lecture construction aggregates
TRANSCRIPT
Construction
Aggregates
1. Uses & Economics in UK
2. Types & Sources
3. Processing & Testing
4. Environmental Impact
1. What are aggregates?
‘granular material used in construction and
may be natural, manufactured or recycled’
• Aggregates are a low cost product used in
very large quantities
1. Primary are extracted from mineral
deposit and are used for first time
2. Secondary & recycled had a previous use
• Demand for aggregates from construction
industry:
• Maintenance of transport infrastructure
• Construction of Affordable housing
• Rail system growth (HS2 & Crossrail
projects)
• Flood & coastal defences
Uses of Aggregates
add additional strength and bulk to composite material, e.g. concrete
as a drainage & filter material as possess high hydraulic conductivities, e.g. coarse gravels in french drains & landfill sites
base material under foundations, roads & railways (madeground)
to make a surface suitable for task, e.g. road stone in asphalt on roads
for building materials and finishing products, e.g. bricks, masonry, plaster
1.
UK Aggregates UK demand for stone is about 200 million
tonnes/year
5.5 tonnes per person in UK
50% goes on road & 50% on concrete
Small amount of dimension stone
More than half the aggregates come from crushed rock (60 %); the rest is sand and gravel (40 %)
Rock strength is the prime requirement, usually UCS > 100 MPa
Main size required is 5 – 50 mm
1.
Economics of UK Aggregates Aggregate consumption
linked with demand from construction industry
Consumption of primary aggregates decreasing since 1989 because of: Decline of manufacturing
economy, road construction & house building
Construction methods
Aggregates used economically
Introduction of landfill tax &
Rise of recycled aggregates
Less demand for primary
1.
Primary Aggregates R
ock
Typ
es
Cut or crushed Fired Mixed Uses
2.
Extracted directly from mineral by quarrying or dredging to become aggregate
Treatment & uses of primary aggregates
UK Aggregate Quarries
BGS mineral planning factsheet
2.
Limestone Quarries
Igneous & Metamorphic
Quarries Sandstone Quarries
Dimension Stone: Building Stone
Bath Abbey constructed of
Oolitic Jurassic Limestone
Edinburgh Castle
constructed of Carboniferous
Sandstone
2.
Dimension stone is quarried
rock used in large blocks;
Some is cut and used as a
building stone or cladding stone
Dimension Stone: Armourstone
Soton.ac.uk
2.
Rough blocks used as
rock armour in coastal
defences to protect
against coastal
erosion
Crushed Stone Aggregates
Crushed stone aggregates can
be either single size or variable
depending on application
Concrete & gabion fill require
single size aggregates
2.
Road Aggregates
Igneous & some metamorphic rocks
are good road stone because;
High rock strength and resistance to
impact, abrasion, polishing, skidding
and frost action;
Laboratory rock property testing
2.
Road surfaces built up of a series of
layers & topped with three layers of
asphalt.
Each asphalt layer uses different
aggregate sizes (fining upwards)
Asphalt is a mix of bitumen & crushed
rock
Outside the Chancellor’s Office on campus
Laboratory property testing of aggregates Aggregate Abrasion Test (AAV)
Slake Durability Test
Aggregate Impact Test (AIV)
3.
5 kg sample is
rotated at 30
revolutions per
minute with 11 steel
balls
15 ‘shock’ blows and sieved
to measure weight lost
Standard aggregate tests
Property Test Procedure Good
value
Poor
value
Road stone
value
AIV - Aggregate
impact value
% fines lost by hammering on standard rig 5 35 <20
AAV- Aggregate
abrasion value
% loss by abrasion on standard rig 1 25 <10
PSV-polishing
stone value
Frictional drag recorded by swinging pendulum 70 30 >60
ACV-aggregate
crushing value
% fines lost by uniform load crushing on a
standard rig
5 35
10% FV – 10%
fines value
Load on an ACV rig to give 10% fines loss 400 20 >100
Flakiness index Weight % particles with minimum thickness<60%
mean
20 70 <3
CBR- California
bearing ratio
Resistance to plunger penetration compared to a
standard
100 60 >90
Water absorption Weight % increase after immersion in water for
24hrs
0.2 10 <2
Frost heave Heave of air-cooled column of sample standing in
water
3 20 <1
3.
