Strength And Durability Investigations On Self Consolidated Concrete With Pozzolanic Filler And Inert Filler

Strength And Durability Investigations On Self Consolidated Concrete With Pozzolanic Filler And Inert Filler

Ms. Priyanka P. Naik*, Prof. M. R. Vyawahare**

* Department of Civil Engineering, Babasaheb Naik College of Engineering Pusad, Amravati University Pusad-445215, Yavatmal, Maharashtra, India

** Associate Professor of Civil Engineering Department, Babasaheb Naik College of Engineering Pusad, Amravati University, Pusad-445215, Yavatmal, Maharashtra, India

ABSTRACT

Concrete is a versatile widely used construction material. Ever since concrete has been accepted as a material for construction, researchers have been trying to improve its quality and enhance its performance. Recent changes in construction industry demand improved durability of structures. There is a methodological shift in the concrete design from a strength based concept to a performance based design. At present there is a large emphasis on performance aspect of concrete. One such thought has lead to the development of Self Consolidated Concrete (SCC). It is considered as the most revolutionary development in concrete construction. SCC is a new kind of High Performance Concrete (HPC) with excellent deformability and segregation resistance. It can flow through and fill the gaps of reinforcement and corners of moulds without any need for vibration and compaction during the placing process.

The primary aim of this study is to explore the feasibility of using SCC by examining its basic properties and durability characteristics i.e. sorptivity and chloride ion penetration. An extensive literature survey was conducted to explore the present state of knowledge on the durability performance of SCC. However because it usually requires a larger content of binder and chemical admixtures compared to ordinary concrete, its material cost is generally 20-50% higher, which has been major hindrance to a wider implementation of its use. There is growing evidence that incorporating high volumes of mineral admixtures

and micro filler as additives in SCC can make it cost effective, however the durability of such need to be proven.

This work consists of: (i) development of suitable mixes of SCC using separately the silica fume and quarry dust as active and inert filler satisfying the requirements of the fresh state. (ii) Casting of concrete samples and testing them for compressive strength, split tensile strength, sorptivity, and chloride permeability test (iii) Comparison of effect of pozzolanic filler and inert filler on strength and durability of self consolidating concrete.

Keyword: Self Consolidated Concrete (SCC), silica fume, quarry dust, strength, durability

1. INTRODUCTION

   SCC is a new kind of High Performance Concrete (HPC) which has an excellent deformability and segregation resistance. By name it can be defined as a concrete, which can flow through and fill the gaps of reinforcement and corners of the moulds without any need for external vibration. SCC compacts itself due to its self weight and de-aerates almost completely while flowing in the formwork. SCC can also be used in situations where it is difficult or impossible to use mechanical compaction for fresh concrete, such as underwater concreting, cast in-situ pile foundations, machine bases and columns or walls with congested

   reinforcement. The high flow ability of SCC makes it possible to fill the formwork without vibration. Since its inception, it has been widely used in large construction works or projects in Japan. Recently, this concrete has gained wide use for different applications and structural configurations across the world.

   High strength concrete can be produced with normal concrete. But these concretes cannot flow freely by themselves, to pack every corner of moulds and all gaps of reinforcement. High strength concrete based elements require thorough compaction and vibration in the construction process. SCC has more favourable characteristics such as high fluidity, good segregation resistance and distinctive self-compacting ability without any need for external or internal vibration during the placing process. It can be compacted into every corner of formwork purely by means of its own weight without any segregation. Hence, it reduces the risk of honey combing of concrete.

   Development of SCC is a very desirable achievement in the construction industry for overcoming the problems associated with cast-in place concrete. It is not affected by the skill of workers, shape and amount 13 of reinforcing bar arrangement of a structure. Due to its high fluidity and resisting power to segregation, it can be pumped over longer distances. It extends the possibility of use of various by products in its manufacturing. The use of SCC not only shortens the construction period but also ensures quality and durability of concrete. It replaces manual compaction of fresh concrete with a modern semi-automatic placing technology.

   In present study attempt is made to investigate the effect of pozzolanic filler and inert filler on the strength and durability of self consolidated concrete. The durability of concrete depends on many factors. Those most often considered are cement reactivity with environment, low permeability, diffusion coefficient of species such as sulphate ions and compressive strength. The water absorption is also very important factor effecting durability. The use of mineral additives may provide a way of improving the durability of SCC depending on the type and amount of mineral additive used. In this experiment silica fume was used as

   pozzolanic filler and quarry dust was used as inert filler.

2. EXPERIMENTAL INVESTIGATION

   1. Materials

      1. Cement

         In this experimental study, Ordinary Portland Cement 53 grade, conforming to IS: 8112-1989 was used. The different laboratory tests were conducted on cement to determine the physical and mechanical properties of the cement used are shown in Table 1.

