Experimental Study on Partial Replacement of Cement by GGBS and Fly Ash in Conventional Concrete

Abstract

Cement concrete is widely used in industrial plants, civil infrastructures, wastewater treatment plants and pipelines. It is a highly prone to acid attacks from the surrounding environment. Since acidic environments will accelerate the deterioration of concrete, various types of polymer coating materials are being used to protect the concrete surfaces. Hence an attempt has been made in this investigation on partial replacement of cement with GGBS along with incorporation of fly ash of 20% of the volume of concrete. Various strength parameters of the concrete specimens are tested. The combination used is GGBS with 10%, 20%, 30%, 40% by the weight of cement for M25 grade concrete at an age of 7 days, 28 days and 56 days. Cubes are cast, curried and tested to assess the influence of partial replacement of cement with fly ash and GGBS and then found the optimum content as 20% of GGBS and fly ash 20% from the experimental results. Then final combination is 20% of cement with GGBS along with incorporation of fly ash of 20% percentages of the volume of concrete. The compressive strength values are increased by 10% than those of conventional concrete mixture at a mixture prepared with 20% GGBS and 20% Fly ash. Further increase in GGBS percentage with constant fly ash percentage proved its incompatibility nature where it is shown low strength when compared with controlled concrete mix. X-ray Diffraction (XRD) technique has also been used to get insights into the quality and composition of the concrete, aiding in the assessment of its suitability for specific construction applications.

Introduction

I. INTRODUCTION

The most predominately used binder in concrete is blended cement. Now a days construction industry is looking for different construction materials as a replacement to conventional concrete in view of its environmental behavior. The Ordinary Portland Cement (OPC) is one of the main ingredients used for the production of concrete and has no alternative in the civil construction industry. Unfortunately, production of cement involves emission of large amounts of carbon-dioxide gas into the atmosphere, a major contributor for greenhouse effect and the global warming, hence it is inevitable either to search for another material or partly replace it by some other material. The search for any such material, which can be used as an alternative or as a supplementary for cement should lead to global sustainable development and lowest possible environmental impact. Substantial energy and cost savings can result when industrial by products are used as a partial replacement of cement. Fly ash, Ground Granulated Blast Furnace Slag, rice husk ash, High Reactive Metakaolin, silica fume are some of the pozzolanic materials which can be used in concrete as partial replacement of cement. A number of studies are going on in India as well as abroad to study the impact of use of these pozzolanic materials as cement replacements and the results are encouraging. Addition of fly ash to concrete has many advantages like high strength, durability and reduction in cement production.

The concrete containing Ground Granulated Blast Furnace Slag (GGBS), on vibration becomes ‘mobile’ and compacts well. Silica fume greatly reduces, or even eliminates bleeding; the particle of Pozzolanic Fly Ash (PFA) is spherical and thus improves the workability. Their inclusion has the physical effect of modifying the flocculation of cement, with a resulting reduction in the water demand. The pore size in concrete is smaller. The fine particles ‘fit in between cement particles, thereby reducing permeability. The Fly ash (FA), Ground Granulated Blast Furnace slag (GGBS), Silica fumes being finer than OPC, less bleeding is observed. The freshly placed concrete is very stable, being very cohesive and having strong internal cohesion. This has a negative effect in the form of plastic shrinkage. The workability increases, and thus water content can be reduced by about 3%. Recent research evaluated the behavior of concrete made with Supplementary Cementations Materials (SCMs) such as fly ash and Ground Granulated Blast-Furnace Slag (GGBS) under a various condition.

Correlations were found among the source and proportion of the Supplementary Cementations Materials (SCM), curing conditions, concrete set time, maturity, strength development, and cracking potential. The production of GGBS is more environmentally friendly compared to the production of OPC, thus producing a more environmentally friendly concrete than the OPC concrete. In this paper, an attempt has been made to study the effects of GGBS as a constant replacement of cement on durability and mechanical properties of concrete and its scope to address environmental pollution caused by industrial by-products.

