, formability, general availability of its raw materials and adaptability to different environmental conditions. With the advancement of technology and increased field application of concrete and mortars, the density, strength, workability, durability and other characteristics of the ordinary concrete is continually undergoing modifications to make it more suiTable for any situation. In order to meet the scarcity of cement and raw materials used in concrete, the use of recycled solid wastes, agricultural wastes and industrial by-products like phosphogypsum, fly ash, blast furnace slag, silica fume, rice husk ash, Expanded polystyrene (EPS) beads etc. came into use. Concrete made with light weight materials are known as light weight concrete. Light weight concrete with density

   varying between 1400 to 2100 Kg/m3 has been used for structural purpose for so many years. The benefit of using light weight concrete is that it leads to overall reduction in dead load of a structure. This results in the reduction of final cost and improved economy of structural elements since they are liable to support lesser amount of dead loads. According to Cook (1983), expanded polystyrene beads are best suited for prefabricated panels, hollow and solid block, light weight sandwich panels and in highway construction as part of sub base where frost is harmful for sub grade stability.

   Glass fibre reinforced gypsum (GFRG) panels are machine made in less than one hour. All GFRG panels are 12 meters length and 3 meters height. The panels are cellular in form and are 124 millimetres thick. Construction using GFRG panels is very fast, low in cost and eliminates the need for bricks, blocks, sand, wall framing and plastering. The selection of structural system, analysis and the design should be performed as per the Structural Design Manual prepared by IIT, Madras, India.

   Phosphogypsum (PG) is a by-product from processing phosphate rock by the "wet acid" method for phosphoric acid production in fertilizer plants. With the installation of more amount of phosphoric acid plant in India, disposal of phosphogypsum becomes difficult. Phosphogypsum contains free phosphoric acid, phosphates, fluorides and organic matter. This brings about environmental impacts on its disposal sites. Disposal of waste phosphogypsum is one of the most serious problems faced in the phosphate industry. Apart from being used as a fertilizer, building material and soil stabilization agent, about 85% of phosphogypsum is dumped in the vicinity of phosphate factories, requiring large disposal areas.

   Expanded polystyrene (EPS) is a light weight cellular plastic material consisting of fine spherically shaped particles. These beads consist of 98% of polystyrene and 2% of air. It has a closed cellular structure and cannot absorb water [1]. Polystyrene foam is a waste material from packing industry. They are non biodegradable and produce disposal problems. When these materials are chemically treated, expanded polystyrene beads are produced. They can be

   effectively used in concrete as partial replacements of aggregates. EPS beads are inert materials and do not contain chloroflurocarbon (CFC) and hydro chloroflurocarbon (HCFC).Hence they are environment friendly and do not contribute to the destruction of earths ozone layer. They are quite resistant to alkalis, methanol, oxidising and reducing agents. However when these beads are exposed to sunlight, they deteriorate and turn into yellow colour. This is an indication of polymer degradation although it may take years. Since they are embedded in concrete, the deterioration of beads are not of major concern. [1]. EPS beads do not carry any loads. They have excellent impact resistance and transfer the load to the surrounding regions. They help to reduce internal stresses and prevents micro-cracking at lower stress levels. Hence they find applications in prefabricated panels at earthquake prone regions.

2. SCOPE OF WORK

   Disposal of phosphogypsum is one of the serious issues faced by the phosphate industry. The effective utilization of this waste material is done by manufacturing of a new construction material known as Glass Fiber Reinforced Gypsum (GFRG) panel, also known in the industry as Rapidwall. These are prefabricated panels used as load bearing and as well as non- load bearing structure. GFRG panels can be unfilled when used as partition walls, but when used as external walls, it is filled with M20 grade concrete (reinforced concrete filling) in order to resist the lateral loads. M20 grade concrete is adopted in order to satify the minimum requirements stipulated in IS 456:2000.

