The Science Behind Rock Fragmentation on Construction Engineering: Exploring Aggregate Properties and Explosives in the Aggregate Industry
1. Introduction
Any substance used to
construct a structure is referred to as a building material. The construction
industry employs a variety of materials for construction depending on their
structural performance. Building materials used in construction are governed by
regional and national standards. On the other hand, architects select building
materials based on cost and attractiveness. Choosing the right material for a
project means extending and improving its lifespan [1]. Steel, concrete, wood,
stone, and brick/masonry are the current construction materials employed.
Aggregates are the main component of them and are utilized mostly for concrete
structures. Aggregates with
different particle size and properties are required in different construction
engineering practices [2].
Aggregates can be
created artificially or naturally. Larger rock formations are typically mined
for natural aggregates using an open excavation (quarry). Usually, mechanical
crushing is used to reduce extracted rock to sizes that can be utilized.
Aggregate that has been manufactured artificially is frequently a byproduct of
other manufacturing industries [3]. The excavated rock that has been processed
into a usable product, such as aggregates or metals, is used almost entirely in
the construction of buildings, bridges, roads, and railways. The primary raw
material for the construction industry is rock aggregates. In 2021, 1.5 billion tons of crushed
stone valued at more than $19 billion was produced by an estimated 1,410
companies operating 3,440 quarries and 180 sales and (or) distribution yards in
50 States in USA [4]. Worldwide demand for aggregates is highest among other
minerals and is estimated to be rising by 4.7% annually [5]. Figure 01
illustrates the worldwide demand for minerals in the year 2021.
Figure
01: Worldwide demand for minerals in 2021
2
Aggregate Properties
2.1 Physical properties
2.1.1 Composition
It must be considered to never utilize
aggregates made of materials that can chemically react with cement's alkalis
and cause excessive expansion, cracking, and other damage to the concrete mix.
As a result, it is required to test aggregates to determine whether or not they
contain any of those parts [9].
2.1.2 Size
The strength and workability of concrete in both its fresh
and hardened states can be significantly impacted by the size of the aggregate.
Both fine and coarse aggregate are comparable in this regard. The maximum size
of coarse aggregate that can be utilized shouldn't be more than 5 mm less than
the minimum clear space between reinforcements in RCC structures or more than
1/4th of the minimum thickness of the structural member [10].
Utilizing aggregates of the largest possible size reduces
the amount of cement used as a binding agent, the amount of water needed, and
the amount of shrinkage and creeping that occurs as new concrete dries. On the
contrary, using a greater proportion of larger aggregate may make concrete less
workable when it is applied. Sand should be used as the fine aggregate in
conventional concreting and a coarse aggregate with a nominal size of 20 mm
should be used for better soundness, compactness, band, and workability of concrete
[11].
2.1.3 Shape
The workability of concrete in its fresh state as well as
its durability, strength, and bonding in its hardened stage can all be impacted
by the shape of the aggregate grains. Visual inspection, along with other
characteristics and indices like the roundness index, sphericity, angularity
number, flakiness index, elongation index, etc., are used to determine the
shape of the aggregates. Round, irregular, angular, flaky, elongated, and flaky
elongated are the several shapes that can be categorized. Each category of
aggregate has varied yields and potential requirements.
Rounded aggregates - need less cement content because of
their reduced specific surface area and low angularity number, which results in
a constant W/C ratio [11].
Angular aggregates - most recommended shape for aggregates
in the concrete manufacturing process is one with high angularity numbers and
higher specific surface area accessible for proper bonding between cement paste
and aggregates as well as superior interlocking properties. However, when this
number rises, the workability of the concrete declines [12].
Flaky and elongated aggregates - having greater specific surface areas yet due to their shape, lack adequate interlocking characteristics. They are also less workable than angular aggregates since they have a larger angularity number [13].
