Significant role of Supplementary Cementing Materials in Concrete for the Assessment of Durability

 

Dr. M. Vijaya Sekhar Reddy¹*, K. Ashalatha²

¹Head of the Department and Assistant Professor, Department of Civil Engineering, Srikalahasteeswara  Institute of Technology, Srikalahasti, Andhra Pradesh, India

²Lecturer, Department of Civil Engineering, Srikalahasteeswara Institute of Technology, Srikalahasti, Andhra Pradesh, India

 

ABSTRACT:

Concrete has today very demanding performance requirements. The concrete durability crisis which started to attract public attention forced the engineers to think about the performance of concrete proper mix design and careful construction using the best available materials and technologies are necessary to achieve quality concrete structures. The February 2007 report issued by the International Panel on Climate Change (IPCC) has started in no uncertain terms that global warming is no longer an issue that has to be debated. According to the report, global warming is here, and drastic actions are needed for the long term sustainability of our environment. Curing of concrete plays a major role in developing the concrete microstructure and pore structure and hence improves its durability and performance. It is in this context that this paper discusses the role of supplementing cementing materials as partial replacement for cement in concrete in reducing green house gas emissions. In the last decade the use of Supplementary Cementing Materials (SCM) has become an integral part of high strength and high performance concrete mix design. The addition of SCM to concrete reduces the heat of hydration and extends the service life in structures by improving both long term durability and strength. The addition of SCM to concrete reduces the heat of hydration and extends the service life in structures by improving both long-term durability and strength. Some of the commonly used SCM’s are Flyash, Silica fume, Blast furnace slag and Metakaoline. This paper presents the results of the durability characteristic properties of M30 grade of concrete without superplasticizer. The durability was evaluated using Rapid Chloride Permeability Test.

 

KEYWORDS: Standard Concrete, Supplementary Cementing Materials (SCMs), Durability, Rapid Chloride Permeability Test.

 

INTRODUCTION:

Durability of concrete plays an important role in the service life of RCC structures. It can be enhanced by improving impermeability, resistance to chloride ion diffusion and abrasion resistance. One of the ways to achieving this is by adding super plasticizers and supplementary cementing materials. Many researchers have demonstrated the beneficial effects of using Ground Granulated Blast Furnace Slag (GGBS) and flyash as Cement Replacement Materials and obtained a reduction in the rate of penetration of chloride ions concrete reducing the potential of chloride induced corrosion [1].

 

Smith Kevin et al., have established a testing regime to optimize the strengths and dura­bility characteristics of a wide range of high-performance concrete mixes. One of the prime methods of optimizing the mixtures was to implement supplemental cementitious materials, at their most advantageous levels. Fly ash, Slag cement, and Micro silica all proved to be highly effective in creating more durable concrete design mixtures. These materials have also shown success in substantially lowering chloride ingress, thus extending the initiation phase of corrosion [2].

 

Swamy, (1996), defines that a high performance concrete element is that which is designed to give optimized performance characteristics for a given set of load, usage and exposure conditions, consistent with requirement of cost, service life and durability [3].

 

One of the main reasons for deterioration of concrete in the past is that too much emphasis is placed on concrete compressive strength rather than on the performance criteria. The deterioration of reinforced concrete structures usually involves the transport of aggressive substances from the surrounding environment followed by physical and chemical actions in its internal structure. The transport of aggressive gases and/or liquids into concrete depends on its permeation characteristics. As the permeation of concrete decreases its durability performance, in terms of physio-chemical degradation, increases. Therefore, permeation of concrete is one of the most critical parameters in the determination of concrete durability in aggressive environments [4].

 

High performance concrete (HPC) is that which is designed to give optimized performance characteristics for the given set of materials, usage and exposure conditions, consistent with requirement of cost, service life and durability. The Ordinary Portland Cement is one of the main ingredients used for the production of concrete and has no alternative in the construction industry. Unfortunately, production OPC involves emission of large amounts of Carbon dioxide (CO₂) gas into the atmosphere, a major contributor for Green House Effect and Global Warming. Hence it is inevitable either to search for another material or partly replace it by SCM which should lead to global sustainable development and lowest possible environmental impact. Another advantage of using SCMs is increase in durability of concrete which consequently results increase in resource use efficiency of ingredients of concrete which are depleting at very fast rate. Long term performance of structure has become vital to the economies of all nations.

