PAVEMENT TYPE SELECTION Hesham Mahgoub, PhD, PE. South Dakota State University South Dakota Department of Transportation, Office of Road Design

P AVEMENT T YPES Flexible Pavement Hot mix asphalt (HMA) pavements Called "flexible" since the total pavement structure bends (or flexes) to accommodate traffic loads About 82.2% of paved U.S. roads use flexible pavement About 95.7% of paved U.S. roads are surfaced with HMA Rigid Pavement Portland cement concrete (PCC) pavements Called “rigid” since PCC’s high modulus of elasticity does not allow them to flex appreciably About 6.5% of paved U.S. roads use rigid pavement P AVEMENT T YPES

F LEXIBLE P AVEMENT Structure Surface course Base course Subbase course Subgrade F LEXIBLE P AVEMENTS

T YPES OF F LEXIBLE P AVEMENT Dense-graded Open-gradedGap-graded T YPES OF F LEXIBLE P AVEMENTS

F LEXIBLE P AVEMENT – C ONSTRUCTION F LEXIBLE P AVEMENTS - C ONSTRUCTION

R IGID P AVEMENT Structure Surface course Base course Subbase course Subgrade R IGID P AVEMENTS

T YPES OF R IGID P AVEMENT Jointed Plain Concrete Pavement (JPCP) T YPES OF R IGID P AVEMENTS

T YPES OF R IGID P AVEMENT Continuously Reinforced Concrete Pavement (CRCP) Photo from the Concrete Reinforcing Steel Institute T YPES OF R IGID P AVEMENTS

R IGID P AVEMENT – C ONSTRUCTION Slipform Fixed form R IGID P AVEMENTS - C ONSTRUCTION

T ERMINOLOGY C OMPARISON – R IGID AND F LEXIBLE P AVEMENTS Subbase Subgrade Base Asphalt Layer Subbase Subgrade Concrete Section Asphalt Section

Asphalt Layer S TRESS D ISSIPATION IN P AVEMENTS pressure < 30 psi pressure  290 psi 18,000 lbs.

Pavement Design Initial Cost Estimate Life Cycle Cost Analysis (LCCA) Justifications Pavement Type Selection Procedures

Pavement Design Design Considerations Design Method Input Parameters Output Parameters

Design Considerations Traffic Subgrade Materials of Construction Design period Environment Drainage Pavement Performance LCCA

AASHTO Method Flexible Pavements Resilient modulus Cumulative ESAL’s Drainage coefficient of unbound materials Reliability level Overall standard deviation Serviceability Rigid Pavements Modulus of subgrade reaction Elastic modulus of concrete Modulus of rupture of concrete Load transfer factor The AASHTO Method yields a structural number for the total pavement and the individual layer thickness Design Method

I NITIAL C OST E STIMATES OF P AVING M ATERIALS Planning Estimating System (PES) Quantity Location Production Rate

L IFE C YCLE C OST A NALYSIS LCCA is an economic method used to compare alternatives that satisfy a need in order to determine the lowest cost. Factors include the following: Initial cost Analysis period Maintenance Rehab User cost Reconstruction cost

Deterministic Approach NPV = Initial Cost + Future Cost x 1 (1 + i) n $ 26 M $ 9 M 4% 20 yrs $ 30.1 M

Monte Carlo Simulation $ % Inputs Net Present Value Results MODELMODEL

NPV = Initial Cost + Future Cost x 1 (1 + i) n Combine variability of inputs generate probability distribution for results

J USTIFICATIONS A combination of LCCA and engineering judgment are documented to finalize the pavement type selection. When the net present worth of both types of pavements is within 10%, other factors are examined such as:

Traffic Soil characteristics Weather Construction consideration Recycling Cost comparison Performance of similar pavements in the area Adjacent existing pavement Conservation of materials and energy Municipal preference Local government preference Local industry

L IFE C YCLE C OST A NALYSIS E XAMPLE R EAL C OST R ESULTS I NCLUDING U SER C OSTS.

Texas Transportation Institute, 2010 R EAL C OST R ESULTS I NCLUDING U SER C OSTS.

Cost Comparison Flexible vs. Rigid Cases with a 4 Percent Discount Rate Texas Transportation Institute, 2010

Michael Bienvenu, Florida International University 2013 COMPARISON OF FUEL CONSUMPTION For Passenger Vehicle, the rigid pavement provided 3.3% better gas mileage than the flexible pavement For Tractor-Trailer, the rigid pavement provided 4.1% better gas mileage than the flexible pavement

Heavy Duty Flexible and Rigid pavements are all suitable for long life and low maintenance pavements. Rigid pavements have a 40 year Design Life compared to 20 years for Flexible. This means that in the cost analysis, a major rehabilitation has to be included in Year 20 for the Flexible. For pavement type selection, assessments should be carried out on technical, financial and economic factors. When the net present worth of both types of pavements is within 10%, other factors are examined. Conclusion

A NY Q UESTIONS ?