Manufactured Sand What it is, what it isnt, and why, plus some - - PowerPoint PPT Presentation

Hugo Pettingell ACSM FIQ September 2012

Manufactured Sand

What it is, what it isn’t, and why, plus some processing methods

SenX Limited, 3 Welmar Mews, London SW4 7DD

Define manufactured sand

MANUFACTURED SAND “The aggregate industry typically has branded any crushed product that is less than 4 mesh (4.75 mm) as “manufactured sand”. This of course is not the case. Manufactured sand should be a product that you have intentionally produced, not merely the waste fraction of a process that is targeting larger aggregate sizes.”

BARRY HUDSON 1999

What Manufactured Sand is – and what it is not!

Manufactured sand

“The equidimensionality and angularity of coarse and fine aggregate particles, the degree and shape of the texture on their surfaces, the amount of surface area caused by the particle shape and degree of relief, and the chemical and physical nature of coatings, if present, are all characteristics that significantly affect the properties of both fresh and hardened concrete.”¹

What affects the performance of aggregates in concrete?

“The impact of the physical characteristics of fine aggregate on the concrete mix properties, in both the plastic and hardened states, is significantly greater than that of the coarse aggregate fraction.”²

Just for comparison....

Particle Size (mm) (spherical) Particle Volume (mm³) Number of particles in 8200 mm3 Surface area in 8200 mm3 (m2) 25 8200 1 0.002 4 33.5 244 0.012 0.075 2x10ˉ4 4x107 0.7 0.002 2x 10ˉ9 2x1012 24

Due to the much smaller particle size, and hence the greatly increased surface area to volume ratio, any detrimental or undesirable particle shape or texture of the fine aggregates will be greatly amplified…” ³

This is why we need to consider particle shape even more critically as particle size decreases.

WHAT MAKES GOOD MANUFACTURED SAND?

• 4. No chemical impurities or Alkali Silica reactivity
• 5. Absence of micas and clays, particularly expansive

types such as smectites

• 1. Excellent particle shape and surface texture

2. Ideal particle size distribution 3. Sufficient microfines with appropriate characteristics Geology Crushing process

Some things we can affect by processing: ...And some we can’t change so readily:

Source rock

Caution!

Be very careful in selecting the source rock: Geology has a huge effect on the suitability of material for manufactured sand Alteration and weathering can vary within a quarry, and may preclude the use of some areas for sand for concrete. There may even be more than one rock type. Proper evaluation of characteristics is essential BEFORE installing equipment – the results will have a bearing on the selection of an appropriate process.

Particle Shape

Why particle shape?

What difference does it make in practice?  Specific surface area – total surface area of a material per unit of mass (usually m²/kg):

• Smaller surface area means less “glue” (cement paste) needed to coat it

 Packing density, or Voids Ratio: Voids ratio may vary up to 10% between extremes of shape and texture, but a normal range is more like 4-5%.

• Lower voids ratio reduces cement paste volume .

 Particle shape affects workability of concrete in the liquid phase

• Lower internal friction leads to better workability and lower water requirement

PARTICLE SHAPE – Some comparative images

0.3-0.15mm 2.5-1.2mm 0.6-0.3mm

Cone BARMAC 65m/s Kemco US7 55m/s

PARTICLE SHAPE – what does it matter?

Solids ratio as measured under JIS.A.5005-1104 (2.5-1.2mm) Calculation of cement saving due to improved solids ratio 1% better solids ratio can save 3-4kg water/m³ of concrete Given W/C(water cement ratio) = 50% Improvement of solid ratio Feed to BM = 1.5% (56.3% – 54.8%) Saving water = 3 - 4 kg/m³ x 1.5 = 4.5 – 6 kg/m³ Cement saving = 4.5 – 6 kg/m³ divided by 0.5 = 9 – 12 kg/m³ Improvement of solid ratio BM to US7 = 1.4% (57.7% - 56.3%) Saving water = 3-4kgs/m³ x 1.4 = 4.2-5.6kg/m³ Cement saving = 4.2-5.6kg/m³ divided by 0.5 = 8.4 – 11.2kg/m3

CONE BM 55m/s BM 65m/s US7 45m/s US7 55m/s 54.8% 56.3% 56.8% 56.9% 57.7%

“To assist with cement paste / aggregate particle bond, it is desirable to have a ‘roughened’ particle surface. It is important that this surface is not too rough or honeycombed, as this will greatly influence the amount of water required to make the concrete workable in its plastic state. Spherical particles in many cases are ‘polished’ and offer little for the cement paste to bond with, and can produce concrete with reduced strengths, particularly flexural strength.” ²

Perhaps crushed rock sand can be better than some very smooth natural materials in respect to surface texture, if properly processed?