   In this work, phosphogypsum and expanded polystyrene (EPS) beads are used as partial replacement of cement and fine aggregates by limiting the strength of concrete to that of M20 grade concrete. Tests pertaining to workability,compression, split tensile and flexural were conducted to study the strength characteristics of the mixes.

3. MATERIALS AND METHODS

   Ordinary Portland cement, fine aggregate, coarse aggregate, phosphogypsum, expanded polystyrene beads and water are used for making concrete mixes in this present study. Properties of constituent materials are tested as per the methods prescribed by the relevant IS codes.

   1. Cement

      Ordinary Portland cement (OPC) confirming to IS 12269- 1999 (43 Grade) was used for the experimental work. Laboratory tests were conducted on cement to determine standard consistency, initial setting time, final setting time, specific gravity, fineness, and compressive strength as per 4031-1967(reaffirmed 1995). The results are presented in Table 1

      TABLE 1. PROPERTIES OF CEMENT

      Sl No	Particulars	Values
      1	Grade	OPC 43
      2	Standard Consistency, %	32.5
      3	Initial setting time, min	80
      4	Final setting time, min	220
      5	Specific gravity	3.16
      6	Fineness, %	7
      7	3rd day compressive strength, N/mm2	25
      8	7th day compressive strength, N/mm2	36
      9	28th day compressive strength, N/mm2	47

   2. Fine Aggregate

      M sand was used as fine aggregate. Laboratory tests were conducted on fine aggregate to determine the different physical properties as per IS 2386 (Part III)-1970.The test results are shown in the Table 2. Fine aggregate used conforms to IS 383:1970 specification (Zone II).

      TABLE 2. PROPERTIES OF FINE AGGREGATE

      Sl No.	Particulars	Values
      1	Specific gravity	2.33
      2	Fineness modulus	2.732
      3	Effective size	0.18mm
      4	Uniformity coefficient	3.83
      5	Sand type	Medium

   3. Coarse Aggregate

      In the construction of GFRG panels, maximum size of coarse aggregate used is 12.5mm. Laboratory tests were conducted on coarse aggregates to determine the different physical properties as per IS 2386 (Part III)-1970. The test results are shown in the Table 3.

      TABLE 3. PROPERTIES OF COARSE AGGREGATE

      Sl No	Particulars	Values
      1	Specific gravity	2.67
      2	Void ratio	0.77
      3	Bulk Density	1.538
      4	Porosity	0.44

   4. Phosphogypsum

      The phosphogypsum used in this investigation was collected from FACT-RCF building products Ltd, Kochi, Kerala. The physical and chemical properties are presented in Table 4 and Table 5 as obtained from ventor.

      Fig .1. Phoshogypsum

      TABLE 4. PHYSICAL PROPERTIES OF PHOSPHOGYPSUM

      Sl No	Physical Properties
      1	Moisture at 50oC	8.72%
      2	Combined Moisture	17.54%
      3	Bulk Density	0.88gm/cc

      TABLE 5. CHEMICAL COMPOSITION OF PHOSPHOGYPSUM

      Sl No	Chemical composition at dried at 250oC
      1	Calcium as CaO	39.54%
      2	Sulphur as SO3	56.48%
      3	CaSO4	95.40%
      4	Total P2O5	0.83%
      5	Water soluble P2O5	0.22%
      6	Citrate soluble P2O5	0.79%
      7	Citrate insoluble P2O5	0.32%
      8	Acid Insoluble	2.26%
      9	Fluorine	0.46%
      10	Sodium as Na2O	0.07%
      11	Potassium as K2O	0.05%
      12	Iron as Fe2O3	0.01%
      13	Aluminium as Al2O3	0.04%
      14	R2O3	0.05%
      15	Magnesium as MgO	0.01%
      16	Chloride	2ppm

   5. Expanded Polystyrene (EPS) Beads

      Polystyrene is a waste material from packing industry. When processed in a special manner, polystyrene can be expanded and used as light weight concrete making material. The properties of EPS beads are shown in Table 6.

