(Manuscript No: I12528-06)

April 17, 2012 / Accepted: April 23, 2012

1

ROCK BLASTING AND AGGREGATE

PRODUCTION WITH GUNPOWDER AS

AN EXPLOSIVE

ONYELOWE, KEN. C.*

COLLEGE OF ENGINEERING AND ENGINEERING TECHNOLOGY,

MICHAEL OKPARA UNIVERSITY OF AGRICULTURE, UMUDIKE,

P.M.B.7267, UMUAHIA, 440109, ABIA STATE, NIGERIA.

TEL: +2348039547350.

ABIA STATE, NIGERIA.

(Email: KONYELOWE@YAHOO.COM)

Abstract - This research work was targeted at the production of gunpowder and its use as an explosive in rock

blasting operations which involves pre-splitting, blasting and post blasting. In addition, it covers to a great

extent, the production of aggregate. At the end of this work, it has been proved beyond reasonable doubt that

gunpowder/black powder is a good replacement for the modern explosives in terms of cost and production ease.

Gunpowder is produced locally and can be produced by anybody using the established ratio of potassium nitrate,

KNO3, charcoal, and sulfur at 15:3:2 in that order. Table 1 also shows the loading density in kg per meter

column diameter of gunpowder of specific gravity 1.25 with respect to the column diameter. Rock blasting

operations has been shown as a very crucial phase in the production of aggregates which takes the greatest

percentage in concrete production and in pavement construction. The waste product of aggregate production i.e.

quarry dust takes a considerable quantity as an admixture in the production of concrete as well and also as an

admixture in cement stabilized lateritic soils used as subgrade materials. Therefore, the present work is worth

the attention of rock blast designers and quarry and aggregate factories.

Keywords: Gunpowder, explosive, aggregate production, rock blasting, potassium nitrate, sulfur.

Introduction

Blasting operations are performed to break rock for the purpose of quarrying for processing in an aggregate

production operation or to excavate a right-of-way, [1]. Blasting is accomplished by discharging an explosive

that has either been placed in an unconfined manner such as mud capping boulders, or is confined as in

borehole, [2]. There are two forms of energy released when high explosives are detonated, shock and gas. An

unconfined charge works by shock energy, whereas a confined charge has a high gas energy output. There are

many types of explosives and methods for using them. However, the use of a locally made explosive known as

gunpowder has attracted interests due to its ability to burn at high speed and build up high energy prior to

explosion releasing shock and gas energy. Gunpowder is a local product of potassium nitrate, charcoal, and

sulfur and combustible organic products like ethanol and baked at high temperature. It is manufactured locally

in commercial quantity in almost all the villages in Isiala Ngwa south L.G.A. of Abia State, Nigeria where it is

primarily used by hunters to charge den guns used for hunting and cannon shots used during ceremonies and

festivities. During the Biafra war of 1967 and 1970, gunpowder was used to produce explosives and mini-bombs

by Biafra soldiers for defense. It is a very reliable explosive used in pre-splitting of rocks, rock blasting and post

blasting operations.

Aggregate production companies like Setraco and Crushed Rock Industries all located in the eastern part of

Nigeria have used gunpowder in their pre-splitting, blasting, and post-blasting operations.

A. RESEARCH OBJECTIVES

The objective of this work is primarily to highlight the modern explosives used in rock blasting and investigate

the use of gunpowder as an explosive in rock blasting and the end product of rock blasting i.e. the processing

and production of aggregates in Nigeria.

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Mirpur area contains a lot of shopping centres, hospitals, educational institutes, highway bus stoppages,

amusement places and so on. Some notable institutions are National Heart Foundation Institute, Grameen Bank,

Ibne Sina Hospital, Prince Bazar, Mukto Bangla Shopping Mall, Mukti jodhdha Shopping Mall, Mirpur Butic

House, Benarorsi Palli, Mirpur Bangla College, Mirpur University College, Mirpur zoo, Botanical garden etc.

B. JUSTIFICATION

Nigeria is a developing country where the use of aggregates is very high because of its infrastructural

development programs. Gunpowder is a very cheap explosive that could reduce the cost of aggregates. The use

of the end product of rock blasting in the construction of highways, railway, airport pavements and all vertical

structures cannot be over-emphasized, therefore the need to carry out a study on the blasting of rock and the

processing and production of aggregates.

