Potentials of particles from crushed abakaliki pyroclastic ...€¦ · (PCC) in parts of Abakaliki area of Ebonyi State, southeastern Nigeria. Particle size distribution, specific

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FUNAI Journal of Science and Technology

3 (2), 2017, 120-133

POTENTIALS OF PARTICLES FROM CRUSHED ABAKALIKI PYROCLASTIC

ROCKS TO REPLACE SAND IN CONCRETE WORKS

Okechukwu Pius Aghamelu

Department of Physics/Geology/Geophysics, Federal University Ndufu Alike-Ikwo, Nigeria

(Received 20 December 2016; Revised 19 July 2017; Accepted:21 July, 2017)

Abstract

Particles derived from crushed pyroclastic rock (CPR) were investigated to determine the

suitability of the material as fine aggregate in general purpose Portland cement concrete

(PCC) in parts of Abakaliki area of Ebonyi State, southeastern Nigeria. Particle size

distribution, specific gravity (SG), and water absorption (Wa) were determined on sand

deposit (commonly used for concrete making within the study area) and CPR that passed 9.5

mm British Standard test sieve opening. The sieve opening (9.5 mm) represents the upper

limit of diameters of sand-sized particles in soils. Coarse aggregate and type IV (normal

hardening) Portland cement were mixed with the two materials to form concrete specimens,

which were subjected to compressive strength tests at periods of 14 and 28 days of curing. The

ratios of sand to CPR were 1:0, 4:1, 1:1, 1:4 and 0:1. Tests results indicate that the CPR have

considerable amount of micro-fines (15%), relatively low Wa (2.52%) and appreciable SG

(2.65). The strength of the PCC, at 14 days curing period, increased from 37 N/mm2 to 40

N/mm2 with addition of 25% CPR but dropped to 29 N/mm

2 when increased to 100%. Study

indicates that mixing sand with about 25% CPR and longer curing period (≥ 28 days), rather

than total sand replacement, would likely yield PCC with generally good performance in service.

Keywords: Abakaliki pyroclastics; Crushed rock particles; Geotechnical properties; Sand;

Portland cement concrete.

1. Introduction

Portland cement concrete (PCC) is an

artificial engineering material made from a

mixture of Portland cement, water, fine

and coarse aggregates. The fine

aggregate is the material passing 4.75 mm

(#4) test sieve and retained in 75µm (#200)

test sieve, and could be natural

or manufactured from crushing of rocks.

Concrete is about the only major building

Potentials of particles from crushed abakaliki pyroclastic rocks... Aghamelu

FUNAI Journal of Science and Technology, 3(2), 2017 Page 121

material that can be delivered to the

construction site in plastic state, hence, it

can be moulded to virtually any form or

shape. Many types of concrete such as

high performance concrete, self

compacting concrete, reinforced concrete

and green concrete (Okamura and Ouchi,

2003), are being used today to construct a

wide variety of structures, such as

highways, bridges, dams, large buildings,

airport runways, irrigation structures,

pavements, silos and farm buildings. The

desirable property of concrete mixtures,

especially its ability to be moulded to any

shape, high demand in numerous

construction projects and the need for more

infrastructural development to cater for an

increasing population have necessitated

increased demand for concrete and its

constituents in many parts of the world.

In a bid to meet the high demand for

concrete and its composite materials in the

Abakaliki Metropolis, Southeastern

Nigeria (Figure 1), and due to inadequate

supply and high cost of

construction sand within the metropolis,

crushed pyroclastic rock particles (CPR), a

product of rock quarrying with particles

that range from fine aggregate to micro

fines (i.e., particles passing 75 µm or #200

sieve), is currently being used by local

builders and engineers in the Abakaliki area

as a substitute for sand including fine

aggregate, especially in concrete mixes. A

number of collapsed building cases have

been recorded in the areas where this

material has been commonly used in PCC

(Aghamelu et al., 2011; Aghamelu and

Okogbue, 2011).