II. MATERIALS USED

The physical properties of cement, fine aggregates, coarse aggregates, fly ash, GGBS and water used for mix design of M25 grade of concrete were tested in laboratory and are mentioned below.

A. Cement

Ordinary Portland cement of 53 grade cements conforming to IS 8112-1989 is used for the present experimental investigation. Cement was tested as per the procedure given in IS: 4031 and IS: 4032. The physical properties of the cement used are as listed in Table 1

Table 1 Physical Properties of Ordinary Portland Cement

B. Fine Aggregate

The fine aggregate conforming to IS 383-1970 in zone-II is used in mix. The sand which was locally available and passing through 4.75mm IS sieve size was used as fine aggregate. The physical properties of the fine aggregates are as listed in table below:

C. Coarse Aggregates

The coarse aggregates with nominal maximum size of aggregates as 20mm (60%) and 10mm (40%) as per Indian standard were used. The physical properties of the coarse aggregates are as listed in Table 2

Table 2 Physical Properties of Coarse Aggregates and fine aggregates

D. Ground Granulated Blast Furnace Slag (GGBS)

Ground Granulated Blast Furnace Slag (GGBS), also known as slag cement or simply slag, is a byproduct of the iron and steel industry. The GGBS was procured from the JSW cement industry, Chennai.

E. Fly ash

Fly Ash is the finely divided mineral residue resulting from the combustion of powdered coal in Thermal power plants. The fly ash (class F) has been taken from the NTPC Simhadri Thermal power plant situated at near Vishakhapatnam.

Table 3 Physical and Chemical Properties of Fly ash and GGBS

The physical and chemical properties of Fly ash and GGBS are shown in Table 3.

F. Water

Potable water was used for mixing and curing which was free from any amounts of oils, acids, alkalis, sugar, salts and organic materials or other substances that may be deleterious to concrete or steel confirming to IS: 3025 – 1964 part 22, part 23 and IS: 456 – 2000 [Code of practice for plain and reinforced concrete]. The pH value should not be less than 6. The solids present were within the permissible limits as per clause 5.4 of IS: 456 – 2000.

III. METHODOLOGY

The aim of this paper is to study the effect of fly ash on compressive strength of concrete by partial replacement of cement with fly ash by 20% constant and varying with 10%, 20%, 30% and 40% of GGBS. The concrete mix of M25 grade was prepared as per IS10262:2009 having mix design ratio as 1:2.13:3 and w/c ratio of 0.45. To carry out the experimental investigation total 30 cubes of size 150mm x 150mm were casted. The compressive strength of specimens is determined after 7days, 28 days and 56 days of curing respectively with surface dried condition as per Indian Standards. Moulds size 150 x 150 x 150mm was used for evaluation of compressive strength. This ultimate load divided by the cross-sectional area of the cube (150mm x 150mm) yields the compressive strength of concrete.

Splitting tensile strength is an indirect method to determine tensile strength of concrete. Splitting tensile strength of concrete was evaluated at age of 7 days, 28 days and 56 days using standard cylindrical specimens of 150mm diameter and 300mm height. Compression Testing Machine (CTM) of 5000 KN capacity was used for the testing of compressive strength of concrete.

When concrete is subjected to bending stress, Compressive as well as tensile stresses are developed at top and bottom fibers respectively. The strength shown by the concrete against bending is known as flexural strength. The standard size of specimen is 150mm x150mm x700mm. The flexural beam specimens are tested at 7 days, 28 days and 56 days. The average of three specimens was reported as the flexural tensile strength. Different mixes with varying combinations of GGBS and fly ash are considered for testing. Various tests are done on concrete at both fresh and hardened stage to evolve the Performance of the concrete. The combinations used are described below.

