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Weathered Crystalline Rock: Suitability As Fine Aggregate In Concrete – A Comparative Study

Eldhose M Mathew1, Shaji M Jamal2, Ranjan Abraham3
Project Engineer, E World Builders and Developers, (E World Electronics India Pvt. Ltd), Kerala, India1
Asst. Prof., Dept. of Civil Engg., Ilahia College of Engg & Tech., Muvattupuzha, Kerala, India2
Asst. Prof., Dept. of Civil Engg., Ilahia College of Engg & Tech., Muvattupuzha, Kerala, India3
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Abstract

Concrete is one of the most versatile building materials used in the world. It is prepared by mixing cement, fine aggregate, coarse aggregate and water in suitable proportions. From earlier days onwards river sand is used as fine aggregate. Nowadays, M-sand, pit sand etc. are also used. Since pit sand is available only at certain regions and due to the scarcity of river sand and M-sand, it has become necessary to find an alternative material, as fine aggregate. The alternative material selected here is sand from Weathered Crystalline Rock. And this type of rock is abundantly available at low cost in tropical areas. This paper discusses the use of Weathered Crystalline Sand as fine aggregate in concrete. A comparison of properties like fineness, specific gravity, bulking of sand, bulk density, compressive strength of mortar cubes and compressive strength of concrete cubes using different fine aggregates is also conducted.

Keywords

Fine aggregate, weathered crystalline rock, river sand replacement, scarcity of river sand, manufactured sand

INTRODUCTION

A. General
Concrete is widely used in domestic, commercial, recreational, rural and educational construction. Communities around the world depend on concrete as a safe, strong and simple building material. It is used in all types of constructions. Despite the common usage of concrete, a few people are aware of the considerations involved in designing strong, durable, high quality concrete. Construction industry has undergone a rapid change in the last century especially with the advancement of different types of concrete. Concrete is the largest produced construction material. The production of concrete is of the order of 10 billion tons annually. Concrete, with the development of technology, has undergone several changes not only in its composition, but also in its performance and application. The versatility and mouldability of this material, its high compressive strength and the discovery of reinforcing and prestressing techniques which help to make up for its low tensile strength has contributed largely to its wide spread use. We can rightly say that we are in the age of concrete.
It is easy to make concrete. Extensive research works were carried out almost from the beginning of this century, not only on the methods but also on the materials used for concrete making. Still, not many men on the job seem to make use of the known techniques and materials for making good concrete, which is necessary for achieving strong, durable and economic construction.
Concrete is a man-made rock, consisting mainly of aggregates dispersed in a hydrated cement paste. Aggregates are the important constituents in concrete. They give body to the concrete, reduce shrinkage and effect economy. Aggregates occupy 65-80 percent of the volume of concrete. Aggregates are mostly natural rocks, either crushed or collected as gravel from rivers or as slag from volcanic rocks and then processed (i.e., washed and graded) for use in concrete. Aggregates can be classified on the basis of size as coarse aggregate and fine aggregate. The aggregate most of which is retained on 4.75mm IS sieve and contains not more than 0 to 10% of finer material is known as coarse aggregate. Broken stone or crushed rock is generally used as coarse aggregate. Aggregate passing through 4.75mm IS sieve and retained on 0.15mm IS sieve is called fine aggregate. Usually we use river sand as fine aggregate, but nowadays other materials like pit sand, M-sand etc. are also used abundantly in the field of construction.
B. Objectives of the Study
The main objective of this project is a study on the viability of using WEATHERED CRYSTALLINE SAND as fine aggregate. Three different types of fine aggregates are used for the test. They are River sand, M-sand and Weathered Crystalline sand. The first two types of fine aggregates are widely used in construction fields nowadays. The third one is the proposed fine aggregate. The comparison of various properties of M-sand and Weathered Crystalline sand with properties of River sand is also done. The tests conducted are grain size analysis, specific gravity test, workability test, bulk density, bulking of fine aggregate, compressive strength of mortar cube and compressive strength of concrete cube by using each type of sand. To determine the components of the weathered crystalline rock, X-Ray Fluorescence Spectrometry Analysis (XRF Analysis) is conducted.
C. Scope of the Study
The scope of the study is limited to investigate the suitability of Weathered Crystalline Sand as fine aggregate by conducting tests on grain size, specific gravity, workability, bulk density, bulking of fine aggregate, compressive strength of mortar cube and compressive strength of concrete cube. Nine mortar cubes were cast by using each variety of sand. Also nine concrete cubes were cast by using each variety of sand. To determine the components of the weathered crystalline rock, X-Ray Fluorescence Spectrometry Analysis (XRF Analysis) was conducted in the X-ray Fluorescence Lab, Centre for Earth Science Studies, Akkulam, Trivandrum.
D. Weathered Crystalline Rock
Weathered Crystalline Rocks are metamorphic rocks seen in the tropical areas like Kerala. They are formed by the weathering action on the rocks. Weathered crystalline rock is the outer layer of the underlying hard rock. Hence excessive mining is not required to obtain these types of rocks. In Kerala, weathered crystalline rock is used for the construction of small compound walls instead of random rubble and laterite bricks.