         Table 1: Properties of Cement

         Physical Property	Result
         Fineness (retained on 90-m sieve)	5%
         Normal Consistency	29%
         Vicat initial setting time (minutes)	75 min.
         Vicat final setting time (minutes)	482 min.
         Specific gravity	3.12
         Compressive strength at 7-days	37.33 Mpa
         Compressive strength at 28-days	53.64 Mpa

      2. Aggregates

         Locally available natural sand with 4.75 mm maximum size confirming to class II- IS 383 was used as fine aggregate, having specific gravity, fineness modulus and unit weight as given in Table 3 and crushed stone with 16mm maximum size having specific gravity, fineness modulus and unit weight as given in Table 3 was used as coarse aggregate. Table 2 gives the physical properties of the coarse and fine aggregates.

         Table 2: Physical Properties of Coarse and Fine Aggregates

         Property	Fine Aggregate	Coarse Aggregate
         Specific Gravity	2.5	2.85
         Fineness Modulus	2.8	7.44
         Surface Texture	Smooth	—
         Particle shape	Rounded	Angular

      3. Water

         Ordinary potale water available in the laboratory has been used.

      4. Chemical Admixtures

         Super plasticizers or high range water reducing admixtures are an essential component of SCC. It is used to provide necessary workability. Glanium B233 (modified P.C. based) was obtained from BASF India Limited, Mumbai.

      5. Quarry Dust

         Quarry dust is used as an inert powder. It has been obtained from stone crusher; Quarry dust of specific gravity 2.5 passing through 90µ sieve is used. Chemical composition of Quarry dust is given in table 3.

         Then the mix was checked for self compacting ability by slump flow test, v-funnel test and L-box test.

         Table 5: Mixture proportion for 1m3 of SCC

         Sr. No.	Constituents	Quantity (%)
         1.	SiO2	70.74
         2.	Al2O3	20.67
         3.	Fe2O3	2.88
         4.	TiO2	0.33
         5.	Na2O	0.11
         6.	K2O	0.19
         7.	MgO	1.57
         8.	M2O2	0.01
         9.	CaO	0.2
         10.	ZnO	0.01
         11.	Pb	625 ppm
         12.	Cr	125 ppm
         13.	LOI	0.72

         Sr. No.	Constituents	Quantity (%)
         1.	SiO2	70.74
         2.	Al2O3	20.67
         3.	Fe2O3	2.88
         4.	TiO2	0.33
         5.	Na2O	0.11
         6.	K2O	0.19
         7.	MgO	1.57
         8.	M2O2	0.01
         9.	CaO	0.2
         10.	ZnO	0.01
         11.	Pb	625 ppm
         12.	Cr	125 ppm
         13.	LOI	0.72

         Table 3: Chemical Composition of Quarry Dust

      6. Silica Fume

         Silica fume imparts very good improvement to rheological, mechanical and chemical properties. It improves the durability of the concrete by reinforcing the microstructure through filler effect and reduces segregation and bleeding. It also helps in achieving high early strength. Silica fume of specific gravity 2.2 is used in this study. Chemical composition of silica fume is given in table 4. Silica fume was obtained form ELKEM materials, Mumbai.

         Table 4: Chemical Composition of Silica Fume

         Sr. No.	Constituents	Quantity (%)
         1.	Sio2	91.03
         2.	Al2O3	0.39
         3.	Fe2O3	2.11
         4.	CaO	1.5
         5.	LOI	4.05

         2.2 Mix Proportion

         The mix proportion was done based on the method proposed by Nan-Su et al. [4]. The mix designs were carried out for concrete grades 25, 35, 45. This method was preferred as it has the advantage of considering the strengths of the SCC mix.

         The details of mixes are given in table 5. All the ingredients were first mixed in dry condition. Then 70% of calculated amount of water was added to the dry mix and mixed thoroughly. Then 30% of water was mixed with the super plasticizer and added in the mix.

         Self Compact ability Tests on SCC Mixes

         Various tests were conducted on the trial mixes to check for their acceptance and self compact ability properties. The tests included flow test and V- funnel tests for checking the filling ability and L-box test for passing ability. The mixes were checked for the SCC acceptance criteria given in table no. 6.