Surface texture

Er...there isn’t one, is there? ...so how can we quantify it?

So what is the specification for fine aggregate particle shape and surface texture?

New Zealand Flow Cone A sample of 1 kg of fine aggregate is passed through a 12-mm orifice mounted under a sample hopper. The material free falls into a collecting container of known volume while the time taken for the sample to pass is measured. The mass of material in the collection container is measured and the un-compacted unit mass of the fine aggregate can be calculated. The specific gravity of the fine aggregate compared with the unit mass allows the un-compacted voids content of the aggregate to be calculated. The results are reported graphically on a plot of voids versus flow time.

But….”Research demonstrates that there are difficulties with the use of the Flow Cone apparatus in testing manufactured sands, and unless these issues were resolved, it would not be practical to use the method for specification. No other suitable procedure was found for specifying the shape and surface texture

• f manufactured sand that did not require

specialised equipment and highly trained staff.”4

Flow cone

Cement Concrete & Aggregates Australia Research Report Manufactured Sand National test methods and specification values January 2007

It seems to work well with a standard grading reconstructed from the test material, eliminating the variation due to particle size distribution

Particle Size Distribution

10 20 30 40 50 60 70 80 90 100 0.01 0.1 1 10 CUMULATIVE % PASSING PARTICLE SIZE (mm)

Ryall Clearwell Clearwell Clearwell ASTM C33 ASTM C33

 Remains the sole criterion for sand specification in most places, apart from deleterious material exclusions.  Useful for defining consistency  Has less relevance in defining performance, because compliant PSD is no guarantee of suitability for concrete

Particle size distribution

BEST WORST

Some real gradings and their performance in concrete

“Members agreed that product grading should not be a specification test. Instead, the product supplier should provide a submitted grading to which the deviation limits current in AS 2758.1 would apply. How these deviation limits might be applied to the broad range of possible product gradings will require careful consideration. Gradings would obviously become a quality control tool with results of interest to individual suppliers and their customers. However, it was considered necessary for the purposes of definition to specify that 'manufactured sands' for use in concrete would have:

• between 90% and 100% passing 4.75-mm sieve;
• between 15% and 80% passing 0.6-mm sieve;
• between 0% and 20% passing 75 micron sieve.”4

THE KEY HERE IS NOT AN ABSOLUTE GRADATION, BUT CONSISTENCY!

Particle size distribution

Cement Concrete & Aggregates Australia Research Report Manufactured Sand National test methods and specification values January 2007

CCAA Proposal:

Particle size distribution – Is there an ideal grading?

10 20 30 40 50 60 70 80 90 100 0.01 0.1 1 10 CUMULATIVE % PASSING PARTICLE SIZE (mm)

Ryall Clearwell Clearwell Clearwell CCAA CCAA

AS SIEVE MAX DEVIATION

6.7

• 4.75

±5 2.36 ±10 1.18 ±15 0.6 ±15 0.3 ±10 0.15 ±5 0.075 ±3 An ideal grading is one that makes good concrete and does not vary

However, there is usually a preference for abundant particles in in the range 250-1000µm

Microfines

For twenty years or more, researchers have been busy proving that microfines are a valuable constituent in concrete, while end users have not been prepared to deviate far from specification-based sand gradings designed for natural sands.

ICAR102-1F:  “Compared to concrete made with lower-fines content natural sand, high-fines manufactured sand concrete generally had higher flexural strength, improved abrasion resistance, higher unit weight, and lower permeability due to filling of the pores with microfines. (Lower permeability is important for reducing corrosion).  Compressive strength varied but was acceptable, and shrinkage, although slightly higher, was within generally acceptable ranges.  Good-quality concrete could be made from nearly all of the aggregates (with microfines contents ranging from 7 to 18%) used in the test program without the use of admixtures.”5

Microfines (<63µm)

…and, according to Kaya, Nagahara & Yamamoto:6

• Microfines with all of the <20µm fraction eliminated can be used as part of the fine

aggregate without detrimental effect on the properties of fresh concrete.