REVIEW OF RELATED WORKS

A. BLASTING TECHNIQUES

It is common to fire several holes or rows of holes at one time. Fragmentation, back break, vibration, and

violence of a blast are all controlled by the firing sequence of the individual blast holes. The order and timing of

the detonation of the individual holes is regulated by the initiation system. Electric and non-electric initiation

systems are available. When selecting the proper system and techniques, one should consider both blast design

and safety, [1]. Electric systems are more sensitive to lightening than non-electric systems, but both are

susceptible.

Use of Hand Charge

The prepared charge including detonator is carried in the control team members’ pack. The person should not be

loaded heavily that skiing is clumsy. Igniters are carried separately from the explosives. Team members keep in

constant contact using radios. Once at the blast position:

i. Ensure all possible run out zones are free of people and traffic. Arrange for signals from an observer

for areas not visible from the blast point.

ii. Work with only one charge at a time.

iii. Step into blasting position and make final check of target and escape route.

iv. Get to a safe position and await detonation, [3].

Electric Blasting Caps

With an electric blasting cap technique, an explosion is caused by passing an electric current through a wire

bridge, similar to an electric light bulb filament. The current approximately 1.5amps, heats the bridge to

incandescence and ignites a heat-sensitive flash compound. The ignition sets off a primer which in turn fires a

base charge in the cap.

Delay Blasting System

Delay blasting caps are used to obtain a specified firing sequence. Such caps are available for daily intervals

varying from a small fraction of a second to about seven seconds. When explosive charges in two or more rows

of holes parallel to a face are fired in one shot, it is desirable to fire the charges in the holes nearest the face a

short time ahead of those in the second row. This procedure will reduce the apparent burden for the holes and

thereby will permit the explosive in the second row to break the rock more effectively, [1]. In the case of more

than two rows, this same delay firing sequence will be followed for each successive row.

ONYELOWE, KEN. C.

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Sequential Blasting Machine

There are condenser-discharge blasting machines for firing electric blasting caps. There special machines have

sequential timers permitting precisely timed firing intervals for blasting circuits. This provides the blaster the

option of many delays within a blast. Since many delays are available, the kilogram of explosive fired per delay

can be reduced to control noise and vibration better.

B. BLASTING EXPLOSIVES

Over the years, four main categories of commercial high explosives: dynamite, slurries, ANFO (ammonium

nitrate and fuel oil), and two-component explosives, [1]. Over ten million kilograms of explosives are used daily

to excavate rock by blasting in mining and construction operations throughout the United States, [4]. Rocks are

blasted every other day at the Setraco Quarry site at Lokpanta in Umunneochi Local Government Council of

Abia State, Nigeria, Crushed-Rock Industries Quarry Site at Ituku, Ozalla, Enugu State, Nigeria, Julius Berger

Quarry Site at Mubi, Adamawa State, Nigeria etc. Over the years, blasting operations have always been a very

expensive operation because of the cost of the modern explosives used.

i. Dynamite

Dynamite, a nitroglycerin-based product is the most sensitive of all the generic classes of explosive in use today.

It is available in many grades and sizes to meet the requirements of a particular job. Dynamite is used

extensively for charging boreholes, especially for the smaller sizes. As cartridges are placed in a hole, they are

tamped sharply with a wooden pole, expanding the cartridges to fill the hole. Dynamites may be fired by a

blasting cap or a prima cord fuse, [1].

ii. Slurries

This is generic term for both water gels and emulsions. They are water-resistant explosive mixtures of

ammonium nitrate and fuel sensitizer. The primary sensitizing methods are the introduction of air throughout the

mixture, the addition of aluminum particles or the addition of nitro cellulose. Slurries are very expensive and

have less energy, [5].

iii. ANFO

This explosive is used extensively on construction projects and represents about 80% of all the explosives used

in the United States. ANFO is synonymous with dry blasting agents. ANFO is the cheapest source of explosive

energy compared to dynamites and slurries. Because it must be detonated by special primers, it is much safer

than dynamite. The explosive is made by blending 0.0105m3 of fuel oil with 45.36kg of ammonium nitrate

blasting prills. This is the optimum mixture ratio. The detonation efficiency is controlled by this ratio. It is less

detrimental to have a fuel extremes affect the blast. With too little fuel, the explosive will not perform properly.