 

Durability of concrete is the ability of concrete to remain fully functional over an extended period under prevailing service conditions for the purpose for which it has been designed. The durability of concrete is classily related to its permeability. The permeability dictates the rate at which aggressive agents can penetrate to attack the concrete and the steel reinforcement. Corrosion related damage to the concrete structure is a major problem associated with high cost of repairs; sometimes replacement of structure. HPC is the key to achieve impermeable, durable and improved protection of embedded steel [5].

 

MATERIALS USED IN THE PRESENT STUDY:

Cement:

Ordinary Portland cement Zuari-53 grade conforming to IS: 12269-1987 [6] were used in concrete. The physical properties of the cement are listed in Table 1.

 

Aggregates:

A crushed granite rock with a maximum size of 20mm and 12mm with specific gravity of 2.60 was used as a coarse aggregate. Natural sand from Swarnamukhi River in Srikalahasthi with specific gravity of 2.60 was used as fine aggregate conforming to zone- II of IS 383-1970 [7]. The individual aggregates were blended to get the desired combined grading.

 

Water:

Potable water was used for mixing and curing of concrete cubes.

 

Supplementary Cementing Materials:

Flyash:

Fly ash was obtained directly from the M/s Ennore Thermal Power Station, Tamilnadu, India. The physicochemical analysis of sample was presented in Table 2.

 

Table 1. Physical Properties of Zuari-53 Grade Cement

Sl. No.	1	2	3	4	5
Properties	Specificgravity	Normalconsistency	Initial settingtime	Final settingtime	Compressive strength (Mpa)
Values	3.15	32%	60 min	320 min	3 days	7 days	28days
					29.4	44.8	56.5

 

 

Table 2. Physicochemical properties of Flyash sample.

 

Table 3. Chemical composition of Silica Fume.

Chemical Composition	Silica (SiO2)	Alumina (Al2O3)	Iron Oxide (Fe2O3)	Alkalies as (Na2O+K2O)	Calcium Oxide (CaO)	Magnesium Oxide (MgO)
Percentage	89.00	0.50	2.50	1.20	0.50	0.60

 

Table 4. Chemical composition of Metakaoline

Chemical Composition	SiO2	Al2O3	Fe2O3	TiO2	CaO	MgO	SO3	Na2O	K2O	LOI
Mass Percentage (%)	52 to 54	42 to 44	< 1 to 1.4	< 3	0.1	< 0.1	<0.1	< 0.05	<0.4	< 1

 

Silica Fume:

The silica fume used in the experimentation was obtained from Elkem Laboratory, Navi Mumbai. The chemical composition of Silica Fume is shown in Table 3.

 

Metakaoline:

The Metakaoline was obtained from M/s. 20 Microns Limited, Baroda, India. The chemical composition of Metakaoline is shown in Table 4.

 

RESULTS AND DISCUSSIONS:

In the present work, proportions for high performance concrete mix design of M₃₀ were carried out according to IS: 10262-2009 [8] recommendations. The mix proportions are presented in Table 5.

 

The standards cylindrical disc specimens of size 100 mm diameter and 50 mm thick after 90 days water curing were used in this test. As per ASTMC 1202-1997 [9]. The test results of M₃₀ mix of Binary system of concrete were compared with and without SCMs.

 

RAPID CHLORIDE PERMEABILITY TEST

The rapid chloride permeability test for different concrete mixtures was carried out as per ASTM C1202 [9]. Standard cylindrical disc specimens of size 100mm diameter and 50mm thick after 90days water curing were used. This test method covers the determination of the electrical conductance of concrete to provide a rapid indication of its resistance to penetration of chloride ions.

 

The apparatus consists of variable D.C. power supply which feeds constant stabilized voltage to the cells. The cells are made up of polymethyl methacrylate. The concrete specimens are kept in between the cells. The cells are connected to main instrument through 3 pin plug and socket for voltage feeding. The charge of current flowing through the specimen is measured by using an accurate digital current meter. The cells have grooved recess on one face and closed at other end. The specimen can be fit into the open faces of the cells. One of the cells is filled with sodium chloride (NaCl) solution 2.4M concentration and the other is filled with 0.3M Sodium hydroxide (NaOH-0.3M) solution.

 

The cylindrical disc specimen are coated with quick setting epoxy on their curved faces and mounted in the open spaces of the two cells. After checking the leak proofness, a 60V potential difference is applied between the electrodes. The electrochemical cell in the assembly results in migration of the chloride ions from sodium hydroxide solution through the pores of the concrete specimen. The current passed was noted at every 30 minutes over a period of 6 hours and the total electric charge passed through the specimen is calculated using the expression. The Table 6 shows the rating of chloride permeability according to ASTM C1202-1997[9].