2.1.4 Surface texture
The
degree to which a particle of aggregate's surface is smooth or rough, polished
or dull, is measured by the surface texture of the aggregate. The parent source
rock's pore properties, hardness, and grain size all affect a crushed
aggregate's surface texture. This can be decided through visual inspection. The
water content of the concrete mix and its workability in its fresh condition
can both be significantly influenced by the surface texture of the fine and
coarse aggregate. Due to the existence of voids and pores, rough texture
aggregates are known to make stronger bonding with cement paste than other
textured aggregates. Conversely, glass-like smooth aggregates absorb less water
than coarse aggregates, which may affect the water requirement as previously
mentioned [14].
2.1.5 Specific gravity
This
ratio provides the aggregates' apparent specific gravity since it accounts for
the aggregates' volume of impermeable pores (not capillary voids). Compared to
absolute specific gravity, apparent specific gravity is more beneficial. Most
natural aggregates have a specific gravity between 2.6 and 2.9. In the case of
lightweight aggregates, it can be below this range. The appropriateness and
quantity of the aggregates for the specified volume of concrete can be
determined using specific gravity [15].
Aggregates
having a greater specific gravity are often compact, solid, and robust. They
also have fewer holes and a lower water absorption rate, making them desirable
aggregates. Aggregates having a lower specific gravity, on the other hand, may
be porous, frail, and mostly water absorbing [16].
2.1.6 Bulk density
Bulk
density can be applied to transform volume batches from weight batches.
Additionally, it is influenced by the particle's shape and size distribution.
Similar-sized grains or particles produce more voids and have lower bulk
densities, whereas aggregates with a range of particle sizes have a lower void
content and a greater bulk density. The void ratio under typical conditions can
be calculated using the bulk density under saturated and surface dry
conditions. The amount of cement paste used in a concrete mix is impacted by
this void ratio [17]. Similar to how rounded and angular aggregates produce
less void than elongated and flaky ones. This raises the needed cement content.
When the mixture contains 35–40% fine aggregate by the total mass of the
aggregate mix, the bulk density of the aggregate is at its highest.
2.1.7 Porosity, water absorption and moisture content
The bond between aggregate and cement paste, durability, chemical
stability of the concrete, resistance to abrasion, resistance to freezing and
thawing, and a specific gravity of the concrete and aggregate itself are all
significantly influenced by the porosity, permeability, and absorption of the
aggregate.
In most cases, pores develop through the formation of rocks
or other natural processes like the generation of fossils and decomposition.
This pore may be on the surface of the rock or enclosed within it, and its
sizes and shapes may vary from rock to rock. It is discovered to vary between 0
and 50% of the aggregate volume.
The volume, pace, and size of these pores influence how much
and how quickly water permeates the aggregates, which in turn influences the
aggregate's capacity to absorb water. The initial moisture content has an
impact on the amount of water needed to mix concrete [18].
2.2 Thermal properties
The main thermal attributes that might influence how well
concrete performs are the coefficient of thermal expansion, specific heat, and
thermal conductivity of the aggregate. It has been discovered that the
durability of the concrete may be considerably impacted when exposed to a
freezing and thawing environment if the coefficient of thermal expansion of the
aggregates differs by more than 5.5 x 10-6 per °C from that of
cement paste [19]. The insulation performance of the concrete structure may be
impacted by the specific heat and thermal conductivity [20].
Hazardous
substances, organic debris, clay, and other fine materials have an impact on
the bonding properties and render concrete fragile and unreliable. Concrete
that contains salt minerals will become hydrophobic, absorbing moisture from
the air and producing efflorescence. Washing the aggregates with fresh water
will prevent this effect [18].
2.3 Chemical properties
2.3.1 Chemical composition of aggregates
Natural aggregates are composed of a variety of substances,
including clay minerals, iron oxide, silica minerals, feldspars, micaceous
minerals, carbonate minerals, sulfate minerals, and iron sulfide minerals. To
be utilized as aggregates for concreting or other applications, all of these
mineral aggregates should have all the qualities of a good aggregate as
described above. All components that can reduce the stability, toughness, and
durability of concrete must be removed.