With too much fuel, maximum energy output is reduced, [1].

METHODOLOGY

A. BLAST DESIGN USING GUNPOWDER AS AN EXPLOSIVE

The Chemistry of Gunpowder Production

Gunpowder, also known as black powder is an explosive that has been on ground, literarily, for centuries. The

exact origins of the formula are lost in time, but it is known that the Chinese used black powder in weaponry at

least 1000 years ago, [6]. Gunpowder has a specific gravity of 1.25 and burns at great speed releasing both

shock wave and high vibrations (sound) when compressed and enclosed. Technically, black powder burns by a

process known as deflagration. This differs from detonation in that black powder produces subsonic shock

waves. The powder burns at a very high temperature and is easily ignited. High grade powder doesn’t need

flame to ignite.

Gunpowder has traditionally consisted of three ingredients: potassium nitrate, KNO3, also known as saltpeter,

sulfur and charcoal. The sulfur and charcoal provide fuel for the reaction, while the potassium nitrate provides

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oxygen. By themselves, charcoal and sulfur will burn, albeit very slowly. The addition of an oxidizer such as

KNO3 greatly speeds up the burn rate of the fuel, resulting in an explosive reaction.

The traditional ratio of the ingredients is 15:3:2 of KNO3, charcoal and sulfur by weight not volume, [7]. A

decent sized batch would be 300grms KNO3, 60grms charcoal and 40grms sulfur, [8]. The quality of the

resulting powder depends on a number of factors. The most important of these is binding, [9]. Binding refers to

how tightly the KNO3 is mixed with the charcoal/sulfur mixture. The quality of the powder is defined by its

burn rate, usually expressed in cm3/s. so the ability to produce gunpowder of burn rate above 14cm3/s

determines the success of the production of a good explosive, [10] and [11].

Blast Design

Rocks are made from various types of minerals. Minerals are substances of crystalline form made up from a

particular chemical composition. The main minerals found in rocks include quartz, feldspar, calcite, and mica

and in blast design, the effects of these minerals are taken into consideration because of changes in the specific

gravity of the rock, [12]. Every blast must be designed to meet the existing conditions of the rock formation and

overburden, and to produce the desired final result. There is no single solution to this problem, [1]. Rock is not a

homogeneous material. There are fracture planes, seams, and changes in burden to be considered. Wave

propagation is faster in hard rock than in soft rock. Initial blast designs used idealized assumptions.

Because of these facts, it must always be understood that the theoretical blast design is only the starting point for

blasting operations in the field. A trial blast should always be performed. It will either validate the initial

assumptions or provide the information needed for final blast design. The most critical dimension in blast design

is the burden distance B (m) expressed as:

1. (

)

B is the distance to the free face in an excavation, whether a quarry situation or a highway cut. Rocks will be

thrown for excessive distances from the face when the burden distance is insufficient.

Stemming

The purpose of stemming is to confine the explosive (gunpowder) energy to the blast hole. To function properly,

the stemming material must lock into the borehole.

Stemming distance is expressed as:

2.

Peak Particle Velocity

To determine the weight of gunpowder that can be detonated without off-site damage, the following blast

expression formula that relates peak particle velocity to distance and the weight of explosives fired in a single

delay period is:

3. (

√ )

k and a are variables that depend on site conditions. Ideally, values for k and a are generally derived from blast

vibration monitoring at a site and define a line that represents a relationship between PPV and weight of

explosives for those conditions. However, the Federal Highway Administration (FHWA) developed the values

of k and a as 100 and -1.6 in that order, [13].

Blast Size

Blasthole is achieved by rock core drilling which is accomplished with mechanical engine-powered rotary drills

designed to drill rock and to recover cylindrical cores of rock material. Most coredrilling equipment are

designed with gear or hydraulically driven variable speed hollow-spindle rotary drill heads, [14]. The diameter

of the blast hole will affect blast considerations concerning fragmentation, air blast, fly rock, and ground

ONYELOWE, KEN. C.

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vibration. In “Table (1)”, it is shown the effects of blast hole and the specific gravity of gunpowder on the

charge of gunpowder or loading density.