         Table No. 6 SCC Acceptance Criteria

         Method	Properties	Range of values
         Slump flow	Filling ability	650-800mm
         V-funnel	Viscosity	6-12 sec.
         L-box	Passing ability	0.8-1.0

         Table 7: SCC Test Results of SCC Mixes

         Mix Code	Flow (mm)	V-funnel time (s)	L-box (p/p)	Segregation	Remark
         S1	660	8.6	0.90	No	SCC
         S2	680	8.9	0.88	No	SCC
         S3	710	9.4	0.97	No	SCC
         D1	720	8.8	0.95	No	SCC
         D2	705	9.3	0.93	No	SCC
         D3	690	9.5	0.90	No	SCC

         The result of the self compact ability tests are tabulated in table 7. All the mixes satisfied the acceptance criteria for self compacting concrete. Hence these mixes were chosen as the successful mixes. The cube specimens of size 150 x 150 x 150 mm were cast for the successful mixes and were tested for the 7-day 28-day compressive strengths. Also cylindrical specimens of size 300mm height and 150mm diameter were cast and tested for 28-days split tensile strength.

3. TEST CONDUCTED

   COMPRESSIVE STRENGTH

   The compressive loading test on concrete cubes was carried out on a compression testing machine of capacity of 2000KN. For compressive strength test, the specimens used were 150mm x 150mm x 150mm cubes. The strength measurements of concrete specimens were performed at 7 and 28 days. Three specimens tested for each mixture.

   SPLIT TENSILE STRENGTH

   Cylindrical specimens of size 150mm diameter and 300mm height were used. The test was carried out by placing a cylinder horizontally between the loading surfaces of a compression testing machine and the load is applied until failure of the cylinder, along the vertical diameter. The strength measurements of concrete specimens were performed at 7 and 28 days.

   SORPTIVITY

   To examine the durability characteristics of SCC, sorptivity was employed. Sorptivity characteristics of SCC for structures located above ground level would be more appropriate; sorptivity coefficient can be determined by following method.

   Test Method

   Standard 100mm cube specimens were cast. On the following day of casting, the specimens were de-moulded and located in water curing condition for the periods of 28 days.

   Water absorption (sorptivity) tests was carried out to determine the sorptivity coefficient of concrete specimens which were preconditioned in oven at 1050C for 24 hr. and then cooled down within desiccators for 24h to achieve a constant moisture level. Then, four sides of the concrete specimens were sealed by electrical tape to avoid evapoative effect as well as to maintain uniaxial water flow during the test and the opposite faces left open see in fig. 4. Before locating the specimens on water, their initial weight was recorded. One face of specimen was in contact with water, while the water absorption at predefined intervals was noted by taking weight. The specimen was submerged 5mm in water. Procedure was repeated, consecutively at various time intervals 15 min., 30 min., 1 hr, 2 hr, 4 hr, 6 hr, 24 hr, 48 hr and 72 hr until

   the last reading. Sorptivity coefficient can be calculated by the following expression.

   S=

   Where,

   S = Sorptivity (cm/s1/2)

   Q = Vol. of water absorbed in cm3

   A = Surface area in contact with water in cm2 t = the time (s)

   Fig. 1: Experimental Set-up for Water Sorptivity Test

   CHLORIDE PERMEABILITY TEST

   In chloride permeability test, Concrete blocks were immersed in 3% NaCl solution after period of 28days the specimens were removed from curing tank and their surfaces were cleaned with soft nylon brush to remove weak reaction products.

   After a specified duration (28 days) specimens were removed from solution, split and the depth of chloride penetration was determined in one half of the specimen using a colorimetric technique in which silver nitrate solution was used as a colorimetric indicator.

   When silver nitrate solution was sprayed on a concrete containing chloride ions, a chemical reaction occurred. The chlorides bind with the silver to produce silver chloride, a whitish substance. In the absence of chlorides, the silver instead bonds with the hydroxides present in the concrete creating a brownish colour. A whitish colour at the border of specimen shows the depth of penetration.

   Fig. 2: Chloride Permeability Test

4. RESULT AND DISCUSSION

   1. STRENGTH PROPERTIES OF SCC MIXES Compressive Strength of SCC Mixes

      Table 8 and fig. no. 3 gives the cube compressive strength of the mixes. It can be seen that strength increases with decreasing Silica Fume and Quarry Dust content. Four standard cubes each for various mixes were tested to determine 7 days and 28 days compressive strength, compressive strength increased with decrease in W/C ratio.

      The strength of SCC with silica fume and SCC with quarry dust ranges from 45 MPa to 62 MPa and 31 MPa to 52 MPa respectively, average compressive strength of SCC having silica fume at 28-days compared to SCC having quarry dust was increased by 25.51%. Depending upon the mineral admixture, curing condition, the result indicates that the Mineral admixture addition helps in gain of compressive strength than that of Quarry dust. The compressive strength of SCC containing silica fume was greater than that of SCC containing Quarry dust.

