what the heck is it and why the heck should i care? · optimized gradation for concrete txdot...

WHA T THE HECK IS IT

A ND

WHY THE HECK SHOULD I CA RE?

Optimized Gradation for Concrete


Discussion Topics

Specifications and Test Methods

Lessons Learned

Summary

Contacts and Questions


Specifications and Test Methods


TxDOT Standard Specification allows the use of ACI 211 or other approved concrete mix design method

HCCMxDes2.xls is the Xite Manager template used to document mix design proportions


Special Provision 0421-035 allows for Tex-470-A to be used to furnish concrete mix designs

Tex-470-A is TxDOT’s procedure to design concrete with an Optimized Aggregate Gradation (OAG)

Use the same Xite Manager template and form 2227 in Tex-470-A to document the mix design

Reference OAG tab to verify compliance with specifications and test method


THE BIG SECRETE - An intermediate aggregate is used to fill in voids between coarse aggregate particles

Typically crusher “waste”

This will minimize paste content

Optimized Gradation for Concret

Sieve Size Sieve Size (in) Coarse Agg. 1 % Passing

Coarse Agg. 2 % Passing

Intermediate Agg. 1

% Passing

Intermediate Agg. 2

% Passing

Fine Agg. 1 % Passing

Fine Agg. 2 % Passing

Combined % Passing

Combined Cumulative %

Retained

Combined % Retained

2 1/2 in 2.500 100.0 100.0 100.0 100.0 100.0 0.0 0.0 2 in 2.000 100.0 100.0 100.0 100.0 100.0 0.0 0.0

1 1/2 in 1.500 100.0 100.0 100.0 100.0 100.0 0.0 0.0 1 in 1.000 72.0 100.0 100.0 100.0 95.8 4.2 4.2

3/4 in 0.750 12.0 97.0 100.0 100.0 85.5 14.5 10.3 1/2 in 0.500 72.0 100.0 100.0 73.0 27.0 12.6

3/8 in 0.375 54.0 100.0 98.0 64.5 35.6 8.5 No. 4 0.187 13.0 100.0 92.0 44.5 55.5 19.9 No. 8 0.093 40.0 86.0 34.5 65.5 10.0 No. 16 0.047 20.0 79.0 31.1 68.9 3.4 No. 30 0.024 10.0 61.0 23.8 76.2 7.3 No. 50 0.012 21.0 8.1 91.9 15.8

No. 100 0.006 2.0 0.8 99.2 7.3 No. 200 0.003 0.3 0.1 99.9 0.7

Pan 0.000 0.0 0.0 0.0 0.0 0.0 0.0 0.0 100.0 0.1

Mix Design Percentages 15.0 43.0 3.5 38.5 100.0

Cementitious Materials Weight = 611 (lb/CY)

Workability

Factor = 35.8

Coarseness

Factor = 54.3


Increase performance by relying more on the aggregate strength.

Enhances concrete workability.

Minimizes Shrinkage cracking

Saves money by reducing the amount of paste in the mix.


Lessons Learned


Gradations in ITEM 421 Table 3 no longer apply

Maximum nominal aggregate determined from Coarse Aggregate Grades in ITEM 421 Table 5 apply

Fineness Modulus no longer used

Sand Equivalent continues to influence concrete performance

Statistical variation reduced

Batching tolerance (ITEM 421 table 9 ) versus staying in the box/meeting strength requirements


Allows the Material Supplier to streamline crushing and stockpiling operations

Improves mix performance by reducing strength variability

When used with Concrete Works, mix designs are crack resistant and have improved performance

OAG has reduced the water demand by up to 1 gallon per cubic yard

AEA dosage rates are more consistent with OAG mix designs


Aggregate Stockpiles are not just for DOT usage

NMDOT uses OAG mixes; Coarseness Factor and Workability are held constant to control mix designs


Some issues which need to be addressed SiteManager and the Guide Schedule are not set up for the

combined aggregate gradation

Test method relies on strength and “staying in the box” to control batching

Guide schedule does not address OAG for sampling and testing

Sampling and testing aggregate is addressed in test method

CST-M certification is being developed

Aggregate must be clean and durable to achieve performance


OAG is not a cure all but a method to maximize concrete performance

Continue to use sound concrete practices to ensure acceptable performance


Summary


The El Paso District has used OAG mixes for the last three years

The District, Material Suppliers, and Contractors are pleased with the improvements OAG has brought to the concrete mix designs

Concrete with Optimized Aggregate Gradation

What the heck is it? TxDOT’s latest methodology for concrete mix designs

Relies on aggregate strength

Presents challenges as well as opportunities

Concrete with Optimized Aggregate Gradation

Why the heck should I care? Improves performance

Potential to reduce material cost

IT’S CONCRETE – IT’S BETTER THAN THE ALTERNATIVE! (mis-quote from Dale Rand – HMAC guru)


Contacts and Questions


Lisa Lukefahr, P. E. 512-506-5858

Andy Naranjo, P. E. 512-506-5849

Don’t call me (joking) Tomas A. Saenz, P. E. 915-790-4350

Questions?

what the heck is it and why the heck should i care? · optimized gradation for concrete txdot...

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