Manufactured Sand. What it is, what it isn t, and why, plus some processing methods. Hugo Pettingell ACSM FIQ September 2012

Transcription

1 SenX Limited, 3 Welmar Mews, London SW4 7DD Manufactured Sand What it is, what it isn t, and why, plus some processing methods Hugo Pettingell ACSM FIQ September 2012

2 Define manufactured sand

3 What Manufactured Sand is and what it is not! 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

4 Manufactured sand

5 What affects the performance of aggregates in concrete? 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 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

6 Just for comparison... Particle Size (mm) (spherical) Particle Volume (mm³) Number of particles in 8200 mm3 Surface area in 8200 mm 3 (m 2) x10ˉ4 4x x 10ˉ9 2x 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.

7 WHAT MAKES GOOD MANUFACTURED SAND? Some things we can affect by processing: Crushing process 1. Excellent particle shape and surface texture 2. Ideal particle size distribution 3. Sufficient microfines with appropriate characteristics...and some we can t change so readily: Geology 4. No chemical impurities or Alkali Silica reactivity 5. Absence of micas and clays, particularly expansive types such as smectites

8 Source rock

9 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.

10 Particle Shape

11 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

12 PARTICLE SHAPE Some comparative images Cone VSI X VSI Y mm mm mm NOTE Not all Vertical Shaft Impactors were created equal!

13 PARTICLE SHAPE what does it matter? Solids ratio as measured under JIS.A ( mm) CONE VSI X 55m/s VSI Y 55m/s 54.8% 56.3% 57.7% 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) Improvement of solid ratio Feed to VSI X Saving water Cement saving Improvement of solid ratio VSI X to VSI Y Saving water Cement saving = 50% = 1.5% (56.3% 54.8%) = 3-4 kg/m³ x 1.5 = kg/m³ = kg/m³ divided by 0.5 = 9 12 kg/m³ = 1.4% (57.7% %) = 3-4kgs/m³ x 1.4 = kg/m³ = kg/m³ divided by 0.5 = kg/m³

14 Surface texture 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?

15 So what is the specification for fine aggregate particle shape and surface texture? Er...there isn t one, is there?...so how can we quantify it? 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.

16 Flow cone Cement Concrete & Aggregates Australia Research Report Manufactured Sand National test methods and specification values January 2007 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 of manufactured sand that did not require specialised equipment and highly trained staff. 4 It seems to work well with a standard grading reconstructed from the test material, eliminating the variation due to particle size distribution

17 Particle Size Distribution

18 CUMULATIVE % PASSING Particle size distribution 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 BEST WORST PARTICLE SIZE (mm) Ryall Clearwell Clearwell Clearwell ASTM C33 ASTM C33 Some real gradings and their performance in concrete

19 Particle size distribution Cement Concrete & Aggregates Australia Research Report Manufactured Sand National test methods and specification values January 2007 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 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!

20 CUMULATIVE % PASSING Particle size distribution Is there an ideal grading? CCAA Proposal: AS SIEVE MAX DEVIATION ± ± ± ± ± ± ± PARTICLE SIZE (mm) Ryall Clearwell Clearwell Clearwell CCAA CCAA 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 µm

21 Microfines

22 Microfines (<63µm) 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

23 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 of 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?

24 Grading and Microfines Specification 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!

25 Other quality issues

26 Loss of consistency due to : Segregation of dry manufactured sand Wind and weather action Stratification on conveyors Careless handling Transfer to stockpiles Water adding mixer (c. 3%) Excessively dry sand may absorb water when concrete mixing and cause slump loss. Luffing radial stockpiler

27 Sand manufacturing equipment

28 CUMULATIVE % PASSING Crushers 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. 100 IMPROVE THE SHAPE THROUGHOUT REDUCE THIS CONTROL THIS PARTICLE SIZE (mm) Clearwell Limestone Cribarth Gritstone Belgard Limestone Ledinge ASTM C33 ASTM C33

29 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

30 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

31 Applications how are they used? Autogenous Vertical Shaft Impactors Frequently and erroneously - regarded as merely a shaping machine, the Autogenous VSI is indeed a producer of wellshaped 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 usually 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 other 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

32 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 top size long fraction It is not as efficient as a size reducer as either a cone or HSI...or is it? It usually produces more microfines It does not produce any greater abundance of μm...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

33 VSI PERFORMANCE CONTROLS - 1 Rotor speed Cascade (Metso) / Bi-Flow (Sandvik)

34 VSI PERFORMANCE CONTROLS - 2 Feed Gradation Closed circuit aperture

35 VSI PERFORMANCE CONTROLS - 3 Rotor design

36 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. It can be suggested that the best particle shape is dependent upon abrasion... 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.

37 Range of sizes Motor power from 7.5kW to 500kW or more Throughput capacity from 4 to 500t/h or more

38 Applications (1) Granite Quarry in Malaysia, 1995 Feed from jaw/cone crushers

39 Applications (2) Granite Quarry in Malaysia, 1996 Feed from jaw/cone crushers

40 Applications (3) 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

41 MM GRAIN SHAPE COMPARISON ROD MILL mm VSI SOLIDS CONTENT KEMCO VSI 55.6% ROD MILL 53.9% SEA SAND 53.9% SEA DREDGED SAND

42 Example of grading adjustment using Wet Process VSI Passing(%) Fineness Sieve Size (mm) Modulus VSI FEED VSI PRODUCT PRODUCT 100% FINES REMOVED PRODUCT 30% FINES REMOVED

43 Cum % Passing Applications (4) To make an all-in aggregate for specialised concrete: Very high speed and specialised rotor to generate large amount of microfines Replace fly ash VSI Feed VSI Prod Screen prod Sieve Size (mm.)

44 Acknowledgements and references I have used material from Metso (previously Svedala), Sandvik, Oresizer, Remco, Kemco and some others publications in the public domain. Individuals work as follows: ¹ AGGREGATE SHAPE AFFECTS CONCRETE COST - B P Hudson, Quarry Magazine, November IMPACT OF MANUFACTURED SAND IN CONCRETE - B P Hudson, Quarry Magazine, December MINERAL FINES, TODAY S OPPORTUNITY, TOMORROW S SUCCESS - R.H. Brown, Vulcan Materials Company. - Paper presented at Center for Aggregate Research March 2-4, MANUFACTURED SAND - NATIONAL TEST METHODS AND SPECIFICATION VALUES - Cement Concrete & Aggregates Australia Research Report January 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 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 SenX Limited, Quarry Process Consultants, 3 Welmar Mews, London SW4 7DD