      Fig 2. EPS Beads

      TABLE 6. PROPERTIES OF EPS BEADS

      Sl No.	Properties	Description
      1	Appearance	White emulsion
      2	Specific gravity	0.0075
      3	Freeze / thaw resistance	Excellent
      5	Flammability	Non flammable
      6	Compatibility	Can be used with all types of Portland cement

   6. Concrete Mixes

   Mixes M20 and M25 grade concrete were designed as per IS 10262:1982 and IS 10262:2009. Several trail mixes were casted to arrive at the appropriate mix proportion. The Table 7 and Table 8 show the details of test specimen and mix proportioning of concrete.

   TABLE 7. DETAILS OF TEST SPECIMEN

   Sl No	Specimen	Size (mm)
   1	Cube	150x150x150
   2	Cylinder	150×300
   3	Beam	100x100x500
   4	GFRG panel	300x300x124

   TABLE 8. MIX PROPORTIONING

   Mix	Cement (Kg/m3)	Water (Kg/m3)	FA (Kg/m3)	CA (Kg/m3)	w/b Ratio
   M20	345	183	758	941	0.53
   M25	382	183	745	925	0.48

4. EXPERIMENTAL PROCEDURE

   A. Preparation Of Mixes

   M25 grade concrete mix is taken as the reference mix and designated as MR. The optimum percentage replacement of cement with phosphogypsum was found by preparing samples with various replacement levels of 0%, 2.5%, 7.5%, and 10%.Water cement ratio of the reference mix was kept at

   1. The optimum percentage of phosphogypsum was found to be 5%. This mix with optimum percentage of phoshogypsum is used further to find the optimum percentage of EPS beads. Fine aggregate is replaced with 0%, 5%, 10%, 15%, 20% and 25% EPS beads to find the optimum percentage. Phosphogypsum is replaced in terms of its weight and EPS beads in terms of its volume. The details of the mix proportioning for optimum percentage of phosphogypsum and optimum percentage of EPS beads is furnished in Table 9 and Table 10 respectively.

      TABLE 9. MIX PROPORTIONS FOR VARIOUS PERCENTAGES OF PHOSPHOGYPSUM

      Mix	Phosp hogyp sum (%)	Cement (Kg/m3)	Phospho gypsum (Kg/m3)	Fine Aggregate (Kg/m3)	Coarse Aggrega te (Kg/m3)
      MR	0	382	0	745	925
      MR 2.5	2.5	372.45	9.55	745	92
      MR 5	5	362.5	19.1	707.75	925
      MR 7.5	7.5	353.35	28.65	670.5	925
      MR 10	10	343.8	38.2	633.25	925

      TABLE 10. MIX PROPORTIONS FOR VARIOUS PERCENTAGES OF EPS BEADS

      Mix No	Cement (Kg/m3)	Phospho gypsum (Kg/m3)	Fine Aggregate (Kg/m3)	EPS Beads (Kg/m3)	Coarse Aggreg ate (Kg/m3)
      MR	382	0	745	0	925
      MR 5,0	362.5	19.1	745	0	925
      MR 5,5	362.5	19.1	707.75	0.12	925
      MR 5,10	362.5	19.1	670.5	0.24	925
      MR 5,15	362.5	19.1	633.25	0.36	925
      MR 5,20	362.5	19.1	596	0.48	925
      MR 5,25	362.5	19.1	558.75	0.6	925

      Where MR X,Y represents mix with x% replacement of cement with phosphogypsum and y% replacement of fine aggregates with EPS Beads.

      Different tests were conducted to study the workability and strength parameters of the concrete. The workability of various mixes was assessed by determining compacting factor as per the IS 1199:1959 specification. Tests for the determination of compressive strength, flexural strength and modulus of elasticity of cement concrete were conducted as per IS 516:1959 and split tensile strength as per IS 5816:1999.