 

The following formula, based on the trapezoidal rule can be used to calculate the average current flowing through one cell. 

Total Charge Passed in Coulomb’s (Qc)

Q  = (I₀+2I₃₀+2I₆₀+2I₉₀+2I₁₂₀+…+2I₃₀₀+2I₃₃₀+I₃₆₀)

Where,

Q = current flowing through one cell (coulombs)

I₀   = Current reading in amperes immediately after voltage is applied, and

I_t  = Current reading in amperes at t minutes after voltage is applied

 

 

Table 5. Mix Proportion for M₃₀ Concrete.

 

 

Table 6. Rating of chloride permeability

 

The object of the test was to evaluate the durability performance of M₃₀ mix and compared with conventional concrete. The Rapid Chloride Permeability test result of M₃₀ is represented in Table 7 and corresponding graphical picture is shown in Figure 1 respectively.

 

Table 7: Permeability of Chloride in Cement Concrete (M₃₀) for every 30 min. interval up to 6 hrs. By using RCPT apparatus for different dosages of SCMs without Super plasticizer

Grade of Concrete	Cement + Admixture	I average in coulombs	Penetrability of Chloride
M30	100% OPC	2230	Moderate
	20% FA	1350	Low
	10% SF	1255	Low
	10% MK	1310	Low

 

 

Fig 1: Permeability of Chloride in Cement Concrete (M₃₀) for every 30 min. interval upto 6 hrs. by using RCPT apparatus for different dosages of SCMs without Superplasticizer

 

CONCLUSIONS:

Rapid Chloride Permeability test results reveals that the total charge passed in Coulomb’s is low for M₃₀ grade of concrete with replacement of 10% Silica Fume. But the total charge passed in Coulomb’s for conventional concrete is slightly higher than the concrete replaced with SCMs.

 

The addition of SCMs causes pozzolanic reaction and thus resulting in improvement of pore structure of concrete leading to lower permeability, causing higher resistance to chloride ion penetration at the higher percentage replacement compared to conventional concrete. The incorporation of SCMs acts as super filler and induces high pozzolanic reaction, which consumes the CH crystals produced during hydration and converts to C-S-H gel.

 

REFERENCES:

1.       Bhaskar .S, Ravindra Gettu, Bharatkumar. B.H and Neelamegam. M, (2012) “Strength, bond and durability related properties of concretes with mineral admixtures”, Indian Concrete Journal, Vol. 86(2), pp. 9-16.

2.       Smith Kevin. M, Schokker Andrea. J, and Tikalsky Paul. J, (2004) “Performance of supplementary cementitious materials in concrete resistivity and corrosion monitoring evaluations”, ACI Materials Journal, Vol. 101(5), pp.385-390.

3.       Swamy. R. N (1996) “High Performance Durability through Design. International Workshop on High Performance Concrete”, ACI-SP, Vol.159 (14), pp. 209-230,

4.       Vaishali Ghorpade and Sudarsana Rao. H, (2011) “Chloride Ion Permeability Studies of Metakaoline based, High Performance Concrete”, International Journal of Engineering Science and Technology (IJEST), Vol.3 (2), pp.1617-1623.

5.       Khadiraranaikar. R.B, Chandrabansi. G. B. and Md. Asif Maruf,(2012) “Durability of High Performance Concrete Congaing Rice Husk Ash using Rapid Chloride Penetration Test, In Proceedings of International conference on Sustainability Challenges and advances in concrete technology (SCACT)”, Organized by Dept of Civil Engg, PSG College of Technology, Coimbatore, India.

6.       IS: 12269-1987, Specification for 53 Grade Ordinary Portland Cement, Bureau of Indian Standards, New Delhi, India, 1989.

7.       IS: 383-1970: specifications for coarse and fine aggregates for natural sources of concrete, Bureau of Indian standards, New Delhi.

8.       IS: 10262-2009: Concrete Mix Proportioning-guidelines, Bureau of Indian Standards, New Delhi.

9.       Standard test method for electrical indication of concrete’s ability to resist chloride ion penetration, ASTMC 1202-97, Annual book of ASTM standards, vol.04.02,pp.639-644.

 

 

 

 

 

Received on 11.04.2017                             Accepted on 16.05.2017

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