No documented or published data or

information exists on the appropriateness of

the CPR as a replacement or a constituent

of PCC mixtures. Aghamelu and

Okogbue (2013) had, however, noted that

the pyroclastic rock could only serve

marginally well as coarse aggregate

source in most types of concrete.

Previous researchers (Wong et al., 2001)

have listed the factors that influence the

workability and performance of concrete

to include the properties and amount of

the cement, grading, shape, angularity and

surface texture of the fine and coarse

aggregate. It has been noted that

manufactured fine aggregate processed

from crushed stone generally contain a

greater quantity of fines than natural sands

and often mask their good workability with

low slump test results (Daniel, 2006).

Earlier works (American Concrete



Institute, 1990; British Standard

Institute, 1881, 1993; American Society for

Testing and Materials, C143, 1994) have

presented and described in details some

basic test procedures for assessing

concrete materials and concrete mixes.

This study, therefore, attempts to use

standard laboratory tests to investigate the

qualities of crushed rock particles from the

Abakaliki Pyroclastics and the PCC in

which it serves as fine aggregate.

Highlights on the suitability of the CPR

as fine aggregate for concrete are mainly

from the viewpoint of the analysis

conducted on both the raw crushed rock

particles and concrete sample.

Figure 1. Map of Southeastern Nigeria showing the position of Abakaliki, Ebonyi State and other surrounding states

1.1 Production of crushed aggregates in

the Abakaliki area of Ebonyi State

Rock quarrying and crushing industry

thrives in the Abakaliki area. This industry

is sustained by the abundance of pyroclastics

and other minor intrusives within the area.

The pyroclastic rocks are among the

volcanic rock suite that was produced by

explosive activity within the Asu River

Group in the Abakaliki area. The rocks are

best exposed in the area within a 12 km

radius of the Abakaliki Metropolis;

specifically in the areas around the

Government House, Onwe Road, Gulf

Course, near the Federal Teaching Hospital,

Abakaliki (FETHA) II, Juju Hill, Nkaliki,

Onyikwa, Aghameghu, Aguogboriga,

Sharon and Amike Abba. The Abakaliki

Pyroclastics consist of a sequence of mafic

lavas, pyroclastic flows, tuffs, agglomerates

and amygdaloidal lavas of basaltic

composition and alkaline in nature

(Aghamelu and Okogbue, 2013; Ofoegbu

and Amajor, 1987; Obiora and Umeji,

1995). At the Umuoghara crushers’ cluster,

near Abakaliki metropolis, about 10,000

metric tons of different sized coarse

aggregates of pyroclastic rocks are

produced. The coarse aggregate sets are

being supplied to contractors and builders

mainly for construction of major projects

(especially roads and concrete for

buildings) within and around the

Southeastern Nigeria. Pyroclastic rock dust

(PRD), a trade name for the by-product of

the massive pyroclastic rock quarrying



activity, is considered almost a waste

product owing to large tonnage produced

and its very low commercial value. While

sand, which conventionally serves as fine

aggregates in PCC mixes in the area is sold

at the rate of N 25, 500 (fifteen thousand

Naira, about seventy US dollars) per metric

ton, the PRD is supplied at a price of N 7,

000 (three thousand naira, about twenty US

dollars) or less per metric ton to local

builders and contractors. These local

builders and contractors, due to mainly

economic reasons, commonly use PRD

instead of sand as fills or fine aggregates in

concrete (both asphalt and Portland cement

varieties) or as mortars and plasters, with

little or no effort to ascertain its field

performance or suitability in those projects.

2. Materials and methods

2.1 Material sampling

The CPR sample was collected from the

Umuoghara crushers’ cluster near Abakaliki

Metropolis, while the sand sample was

river sand deposit from Emene River,

near Oye market in Enugu, southeastern

Nigeria, commonly sourced for concrete and

other construction projects within the area.