For a rock to be used as a road stone it must possess certain properties:
Typical UK aggregate properties
Material Location 10%
FV
AIV AAV PSV
Granite Dartmoor 280 16 5 60
Dolerite North Pennines 360 10 4 60
Greywacke Pennines 220 14 7 65
Limestone Pennines 120 20 12 40
Flint Thames gravels 450 23 1 35
Coarse sandstone Peak District 90 40 26 74
3.
10% Fines Value: a measure of aggregate strength
The load applied to an aggregate sample to cause 10 % loss of
fines. Uses aggregate crushing rig (ACV).
How UK aggregates compare to essential road stone properties:
Red indicates road stone
property criteria fulfilled
http://www.youtube.com/watch?v=UW7iRsut4ck
Tarmac Swinden Limestone Quarry, Cracoe,
North Yorkshire Fairport.co.uk
What are the 6 processes of quarrying?
3.
Schematic diagram of an impact crusher 3.
Used for secondary
crushing stage of
quarrying
Stones then go to
sorting
Laboratory impact crusher
Size-specific filter
Gravels & Sands Land-won or marine deposits
BGS mineral planning factsheet
2.
Locations of pits and a
licensed dredging area for
sands & gravels
Gravels & Sands
• Superficial deposits are sediments
deposited within the last 2 million
years mostly during interstadials
• River sands & gravels deposited in
major river valleys or terraces
• 1 -10 m thick deposits
• Well sorted and often mature
2.
Land-won aggregates can be either superficial deposits or
bedrock
Gravels & Sands
• Superficial deposits are sediments
deposited within the last 2 million
years mostly during interstadials
• River sands & gravels deposited in
major river valleys or terraces
• 1 -10 m thick deposits
• Well sorted and often mature
2.
Land-won aggregates can be either superficial deposits or
bedrock
Gravels & Sands
• Bedrock deposits
• Include poorly-consolidated:
• Sands of Lower Cretaceous
Folkestone Formation of the Weald
• Conglomerates of Triassic Sherwood
Sandstone Formation in the Midlands
2.
Land-won aggregates can be either superficial deposits or
bedrock
Marine Gravels & Sands • Marine aggregates are dredged
from the seabed
• Relict quaternary fluvial deposits,
deposited when sea-level much
lower during glacial maxima
• Dredging takes place less than 25
km offshore in 18-35 m depth
• Extraction constrained by pipelines,
cable routes, wind farms, fisheries &
shipping lanes
• Most important regions are offshore
Norfolk, Humber-Wash area and
Bristol Channel
2.
Secondary & recycled aggregates
Construction & demolition
wastes such as concrete and
masonry are the largest source
of recycled aggregates.
60 % of C&D waste currently
used as construction fill.
By-products of quarrying &
mining operations are the
main source of secondary
aggregate
Geograph.org
Imerys exporting china clay waste to South-
east & Germany as a mortar replacement
2.
Hallsands village:
This south Devon village stood on a rock platform with a protective beach
in front of it. In 1887 offshore shingle dredging steepened the seabed
sediment profile. Natural response was lowering and removal of the beach
within 5 years, exposing the houses to wave attack. The village was
destroyed in a storm in 1917. The shingle was used in the construction of the
Devonport docks.
Environmental Impact of Dredging 4.
Before dredging After dredging
Aggregate Resource Planning Extractable resources (reserves) can be extracted as they are
an economically viable commodity
‘Conditional
resources’ have
been discovered
but are not
economically viable
4.
Economic viability
governed by
price:cost ratio;
a function of mineral
grade,
concentration,
market price
Bulk Resources &
Aggregates
1. Uses & Economics in UK
2. Types & Sources
3. Processing & Testing
4. Environmental Impact
Summary
Aggregates and water are the major
resources investigated by applied
geoscientists outside the hydrocarbons and
metaliferous industries
Aggregate testing is carried out according to
Eurocode 7 and BS 812
Assessment of reserves requires a detailed
understanding of the geology
Ground subsidence associated with mine
workings
a)Failure in old pillar and stall workings or bell pits
b)Effects of multiple pillar collapses
c)Long wall mining effects