Caltrans Districts

Someone asked me about the districts in California.  There are 12 districts in the California Department of Transportation (Caltrans).  They are divided along county lines and can be seen in the diagram below:  

Retrieved 9/22/11 from http://www.dot.ca.gov/dist3/other.htm

New Spin on Tanks and Silos

Today I was reading this article: California Plant Becomes Reality about a state of the art hot plant that was permitted and erected in Southern California. It has all the bells and whistles like a double drum, warm mix, and automated controls but I was particularly intrigued with two items. The first was their oil tanks as seen in the photo below:

Traditionally oil tanks are laid down horizontally.  I believe this was under the theory that if you place the heating elements on the bottom of the tank you can cover more surface area to keep the oil warm and consistent.  One of the plants I worked at also stood their tanks up vertically like the tanks shown above and when I asked why they did this I was pleasantly surprised.  One of the biggest reasons is space.  Many hot plant locations are in urban areas and they do not typically have space to lay out the tanks horizontally, as seems to be an issue with the plant above.  As you may have noticed, standing the tanks up vertically takes up less than 1/4 the space it would take to lay them down horizontally.  The other reason was an engineering reason.  Heat rises.  Each tank has a heating element on the floor of the tank and as the bottom of the tank is heated, the heat rises to heat the rest of the oil in the tank.  With good insulation, you can use less energy with a smaller heating element to heat the entire tank, granted it might take a little longer than it would with a horizontal oil tank.  In addition, many vertical tanks also have circulators that move the oil around in the tank to maintain a consistent temperature.  It's a pretty neat technique that can save the company money and space.

The other item that I thought was interesting was that this facility is storing their aggregates in silos instead of in stockpiles.  This setup is seen in the background of the photo above and in the photo below:

I've actually never seen a setup like this one and I was extremely excited when I saw it.  The grate above is a drive over depository for aggregates.  Bottom dump trucks, transporting the plant's aggregate supply from a nearby quarry, drive over this grate and dump their load through the grate (also called a grizzly).  The grates stop any over sized materials (if any) and the rest of the rock drops through to the conveyor coming out from underneath it.  This conveyor takes the rock to the top of one of the designated aggregate silos where it is deposited for future use at the hot plant.  The hot plant can meter the amount of rock from each aggregate silo using their automated controls and no loader is used at all!  What I love about this set up is that not only is it going to lead to lower operating costs but also that it is all enclosed.  California is quickly moving towards tougher and tougher dust regulations for hot plants and this setup will come close to eliminating dust at their hot plant.  In addition, (as if that wasn't enough!) having the rock enclosed in silos with this setup will also help out a ton with storm water requirements since you don't have aggregates which could have chemicals or minerals that can negatively affect runoff sitting in the rain.  AND not having wet material because of the rain means lower dryer costs!

As an operations person I'm really excited to see these types of developments but as a quality control person I'm also a little hesitant.  One of the reasons that many operations choose not to use aggregate silos is that they have a propensity to segregate material.  As I mentioned here when aggregates are dropped from a distance the coarse materials can roll to the outside and the fines stick in the middle.  This could lead to coarse materials on the outside edges of your silos and fine materials in the center which can affect your hot mix.  There are several ways to combat this though, such as using a gob hopper, so I think that aggregate silos still have a chance at being really great if they are set up and monitored properly.  My other curiosity is whether the inherent moisture from the aggregates in the silos will drip down to the bottom of the silo leaving the moisture content of your aggregates inconsistent and possibly affecting your oil content (especially with a drum plant).  However, with traditional moistures around 2-3% I'm not sure that it will make that big of a difference in the long run.  I just thought I'd let you all in on some of the possible negatives though since there is no such thing as a perfect setup.  Overall I think that this facility, belonging to Kelterite, is leading the way to what we're going to be seeing more and more of in the future.
  

CT 304 Still Being Updated

Thanks to one of our readers we've found out that the new CT 304 that I spoke about a couple months back (here) is not to be used yet.  Soon after the new version was posted on the Caltrans website it was taken down.  I looked into it and this is because they are revisiting whether the binder content should be reported as total weight of dry aggregates or as total weight of mix.  I'll keep you all updated when the new version is re-posted on the Caltrans website and let you know what they decide.  Sorry about the confusion!

Cracking from Tree Roots

I was on vacation this past weekend and stumbled upon this patch of road and being the nerd that I am I had to take a photo and share it with you all.

A few weeks ago someone asked me if alligator cracking can be caused by tree roots.  The photo above is an example of cracking caused by tree roots.  As you can see, the cracks are actually raised up from the ground instead of depressed like you will commonly see with alligator cracking.  Maintenance for roads with cracking due to tree roots is a little complicated.  In 99% of cases you will need to remove the tree to fix this on-going problem because even if you dig out the roots that are currently under the pavement, the tree will grow new ones and you will be right back where you started. 

The tree shown in the picture above is in a state park so the solution to remove it will not work.  If you need to keep the tree in place you'll need to find a way to reduce the roots below the pavement.  Typically a tree will have 6 to 10 large roots that grow outwards from the tree trunk which provide stability for the tree.  It is not advisable to cut these roots because the tree may loose its stability and become a safety hazard.   Cutting these major roots will also leave a large portion of the root exposed to the elements which can cause rotting and decay under the soil's surface and may ultimately result in the tree dying.  If you find that these roots are the ones that are causing your cracking, you are better off removing the tree.  If not, you will dig out the area below your pavement, saw off the roots that are under the pavement area and install a root barrier at the edges of your pavement.  The barrier should be placed to a depth of 18-24 inches.  If you have good soil depth, the roots will grow down and continue to grow laterally below the barrier but will not have as large of an impact on the pavement you install. 

A common mistake that contractors make is by only trenching along the edge of the pavement to cut the roots and install the root barrier.  By doing this they leave dead roots under the pavement which will rot and decompose.  Once this happens, the pavement can shift and create more cracking.  It is better to dig out the entire root system under the pavement. 

Another option is to pave with rubberized asphalt.  Although the rubberized pavement will still upheave from the roots, it will not crack into sharp cracks as you see above and form rounded mounds instead.  This can help aesthetically as well as reduce the tripping hazards from pedestrians and bicyclists.        

If you are planning on planting new trees near pavement keep some things in mind.  Most tree roots are 2-3 feet below the surface where the good soil is and can be as much as three times the length of the longest branch on the tree.  It is recommended that your pavements are 5 feet from any trees to eliminate the chances of the roots damaging it.  There are also certain species of trees that will be better suited for planting neared paved areas.  Avoid trees with roots that swell and raise near the surface.  Also avoid trees with dense canopies that will reduce the amount of sunlight available to the pavement.  The lack of sunlight will make it harder for moisture to evaporate which can encourage water damage to your pavement.  Some good choices for trees to plant near pavements or sidewalks are hedge maple, cornelian cherry, green ash, chinese juniper, crabapple, scarlet oak, and lacebark elm.  A few of the trees that you want to avoid when planting near a paved surface due to large surface roots are red maple, beeches, live oak, pin oak, willow oak, weeping willow, and american elm.