MTV and Pavement Smoothness

Jeff Ensell

Benefits of Smooth Pavements

1. Smoother roads are important to the road users (taxpayer)

2. Smoother roads last longer

3. Smoother roads stay smoother longer

4. Smoother roads save money

5. Smoother roads are safer

6. Smoother roads improve mobility

What is a MTV

What do they do?

An MTV transfers material from a truck and puts it directly to a laydown machine.

A Mobile Silo and Mixer

• The MTV is a part of the asphalt mixing plant on the

job site.

• It receives the material from the delivery truck and then remixes and blends

this to the original plant specification.

Why Use a MTV

• Eliminate Physical Segregation

• Re-Mix HMA

• Provide Site Storage

• Stop Truck Delays

• Eliminate Paver Stops/Start

• Smoother Roads Last Longer

• Require Less Maintenance

Stopping Cost Money!

35’ / min * 60 min= 2100’ / HR

150’ stop for 2.5 min

2100’ stopped 14 times

35’ / min * 2.5 min= 87.5’

87.50 * 14= 1225’

2100 – 1225= 875’ / HR

Production

Thermal Segregation

• 20°F (11°C) Differential = 1%

to 2% Air Voids

• Over 7% Air Voids Reduces Life

• Each 1% Over 7% Reduces Life

by 10%

Source: WSDOT

Thermal Segregation

Temperature Differentials greater

than 25°F results in 2% increase

in air voids and result in failing

density profiles approximately 90

percent of the time.

Source: WSDOT

Why Use a MTV

No matter how simple the truck

No matter how complex the truck

Insulated Truck owned by a large Dutch Contractor

Both Loose Heat

Thermal Segregation is one of the reasons that

asphalt pavement prematurely fails.

Aggregate Size Segregation is caused by the

same movement of the delivery vehicle as

Thermal.

I Want My MTV

Why Use a MTV

Bring your machine up to the truck and then raise the bed when

possible.

When unloading a truck, discharge the material as a mass instead

of dribbling the material into a paver.

RP195

Truck Exchanges

What about Time ? Time =Production

Pulling Force( Force P )

Head Of Material( Force M )

Shear Force BetweenThe Material and the Screed. ( Force F )

Reaction Of MaterialUnder The Screed

( Force R )

Weight Of The Screed( Force W )

FR

M

P W

Forces acting on the screed

Day 1 Infrared Data – 1000 ft. by 12 ft. lane

Cold spots (blue) at 130 ft. intervals (truck ends)

6.4%

Voids14.8%

Voids

Severe Thermal Segregation

Mean mix temp has dropped ~ 20 F

Localized temperature differential is key

Paver stop ~ 35 minutes ~ 20 ft of

mat not rolled during this time.

Area becomes low density

regardless of temp at time

of placement Bump felt at transition

Rolling delay

Surface temp ~ 117

F before rolling

15.0 % Voids

Paver Stops

• Remove trucks from paver

• Trucks are not bumping

paver causing it to change

speed and put marks in mat

Non-Contact Paving

Constant Speed Paving

• Changing speeds while

paving changes the forces on the screed

• Shuttle Buggy allows paver

to keep moving

• Stores mix on site

• Paver doesn’t slow down to accept truck

Dump Person

Be sure the truck driver and the paver operator know

when you are between them.Be aware if the back up alarms on the trucks are not

working.

Communicate well with the truck driver when it comes

time to pull out in live traffic. Make sure it is safe.

Keep unwanted material off the road in front of the

paver

Looks out for power lines and limbs

Infrared Data – with MTV

Proper material transfer

Material Flow & Loading Material

RP195

Remember, make sure that the C2 has at least 1/3rd to

2/3rd capacity at all times.

Proper material transfer

RP195

If the insert is always out or low, you will

see the same problem with Material

Segregation.

Proper material transferThink of how sand would come out of a

glass at different heights.

What about the Insert?

If the insert is always out or low you will see

problems with Material Segregation.

Stop the paver before the material drops

below flow gate.

Keep the conveyor deck covered with a

minimum of 12 to 24 inches of material.

What Insert??

I have a transfer machine….. What’s

the problem??

The Other Reasons…..

Moba Pave IR

Moba Pave IR

If you need to know why you should use a MTV this will show you the way!

REPORT

REPORT

CONCLUSION:

• Initial Ride Quality can be improved by minimizing stops and including a material transfer device

• When used properly, Shuttle Buggy improved the ride quality and eliminated thermal & physical segregation

• Results show no significant thermal segregation when a material transfer device was used

Source: Texas Transportation Institute

Why? Because they make you Happy