• A suitably modified fines gradation is better than the original fines gradation for the

properties of fresh concrete, including maintaining favourable slump.

• Reduced compressive strength was not evident, regardless of increased blending ratio
• f original and modified fines gradation
• Slump in concrete using the +120µm, 75µm, and 40µm fractions of modified fines

gradation was not markedly reduced. Do we need to reconsider the size below which we eliminate crushed rock fines?

Microfines (<63µm)

• What is certain is that there will be limits applied to the microfine content of

manufactured sand until we accept that such material is useful, and adjust its specifications and mix designs accordingly.

• Narrow grading limits are also of doubtful usefulness in defining performance.
• In many places, existing prescriptive specifications are poisonous to progress in

adapting to manufactured sand, and need replacing with a performance approach, including measures to ensure consistency. Nominated gradings with tolerances would be more meaningful

• The asphalt industry adopted this approach to specification in the late 1970’s in

the UK - over 30 years ago!

Grading and Microfines Specification

Other quality issues

Loss of consistency due to :  Wind and weather action  Stratification on conveyors  Careless handling  Transfer to stockpiles

Segregation of dry manufactured sand

Luffing radial stockpiler Water adding mixer (c. 3%)

 Excessively dry sand may absorb water when concrete mixing and cause slump loss.

Sand manufacturing equipment

Assuming we already have a competently designed and operated crushing plant, we need to consider only the final stage or two of reduction and sizing. Manufacture of sand is usually, in practice, a matter of turning crushed rock fines produced using compression crushers or possibly HSI’s into something of superior quality.

Crushers

10 20 30 40 50 60 70 80 90 100 0.01 0.1 1 10 CUMULATIVE % PASSING PARTICLE SIZE (mm)

Clearwell Limestone Cribarth Gritstone Belgard Limestone Ledinge ASTM C33 ASTM C33

REDUCE THIS CONTROL THIS IMPROVE THE SHAPE THROUGHOUT

Autogenous VSI Crushers – the essential ingredient?

In the years between 1979 and 2012 many explanations and theories have been put forward about how the VSI actually works. Most theories have merit and must be accepted as valid points of view. As nobody can show hard evidence of “seeing the machine work” we can only rely on what goes in and what comes out: Our rotors work well in nearly all the applications we use them in, but be warned that we have records of rotors underperforming dramatically in applications we took for granted! We now know why they failed and this is one of Oresizer’s strengths. We know what doesn’t work!” Peter Crymble, Oresizer

Autogenous Vertical Shaft Impactors

REMco, Kemco, Oresizer, Milestone,

• etc. autogenous machines

Kemco hybrid machine for sand only Metso Barmac, Sandvik, and most Indian and Chinese copies

Autogenous Vertical Shaft Impactors

Applications—how are they used?

 Frequently – and erroneously - regarded as merely a shaping

machine, the Autogenous VSI is indeed a producer of well- shaped aggregates. For this task it is often used in open circuit, just to decrease the flakiness and elongation of a compression crusher product

 Crushing action simulates nature, selectively disintegrating weak

material, unlike compression crushing

 Since it has no closed side setting to limit the product top size, it

is invariably necessary to install it in closed circuit with a screen. Much larger circulating loads are usual than with compression crushers

 Unlike compression crushers and rock-on-steel machines, the

superior particle shape created in a VSI persists throughout the size range, even into the microfines. This is most beneficial in the production of sand from crushed rock or gravel, and sand from a VSI will invariably perform better than that from

• ther machines.

 It is usually the case that if a VSI fails to give satisfaction it has

been misapplied!

 Properly-applied, it is extremely cost-effective in crushing very

abrasive and tough materials

“It makes the best sand in the world?” …Why?

PARTICLE SHAPE!

