Properties of Some Natural Fine Aggregates in Minna, Nigeria and Environs

 

M. ABDULLAHI

 

Civil Engineering Department, Federal University of Technology, Minna, Niger State, Nigeria, abdulapai@yahoo.com 

 

 

Abstract

This paper investigates the properties of some natural fine aggregates in Minna and its environs. Nine soil samples were obtained from different locations and transported to Civil Engineering Laboratory, Federal University of Technology, Minna, Nigeria. Tests conducted on the soil samples include: specific gravity, sieve analysis, bulk density and silt content. Test result revealed the specific gravities of the soils to be between 2.60 to 2.84, compacted bulk densities to be between 1470 Kg/m3 to 1867 Kg/m3, loose bulk densities to be between 940 Kg/m3 to 1013 Kg/m3 and silt contents to be between 0.97 to 5.50 natural fine aggregates are suitable for construction purposes. Most of the soils satisfy the overall grading limits for natural fine aggregates and they are mainly fine grading except samples 6 and 9 which are medium grading and sample 2 which is coarse grading. These soils can be used for construction purposes but a good knowledge of mix design is essential and soils should be tested before use to obtain durable product.

Keywords

Natural fine aggregates, Soil samples tests

 

 

Introduction

 

Aggregates are generally divided into two groups: Fine and Coarse. Fine aggregate consists of natural or manufactured sand with particles sizes up to 5mm. It consists of inert natural sand conforming to [1]. It does not contain more than a total of 5% by weight of the followings: shale, silt and structurally weak particles [2].

Aggregates make up or occupy 60% to 80% of concrete volume making its selection highly important [3]. Aggregate should consist of particles with adequate strength and resistance to exposure condition and should not contain materials that will cause deterioration of concrete. All natural aggregate particles originally formed a part of a larger parent mass. This may have been fragmented by natural processes of weathering and abrasion or artificially by crushing. Thus, many properties of the aggregate depend entirely on the properties of the parent rock, for example, chemical and mineral composition, petrologic character, specific gravity, hardness, strength, physical and chemical stability, pore structure and colour [4]. Fine aggregates provide support function to the finer solids by producing voids of a size which do no contain or support the finer particles. Particle shape affects the behaviour of the water, harsh angular aggregates not packing well and resulting in high void content [5]. Such aggregates may have a high surface area, but because of a lack of contact between the particles, it does not effectively control the finer particles. Smooth rounded aggregates have the disadvantage that, although theoretically it should pack together and produce low voids, this situation does not necessarily occur in a graded material of this type.

Aggregates for mortar must be clean, sharp and free from salt and organic contamination. Most natural aggregates contain a small quantity of silt or clay. A small quantity of silt improves workability. Marine or estuarine aggregate should not be used unless washed completely to remove the magnesium and sodium chloride salts which are deliquescent and attract moisture [6]. The most suitable aggregate would appear to be one that is well graded with a balance between rounded and angular particles and a surface texture that is not too smooth. In practice it has been found that a natural river aggregate with a grading complying with [1] is the most suitable. Sea-dredged and crushed aggregates produce more extreme types, either all smooth and rounded or harsh and angular and generally requiring greater care in design.

The realization of the usefulness and effect of fine aggregate on the strength of concrete and sandcrete in the building and construction industry has put into the minds of Engineers and researchers to lay more emphasis into the study of the Civil Engineering properties and its usefulness. Emphasis is made on such properties like bulk density, specific gravity, silt content and particle size distribution. The aggregates used in construction works in Minna, being the case study, are obtained from rives, borrow pits and eroded materials.

 

 

Methodology

 

For the purpose of this work nine natural fine aggregates samples were obtained from areas currently in use for construction purposes in Minna, Nigeria. The nine locations used in this study are shown in Table 1.

 

Table 1. Sample Location

Sample

1

2

3

4

5

6

7

8

9

Location

Rafintofao

Tagwai dam

Dogo

Kodo

Gwada

Pyata

Shata

Paiko

Takuti

Area

Maikunkele

Chanchanga

Garatu

(Bida road)

Along

Beji

Kuta

road

Along cais

Road

Maikunkele

Paiko

Along

Lapai

 

These soil samples were transported to Civil Engineering laboratory, Federal University of Technology, Minna, Nigeria. The tests carried out were: specific gravity and sieve analysis in accordance to [7] and bulk density and silt content in accordance to [8].