II. MATERIALS USED IN THE STUDY

A. General
The ingredients of concrete are cement, coarse aggregate, fine aggregate and water. The physical and chemical properties of each of the ingredients have considerable role in the desirable properties of concrete like durability, strength and workability. Hence special care has been taken in the selection of each of the ingredients. The following section gives an account of the materials used in this study.
B. Cement
Portland Puzzolana Cement conforming to IS 1489-1991 was used for the study. This grade was selected due to the fact that, it is the most commonly used grade of cement for construction works in Kerala.
C. Fine Aggregate
Fine aggregate fills the voids between coarse aggregates. The properties required for good quality fine aggregates are mentioned in IS 383-1970. Three different types of natural fine aggregates used in the study are mentioned below. 1. River sand. 2. M- sand and 3. Weathered crystalline sand.
D. Coarse Aggregate
Coarse aggregate is considered to be the strongest and least porous component of concrete. It is also a chemically inert material. Locally available crushed granite aggregate of 20mm down size conforming to IS 383-1970 was used.
E. Water
Water is an important ingredient of concrete, as it actively participates in chemical reaction with cement. The strength of cement concrete comes from the bonding action of the hydrated cement gel. In the present investigation, potable water was used for mixing and curing.

III. TESTING OF MATERIALS

A. General
The material properties like fineness, specific gravity, bulking of sand, bulk density and workability were tested using each type of fine aggregates. To determine the components of the weathered crystalline rock, X-Ray Fluorescence Spectrometry Analysis (XRF Analysis) was done. The experiments conducted are explained below.
XRF Analysis
The chemical compositions of rocks are used to solve numerous geological problems, including crystallization history of igneous bodies such as granite or basalt, processes of formation of the sea floor, nature of chemical weathering in various climates, stratigraphic correlation of sedimentary and volcanic rocks, processes of ore generation, and many others. Most rocks are composed primarily of silicate minerals, and over 90% of the composition of most silicate rocks can be characterized by oxides of Si, Ti, Al, Fe, Mg, Ca, Na and K. Minor and trace elements present in rocks include practically every other element, many of which are especially useful for geochemical modeling of geological processes. Foresite now has the capability to analyze lead free processed assemblies for RoHS directive compliance utilizing XRF (X-ray Fluorescence) analysis. Utilizing Fischerscope XRF XDAL system, Foresite can examine assemblies with 0.2 mm focal distance. This system is capable of performing both quantitative elemental analysis and thickness measurements in an integrated fashion. It is able to examine each component on an assembly individually through a small spot analysis method. Looking at each layer individually, our XRF XDAL system is able to provide a meaningful and accurate measure of the RoHS compliancy of a product.
B. Sieve Analysis
To determine the particle size distribution of the fine aggregate, fineness modulus, effective size and uniformity coefficient sieve analysis is conducted. The apparatus consists Indian standard sieves (4.75mm, 2.36mm, 1.18mm, 600microns, 300 microns, 150 microns) and sieve shaker.
C. Specific Gravity of Fine Aggregates
This experiment is conducted to determine the specific gravity of given sample of fine aggregates. The apparatus used are balance, oven, pycnometer, tray, an air tight container, filter papers and funnel.
D. Bulking of Fine Aggregates
This experiment is conducted to study the behavior of sand grains under varying percentage of moisture content. The apparatus used are, a 250 ml measuring cylinder, weighing balance etc. A graph is drawn with % water content along X-axis and % bulking along Y-axis. From graph, pick out maximum % of bulking occurred, % of water content at maximum bulking, % of water content when bulking is zero and % of bulking for the initial water content (w) of the sample.
E. Bulk Density and Percentage of Voids
This test was conducted to determine the bulk density and percentage voids of aggregate
F. Slump Test
a. General
Slump test was done to determine the workability (consistency) of prepared concrete and to check the uniformity of concrete. The slump (vertical settlement) measured was recorded in terms of milliliters of subsidence of the specimen during the test. The apparatus used for the test were, mould for slump test, non porous base plate, measuring scale and tamping rod .The mould for the test is in the form of the frustum of a cone having height 30 cm, bottom diameter 20 cm and top diameter 10 cm. the tamping rod is of steel 16mm diameter and 60 cm long and rounded at one end.
b. Method of calculating quantity of materials
In the case of M20 concrete For 50 kg of cement, 250 kg (coarse aggregate + fine aggregate) & 30 litres of water are required.
Coarse aggregate + fine aggregate = 250 kg
Proportion of fine: coarse aggregate = 1:2
Quantity of fine aggregate = 250 x (1/3) = 83.33kg
Quantity of coarse aggregate = 250 x (2/3) = 166.66 kg
Quantity of water = 30 litres
Water cement ratio = 30/50 = 0.6
Therefore the proportion = 50:83.33:166.66:30 = 1:1.66:3.33:0.6
The sum of parts by weight = 1+1.67+3.33+0.6 = 6.6
c. Quantity of materials required for 1m3 of concrete
Weight of 1m3 of concrete = 2400 kg
Weight of cement required = 2400 x (1/6.6) = 363.63 kg
Weight of fine aggregate required = 2400 x (1.67/6.6) = 607.27 kg
Weight of coarse aggregate required = 2400 x (3.33/6.6) = 1210.91 kg
Quantity of water required = 2400 x (0.6/6.6) = 218.18 kg
d. Volume of frustum of a cone
Volume = (1/3)��R2H – (1/3)��r2(H-h), where
R = 10 cm, H = 60 cm, h = 30 cm r = 5 cm
By substituting these values and taking 20% volume extra we get,
Volume, V = 0.006588M
e. Quantity of materials required for 0.006588m3 of concrete
Weight of cement required = 363.63 x 0.006588 = 2.4 kg
Weight of fine aggregate required = 607.27 x 0.006588 = 4.0 kg
Weight of coarse aggregate required = 1210.91 x 0.006588 = 7.98 kg
Quantity of water required = 218.18 x 0.006588 = 1.44 kg

