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Constraints in Using Manufactured

Sands in Concrete Pavements

Ion Dumitru – Technical Manager

Tony Song – Senior Development Engineer

May 2012

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Shortage of natural sands (Eastern coast)

Manufactured sands, recycled products to

be considered

Major issues

– Skid resistance

– Abrasion resistance

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Issues

A: 50% natural sand / 70% quartz (QA R83& R84)

B: MBV x 75 micron

C: < 2 micron

D: Durability

– Micro Deval

– Magnesium sulphate soundness

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A: 50% Natural sand/70% Quartz

Silica issue in some countries

USA

France

United Kingdom

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A: 50% Natural sand/70% Quartz (continued)

USA Guidelines for Skid Resistant Pavement Design

(AASHTO, 1976)

Wear resistance of concrete increases as the cement factor is

increased

Wear resistance of concrete increases as the W/C is decreased

Siliceous particle content in fines aggregates should

be not less than 25%

Durability and wear resistance of the concrete surface is

influenced by the effectiveness of curing

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USA

NCHRP Report 634 (Texturing of concrete pavements)

Curing Protection – for drag and tine textures, immediate

application of curing compound or membrane following the

texturing operation is essential to achieve good pavement

surface durability. If the pavement cures too quickly, the

mortar forming the texture ridges will not set properly, its

durability will be reduced, and its friction (and noise) properties

will be diminished more quickly (FAA, 2004). Generally, curing

compounds can be applied earlier for longitudinal dragging

and tining operations than for transverse tining operations.

A: 50% Natural sand/70% Quartz (continued)

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France French Methods and Experiments for Achieving High Skidding

Resistance on New Pavements

(J. L. Nissoux, 1977)

The in-depth treatment of fresh concrete provides good skidding properties

Macro roughness must be designed as early as the construction of the pavement

There are no limits for silica content in fine aggregates

Avoid - at the time of construction, anything which might reduce the strength of the surface

A: 50% Natural sand/70% Quartz (continued)

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United Kingdom British Road Research Laboratory Report (LR 334, 1970)

The influence of materials and mix design on the skid resistance value and texture depth of concrete

D.E. Weeler and D. P. Maynard

Main conclusion of the report

“ The most important constituent of the mix was the fine aggregate.

The use of high silica content natural sands always yielded high skid resistance value than did relatively soft sands or crushed fine materials”

A: 50% Natural sand/70% Quartz (continued)

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United Kingdom

Fine aggregates used in trial mixes

Flint gravel

Dolomitic limestone (??)

Soft dolerite (?)

Gritstone

Calcinated bauxite

A: 50% Natural sand/70% Quartz (continued)

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Report conclusions:

• The hardness of the sand was of major importance

• Harder sands generally yielded better skid resistance when dry wearing was applied

• Soft sands yielded better resistance when wet polishing was applied

• Calcinated bauxite was always superior to any sand

However, not much silica(!!!)

• There are no limits for silica content in the aggregates

A: 50% Natural sand/70% Quartz (continued)

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The actual definition of high silica content natural

sands in terms of 70% quartz content

“Was developed by former DMR in house

debate and discussed between its resident

petrologist and field geologist”

A: 50% Natural sand/70% Quartz (continued)

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Aggregate properties that have a significant

influence on pavement friction performance

Hardness

Mineralogy

A: 50% Natural sand/70% Quartz (continued)

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Fact 1

Aggregates made up of hard minerals alone typically

resist wear and other forms of degradation

However,

May polish easily under traffic

Fact 2

Aggregates made up of moderately soft minerals

alone, resist polishing

However,

Wear quickly under traffic

A: 50% Natural sand/70% Quartz (continued)

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Fact 3 (Extremely important!)

While a wear resistant aggregate is desired in

a mix,

Some wearing of the pavement surface must

occur to ensure good levels of skid resistance

Note

(1) Blends!

(2) Durability issues e.g. wet/dry 25%

(3) Field trial Tasmania

A: 50% Natural sand/70% Quartz (continued)

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Fine aggregates are the most critical parameter for

polishing/abrasion resistance

Fine aggregates with angular edges and cubical or irregular

shape, provide higher level of microtexture

Rounded edges and elongated shape produced lower

microtexture

A: 50% Natural sand/70% Quartz (continued)

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MOHS has classified minerals

Hard ≥6

Soft 3-5

A: 50% Natural sand/70% Quartz (continued)

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MOHS scale (hardness)

Diamond 10

Corundon 9

Topaz 8

Sillimanite 7.5

Cordierite 7-7.5

Quartz 7

Garnet 6.5-7.5

Olivine 6.5-7

Epidote 6.0-7

Chalcedonia 6

Pyroxenes 5-7

Amphiboles 4-6.5

Apatite 5

Zeolite 3.5-5.5

Fluorite 4

Dolomite 3

Calcite 3

Gypsum 2

TALC 1

Sands containing

these minerals are

excluded if there is

not 70% quartz

Sands containing

these minerals are

excluded if quartz

content is not 70%

A: 50% Natural sand/70% Quartz (continued)

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Factors affecting pavement friction (NCHRP, 2009)

Pavement

surface

characteristics

Value operating

parameters

Tyres

properties

Environment

• micro texture

• Macro texture

• Materials properties

Speed

Braking action

Tread design

Tyre pressure

Water

Ice

Debris

Dirt

A: 50% Natural sand/70% Quartz (continued)

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B: MBV x 75 micron

MBV is a valuable parameter in identifying active components in microfines

CCAA guidelines for manufactured sands

≤150 materials to be accepted

>150 - <200 additional information required

> 250 materials to be rejected

Lower limits could be specified for different concrete applications

Note

Type of microfines are extremely important

Water demand must be considered

A blend with natural sand would have a dilution effect

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B: MBV x 75 micron (continued)

Effects of type of clay on MBV results

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B: MBV x 75 micron (continued)

Effects of dry and wet sieving on MBV results

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C: < 2 micron material

Current limit <1%

(the method is limited to testing sand with at least 4% passing 75 micron)

Test results are affected by the density of solids in suspension

Note:

Results overestimate if montmorillonite (an expansive clay) is present

Results underestimate if kaolinite (a non-expansive clay) is present

There is a need to determine the type of clay if the results are >1%

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C: < 2 micron material (continued)

The test does not pick up the expansive / non-expansive clays

Work carried out by Boral

up to 3-4% kaolinite in concrete results in :

high compressive strength

lower shrinkage

lower permeability

lower chloride diffusion coefficient

Up to 1-2% bentonite

lower compressive strength

high shrinkage

high permeability

high chloride diffusion coefficient

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D: Durability

(Micro Deval)

Current durability test methods for natural and manufactured sand (sodium, sand equivalent, degradation)

are not able to determine

resistance to wear

Difficult to correlate the results

Micro Deval – CSA A 23.2-23A

Test for assessment of fine aggregates friction properties

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D: Durability (continued)

Magnesium sulphate soundness

considered more consistent than

sodium sulphate from results point of

view

(NCHPR report 2009 recommends a

loss of ≤ 10% after 5 cycles)

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Conclusions/recommendations

Discussions between industry and transport authorities should continue in order to address several issues including:

% of natural sands in concrete mixes

% of quartz in natural sand aggregates

MBV × 75micron levels

2 micron limits in manufactured sands

Durability issues

Skid/abrasion resistance of concrete pavements using manufactured sands

We are of the opinion that some of the specifications related to issues above presented, should be reviewed.