2.2 Particle Size Distribution Analysis

The river sand deposit and CPR samples

were both subjected to mechanical (particle

size) analysis. The analyses on both

materials were on particles sizes that

passed the 9.5 mm (#3/8) British Standard

test sieve (which represents the upper limit

of the diameters of sand-sized particles in

soils), and was in accordance with BSI 1377

(1990).

2.3 Specific Gravity and Water Absorption

Tests

Both specific (apparent) gravity and water

absorption determinations in this study

were carried out only on the PRD, and

the test was in accordance with standard

procedures (American Society for Testing

and Materials, C128, 1990; American

Society for Testing and Materials, C117,

1995). About 2 kg of the fine aggregate

fraction, size passing 4.75 mm (#4) test

sieve was subjected to apparent specific

gravity test procedure, using a pycnometer

test bottle. Water bathing was, however,

achieved with a basin filled with distilled

water at room temperature.

2.4 Compressive Strength Test

The compressive strength test was

conducted according to ASTM C39

(1999), and the concrete mixing was in

accordance with ASTM C192 (2000). In

general, compressive



strength was tested at periods of 14 and

28 days on ten 4 in. × 8-in. cylinder

moulded samples. Before testing, the

specimens were cured in a moisture room

at 100 percent humidity, as described in an

earlier work (Quiroga and Fowler, 2004).

The percentages by volume of the various

ingredients used are shown in Figure 2. The

ratios of sand to CPR were 1:0, 4:1, 1:1, 1:4

and 0:1, that is, 100 to 0 %, 75 to 25 %, 50 to

50 %, 25 to 75 % and 0 to 100 %,

respectively. Water/cement ratio was

calculated as the volume of water divided

by the volume of cement.

Figure 2. Proportions, by percentage volume, of ingredients used in the PCC mix

3. Results and discussion

The concrete specimens were from PCC

mixes that have varied percentages by

weight of sand and CPR as fine aggregate

component. The cement was the Type IV

(normal hardening) Portland cement.

Crushed pyroclastics that passed through

25.0 mm (1 in.) sieve, but were retained in

4.75mm (#4) sieve were utilized as the

coarse aggregate.

3.1 Particle size distribution

Results of mechanical analysis on the

particles derived from crushed pyroclastic

rock and natural sand are summarized in

Table 1. The gradation curve of the CPR is

shown in Figure 3. Analysis indicates that

the crushed rock particles contained

significantly higher amount of fine

particles than the experimental sand. It has

been noted that manufactured fine

aggregates from crushed rocks yield greater

amount of fines than natural sands (Daniel,

2006). On the basis of the calculated

fineness modulus in Table 2, the CPR would

classify as fine sand (see Table 3) or poorly

graded sand (SP), according to Unified Soil

Classification System.

Grading or particle size distribution has been

reported as one of the major factors that

affect significantly some characteristics of

concrete like packing density, voids

content, and, consequently, workability,

segregation, durability of concrete

(Scanlon, 1994; Quiroga and Fowler,

2004). Wong et al. (2001) had observed

that the use of fine aggregates with high

amount of micro-fines (percent passing

through No. 200 sieve) requires that more



water be added to achieve the workability

that a coarser sand would provide. As shown

in Table 4 and Figure 3, the CPR is well

within the fine aggregate grading limits

given by ASTM C33 (2003)

and ACI (2007); it is only the quantities of

particles less than 0.3 mm and 0.15 mm,

that is, passing #50 and #100 sieves, that are

above the required specification.

Table 1. Results of sieve analysis on the fine

aggregates used in this study

Sieve size

(mm)

Sieve

No.

