Self Compacted Concrete Beams-Flexural Resistance by Partial Replacement of Cement with Ground Granulated Blast Furnace Slag

Self Compacted Concrete Beams-Flexural Resistance by Partial Replacement of Cement with Ground Granulated Blast Furnace Slag

1T. Soundharya, 2V. Karthikeyan 1Assistant Professor, 2 Assistant Professor 1Civil Engineering

1K.Ramakrishnan College of Technology, Trichy, Tamilnadu

Abstract Self compacting concrete has the property of flowing and compacting due to its own weight. Since compacting of concrete in the presence of grid locked reinforcements are increasing, the need for self flowing concrete is felt very much. Meanwhile Ground Granulated Blast Furnace slag (GGBS) is an effective alternate to cement which contains cement material. In this study, self compacting concretes were considered using GGBS by replacing Portland cement with 10%, 20%, 30%, 40% and 50% by weight. The rheological and mechanical properties of SCG (GGBS incorporated SCC) were found to be increased compared to conventional concrete. Six reinforced concrete beams (SCGB) of shear span to depth ratio (a/d) 2 were tested for flexural capacity and ductile behavior. The experimental cracking moment of SCGB beams were found to be more than the theoretical cracking moment enhancing its flexural resistance. The outcomes show that the use of GGBS in SCC enables higher performance with economy and sustainability.

Index Terms Self Compacting Concrete, GGBS, Flexural Resistance, Ductile Behavior.

1. INTRODUCTION

   Self compacting concrete (SCC) is defined as a concrete that produce a high deformation with good segregation

   resistance. The SCC is distinguished by its high fluidity, passing ability and cohesiveness characteristics that eliminate or reduce to a minimum the need for mechanical compaction. The self-compacting concrete can reach self- leveling work performance in the fresh state by relying on the action of gravity, there is no need of applying external vibrations in construction sites, which improve the quality of concrete placing and can save time and labour needed in the construction sites. Hence in the last 15 years, SCC has been widely used around the world for its constructive ability and higher durability.

2. MATERIALS USED

   1. Cement and Aggregates

      Ordinary Portland cement of 53 grade conforming to IS 12269:1987 with specific gravity of 3.15 was used. River sand obtained from Thoothukudi and the locally available blue metal crushed stone aggregates of size 20mm were used as fine and coarse aggregates respectively. Their specific gravity, bulk density, percentage of water absorption and fineness modulus were obtained as per IS 2386:1963 and shown in Table 1.

      Table 1 Properties of Aggregates

      Type	Fine aggregate	Coarse aggregate
      Specific gravity	2.6	2.67
      Fineness modulus	2.36	4.82
      Water absorption (%)	0.50	1.22
      Bulk density (kg/m3) 1629 1563

   2. Mineral Admixture

      GGBS (Ground Granulated Blast furnace Slag), obtained from JSW Cement Limited, Thoothukudi and conforming to IS 12089:1987 was used as the mineral admixture. The

      physical and chemical properties of GGBS used for this study is given in Table 2.

      Table 2 Properties of GGBS

      Chemical properties
      Parameter	JSW GGBS (%)	Codal provisions
      CaO	36.34	—-
      Al2O3	14.43	—-
      Fe2O3	1.01	—-
      SiO2	37.75	—-
      MgO	8.7	Max. 17%
      MnO	0.019	Max. 5.5%
      Sulphide sulphur	0.38	Max. 2.0%
      Loss on ignition	1.42	—-
      Insoluble residue	1.58	Max. 5.0%
      Glass content (%)	92	Max. 85%
      Physical properties
      Description		Value
      Fineness of GGBS		13.1%
      Specific gravity of GGBS		2.93

   3. Water

      Potable water with pH 7 was used.

   4. Superplasticizer

      The Ceraplast 300 RS(G) of sulphonated naphthalene formaldehyde condensates (SNF) type superplasticizer was used to increase the workability of self-compacting concrete at fresh state given in Table 3.

      Table 3 Properties of SNF type superplasticizer

      Specific gravity (30C)	1.234
      pH (10% solution)	8.5±0.5
      Solid %	43±0.5
      Sodium sulphate content	< 3.9%
      Viscosity (30C)	20±6

3. MIX DESIGN

   The mix design was prepared for M30 grade SCC as per ACI guidelines based on the effect of GGBS as binary blended cement. Based on the strength obtained from trial mix given in Table 4, the actual mix was formulated. The type of mix was established by the combination of powder and Viscosity Modifying Admixture (VMA) which is prepared by increasing powder content i.e. GGBS and using VMA i.e. superplasticizer. The concrete mix proportions of GGBS incorporated SCC here after designated as SCG were as shown in Table 5. The SCG mixes with 0%, 10%, 20%, 30%, 40% and 50% GGBS were termed as SCG0, SCG10, SCG20, SCG30, SCG40 and SCG50 respectively.