Column

Diameter (m)

Loading Density(kg per

m column diameter)

0.0254 0.585

0.0508 2.550

0.0762 5.745

0.1016 10.215

0.1270 15.968

0.1597 22.980

0.1778 31.283

0.2032 40.860

0.2286 51.713

0.2540 63.840

Table 1: Gunpowder Loading Density Chart in kg per meter of Column Diameter for Gunpowder of Specific

Gravity of 1.25

Gunpowder Factor

The amount of gunpowder required to fracture a 0.729m3

of rock is a measure of the economy of a blast design.

Table 1 is a loading density chart which allows the engineer to easily calculate the weight of explosive required

for a blast hole.

Figure 1: Gunpowder Loading Density Chart in Kg per m of Column Diameter.

Loading Density (kg/m column diameter)

B. AGGREGATE PRODUCTION

The production of crushed-stone aggregate involves drilling, blasting, loading, transporting, crushing, screening,

and product handling and storage. In operating a quarry and crushing plant, the drilling pattern, the amount of

explosives, the size of shovel or loader used to load the stone, and the size of the primary crusher should be

coordinated to assure that all stone from the quarry can be economically utilized.

Aggregate Crushers

Crushing plants utilize step reduction because the amount of size reduction accomplished is directly related to

the energy applied. When there is a large difference between the size of the feed material and the size of the

crushed product, a large amount of energy is required. As stone passes through a crusher, the reduction in size

may be expressed as a reduction ratio: the ratio of the crusher feed size to the product size. The sizes are usually

fined as the 80% passing size of the cumulative size distribution. Crushers are classified by their method of

mechanically transmitted fracturing energy to the rock.

i. Jaw, gyratory, and roll crushers work by applying compressive force. The main classes of aggregate

crushers include,

ii. Jaw crushers

iii. Gyratory crushers

iv. Roll crushers

v. Impact crushers

0

10

20

30

ColumnDiameter(cm)

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A special aggregate processing unit has the following components,

i. Rod mills

ii. Ball mills

iii. Log washers

Sand preparation and classification section, [1]. It is discovered that at the end of aggregate crushing and

production, we are left with quarry dust which is used as admixture for cement stabilized lateritic soils.

DISCUSSION

It has been shown through the blast design and examination carried out at Setraco Quarry site, that gunpowder

could serve as a good replacement for the modern and expensive explosives in rock blasting since it can be

manufactured locally with less cost. In addition, Table 1 is a good guide on the gunpowder loading density in kg

per m of column diameter. The whole idea of rock blasting is to produce aggregates for all civil engineering

works. At the end of the study, aggregates of various sizes were produced as well as quarry dust which is a good

admixture for cement stabilized lateritic soils.

Safety and seismic effect

Accidents involving gunpowder may easily kill or cause severe injury. The prevention of such accidents

depends on careful planning and faithful observation of proper blasting practices.

Because blasting operations may cause actual or alleged damages to buildings, structures, and other properties

located in the vicinity of the blasting operations, it may be desirable to examine and possibly photograph any

structures for which charges of damages may be made later, [15] and [16].

Conclusion

At the end of this research work, it was concluded as follows;

i. That rock blasting occupies an essential phase in the production of aggregates which are used in the

production of concrete and in other civil engineering/geotechnical engineering works such as pavement

sub base and base course constructions,

ii. That gunpowder is a good replacement for the expensive explosives like dynamite, ANFO and slurries

in terms of production simplicity and handling. Consequently, gunpowder used as an explosive during

the blasting of rocks is very cost effective. In addition, gunpowder releases considerable energy and

shock wave needed blast and break any kind of rocks,

iii. That the production of aggregates is very essential to the development of Nigeria as developing nation

because of her developmental project targeted at the millennium developmental goals (MDGs) for 2020

and the use of quarry dust that seems to be a waste product from aggregate production in a quarry site

as an admixture in both the production of concrete and in cement stabilized lateritic soils,

iv. That “Table (1)” and Figure 1 serves as a guide in the use of gunpowder with respect to its loading

density and column diameter,

That gunpowder/black powder is highly recommended to rock blasting factories or companies for use as

blasting explosives in place of the more expensive ones.

ACKNOWLEDGEMENT

I wish to acknowledge the management and staff of Setraco Nigeria Ltd, for the help tgey rendered through this

research work. Also to my friend Arc.N.U.Ogwo for all the relevant assistance she offered me during this

period.

ONYELOWE, KEN. C.

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