Natural

sand*

Crushed rock

particles*

9.5 3/8 100 100

4.75 4 98 91

2.36 8 85 81

1.18 16 66 69

0.6 30 31 53

0.3 50 6 39

0.15 100 1 25

*Percentage passing (%)

Figure 3. Typical grading chart for fine aggregates (Modified from American Society for Testing and Materials, C33, 2003; American Concrete Institute, 2007)



Table 2. Calculation of fineness modulus (FM) of crushed rock particles

Sieve No. Weight retained (%)

Individual Cumulative Cumulative

percent Retained 4 90 90 9

8 100 190 19

16 120 310 31

30 160 470 47

50 140 610 61

100 140 750 75

Pan 250 - -

Total weight 1000 - 242

FM = 242/100 = 2.42

Table 3. Fineness modulus (FM) ranges for fine aggregates

FM* Designation* Crushed rock

particles*

2.3 – 2.59 Fine sand 2.42

2.6 - 2.89 Medium sand -

2.9 – 3.1 Coarse sand -

*data from Army Institute for Professional Development (1992)

Table 4. Crushed rock particles compared with fine aggregate grading limits

Sieve size (mm) Sieve No. Fines percentage

passing*

Crushed rock

particles

Remarks

9.5 3/8 100 100 The crushed rock

particles considerably

meet the grading

limits, with only

particles less than the

#50 sieve failing

outside the limits.

4.75 4 95 – 100 91

2.36 8 80 – 100 81

1.18 16 50 – 85 69

0.6 30 25 – 60 53

0.3 50 5 – 30 39

0.15 100 0 – 10 25

*data from ASTM C33 (2003)



The fact that CPR meets grading limits

could suggest that the material would be

suitable as fine aggregate for PCC. A

comparison of the amount of micro-fines in

the material with the amount of allowed

micro-fines limits in fine aggregates

from some parts of the world is

presented in Table 5, and it indicates that the

material compares well with the allowed

micro fines limits from some parts of the

world. The fineness modulus (FM) of the

CPR also falls within the acceptable limits.

The FM of good fine aggregate should fall

between 2.3 and 3.1 (American Society for

Testing and Materials, C33, 2003).

Reduction in the workability and

strength of concrete made with this

material is to be expected with an increase

in quantity (Wong et al., 2001). Aghamelu

and Okogbue (2013) had noted presence of

clay minerals and secondary carbonates as

lithic fragments in the thin section

specimens of the Abakaliki pyroclastics.

Deterioration caused by weathering of these

minerals could lower the quality and

suitability of the material and the PCC it is

made of over time.

Table 5. Comparison of allowable micro-fines limits from different parts of world

Country Micro-fines allowed (%) Sieve (µm) Fine aggregate type

United States 5 – 7 75 -

Spain 6 63 Natural sand

15 63 Crushed sand

England 15 63 -

India 15 – 20 - -

Australia 25 – 20 - -

France 12 – 18 63 -

Nigeria 15* 75 Crushed rock particle

*data from this study, the rest from Quiroga and Fowler (2004) -unavailable

3.2 Specific gravity and water absorption

The results of specific gravity (SG) and

water absorption (Wa) tests on the CPR,

alongside SG and Wa data of natural and fine



aggregates from some major rock types, are

presented in Table 6. Although specific

gravity SG is not necessarily related to

aggregate behaviour (Quiroga and Fowler,

2004), it has been observed that materials that

have somewhat low SG may display poor

durability as construction materials. This is

because the SG values of most natural

materials, rock or soil, reflect the average

weight of the predominant mineral(s) or

elements they contain (Krynine and Judd,

1957; Eze, 1997).

A comparison of the SG values of fine

aggregates produced from some common rock

types are presented in Table 6. The table

indicates that basic rocks (eg diabase and

basalt) produced fine aggregates with higher

SG values than acidic and alkaline rocks,

granite and Abakaliki pyroclastics,

respectively. Mineralogically, basic rocks

contained higher amount of

heavy minerals than acidic and alkaline

rocks. Most stable and durable minerals

and aggregates have their SG values greater

or equal to 2.65 and their Wa significantly

lower than 2.5 %. High Wa is most often

caused by high content of weak micro-

fines and minerals (Krynine and Judd,

1957). Previous researches (Quiroga and

Fowler, 2004; Kronlof, 1994) indicate that

fine aggregates with very low Wa generally

develop higher strength bonds but produce

less durable mortars than those with slightly

higher absorption.