2.3.2 Alkali - aggregate reaction
Alkali aggregate reaction, or AAR, is a reaction that begins with the attack of alkaline hydroxides, which are made from alkaline oxides (K2O, Na2O) present in the cement, on reactive siliceous minerals or other minerals in aggregate, forming alkali silicate gel with unlimited swelling ability in the presence of water [21]. The integrity, strength, and durability of concrete are compromised by this swelling of leftovers. Adopting a lower W/C ratio, special low alkali cement, a good surface sealer, and sound aggregate itself can help prevent it [22].
2.4 Mechanical Properties
2.4.1 Strength
Strength of the aggregates simply refers to the aggregate's
compressive or crushing strength where Aggregate Crushing Value (ACV) serves as
a representation. ACV, which is often calculated for coarse aggregates, is the
quantifiable resistance offered by aggregates to the gradually applied
compressive/crushing loads. For surfaces other than the wearing surface, the
limitation value for ACV is equivalent to 45% and 30%, respectively [21].
2.4.2 Toughness
The ability of an aggregate to withstand an abruptly imposed
stress or an impact load is referred to as its toughness. Aggregate impact
value, a measurement of an aggregate's resistance to impact load, serves as a
cue. The aggregate impact value is determined by dividing the amount of
material that passes through the 2.36 mm sieve by the sample's total weight. For wearing surface
and other surfaces, limiting impact value is 30% and 45% respectively [16].
2.4.3 Hardness
The aggregate's hardness specifies how resistant the
aggregate is to wear, abrasion, and attrition. It is measured using the
aggregate's abrasion value, which measures how resistant the aggregate is to
wear and abrasion. It can be determined using a variety of tests, including the
Los Angeles, Deval, and Dorry abrasion tests. The percentage of aggregate
passing through the IS sieve of 1.7mm to the total weight of the sample is used
to calculate the aggregate abrasion value. For the wearing surface and other
surfaces, the aggregate abrasion value limitation value is 30% and 50%,
respectively [23].
2.4.4 Bond strength
The compressive and flexural strength and durability of the
concrete are significantly influenced by the bond strength between the
aggregates and cement paste. In order to create a concrete structure that is
strong and enduring, a proper stronger bond between the aggregate and cement
paste is required. Therefore, a number of elements exist, have an impact on how
cement paste and aggregate are bound together. These include the aggregate's
shape and surface roughness, the presence of harmful materials, the composition
of the aggregate, etc. Aggregates and cement paste adhere better to each other
when they are more rugged [24].
Similarly, angular aggregates have a more defined region for improved interlocking and higher bonding. The presence of harmful material may render aggregate surfaces unsuitable for bond formation or negatively impact cement hydration. The tests used to evaluate the bonds' quality are complex and expensive. As a result, it is calculated by looking at the large fragments of broken concrete left over from the crushing value test.
3 Aggregate Classification
Aggregates can be
divided into several categories according to different properties, such as
size, source, and unit weight [6]. Widely used classification is based on
Aggregate size and can be classified as coarse aggregates and fine aggregates
[7].
Coarse aggregate: Coarse aggregates are those that are typically
retained on a No. 4 (4.75 mm) sieve. The typical size range for coarse
aggregate is 5 to 150 mm. The maximum size of coarse aggregate for typical
concrete used for structural elements like beams and columns is around 25 mm.
The maximum size for mass concrete used for dams or deep foundations is 150 mm.
Figure 02 shows some examples of coarse
aggregates.
Figure 02: Examples of coarse aggregates
Fine aggregate (sand): Fine aggregate is
defined as material that passes through a No. 4 (4.75 mm) sieve but is
primarily retained on a No. 200 (75 mm) screen. The most widely utilized fine
aggregate is river sand. Crushed rock fines are another option for fine
aggregate. However, compared to river sand, the finish of concrete with crushed
rock fines is not good.
The workability, durability, strength, weight,
and shrinkage of the concrete are all significantly influenced by the
composition, shape, and size of the aggregate. In precast concrete countertop
mixes, aggregate plays a particularly crucial role in determining how the cast
surface will resemble [8]. The aggregate sizes along with their applications
are summarized in Table 01.