 

 

Results and Discussion

 

Specific Gravity of Soil Samples

            The results for the specific gravities of soil samples are shown in Table 2.

 

Table 2. Specific Gravity of Soil Samples

Samples

1

2

3

4

5

6

7

8

9

Test 1

2.79

2.55

2.72

2.81

2.72

2.81

2.73

2.83

2.77

Test 2

2.79

2.65

2.74

2.79

2.72

2.75

2.73

2.85

2.79

Average

2.79

2.60

2.73

2.80

2.72

2.78

2.73

2.84

2.78

 

The values of the specific gravities range between 2.60 to 2.84. The average specific gravities for various rock groups ranges between 2.54 for flint to 2.80 for basalt and the range of specific gravities reported were between 2.4 to 2.6 (flint) to 2.7 to 3.0 (hornfels) [9]. The experimental results are in line with these standards. This implies that these aggregates have not been contaminated with other materials from the environment.

 

 

Bulk Density of Soil Samples

            The results for the bulk densities of soil samples are shown in Table 3. The compacted bulk densities of the aggregates are between 1407 Kg/m3 to 1867 Kg/m3.

Table 3. Bulk Density of Soil Samples

Compacted

Sample

1

2

3

4

5

6

7

8

9

Test 1

1539

1586

1614

1488

1889

1435

1634

1640

1629

Test 2

1569

1590

1594

1504

1845

1379

1638

1634

1625

Average

Kg/m3

1554

1588

1604

1496

1867

1407

1636

1637

1627

Loose

Test 1

941

1012

934

942

941

739

934

943

809

Test 2

939

1014

934

940

955

735

936

941

797

Average

Kg/m3

940

1013

934

941

948

737

935

942

803

 

The uncompacted bulk densities of the aggregates are between 940 Kg/m3 to 1013 Kg/m3. The bulk density for sand and sandy soils before excavation ranges from 1650 Kg/m3 to 1850 Kg/m3 as reported in [10]. The experimental values are relatively low as the soil sample used for the experiment was a disturbed one. This increases the void spaces between the soil particles and thereby reduces the weight of material required to fill a unit volume and consequently reducing the bulk density of the soil.

 

Silt Contents of Soil Samples

The result for the silt content is presented in Table 4. The [8] permits silt contents to be within the range of 3 to 8 %. Silt is a material between 2mm and 60mm.

 

Table 4. Silt Content of Soil Samples

Samples

1

2

3

4

5

6

7

8

9

Height of Soil Sample (ml)

112.38

103.70

109.60

107.31

109.30

104.90

103.00

109.40

103.15

Height of Silt Layer (ml)

6.18

1.60

4.55

3.46

4.10

2.40

1.00

5.45

1.10

Silt Content (%)

5.50

1.54

4.15

3.22

3.75

2.29

0.97

4.98

1.07

 

Soil samples 2, 6, 7 and 9 have silt content less than 3 % while soil samples 1, 3, 4, 5 and 8 have silt contents between 3 to 8 %. Soil samples with silt content less than 3 % have insufficient fines and will require a considerable amount of cement for a reasonable workability. If such soils are to be used for construction work they have to be blended with suitable finer aggregates from other sources. Soil samples with silt content between 3 to 8 % are quite suitable for construction purposes. This will require optimum water and cement content for a reasonable workability. Silt content of over 8 % is unsuitable as it increases the amount of water needed to wet the particles in the mix [3]. This results in mix with high slump, high dry shrinkage and consequently weak and non-durable concrete.

 

Sieve Analysis of Soil Samples

            The result for sieve analysis is shown in Table 5.