      Split Tensile Strength

      The split tensile strength result shown in table 8 and fig. no. 4. Two standard cylinder specimens each for various mixes were tested to determine 7-days and 28-days split tensile strength. Split tensile strength shows the same trend as compressive strength, increased with decrease in W/C ratio.

      Split tensile strength of SCC containing Silica Fume & SCC having quarry dust ranges from 4.3 MPa to 6.72 MPa and 3.5 MPa to 5.29 MPa respectively. Average split tensile strength of SCC having silica fume at 28-days compared to SCC having quarry dust was increased by 18.06%.

      Silica fume shows the better result in strength properties than quarry dust.

      Table 8: Harden Properties

      Mix Code	W/C	Compressive Strength (MPa)		Split Tensile Strength (MPa)
      		7 Days	28 Days	7 Days	28 Days
      S1	0.45	27.33	45.11	3.07	4.3
      S2	0.40	32.29	57.11	4.87	5.58
      S3	0.35	44.66	61.12	5.86	6.72
      D1	0.45	22.52	31.5	2.1	3.5
      D2	0.40	29.4	39.9	3.4	4.78
      D3	0.35	37	51.2	4.2	5.29

      Fig. 3: Result of Compressive strength

      Fig. 4: Result of Split Tensile Strength

   2. DURABILITY PROPERTIES OF SCC MIXES Sorptivity

Sorptivity coefficient was determined by means of simple test allowing one face of concrete specimen in contact with water and the mass of water absorbed by capillary suction was measured at predefined intervals.

The result of sorptivity tests are given in table 10 and fig. no.5 on the basis of concrete type. It is indicated that SCC containing Silica Fume gives lower sorptivity values than that of SCC containing dust. There is noticeable difference in the capacity of water absorption by capillary action between SCC made with silica fume and SCC with quarry dust. The highest sorptivity value (2.2×10-3)cm/s1/2 has been obtained from SCC with quarry dust and lowest sorptivity value (0.43×10-3)cm/s1/2 obtained from SCC silica fume.

However by using silica fume the sorptivity decreases, as shown in table 9.

It can be suggested, therefore, that using pozzolanic filler such as Silica Fume can enhance the resistivity of SCC against water absorption significantly.

Table 9: Result of sorptivity

Fig. 5: Result of Sorptivity test Chloride Permeability Test

It is evident that the pozzolanic admixture creates a more compact concrete. The chloride ion penetration decreases when admixture added because they physically occupy pores in the cement paste by virtue of their particle size.

The depth of chloride penetration is determined in one half of the specimen using a colorimetric technique in which silver nitrate solution is used as a colorimetric indicator. When silver nitrate solution is sprayed on concrete containing chloride ions, a whitish colour at the border of split specimen shows the depth of penetration.

Fig. no.6 and table no.10 shows that SCC made with Quarry Dust shows highest depth of penetration i.e. 1.24 cm and SCC made with silica fume shows lowest depth of penetration i.e. 0.31cm.

Depth of chloride ion penetration of SCC having Quarry Dust compared to SCC containing silica fume was increased by 47.68%, 64.76%, and 72.80% for each grade respectively.

Table 10: Chloride Permeability Test

Fig. 6: Result of Chloride permeability test

Conclusion

In the present study of self compacting concrete using pozzolanic filler and inert filler following conclusions were arrived from the experimental investigation. Because of extreme fineness and very high amorphous silicon dioxide content, silica fume is a very reactive pozzolanic material. Hence SCC withsilica fume shows the good result in both strength and durability properties.

1. Silica fume was observed to improve the mechanical properties of SCC because of the pozzolanic action of silica fume.

2. Average compressive strength of SCC having silica fume at 28-days compared to SCC having quarry dust was increased by 25.51%.

3. Average split tensile strength of SCC having silica fume at 28-days compared to SCC having quarry dust was increased by 18.06%.

4. It has been indicated that SCC having Silica Fume have higher compressive strength and split tensile than those of SCC having inert powder as additional filler i.e. quarry dust. The silica fume has contributed to large extent in development of strength.

5. As the water cement ratio reduces and cements content increases, strength increases in SCC made with silica fume and SCC made with quarry dust.

6. It has been indicated that SCC having Silica Fume has lower soprtivity values in comparison with by SCC containing quarry dust.

7. Proper curing and use of pozzolanic admixture such as Silica Fume as additional powder component enhance the resistivity against sorptivity significantly.

8. The chloride permeability result shows that SCC having silica fume has superior performance in durability properties than SCC having quarry dust.

9. As the water cement ratio reduces strength as well as durability increases in SCC with silica fumes and SCC with quarry dust.

10. Durability of SCC with silica fume is more than that of SCC with quarry dust because of the pozzolanic action of silica fume.

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