Constraints in Using Manufactured Sands in Concrete Pavements

Transcription

1 Constraints in Using Manufactured Sands in Concrete Pavements Ion Dumitru Manager Tony Song Senior Development Engineer May 2012

2 Shortage of natural sands (Eastern coast) Manufactured sands, recycled products to be considered Major issues Skid resistance Abrasion resistance

3 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

4 A: 50% Natural sand/70% Quartz Silica issue in some countries USA France United Kingdom

5 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

6 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.

7 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

8 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

9 United Kingdom Fine aggregates used in trial mixes Flint gravel Dolomitic limestone (??) Soft dolerite (?) Gritstone Calcinated bauxite

10 United Kingdom 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

11 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

12 Aggregate properties that have a significant influence on pavement friction performance Hardness Mineralogy

13 Fact 1 Fact 2 Aggregates made up of hard minerals alone typically resist wear and other forms of degradation However, May polish easily under traffic Aggregates made up of moderately soft minerals alone, resist polishing However, Wear quickly under traffic

14 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

15 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

16 MOHS has classified minerals Hard 6 Soft 3-5

17 MOHS scale (hardness) Diamond 10 Corundon 9 Topaz 8 Sillimanite 7.5 Cordierite Quartz 7 Garnet Olivine Epidote Chalcedonia 6 Pyroxenes 5-7 Amphiboles Apatite 5 Zeolite 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%

18 Factors affecting pavement friction (NCHRP, 2009) Pavement surface characteristics Value operating parameters Tyres properties Environment micro texture Speed Tread design Water Macro texture Braking action Tyre pressure Ice Materials properties Debris Dirt

19 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

20 B: MBV x 75 micron (continued) Effects of type of clay on MBV results

21 B: MBV x 75 micron (continued) Effects of dry and wet sieving on MBV results

22 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%

23 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

24 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 A Test for assessment of fine aggregates friction properties

25 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)

26 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.