5. RESULTS AND DISCUSSIONS

   1. Workability Tests

      The results of workability test for various percentage replacements of cement and fine aggregates with phosphogypsum and EPS beads are as follows.

      Compaction Factor Vs Mix

      0.925

      0.92

      0.915

      0.91

      0.905

      0.9

      0.895

      0.89

      Mix

      Compaction Factor Vs Mix

      0.925

      0.92

      0.915

      0.91

      0.905

      0.9

      0.895

      0.89

      Mix

      The optimum percentage replacement of cement with phoshogypsum was found at 5% replacement level.

      Compaction Factor

      Compaction Factor

      C. Compressive strength Vs percentage of EPS beads

      The variation in cube compressive strength for the

      concrete mix (MR 5) with various percentages of EPS beads

      Compaction Factor

      Compaction Factor

      Fig .3. Compaction factor of cement replaced with phopshogypsum Vs mix

      Compaction Factor Vs Mix

      0.92

      0.91

      0.9

      0.89

      0.88

      0.87 Compact

      0.86 ion

      0.85 Factor

      0.84 M20

      0.83 grade

      0.82

      Compaction Factor Vs Mix

      0.92

      0.91

      0.9

      0.89

      0.88

      0.87 Compact

      0.86 ion

      0.85 Factor

      0.84 M20

      0.83 grade

      0.82

      Fig .4. Compaction factor of mix with phosphogypsum and EPS beads

      Compaction factor tends to decrease with increase in percentage of EPS beads due to the increase in the volume of voids. Compaction factor of M20 grade casted is also shown in the figure.

   2. Compressive strengthVs percentage of phosphogypsum

      Compressive strength (N/mm2)

      Compressive strength (N/mm2)

      The variation in cube compressive strength for the concrete mix (MR) with various percentages of phosphogypsum( replacing cement) is furnished in figure 5.

      Compressive strength Vs Mix

      Compressive strength Vs Mix

      40

      38

      36

      34

      32

      30

      28

      26

      24

      22

      20

      7 days

      28 days

      40

      38

      36

      34

      32

      30

      28

      26

      24

      22

      20

      7 days

      28 days

      Mix

      Mix

      Fig .5. Compressive strength Vs Mix

      (replacing fine aggregate) is furnished in figure 6.

      Compressive strength Vs Mix

      Compressive strength Vs Mix

      45

      40

      35

      30

      25

      20

      15

      10

      5

      0

      MR 5,0

      MR 5,5

      MR 5,10

      MR 5,15

      MR 5,20

      45

      40

      35

      30

      25

      20

      15

      10

      5

      0

      MR 5,0

      MR 5,5

      MR 5,10

      MR 5,15

      MR 5,20

      0 7 28 56

      days days days

      Mix

      0 7 28 56

      days days days

      Mix

      MR 5,25

      MR 5,25

      Compressive strength (N/mm2)

      Compressive strength (N/mm2)

      Fig .6. Compressive strength Vs Mix

      The compressive strength of concrete cubes decreased gradually as the percentage of EPS beads was increased. The mean target strength of M20 grade concrete is 26.6MPa and the compressive strength of the specimens with upto 20% replacement exceeded this value.

   3. Density

      Density (Kg/m3)

      Density (Kg/m3)

      Density of concrete prepared using various percentages of EPS beads is illustrated in figure 7.

      Density Vs Mix

      Density Vs Mix

      2706

      2506

      2306

      2106

      1906

      1706

      1506

      Density (Kg/m3)

      M20

      grad

      e

      2706

      2506

      2306

      2106

      1906

      1706

      1506

      Density (Kg/m3)

      M20

      grad

      e

      Fig .7. Density Vs Mix

      As expected, the density of concrete decreased with the addition of EPS beads since they are light weight materials having low specific gravity.