Table 01: Aggregate sizes with their applications
4 Fragmentation requirements in aggregate industry
4.1 Rock Fragmentation requirements for construction industry
In the construction industry, rock
fragmentation is an essential process for breaking down large rocks and
boulders into smaller, more manageable pieces that can be used for construction
purposes. There are several requirements for rock fragmentation in the
construction industry, including:
Size: The rock fragments must be of a size
that is appropriate for the construction project. This will depend on the specific
application, but generally, smaller pieces are more desirable for easier
handling and placement.
Shape: The shape of the rock fragments is also
important. Irregular shapes can make it difficult to lay the fragments properly
and can result in gaps between the pieces.
Consistency: The fragments should be uniform
in size and shape to ensure consistency in the construction process. This is
important for achieving a uniform strength and stability in the finished
product.
Safety: Safety is paramount during rock
fragmentation, and all necessary precautions must be taken to protect workers
and equipment. This may include the use of protective gear, safety barriers,
and monitoring equipment.
Environmental impact: The process of rock
fragmentation can have a significant impact on the environment, particularly in
terms of noise, dust, and vibration. It is important to minimize these impacts
through the use of appropriate equipment and techniques.
Overall, the requirements for rock
fragmentation in the construction industry are focused on producing rock
fragments that are safe, consistent, and suitable for the intended construction
application.
4.2 Importance of degree of rock fragmentation on construction engineering requirements
The degree of rock fragmentation is an important
factor that can significantly affect the construction engineering requirements.
Here are some reasons:
Material handling: The degree of fragmentation
determines the size of the rock fragments, and this affects the equipment
needed to handle them. If the rock is not fragmented enough, it may require
larger equipment, such as excavators or bulldozers, to handle the larger
pieces. On the other hand, if the rock is fragmented too much, it may require
smaller equipment, such as loaders or trucks, to handle the smaller fragments.
Placement and compaction: The degree of rock
fragmentation also affects how the fragments can be placed and compacted. If
the fragments are too large, they may not fit together well, leaving gaps that
can weaken the structure. If the fragments are too small, they may not be able
to be compacted effectively, which can also lead to reduced strength.
Structural stability: The degree of
fragmentation can affect the structural stability of the finished construction.
The fragments need to be of a consistent size and shape to ensure that they fit
together well and create a stable structure. If the fragments are too large or
irregularly shaped, they may not fit together tightly, which can weaken the
structure.
Time and cost: The degree of fragmentation can
also affect the time and cost of the construction project. If the rock is not
fragmented enough, it may take longer to break it down and handle it, which can
increase the time and cost of the project. On the other hand, if the rock is fragmented
too much, it may require additional processing to achieve the desired size and
shape, which can also increase time and cost.
In summary, the degree of rock fragmentation is an important factor that affects various aspects of construction engineering requirements, including material handling, placement and compaction, structural stability, and time and cost. Therefore, it is essential to carefully consider the degree of fragmentation needed for a specific construction project to ensure that the finished product meets the desired requirements. To fragment the in-situ rocks in to a desired size, explosive selection play a major role.
5 Explosives used in aggregate industry.
Explosives are a
crucial tool used in the aggregate industry for breaking and excavating rock,
as well as for preparing construction materials. The selection of the right
type of explosive is essential to ensure the best possible outcome. This
section will cover the different types of explosives used in the aggregate industry
and their properties, advantages, and disadvantages, with references to
scientific studies and industry reports.
The two main types of
explosives used in the aggregate industry are high explosives and low
explosives. Figure 03 shows a
diagram of a reacting cartridge of low explosive. If the reaction is stopped
when the cartridge has been partially consumed and the archived pressure
profile is examined, it can be observed that there is a steady rise in pressure
at the reaction until the maximum pressure is reached. Low explosives only
produce gas pressure during the combustion process. A high explosive detonates
and exhibits a totally different pressure profile (Figure 03).
Figure
03: Pressure profiles of Low and High explosives
High explosives include dynamite, ammonium nitrate/fuel oil (ANFO), and emulsion explosives, while low explosives include black powder and safety fuse.
