Mineral resources and aggregates Flashcards
two groups of mineral resources relevant to engineering
- metallic minerals
2. industrial minerals/aggregates
industrial minerals
geological materials mined for their commercial value
petroleum is an industrial mineral
TRUE or FALSE
false. fuel sources are not industrial minerals and are not sources of metals
non-metallic industrial minerals uses
used in construction, ceramics, paints, electronics, glass, paper, detergents, etc.
Are non-metallic industrial minerals finite or infinite?
finite - they are mined from the ground
construction stone
stone which is actively quarried or mined to provide materials for buildings or major engineering projects such as roads. highest quality stone, usually used raw
3 categories of construction stone
- dimension stone
- decorative stone (non load-bearing)
- armourstone and rip-rap
dimension and natural stone
classified according to the rock type and its end use
- masonary stone
- stone cladding
- flooring stone
- roofing
- pavement construction
what is the most common modern day use for natural stone?
facings on buildings for decorative purposes. Very seldom used to transfer structural loads
what is the minimum compressive strength of concrete, which dimension stones should meet to be used in construction?
27MPa
when talking about the durability of natural stone, what is being referred too?
what does this depend on?
resistance of the stone to exposure and weathering. The durability depends on atmosphere (e.g. acid rain) and sub-surface features (e.g. constant wetting/drying = salt growth in pore spaces = physical breakdown)
when measuring materials durability, which 4 aspects of porosity measured
- porosity % (more pores = more weathering)
- saturation coefficient (ammount of water absorbed by fully immersed rock for 24h : volume of rock)
- microporosity (% small pores < 5 micrometers)
- capillarity (rate of water uptake)
why are small pores < 5micrometers bad for durability?
they retain water after vacuum
other than porosity, what else should be tested to judge the durability?
crystallisation test and acid immersion test.
criteria used to pick natural stone for construction
- durability
- appearance
- ease of working
- availability
using the example of greywacke, explain why ease of working is important when choosing a natural stone for construction
greywacke is notoriously hard to split, so would not be economical to use as a building/ornament stone.
availability of natural stone today vs historically
used to only use locally sourced rocks, but now ease of transport has increased, we can source rocks from all over the world, e.g. granite from China.
aggregates
- particles of rock which, when bounded together form a construction material.
- particle size ranges from sand to cobble.
what determines the performance of aggregates?
the particle size
aggregates are infinite resources
TRUE or FALSE
False, finite
use of aggregates in today’s construction projects
- expensive to quarry, mine process and transport
- financial viability depends on having suitable and plentiful aggregate supply nearby.
- used in concrete therefore they are basically in every construction project.
aggregate sources
- fluvial deposits
- basalts and andesites
- greywacke
important issue when choosing an aggregate, is determining the amount of unusable material.
How does greywacke compare to fluvial deposits in this regard?
greywacke is full of unusable mudstone (high clay content), whereas, fluvial deposits have already been transported by the river, so most of the weak materials have already been eroded away.
artificial aggregates =
natural aggregates =
synthetic/ recycled aggregates =
heavy aggregates =
artificial aggregates = quarried, crushed and screened
natural aggregates = fluvial sands and gravels
synthetic/ recycled aggregates = it is what it is
heavy aggregates = magnetite and iron to produce concrete
synthetic aggregates, where is it from and why is it good?
by-products of an industrial process, e.g. blast furnace slag or pulverised fuel ash (from Huntly).
Its lightweight and often used in road embankments or bridge abuments - limits the ammount of settlement.
when we want lightweight aggregate in nz what do we normally use?
pumice or scoria
importance of using the right aggregate in concrete
certain aggregates can cause deterioration in the long term strength of concrete, which in something like a dam can lead to failure.