IV. X-RAY DIFFRACTION (XRD) ANALYSIS

Divergence could be a physical paradox that's composed in EM radiation warding off limitations in case the scale of the barriers matches to the frequency. This paradox has carried out for the investigation of specimens since the particle plans are positioned at similar stretch   to X ray lengths. X rays are EM waves much like light, but whose frequency is more concise (λ=0, 2 to 200 Å). XRD is generated as a reflection at legitimately characterized viewpoints. Each crystalline segment has its self-diffraction picture.

For the XRD assessment we utilize diffraction gadgets, particularly admit to the Bragg–Brentano framework. The basic pattern revolves at a divergent attitude as “θ”, even as the sensor revolves at the angle of “2θ”.

A series of divergent peak values are inverted by the equipment called diffractogram. Then the range of depth of the divergent X ray is displayed and measured in the form of pulses or second. Along with this, the Bragg angle is also determined in terms of degrees and it is denoted as “θ”. Each structure of the specimen has its own divergent image depends on the individual type. 

The diffraction system permits overall execution in subsequent research: The details of crystalline structures were found in terms of qualitative and quantitative investigation. The segment alterations were examined for the identification of many factors such as the crystallographic type, the scale of the inner components of the particular specimen and many others. The X ray divergent technique is used to describe and complete the crystalline phases, if the respective phase Imitate extra of 3 to 4% mass. Few software’s are used to explain the Bragg’s relationship, shown in (1) such as match software, in the Powder Diffraction File (PDF) database.

2dsinθ = n λ                                                                                (1)

Where,

 d is the spacing between diffracting planes,

θ is the incident angle,

 n is an integer,

 λ is the beam wavelength.

The fine powder was then sieved through a sieve of 60 micron and portion of the powder passing 60 microns was used for X-ray diffraction testing. X-ray diffraction pattern was recorded with X-ray diffractometer with Cu Kα radiation (λ= 54 Å) at diffraction angle 2θ ranged between 10° to 80° in steps of 2θ = 0.013°. Different phase present in the cement paste at 28days were identified analysing the peaks of X-ray diffraction patterns with the help of ‘X’ Pert High Score Plus” software tool. Figure 5 illustrates the X-Ray diffraction principle.

Conclusion

This experimental study shows that the combination of fly ash and GGBS will enhance the performance of the concrete in terms of Workability & Mechanical properties. The following conclusions were drawn: 1) The Cement replacement by 20% Fly ash and 20% GGBS gives a gradual increase in compressive strength. 2) It can be observed at 7 days Compressive strength of M3 mix (20% FLYASH & 20% GGBS) is more than that of M1 mix (Controlled mix) by 9.59%., 28 days compressive strength of M3 mix is more than that of M1 mix by 8.22% and 56-days compressive strength of M3 mix is more than that of M1 mix by 12.62%. 3) It can be observed at 7 days Split tensile strength of M3 mix (20% GGBS & 20% FLYASH) is more than that of M1 mix (Controlled mix) by 11.80%, 28 days Split tensile strength of M3 mix is more than that M1 mix by 15.66% and 56 days Split tensile strength of M3 mix is more than that M1 mix by 16.66%. 4) It can be observed at 7 days Flexural strength of M3 mix (20% GGBS & 20% FLYASH) is more than that of M1 mix (Controlled mix) by 5.16%, 28-days flexural strength of M3 mix is more than that M1 mix by 4.98% and 56-days flexural strength of M3 mix is more than that M1 mix by 5.0 %. 5) Considering the mechanical behaviour, the optimum mix is M3 mix i.e., Cement replaced with 20% Fly ash and 20% GGBS. 6) It also shown that workability decreases with increase in GGBS %. 7) Further replacement of cement with Fly ash and GGBS shown decreased strength which shows the incompatibility nature of materials used. 8) It is observed that from the XRD Analysis Results, a sharp peak of C-S-H, Bellite which are responsible for early age strength and small peak of CH indicates low porosity which may reduce corrosion.

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Copyright

Copyright © 2023 K. Gopala Rao, Dr. B. Krishna Rao. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.