IV. TESTING OF SPECIMENS

A. General
The test was conducted on hardened mortar and hardened concrete after required curing. The compressive strength of mortar cubes after 3 days, 7 days and 28 days curing and the compressive strength of concrete cubes after 7 days, 14 days and 28 days curing were tested. The new fine aggregate used was expected to give sufficient strength to the specimen. This section gives an account of the various tests conducted on hardened mortar cubes and concrete cubes.
B. Compressive Strength of Mortar Cubes
The testing of mortar cubes were carried out in a compression testing machine as per IS 4031, 269, 12269, 516 guidelines. The bearing surfaces of the testing machine was wiped clean and any loose sand or other material was removed from the surfaces of the specimen. In the case of cubes, the specimen was placed in the machine in such a manner that the load was applied to opposite sides of the cube as cast, i.e. not to the top and bottom. The axis of the specimen was carefully aligned with the centre of thrust of the spherically seated platen. No packing was used between the faces of the test specimen and the steel platen of the testing machine. As the spherically seated block is brought to bear on the specimen, the movable portion was rotated gently by hand so that uniform seating was obtained. The load was applied without shock and increased continuously at the rate of approximately 350kg/cm2/minute until the resistance of the specimen to the increasing load breaks down and no greater load can be sustained. The maximum load applied to the specimen was then recorded and the appearance of the mortar cube and any unusual features in the type of failure were noted. The measured compressive strength of the specimen was calculated by the formula,
Compressive strength = Load in N / Area in mm2
Range calculation:
Size of the cube = 7.05cm x 7.05cm x 7.05cm
Area of specimen (from the mean size of the specimen) = 50cm2 = 5000mm2
Expected load (stress x area x factor of safety) = 53x5000x1.5 = 397500 N = 397.5kN
Range to be selected is 0-500kN
C. Compressive Strength of Concrete Cubes
The concrete cubes were tested in a compression testing machine as per IS 516 guidelines. The bearing surfaces of the testing machine was wiped clean and any loose sand or other material removed from the surfaces of the specimen. The specimen was placed in the machine in such a manner that the load was applied to opposite sides of the cube as cast, i.e. not to the top and bottom. The axis of the specimen was carefully aligned with the centre of thrust of the spherically seated pattern. No packing was used between the faces of the test specimen and the steel platen of the testing machine. As the spherically seated block was brought to bear on the specimen, the movable portion was rotated gently by hand so that uniform seating was obtained. The load was applied without shock and increased continuously at the rate of approximately 140kg/cm2/minute until the resistance of the specimen to the increasing load breaks down and no greater load could be sustained. The maximum load applied to the specimen was then recorded and the appearance of the concrete cube and any unusual features in the type of failure were noted. The measured compressive strength of the specimen was calculated by the formula,
Compressive strength = Load in N / Area in mm2
Range calculation:
Size of the cube = 15cm x 15cm x 15cm
Area of specimen (from the mean size of the specimen) = 225cm2 = 22500mm2
Characteristic compressive strength (fck) at 28 days = 20N/mm2
Expected maximum load (stress x area x f.s.) = 20x22500x1.5 = 675kN
Range to be selected is 0-1000kN