thermal expansion in concrete determines…. what does this have to do with the aggregate
cooling induced tensile stress. As concrete cures it releases heat which can lead to thermal cracking, aggregates can decrease the coefficient of thermal expansion by 2, or can be artificially cooled
some uses of aggregate on concrete
- cheap filler to bulk concrete
- resistance to loads
- resistance to abrasion
- resist penetration of moisture
- resist weathering
- reduce volume change during curing
4 contributions of aggregate to concrete
- increase strength, elasticity, durability
- reduce workability and increase density
- the more aggregate the lower the cost of the mix
- the more aggregate in the mix, the less volume change
how does the particle shape of the aggregate affect the final concrete
coarse/angular particles are harder to work, but have a stronger bond with cement after curing, opposite is the case with smooth particles
is cement itself an aggregate? what is it made of?
originates from the crushing of limestone. It can itself be considered an aggregate.
all aggregates must be chemically stable/inert.
yeah or nah?
yeah
size of aggregate particles affect on concrete mix
the larger the particles, the lower the workability and less water required
how do the following substances reduce the strength and durability of concrete:
- organic impurities
- particles finer than 75microm
- coal, lignites, and other lightweight materials
- soft particles
- clays
- alkali-reactive aggregates
- evaporate salts
- organic impurities = affects setting and hardening. May cause deterioration.
- particles finer than 75microm = affect bond strength and increases water required
- coal, lignites, and other lightweight materials = affects durability and may cause stains and popouts
- soft particles = affects durability
- clays = affects workability and durability
- alkali-reactive aggregates = causes abnormal expansion, cracking and popouts
- evaporate salts = affect hydration characteristics and can degrade steel reinforcing
Alkali-silica reactions. cause and implications
alkalis (Na and K) in the concrete can enter solution and combine with the silica to form a gel which swells and absorbs water. This causes cracking and loss of structural integrity
which aggregates are prone to alkali-silica reactions?
volcanic glass and argillites (found in greywacke) are prone to these reactions.
petrographic examination
a method to ensure an aggregate is suitable for use in concrete
the effect of clay in concrete
contained either in aggregate particles or as coatings on the particles.
They weaken the bond strength of the mix which reduces both the tensile and compressive strength of the concrete.
If the clays swell, they will absorb a lot of the water and the concrete will not cure properly
salts vs. concrete
salts such as sulphates and chlorides may be present in the ground and need to be considered when specifying concrete for foundations. Over time these salts will degrade and the foundation will be lost
how do we specify concrete for the marine environment
an aggregate must be chosen which makes the concrete resistant to aggressive chemical and physical attack
mica in aggregates and its effects on concrete mix
mica is a sheet silicate which is present in many rock types and affects the ammount of water needed to obtain a workable mix.
Thermal effects can also change mica into other materials.
Mica is almost impossible to remove so its pretty aids and alternative sources should be used .
how do we reduce the amount of heat in large pours (when building dams)
we use less water and concrete by choosing a coarse aggregate with 2 distinct particle sizes.
The two sizes produce a placed aggregate with minimum void space. less void space = less concrete.
2 aggregate uses in road construction
- bound (as bitumen mixes)
2. unbound (as road sub-base)
aggregate size, shape, strength, durability, and wear resistance required for road construction
aggregate size = base course (38mm), wearing course (19-25mm)
aggregate shape = flattened aggregates with cleavage (flakiness)
strength = ability to withstand mechanical crushing (aggregate crushing value ACV, aggregate impact value AIV)
durability = resistance to normal weathering effects (sulphate crystallisation test)
wear resistance (AAV and PSV) = aggregates can become polished - reducing friction. aggregate should be chosen to wear slowly enough to prevent polishing, but last long enough to be economical
what does a low ACV - aggregate crushing value, represent
the test simulates heavy traffic and a lower value = more resistance to crushing
which aggregates perform well in the AIV - aggregate impact value
fine-grained siliceous rocks and igneous rocks perform well.
coarse-grained igneous and sedimentary rocks dont perform so well
aggregate abrasion value (AAV)
comparison of weight before and after abrasion test. Low AAV = low crushing and impact value
polished stone value (PSV)
resistance to tyre polishing.
higher PSV = greater resistance
railway ballast
igneous and non-platy metamorphic crystalline rocks are chosen because of their high compressive strength, resistance to weathering and impervious nature