5.1 High explosives
Dynamite is a common
type of high explosive used in the industry, which is a mixture of
nitroglycerin, sorbents (such as powdered shells or clay), and stabilizers.
According to a study by L. G. Hill et al. (1994), dynamite is commonly used for
breaking down hard rock and produces a rapid and powerful shock wave, making it
an effective explosive for the aggregate industry. However, the study notes
that dynamite is sensitive to shock and friction, making it dangerous to handle
and transport [25].
ANFO is another
popular high explosive used in the aggregate industry, which is a mixture of
ammonium nitrate and fuel oil. ANFO is cheaper and safer to use than dynamite
but is less powerful, making it suitable for breaking down softer rocks.
According to an industry report by the Mine Safety and Health Administration
(MSHA) (2010), ANFO is commonly used in the aggregate industry because it is
economical and has a lower risk of accidental detonation than dynamite [26].
Emulsion explosives
are a type of high explosive that are made by mixing an oxidizer and fuel with
water (very least
ammonium nitrate, water, oils and a surfactant), producing a
gel-like substance. Emulsion explosives are safer to handle and more stable
than dynamite, but they are less powerful. Y. Liu et al. (2019) found that
emulsion explosives are effective for rock breaking in the aggregate industry,
with less damage to the surrounding environment and structures [27].
5.2 Low explosives
Black powder is a low
explosive used for small-scale blasting operations and is made from a mixture
of potassium nitrate, sulfur, and charcoal. According to the MSHA (2010)
report, black powder is still used in some small-scale mining and quarrying
operations. Safety fuse is another type of low explosive used in industry,
which is a cord-like material that burns at a set rate, allowing workers to
time the detonation of the explosive [28].
The use of explosives
in the aggregate industry must follow strict regulations and guidelines to
ensure the safety of workers and the public. Proper training, handling,
storage, transportation, and disposal of explosives are crucial for minimizing
the risk of accidents and damage to the environment. According to an industry
report by the National Stone, Sand & Gravel Association (NSSGA) (2019), the
industry is committed to following best practices for the safe use of
explosives, including training and certification of workers, proper storage and
transportation of explosives, and following federal and state regulations for
blasting operations.
In conclusion, the use of explosives in the aggregate industry is necessary for efficient and productive rock excavation and preparation of construction materials. The selection of the right type of explosive is critical, considering the nature of the rock and the safety of workers and the public. Therefore, the industry must follow strict regulations and guidelines to ensure the safe and efficient use of explosives.
6 Conclusion
This article delves into the crucial role of rock
fragmentation in the aggregate industry and its profound impact on construction
engineering requirements. It begins by introducing rock aggregates and
highlighting their significance in construction projects. The properties of
aggregates are then discussed, emphasizing their influence on the overall
quality and performance of construction materials.
Next, the article delves into fragmentation requirements
specific to the aggregate industry. The importance of meeting fragmentation
requirements is emphasized, as it directly affects factors like concrete
strength, compaction, stability, and overall project success. The article
further examines the explosives used in the aggregate industry to facilitate
rock fragmentation. It highlights the types of explosives commonly employed,
focusing on their safety considerations, performance characteristics, and
environmental impact. The responsible usage of explosives is emphasized,
ensuring that quarrying operations maintain a balance between efficiency and
environmental sustainability.
Throughout the article, the intricate relationship between
rock fragmentation and construction engineering requirements is underscored.
The degree of rock fragmentation significantly influences the workability,
strength, and durability of construction materials derived from aggregates.
Understanding the science behind aggregate properties enables engineers and
industry professionals to optimize construction outcomes and meet project
specifications.
By shedding light on the crucial link between rock
fragmentation, aggregate properties, and construction engineering requirements,
this article provides valuable insights for professionals in the aggregate
industry, engineers, and anyone involved in construction projects.
Understanding and optimizing rock fragmentation can lead to enhanced
construction outcomes, improved resource utilization, and sustainable practices
in the aggregate industry.
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