PERFORMANCE RELATED SPECIFICATION FOR HMA CONSTRUCTION Mohamed El-Basyouny, Ph.D.
Kuwait Asphalt Conference December 2012
Content
Background
Objectives
General Approach
Conclusions
Background ď Ź
HMA Construction QC/QA: 1. Aggregate Gradation 2. Relative Compaction 3. Volumetric Properties: air voids and bitumen content
4. No Bonus for better quality 5. Penalty for delay but not for quality 6. No information of how the pavement will perform over time.
Background
What is Pavement Performance? • It is how pavement respond to the traffic loads over time.
• It is reflected by the amount of distresses • Now, there is Mechanistic-Empirical models to predict Pavement Performance such as Rutting and fatigue cracking.
Objectives ď Ź
Develop a Performance related specification for HMA construction that: 1. Predict Pavement performance and relate this to construction Quality 2. Include a Pay Factor (Bonus / Penalty) for quality
General Approach ď Ź
To develop a performance related specification the following is needed: 1. Consider the Climatic effect 2. Consider Traffic 3. HMA material properties 4. Use of the developed pavement distress prediction models 5. Relate pavement distress to pavement life
General Approach 6. Conduct this on the design mix as well as the as-built mix 7. Compare the design and the as-built (for daily production) 8. Estimate Pay factor (penalty/ bonus) for each lot.
9. Pay Factor is defined by the agency. 10.The initial roughness can be included.
General Approach 1. Climate effect through Effective temperature concept
For Rutting
Teff 14.62 3.361Ln( f eff ) 10.940( z ) 1.121( MAAT ) 1.718(sMMAT ) 0.431(Wind ) 0.333( Sunshine) 0.08( Rain )
Teff
= effective temperature, oF
feff
= effective frequency
z = Critical Depth, inch
MAAT = mean annual air temperature, oF
sMMAT = standard deviation of the mean monthly air temperature within a
Sunshine = mean annual sunshine, %
Wind
Rainfall = mean cumulative rainfall depth, inches
given year, oF
= mean annual wind speed, mph Elbasyouny, Witczak, and Jeong, 2009
General Approach 2. Traffic can be considered through the Equivalent Single Axle Loads (ESAL)
3. Material Properties: Use of fundamental properties such as the Dynamic modulus of HMA, testing or predictive models Witczak, 1998 Log E *eff 1.249937 0.029232 p 200 0.001767 p 200 2 0.002841 p 4 0.058097 Va 0.8022
Vb eff Vb eff Va
3.87197 0.0021 p 4 0.003958 p 38 0.000017 p 38 2 0.00547 p 34 1 e
0.6033130.31335logf eff 0.393532logTeff
General Approach
4. Pavement Distress Prediction and relate it to pavement life
N  k1 (ď Ľ ) ( E ) k2
k3
This model need to be developed for local conditions.
General Approach
Cumulative Frequency Distribution, CFD
5. Compare design to as-built – Statistical Analysis can be used 100 Bad Mix
Design Mix - Years
+ Years
Good Mix
50
0 Design life (Years) (Target) Years
(increasing)
General Approach 6. Pay Factor
General Approach 7. Initial Roughness to be included to the Pay Factor
NCHRP report 704, 2011
Conclusions
Relate pavement construction to pavement performance.
Encourage contractor for better quality
Have more fundamental analysis of HMA mixtures
Consider Initial roughness