 

Table 5. Sieve Analysis of Soil Samples

Sieve Size (mm)

5.00

3.35

2.36

1.18

0.60

0.30

0.15

0.075

PAN

Samples

Percentage Finer (%)

1

99.19

98.90

98.51

94.15

74.94

42.30

31.28

24.27

0.00

2

96.20

77.46

72.48

49.21

19.50

3.29

3.02

1.54

0.00

3

98.02

95.73

92.24

85.73

79.18

66.66

59.92

46.25

0.00

4

98.31

97.41

95.56

86.56

66.05

33.03

21.24

10.95

0.00

5

98.76

97.94

96.58

91.34

76.28

50.14

39.44

22.30

0.00

6

98.44

97.23

94.83

80.94

50.49

19.20

15.86

7.30

0.00

7

99.12

98.44

96.73

88.23

66.03

15.68

13.37

7.37

0.00

8

98.76

96.95

94.41

84.44

72.20

56.15

46.42

29.35

0.00

9

98.62

97.11

93.62

72.53

44.82

8.91

8.65

6.64

0.00

 

Soil sample 1 satisfy the overall grading limit except the percentage finer than 150mm sieve size which was 31.28 % falling outside the range (0-15 %). The soil is also fine grading. Soil sample 2 satisfy the overall grading limit except the percentage finer than 300mm sieve size which was 3.29 % falling outside the range (5-70 %). The soil is also coarse grading with percentage passing 300mm sieve size of 3.29 % falling outside the range (5-40 %). Soil sample 3 is fine grading and satisfy the overall grading limit except the percentage finer than 150mm sieve size which was 59.92 % falling outside the range (0-15 %). Soil sample 4 is fine grading and satisfy the overall grading limit except the percentage finer than 150mm sieve size which was 21.24 % falling outside the range (0-15 %). Soil sample 5 is fine grading and satisfy the overall grading limit except the percentage finer than 150mm sieve size which was 39.44 % falling outside the range (0-15 %). Soil sample 6 is medium grading and satisfies the overall grading. Soil sample 7 is fine grading and satisfies the overall grading limit. Soil sample 8 is fine grading and satisfy the overall grading limit except the percentage finer than 150mm sieve size which was 46.42 % falling outside the range (0-15 %). Soil sample 9 is medium grading and satisfies the overall grading limit. The soil samples agree reasonably well with [1] and are recommended for construction purposes. It does not mean that any grading is recommended; a wide range of grading may be acceptable through a trial and error approach [3].

 

 

Conclusions

 

            The specific gravities of the soil samples were found to be between 2.60 to 2.84. The bulk compacted densities of aggregates are between 1470 Kg/m3 to 1867 Kg/m3 and the un-compacted (loose) bulk densities are between 940 Kg/m3 to 1013 Kg/m3. The deviations from standard are due to sample disturbance. Four of the nine soil samples have silt content less than 3 %. Five of the other soil samples have silt content in the range of 3 to 8 %. The nine soil samples satisfy the overall grading limit with greater value for percentage finer than sieve size 150mm for soil samples 1, 3, 5 and 8. This indicates excess finesse greater than normal. Such soils will produce poor mix with insufficient cement content if they are not mix with other aggregates. The soil samples 1, 3, 4, 5, 7 and 8 are fine grading, soil samples 6 and 9 are medium grading and soil sample 2 is coarse grading. Soils for construction works should be analysed before they are used. This will enable the users to prepare accurate mix to ensure workability, minimum dry shrinkage, durability and high strength.

 

 

References

 

[1] BSI, BS 882: Specification for Aggregates from Natural Sources for Concrete, 1992.

[2] Grow T. A., Construction, A Guide for the Professionals, McGraw-Hill, 1938.

[3] Neville A. M., Properties of Concrete, Pearson Education Asia, 2000.

[4] Neville A. M., Properties of Aggregates, Pitman Books Limited, 1981.

[5] Neville A. M, Chatterton M., New Concrete Technologies and Building Design, Longman Inc., 1979.

[6] Hendry A. W., Sinha B. P. Davies S. R., Load Bearing Brickwork Design, Ellis Horwood, 1987.

[7] BSI, BS 1377: Methods of Testing for Soils For Civil Engineering Purposes, 1990.

[8] BSI, BS 812: Sampling and Testing of Mineral Aggregates, Sand and Fillers, 1989.

[9] Road Research Laboratory, Roadstone Data Presented in Tabular Form, DSIR Road Note No. 24, 1959.

[10] Jackson N., Dhir R. K., Concrete, Macmillan Education Ltd, 1988.