V. RESULTS AND DISCUSSION

A. General
The tests on grain size, specific gravity, workability, bulk density, bulking of fine aggregate, compressive strength of mortar cube, compressive strength of concrete cube and XRF Analysis were conducted. Nine mortar cubes were cast by using each variety of sand. Also nine concrete cubes were cast by using each variety of sand. That is total 27 mortar cubes and 27 concrete cubes. To determine the components of the weathered crystalline rock, X-Ray Fluorescence Spectrometry Analysis (XRF Analysis) was conducted in the X-ray Fluorescence Lab, Centre for Earth Science Studies, Akkulam, Trivandrum.
B. XRF Analysis
Chemical combination of the weathered crystalline rock is almost similar to the chemical combination of natural occurring rocks. The silica is the major constituent in natural sand, in the case of weathered crystalline rock silica constitutes the major part about 60-70% which determines the strength parameter, being strength is the major concern regarding the material as a fine aggregate. Other constituents like oxides of Manganese, Magnesium, Iron, Aluminum etc. are in the safe limits. Other trace elements are in the range of ppm those are not at all affects the chemical activity of fine aggregate.
C. Grain Size Analysis
As per IS specification, value of fineness modulus of fine aggregate lies between 2 and 3.5
D. Specific Gravity
According to IS 2386 (Part III), the specific gravity of fine aggregate should lie between 2.6 and 2.8
E. Bulking of Sand
Bulking of fine aggregate ranges from 15-30%
F. Bulk Density
Bulk density of fine aggregate is between 1.45 kg/l and1.65 kg/l.
G. Workability
The workability of the given mix is low. This slump is suitable for mass concrete, lightly reinforced sections in slabs, beams, walls etc.
H. Compressive Strength of Mortar Cubes
Minimum compressive strength of mortar cubes after 3 days, 7 days and 28 days should be 16N/mm2, 22N/mm2 and 33N/mm2 respectively.
I. Result of Compressive Strength of Concrete Cubes
Compressive strength of concrete cubes after 28 days should be 20N/mm2 and its 2/3rd strength should be attained in their early stages.

VI. CONCLUSIONS

 Weathered crystalline sand is suitable for construction works instead of M-sand.
 Extensive mining is not required, since weathered crystalline rock is the outer layer of the underlying hard rock.
 Like river sand weathered crystalline sand attains strength gradually while M-sand attains its compressive strength at an earlier stage.
 More economy can be attained, as cost of weathered crystalline sand is very less as compared to river sand and Msand.

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References

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[9] IS 383:1970, “Indian Standard specification for coarse and fine aggregates from natural sources for concrete”, Bureau of Indian Standards, New Delhi, April 1971.
[10] IS 456:2000, “Indian Standard code for Plain and reinforced concrete- Code of practice”, Bureau of Indian Standards, New Delhi, July 2000.
[11] IS 516:1959,”Indian Standard code for Methods of tests for strength of concrete”, Bureau of Indian Standards, New Delhi, Edition 1.2, 1991-07.
[12] IS 1199:1959, “Indian Standard code for Methods of sampling and analysis of concrete”, Bureau of Indian Standards, New Delhi, December 1959.
[13] IS2386:1963(Part I-VIII), “Indian Standard code Methods of test for aggregates for concrete”, Bureau of Indian Standards, New Delhi, 1963.
[14] IS 2430:1969, “Indian Standard code for Methods for sampling of aggregates for concrete”, Bureau of Indian Standards, New Delhi, June 1987.