The Autogenous VSI Crusher produces particles of better shape than almost any other machine... Is that all?  It has a limited feed acceptance – 40/50mm – long fraction  It is not as efficient as a size reducer as either a cone or HSI  It usually produces more microfines  It does not produce any great abundance of 500-1000μm...BUT...  Weak material is reduced to powder  Its product is consistent throughout the life of its wear parts  Properly applied, it is very cost-effective, especially in abrasive rock

VSI PERFORMANCE CONTROLS - 1

Rotor speed Cascade (Metso) / Bi-Flow (Sandvik)

VSI PERFORMANCE CONTROLS - 2

Feed Gradation Closed circuit aperture

VSI PERFORMANCE CONTROLS - 3

Rotor design

Rotor design

 Most manufacturers still mainly offer 3-port designs.  Some manufacturers offer 4-, 5-, and 6-port rotors, and Oresizer has developed 7- and 8-port versions  Additional ports increase the number of ‘rock pulses’ that occur during each revolution, improving the continuity, and thus the

efficiency of the crushing action.

 The fewer the ports, the longer the internal grinding path inside the rotor, resulting in more abrasive reduction, and greater

microfines generation. However, it can be suggested that the best particle shape is dependent upon abrasion...

 Extra ports also spread the tip wear over a larger number of tips and as a result further lengthen the period between tip changes.  Some rotor designs offer improved serviceability, and some extravagant claims are made in regard to operating cost.  It is easy to persuade most reputable manufacturers to put their rotors into customers’ machines on a trial basis.

Range of sizes

 Motor power from 7.5kW to 500kW or more  Throughput capacity from 4 to 500t/h or more

Applications (1)

Granite Quarry in Malaysia, 1995

Feed from jaw/cone crushers

Applications (2)

Granite Quarry in Malaysia, 1996

Feed from jaw/cone crushers

Example of grading adjustment using Wet Process VSI

 Wet sand manufacturing process

 Rod mill product lacks fines, poor shape  Solution: Add VSI to circuit  Special Kemco design to handle 20% moisture content  May be applicable to existing crusher dust washing processes

Applications (3)

0.3 – 0.15MM GRAIN SHAPE COMPARISON

KEMCO VSI

ROD MILL SEA DREDGED SAND

2.5 -1.2mm SOLIDS CONTENT KEMCO BM 55.6% ROD MILL 53.9% SEA SAND 53.9%

Example of grading adjustment using Wet Process VSI

Sieve Size (mm) 0.075 0.15 0.3 0.6 1.2 2.5 4 BARMAC FEED 1.6 6.4 17.4 34.1 59.0 89.7 100.0 2.93 BARMAC PRODUCT 4.4 11.4 26.1 43.9 69.1 93.1 100.0 2.56 PRODUCT 100% FINES REMOVED 1.7 6.9 20.0 38.9 65.2 92.9 100.0 2.76 PRODUCT 30% FINES REMOVED 3.2 9.4 22.9 39.9 65.3 91.9 100.0 2.71 Passing(%) Fineness Modulus

Applications (4)

10 20 30 40 50 60 70 80 90 100 0.01 0.1 1 10 100

Cum % Passing Sieve Size (mm.)

VSI Feed VSI Prod Screen prod.

To make an all-in aggregate for specialised concrete: Very high speed and specialised rotor to generate large amount of microfines Replace fly ash

Sand manufacturing equipment – beyond the VSI

Wet or dry?

DRY PROCESS: Positives:  Lower capital investment.  Lower running cost.  Smaller space requirement.  Disposal of industrial waste to landfill or silt lagoons is not necessary.  Classified fillers are a saleable product …or should be! Negatives:  Need <2% moisture in feed, possibly less.  May not be possible to remove strongly adhering clay coating from aggregate particles without wet scrubbing. NOTE: If feedstock valuation is realistic (it is often unsaleable, or cost of stockpiling may produce negative value), then drying may be an option.

A dry sand process should include:  The means to produce the right amount of the right-sized and right-shaped grains  A screen to set the top size, and return unwanted coarse particles for further crushing  A microfines extraction system able to control the quality and quantity of filler retained in the sand

Dry processing equipment

10 20 30 40 50 60 70 80 90 100 0.01 0.1 1 10 CUMULATIVE % PASSING PARTICLE SIZE (mm)

Clearwell Limestone Cribarth Gritstone Belgard Limestone Ledinge ASTM C33 ASTM C33

REDUCE THIS CONTROL THIS IMPROVE GRAIN SHAPE THROUGHOUT

THE DEVELOPMENT OF THE KEMCO V7 DRY SAND MAKING SYSTEM  Dry process  Control of:

• Particle size distribution
• Top size
• Microfines

 Improved particle shape  Consistent product  Product adjustable to meet specification  Small footprint  Minimal environmental impact OBJECTIVE: TO DESIGN A FULLY INTEGRATED SYSTEM FOR DRY PROCESSING OF CRUSHER DUST OR GRIT TO MAKE SPECIFICATION SAND.

