Australian Society for Concrete Pavements

The Role & Influence of Aggregates in Lean Mix Concrete Subbase (LMCS)

The Role & Influence of Aggregates in LMCS

Today We will cover:

•What aggregates are used in Lean Mix Concrete Subbase (LMCS)?

•What properties of these aggregates are important?

•The role aggregates play in performance of LMCS

•How to avoid potential problems in LMCS by correct aggregate selection and monitoring.

What aggregates are used in Lean Mix Concrete

Subbase (LMCS)??

The Role & Influence of Aggregates in LMCS

•Coarse Aggregate- normally 20mm,14mm, 10mm or 7 mm

•Fine Aggregate- Coarse Sand (or Manufactured Sand) and Fine Sand – Dune, river or other fine sands.

• R82- Aggregates-Tested & delivered from dedicated stockpiles or material onsite

Aggregates maybe:• From an established source with a

history of test results on aggregate performance.

• From a more recently established new deposit or process or

• won from site, tested and approved

Where are these quarry aggregates from?

The Role & Influence of Aggregates in LMCS

Aggregates must be tested to confirm their properties are consistent and measurable – AS2758.1- 1998

AS2758.1- 1998/ RTA R82• Grading- AS1141.11

individual and combined• Individual- 1 /400T• Combined by calc- 1/800T

or Wet sieved- with trial mix or within12mths prior

• R82- Production tolerances on Combined grading

What properties of these aggregates are important?

The Role & Influence of Aggregates in LMCS

Grading of each individual aggregate is important as it affects the total combined grading.

What properties of these aggregates are important?

The Role & Influence of Aggregates in LMCS

Subbase Concrete- Total Combined Aggregate Grading

26.519

13.2

9.5

6.7

4.752.36

1.180.600

0.300

0.15005

101520253035404550556065707580859095

100

0.1 1 10 100

Size (mm)

% P

assin

g

C Grading 1 MAX MIN C Grading 2

• AS1141.14- 2:1 (<35%) and 3:1 (<10%)

Concrete Aggregates – Particle Shape

The Role & Influence of Aggregates in LMCS

More Desirable Less Desirable

• Mat <75um (F<10%, C< 2%)

• Mat <2um (F < 1%, C <1%)

• Organic impurities (<0.5%)

• Sugar Content(<1part:10,000)

• Salts- Cl (<0.8kg/m3), S03 ( <5%) from aggregates or in hardened concrete.

Concrete Aggregates – Impurities

The Role & Influence of Aggregates in LMCS

• Durability– Wet Strength (> 50kN)

– Wet/Dry Strength Variation (<35%)

– Sodium Sulphate Soundness (<12%)

Concrete Aggregates – Properties

The Role & Influence of Aggregates in LMCS

• Aggregates occupy the largest volume within the concrete mix hence have a very large influence on concrete mix performance.

The Role Aggregates play in LMCS

The Role & Influence of Aggregates in LMCS

PropertyConcrete workabilityPlace ability Surface finish Bleed Drying shrinkage Mix Economy

Effected By…..………...Grading & Shape

………….…Grading, Shape & quantity…………….Fine aggregate Grading

………………Grading, Silt and Fines content

……Type & amount of aggregate …………….Shape, grading, strength

The Role & Influence of Aggregates in LMCS

The Role & Influence of Aggregates in LMCSAvoiding Problems in LMCS – Control charting of Individual and Combined Grading

G9 = C6 x C9 + D6 x D9 + E6 x E9 + F6 x F9 =100%

Coarse Aggregate Grading-20mm

0

10

20

30

40

50

60

70

80

90

100

01-Jan-

07-Jan-

13-Jan-

19-Jan-

25-Jan-

31-Jan-

06-Feb-

12-Feb-

18-Feb-

24-Feb-

01-Mar-

07-Mar-

13-Mar-

19-Mar-

25-Mar-

31-Mar-

Sample Date

% P

AS

SIN

G

26.5

19

13.2

9.5

The Role & Influence of Aggregates in LMCS

Dedicated Stockpiles- Grading / 400T

Avoiding Problems in LMCS –

Lot 1-400T

Lot 2- 400T

Lot 3-400T

Lot 5- 400T

Lot 4- 400T

5 sample increments

5 sample increments

5 sample increments

5 sample increments

5 sample increments

First 2000 T Aggregate stockpile

Need to understand and audit how the quarry is conducting this throughout the project?

The Role & Influence of Aggregates in LMCS

Aggregate Sampling- AS 1141.3.1-1996

Samples- at least five sample increments of approx equal mass.

(E.g. 20mm aggregate- 5 sample increments of 4kg min each).

Table 2

Minimum Mass per Sample

Nominal size, mm 75 40 28 20 14 10 7 5 <5

Mass, Kg graded material

50 30 25 20 15 10 10 5 5

The Role & Influence of Aggregates in LMCS

Avoiding Problems in LMCS –

•Monitoring of Clay & silt in natural fine aggregates•Monitor bleed of plastic concrete •Compare Bleed with combined aggregate and individual fine aggregate grading – especially with mixes containing Man Sands.

The Role & Influence of Aggregates in LMCS

Aggregates influence

CONCRETE

Questions?