Glanville et al. (1947) and Galloway

(1994) had noted that a general increase in

fine aggregate/coarse aggregate ratio

generally increases the water content required

to produce a given workability in concrete.

Aggregates with high absorptive micro-fines

present a special case because, if they are

batched with a large unsatisfied absorption,

they can remove water from the final concrete

mixture and, hence, reduce workability (Wong

et al. 2001).

3.3 Compressive strength

Result of concrete compressive strength tests

on concrete specimens, made of varied ratios

of sand and CPR and different curing

periods, is graphically presented in Fig. 4. It

can be observed from the figure that the



compressive strength of the PCC increased

from 37 N/mm2

to 40 N/mm2 with the

addition of 25 % CPR into the mix, at 14

days curing period. The

strength value, however, dropped to 40

N/mm2 and 37 N/mm

2 with the addition of 50

% and 75 % crushed rock particles,

respectively, at the same curing period. The

lowest strength values (29 N/mm2 and 30

N/mm2, for 14 and 28 days periods of

curing, respectively) were recorded when

sand was completely (100 %) replaced with

CPR. Longer period of curing (from 14 to

28 days), as shown in Fig. 4, however,

brought about slight increases in the

strength of the PCC samples (between 2 and

22 % increase in strength values). Possible

explanation to the decrease in strength (from

40 N/mm2

to 29 N/mm2, at 14 days of curing)

of the concrete with increased CPR (from 25

to 100 %) could be that blending to total

substitution of sand with the crushed rock

particles brought about an increase in the

amount of weak particles, especially in the

micro-fines fraction. Although, addition of

small amounts of the material improved the

strength, workability, and density for lean

concrete mixtures (Forster, 1994; Hudson,

1997, 1999), in excess micro-fines

constituent of the material produced the

reverse of these qualities in concrete.

Figure 4. Plot of compressive strength against percent crushed rock particles



4. Summary and conclusions

This study subjected CPR from the Abakaliki

pyroclastics and the PCC samples made using

varying percentages of sand and the CPR to

laboratory analyses to determine the potentials

of the rock particles as fine aggregate for

concrete making. The following findings were

made;

1. Crushing of pyroclastic rock yielded

particles with very significant amount of

fine

particles. The micro-fines so yielded,

however, fall within the allowable limits in

fine aggregates used in some parts of the

world.

2. The CPR recorded relatively high specific

gravity (2.65), low water absorption (2.52

%), and micro-fines that fall within allowable

limits, suggesting fair to good suitability as

fine aggregate for PCC. In excess quantity,

however, the CPR may cause a general

increase in the water content required to

produce good workability in concrete.

3. Strength analysis on the concrete specimens

made with the CPR, however, indicates that

the compressive strength reduced drastically

with 100 % increase. This suggests that a total

replacement of sand with CPR may have

introduced an appreciable amount of weak

particles, coming especially from the micro-

fine fraction, into the concrete mixture

resulting in low workability and strength.

4. This study reveals that blending sand

with about 25 % crushed pyroclastic rock

particles and longer period of curing (≥ 28

days) would likely yield PCC with good

performance in service. Any other mix

design, involving CPR, may be used but with

caution.

Acknowledgements

Babadiya Gbadebo of the Material laboratory

of Ebonyi State Ministry of Works and

Housing, Abakaliki, and Joseph Nna, formerly

of the Department of Geology, Ebonyi State

University, Abakaliki, are warmly appreciated

for assisting in the sampling and laboratory

analyses.

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Documents

Potentials of particles from crushed abakaliki pyroclastic ...€¦ · (PCC) in parts of Abakaliki area of Ebonyi State, southeastern Nigeria. Particle size distribution, specific