An integrated dry process

Basic layout

• Based on proven Barmac design
• Specially-developed 5-port rotor
• Highly-modified crushing chamber
• Designed to give effective impact crushing of fine particles
• Minimises recirculation and microfines production

The crusher

10 20 30 40 50 60 70 80 90 100 0.01 0.1 1 10 100 CUMULATIVE % PASSING PARTICLE SIZE (mm)

FEED Barmac US6 ASTM C33 ASTM C33

Advantages

 Improved reduction without extra microfines  More abundant 500-1000µm  Improved particle shape

BM 55m/s BM 65m/s US7 45m/s US7 55m/s 56.3% 56.8% 56.9% 57.7%

The air screen

 Effective screening down to 1mm  Minimal pegging  Variable recirculation  Variable microfines extraction  Low maintenance

The circuit

Process is:  Dry  Consistent  Automatic  Emission free  Low noise  Space efficient

OVERSIZE PLUS % COARSE UNDERSIZE NEW FEED RECIRCULATION FILLER TO COLLECTOR SAND PRODUCT

BLOWER

CRUSHER AIRSCREEN WATER 3% SKIMMER MIXER

CONTROL PANEL

What can it do?

 Take low value feed (max 5-16mm, 2% H₂O)  Produce sand of excellent particle shape to any reasonable specification  Product can entirely replace natural concrete sand  Make sand to other specifications  Low running cost  High added value

Particle shape

0.3-0.15mm 2.5-1.2mm 0.6-0.3mm

FEED BM 65m/s US7 55m/s

Running costs

Crusher SCREEN 2～5 5～10 45～55 40～55 70～80 100～175 10～20 Type of rock SiO₂ (%) Cost per product tonne (€/100) Limestone Diabase, Basalt Strong Granite

Power cost Wear cost

Approximately 8-10kWh/tonne

A TYPICAL TEST REPORT

10 7 5 2.5 1.2 0.6 0.3 0.15 0.075 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% % Passing Sieve size (mm)

①Raw material ②V7 product ③V7 filler ④After Preduster ⑤Final filler ⑥Final product BS 0/2（MP） JIS

①Raw material ②V7 product ③V7 filler ④After Preduster ⑤Final filler ⑥Final product weight(t/h) 3.00 1.96 1.04 0.39 0.65 2.35 yield ratio 100.0% 65.3% 34.7% 13.0% 21.7% 78.3%

Density（Size：2.5-1.2mm） ①Raw material ②V7 product Density(surface dry)（g/cm³） 2.68 2.69 Density(oven dry)（g/cm³） 2.65 2.67 Water absorption ratio(%) 0.88 0.69 Solid content（%） 54.0 57.0

Limestone example

10 20 30 40 50 60 70 80 90 100 0.01 0.1 1 10 PARTICLE SIZE (mm) CUMULATIVE % PASSING Limestone Feed FM 3.67 V7 Product #1 FM 2.38 V7 Product #2 FM 2.15 BS12620 Max BS12620 Min

Granite Example

10 20 30 40 50 60 70 80 90 100 0.01 0.1 1 10 PARTICLE SIZE (mm) CUMULATIVE % PASSING GRANITE FEED FM 4.58 V7 Product #1 FM 2.45 V7 Product #2 FM 2.67 V7 Product #3 FM 2.40 BS12620 Max BS12620 Min

Concrete tests - limestone example

Results : - Strengths (N/mm²)

Cement Content kg/m3 Strength N/mm² @ 28 days Control Product A Product B Product C 250 32.0 32.0 33.5 34.0 350 56.0 57.5 54.5 55.5 450 64.5 66.0 65.5 66.0

Results : - Fresh Wet Properties

Scope The following trials were carried out to evaluate the performance of three samples of UK Quarry X dust produced by Kemco, in comparison to natural Trent Valley Sand as currently used within the Midlands Area. The samples are identified as A, B and C with proportionately higher fines contents from A - C. Sample A produced concrete coarser in nature and appeared prone to segregation, whilst sample C resulted in higher water demands and appeared sticky. Sample B produced the better looking concrete and resulted in water demands almost identical to natural Trent Valley Sand. Likewise strengths were comparable.