   Figure 5 were found to decrease by 0.003%, 2.4%,

   4.9%, 5.8%, 7.5% and 27.18%, 30.23%, 35.74%,

   14.25%, 16.73% with the replacement of 10%, 20%,

   30%, 40%, 50% GGBS to SCC respectively. Bouzoubaa et al has reported that increase in percentage of fly ash decreases the slump flow, the same holds good for GGBS also as shown in Table 6 and Figure 2. It is clearly evident from Table 6 and Figure 3 that the time taken by the SCG mixes to flow through the V- funnel decreases by 1.7%, 0.01%, 1.7%, 0.01% with replacement of 10%,

   20%, 30%, 40% GGBS and increases by 0.01% with replacement of 50% GGBS in SCC respectively which is not in good agreement with O.R.

   Table 4 Trial Mix

   Designation of mix	Cementitious binder by weight		FA by weight	CA by weight	Water content by weight of cement	Percentage of SP by volume of concrete	Compressive strength at the age of 28 days (N/mm2)
   	OPC	GGBS
   Trial 1	1	0	1.51	1.78	0.35	6.0	28.6
   Trial 2	1	0	1.51	1.78	0.35	4.0	30.5
   Trial 3	1	0	1.51	1.78	0.35		36.8

   Table 5 Validation of Mix design

   Designation of mix	Cementitious binder by weight		FA by weight	CA by weight	Water content by weight of cement	Percentage of SP by volume of concrete
   	OPC	GGBS
   SCG0	1	0	1.51	1.78	0.35	2
   SCG10	0.9	0.1	1.51	1.78	0.35	2
   SCG20	0.8	0.2	1.51	1.78	0.35	2
   SCG30	0.7	0.3	1.51	1.78	0.35	2
   SCG40	0.6	0.4	1.51	1.78	0.35	2
   SCG50	0.5	0.5	1.51	1.78	0.35	2

4. RHEOLOGICAL PROPERTIES

   The rheological properties of SCG mixes were found using slump test, V- funnel test, L – box test and U – box test as per EFNARC[16] recommendations and seen through Figure 1.

5. COMPRESSIVE STRENGTH

   150 × 150 × 150 mm cubes were prepared for checking compressive strength using SCG mixes and tested in a universal testing machine at 7, 28 and 56 days respectively. The average of three specimens is the reported strengths.

6. RESULTS AND DISCUSSION Table 6 Fresh Concrete properties

   Mix	SCG0	SCG10	SCG20	SCG30	SCG40	SCG50	EFNARC values
   Slump flow (mm)	708	706	691	673	667	655	650 – 800
   V-funnel test (sec)	11.5	11.3	11.4	11.3	11.4	11.6	6 – 12
   L-box (mm)	0.876	0.968	0.973	0.984	0.832	0.829	0.8 – 1
   U-box (mm)	5.26	3.83	3.67	3.38	4.51	4.38	0 – 30

   1. b)

   c) d)

   Figure 1. a) Slump flow test b) V- Funnel test c) L-Box test d) U- Box test

   Figure 2 Slump flow of SCG mixes Figure 3 Filling ability of SCG mixes from V- funnel

   Figure 4. Passing ability of SCG mixes from L box Figure 5 Passing ability of SCG mixes from U box

7. COMPRESSIVE STRENGTH

   Table 7 Compressive strength of SCG beams

   Sl.no	Specimen	Compressive strength (N/mm2)
   		7th day	28th day	56th day
   1	SCG0	27.55	36.81	39.85
   2	SCG10	26.45	28.57	40.95
   3	SCG20	27.15	29.37	41.15
   4	SCG30	28.35	30.73	41.75
   5	SCG40	29.75	32.33	42.85
   6	SCG50	27.65	29.88	41.95

   Compressivestren gth

   2)(N/mm

   50

   40 SCG0

   30 SCG10

   20 SCG20

   10 SCG30

   0 SCG40

   7th day 28th day 56th day SCG50

   Age of concrete

   Figure 6 Compressive strength of SCG mixes

   1. Beam Geometry

   2. Test procedure

8. FLEXURAL CAPACITY OF SCG BEAMS

Figure 7 Reinforcement cage

Figure 8 Beam reinforcement outline

Figure 9 Test setup sketch

Figure 10 Experimental test set up

1. Crack pattern and failure mode of control beam

   Figure 11 Crack pattern of control beam

   The initial crack and the final crack in the control beam specimen were noticed for the loading of 3T and 11.5T respectively. The control beam is failed by developing diagonal crack in the shear region which extended up to

   the middle fibre as seen in Figure 11.