   4. Split tensile strength, Flexural strength and Modulus of elasticity

      Split Tensile Strength Vs Mix

      4

      3.5

      3

      2.5

      Split

      2 Tensile

      Strength

      Split Tensile Strength Vs Mix

      4

      3.5

      3

      2.5

      Split

      2 Tensile

      Strength

      Split tensile strength (N/mm2)

      Split tensile strength (N/mm2)

      The split tensile strength, flexural strength and modulus of elasticity of concrete obtained for the concrete specimens prepared using various percentages of EPS beads are represented in the following figures.

      Mix

      Mix

      1.5

      1.5

      (N/mm2)

      (N/mm2)

      1

      1

      M20

      grade

      M20

      grade

      Fig .8. Split tensile strength Vs Mix

      Fig .9. Concrete with 10% replacement of EPS beads

      Fig .10. Concrete with 20% replacement of EPS beads

      Flexural strength Vs Mix

      3.5

      3.4

      3.3

      3.2

      3.1

      3

      2.9

      2.8

      Flexural Strength (N/mm2) M20

      grade

      Flexural strength Vs Mix

      3.5

      3.4

      3.3

      3.2

      3.1

      3

      2.9

      2.8

      Flexural Strength (N/mm2) M20

      grade

      Mix

      Mix

      31

      30

      29

      28

      27

      26

      25

      24

      23

      31

      30

      29

      28

      27

      26

      25

      24

      23

      Modulus of elasticity (N/mm2)

      Modulus of elasticity (N/mm2)

      Flexural strength (N/mm2)

      Flexural strength (N/mm2)

      Fig .11. Flexural strength Vs Mix

      Modulus of Elasticity Vs Mix

      Modulus of Elasticity Vs Mix

      Mix

      Mix

      Modulus of Elasticity

      Modulus of Elasticity

      M(N/mm2)

      M(N/mm2)

      20

      grade

      20

      grade

      Fig .12. Modulus of elasticity Vs Mix

      Though the split tensile strength, flexural strength and modulus of elasticity of concrete reduced with the addition of EPS beads to the concrete,the values exceeded that of M20 grade concrete upto the addition of 15% of EPS beads.

   5. Cost comparison

   The cost of materials for one cubic meter of concrete for different mixes is given in Table 11.

   TABLE 11. COST OF MATERIALS

   Mix No	Cement (Kg/m3)	Phosphgypsum (Kg/m3)	Fine Aggregate (Kg/m3)	EPS Beads (Kg/m3)	Coarse Aggregate (Kg/m3)	Cost (Rs)
   M 20	345	0	758	0	941	4073.6
   MR	382	0	745	0	925	4355.73
   MR 5,0	362.5	19.1	745	0	925	4208.44
   MR 5,5	362.5	19.1	707.75	0.12	925	4171.75
   MR 5,10	362.5	19.1	670.5	0.24	925	4135.05
   MR 5,15	362.5	19.1	633.25	0.36	925	4098.33
   MR 5,20	362.5	19.1	596	0.48	925	4061.65
   MR 5,25	362.5	19.1	558.75	0.6	925	4024.96

   Cost of M25 grade concrete is slightly higher than M20 grade concrete. But this difference in cost is compensated by making the concrete light weight as a result of which there is an overall reduction in dead load and optimization of structural elements including the foundation.

6. CONCLUSION

Replacement of cement with phoshogypsum yielded maximum compressive strength at 5% replacement level. Though workability and strength parameters of the concrete decreased with the addition of EPS beads, the mix with upto 15% replacement of EPS beads yielded better results than that of M20 grade concrete.

Hence mix with 5% phosphogypsum and 15% EPS beads as partial replacement of cement and fine aggregate can be used as a alternative to M20 grade concrete.

Cost comparison of alternate mix with M20 grade concrete showed a marginal increase in cost (0.6%) of concrete per cubic meter which is neutrilized by the fact that resultant mix is having lower density than M20 grade concrete (5.27%) and as such there will be considerable reduction in the structural loads due to self weight.

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