Total Free water l/m³ Total Free W/C Ratio Plastic Density Kg/m³ Cement content kg/m³ Control Prod A Prod B Prod C Control Prod A Prod B Prod C Control Prod A Prod B Prod C 250 176 176 171 181 0.704 0.704 0.684 0.724 2389 2349 2402 2402 350 174 174 176 182 0.497 0.497 0.503 0.520 2412 2414 2402 2408 450 182 186 182 193 0.404 0.413 0.404 0.429 2420 2438 2424 2399

V7 dry sand making plant

Other sand manufacturing equipment – Screening and classification

Metso - Buell

Designed for cut points from 300 to 63µm Designed for cut points from 10 to 63µm. Will complement AC27 and AC30 for making speciality products and decrease filler top size

Kemco air screen range

 Maximum of four decks - wide screening size range from coarse aggregates down to micro-fines.  High efficiency screening - 2.5 to 3 times better screening efficiency compared with conventional vibrating screen.  Wash effect by air - dust adhering to the surface

• f particles is blown away by air draught.

 Compact size – required screen area is just 1/3

• f that of a conventional screen.

 Environmentally friendly - dust encapsulated.  Easy maintenance.  Less pegging of fine screen mesh.

Applications

MODEL AS RCAS DECKS 1+ RELIEVING DECK 4 SIZE 1200/1600/2500 1200/1900/2500 APPLICATIONS SAND-MAKING (V7) RECYCLING AND AGGREGATES CAPACITY Up to 250t/h depending on application

• MAX. FEED SIZE

20mm 40mm

What can it do?

 Replace conventional screen after a third or fourth stage crusher  Remove microfines and scrub adhering fines from aggregate (e.G. Dry scalpings)  Allow recirculation of both oversize coarse aggregate and coarse grit sizes for further reduction  Improve sand grading from standard vsi to some degree by selective recirculation  Reduce dust emissions

A cheap and cheerful option for adjusting filler content

Ducting outlet Skimmer Access doors Adjustable damper Scalper unit Feed inlet

 Used in conjunction with existing or dedicated bag filter

 Adjustable air flow liberates and extracts fine material  Skimmer returns desirable larger grains to product

Acknowledgements and references

¹

AGGREGATE SHAPE AFFECTS CONCRETE COST - B P Hudson, Quarry Magazine, November 1998

2

IMPACT OF MANUFACTURED SAND IN CONCRETE - B P Hudson, Quarry Magazine, December 1998

3

MINERAL FINES, TODAY’S OPPORTUNITY, TOMORROW’S SUCCESS - R.H. Brown, Vulcan Materials

• Company. - Paper presented at Center for Aggregate Research March 2-4, 1995.

4 MANUFACTURED SAND - NATIONAL TEST METHODS AND SPECIFICATION VALUES - Cement

Concrete & Aggregates Australia Research Report January 2007

5 ICAR Report 102-1F, AN EXPERIMENTAL STUDY ON THE GUIDELINES FOR USING HIGHER

CONTENTS OF AGGREGATE MICROFINES IN PORTLAND CEMENT - Namshik Ahn & David W. Fowler, International Centre for Aggregate Research, The University of Texas, Austin, Texas Dec.2001

6 RESEARCH INTO THE OPTIMUM LEVEL OF ROCK-DERIVED MICRO-FINE PARTICLES IN SAND

FOR CONCRETE - T.Kaya, Kotobuki Eng. and Mfg. Co, Ltd., Kure, Hiroshima, Japan; Y.Nagahara, Kotobuki Eng. and Mfg. Co, Ltd., Kure, Hiroshima, Japan; H.Yamamoto, Graduate School for International Development and Cooperation, Hiroshima University, Hiroshima Japan – November 2008 I have used material from Metso (previously Svedala), Sandvik, Oresizer, Remco, Kemco and some others’ publications in the public domain. Individuals’ work as follows:

SenX Limited, Quarry Process Consultants, 3 Welmar Mews, London SW4 7DD