2. Crack pattern and failure mode of SCG beams

   (a)

   (b)

   (c)

   (d)

   (e)

   Figure 12 Crack pattern of SCG beams

   Table 8 Initial and Final crack load of SCG beams

   Beam ID	Initial crack load (T)	Final crack load (T)
   CC	3	11.5
   SCGB10	4	12
   SCGB20	3.5	12.5
   SCGB30	4	14.5
   SCGB40	3.75	11.5
   SCGB50	3.5	11

   16 14.5

   LOAD (Ton)

   11

   14 11.5 12.5 12.5 11.5

   12

   10

   8

   3

   6 4 3.5 4 3.75 3.5

   4

   2

   0

   SCG 0 SCGB10SCGB20SCGB30SCGB40SCGB50

   Various combinations of mix

   Initial crack load

   Figure 13. Initial and final crack load of SCG beams

3. Moment carrying capacity

   Table 9 Theoretical and Experimental cracking moment

   Specimen	Mcr (theoretical) (kNm)	Mcr (experimental) (kNm)
   SCGB0	3.93	8.63
   SCGB10	4.00	11.50
   SCGB20	4.02	10.06
   SCGB30	4.05	11.50
   SCGB40	4.12	10.78
   SCGB50	4.06	10.06

   Theoretical cracking moment Mcr (theoretical) (kNm)

   4.18 Mcr Poly. (Mcr)

   4.14

   4.10

   4.06

   4.02

   3.98

   3.94 y = -0.0625×3 + 1.86×2 – 18.271x + 63.289

   R² = 0.8772

   3.90

   8.50 9.50 10.50 11.50

   Experimental cracking moment

   Mcr (experimental) (kNm) Figure 14 Cracking moment comparison

   The R-squared value equals 0.8772, which is a best. Since it is closed to 1, it can be concluded that the experimental cracking moment is in depends with theoretical cracking moment.

4. Ductility factor

   The ductility of SCGB beams were analyzed theoretically using ductility factor (µ) which is the ratio of ultimate deflection (u) to yield deflection (y) as given in (3). Ultimate deflection is defined as the deflection

   corresponding to the ultimate load and yield deflection is the deflection caused by the member during yielding.

   Table 10 Ductility factor of SCG beams

   Sl.no	Beam specimen	Ultimate	Yield deflection	Ductility factor
   		deflection (u)	(y)	µ = u/y
   1/p>	SCGB0	13.7	4.3	3.19
   2	SCGB10	14.6	3.7	3.94
   3	SCGB20	15.2	3.8	4
   4	SCGB30	15.9	4.1	3.88
   5	SCGB40	14.8	4.7	3.15
   6	SCGB50	13.9	4.5	3.08

   It is observed from Table 9 that ductility factor of SCGB10, SCGB20, SCGB30 were 19.0%, 20.2%, 17.78% higher than conventional concrete where as SCGB40 and SCGB50 were 1.25% and 3.45% lesser than conventional concrete.

   CONCLUSION

   • The use of GGBS as partial replacement for OPC in SCC not only reduces the CO2 emission from OPC but also produce the mechanical and rheological properties of SCC.

   • The workability of Self Compacting Concrete found by slump decreases with increase in percentage of GGBS, the time of flow through the V- funnel test time decreased with addition of GGBS in SCC and the blocking ratio obtained from L- box was found to be satisfactory up to 30% replacement of OPC with GGBS in SCC.

   • At the 7 days, the compressive strength of SCG10 and SCG20 were found to drop by 5.58% and 18.91% while compressive strength of SCG30, SCG40 and SCG50 were enhanced by 4.02%, 10.17% and 0.01% respectively from conventional mix.

   • It was pointed that the compressive strength of SCG10, SCG20, SCG30, SCG40, SCG50 were reduced by 28.85%, 26.05%, 21.29%, 15.68% , 24.26% and improved by 3.39%, 3.89%, 5.67%, 8.79%, 6.25% at the age of 28 and 56 days respectively from conventional mix.

   • SCGB beams with higher percentage of GGBS exhibits higher ductility.

   • The experimental cracking moment of SCGB0, SCGB10, SCGB20, SCGB30, SCGB40 and SCGB50 is 54.46%, 65.21%, 60%, 64.78%, 61.78% and 59.64% higher than the theoretical cracking moment. This exhibits that the replacement of GGBS to OPC in SCC produces the flexural behavior of self compacting concrete beams.

   • Ductility factor of SCGB10, SCGB20, SCGB30 were 19%, 20.2%, 17.78% higher than conventional concrete where as SCGB40 and SCGB50 were 1.25% and 3.45% lesser than conventional concrete mix. Hence, it can be concluded that upto 30% replacement of GGBS to OPC in SCC is effective.

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