We laid hot mix on one of our projects yesterday and that made my day. Putting down asphalt is close to the end of most projects which partially explains my happiness. But more than that is the process itself. It’s tied with concrete work as my favorite part of a road construction project.
Although I can make concrete from scratch in my backyard, I don’t think I can make asphalt. Maybe but probably not in a usable quantity. I use my batches of concrete to pour benches and stepping-stones. I’m learning how to make concrete counters since that’s what I want when I remodel my kitchen.
Although I could cook asphalt in my oven, I can’t make enough to do anything useful except maybe patch the smallest pothole on my street. And the City of Portland, Texas might not appreciate my usurping their responsibility which they are steadfast about ignoring. There’s enough material in that statement to write a whole other blog.
When I started working in construction, the asphalt crew fascinated me. Not the men. The equipment and the work. I had never thought about how people built roads. I had been oblivious to the procedure that concluded in a paved road. In those days, everything astonished me. I had never thought about where toilet contents disappeared to after the flush. How did water end up from the river to my house in a drinkable condition? What was the purpose of concrete curbs? I would have wondered about inlet boxes, too, but I wouldn’t have known what they were or what to call them. There was a lot that I didn’t know and didn’t know that I didn’t know. If that makes any sense at all.
Constructing roads in my part of south Texas starts with subgrade, the dirt under the road. Unless you are building a road in Flour Bluff or on the island, you’ll need to add something to the dirt. Dirt in Corpus Christi and most of the surrounding area is clay and clay shrinks and swells with moisture which is plentiful on the Gulf Coast. When I started in construction, it wasn’t treated chemically and the roads buckled and rutted within a couple of years. In the 80’s engineers started calling for contractors to add lime to the clay; lime broke down the clay and stopped it from swelling. That’s extended the life of roads. In the past 10 years, a polyester grid is sometimes placed on the raw clay in place of lime and that seems to work well at a lower cost.
Next, workers place limestone aggregate base on the stabilized clay. Trucks haul it from central Texas; road crews place it as support for the asphalt. That’s why it’s called the base. Until the past 6 or 7 years, engineers usually used caliche as a base for the asphalt. It’s a naturally available resource but it has been over-mined and isn’t as effective as limestone base.
Once the base has passed tests for hardness, it’s primed with either straight oil or an emulsified oil. That permits the base to maintain its strength and reduces dust. Within a few days, the laydown machine shows up and hot mix gets placed on the job. In the 70’s pea gravel, sand and oil mixed together made hot mix; before that, shell was sometimes used in place of pea gravel. Engineers discovered that shell made a stronger hot mix. Pea gravel didn’t absorb the oil and the hot mix was a little mushier. Shell did absorb the oil and strengthen the asphalt mix. Since shell was scarce by that time, engineers started designing mix with limestone rock.
The first time I got to help out on a construction project was with the asphalt crew. I had watched them work from an air-conditioned car and the work didn’t seem all that hard. After begging for a few months and asserting my feminist belief that women can do anything men can do, my boss let me leave the office and help lay asphalt. It was a blue sky day in January with temperatures in the high 60’s. Perfect day for laying hot mix since asphalt comes out of the truck at about 280 degrees. On a summer day the reflective heat is a killer.
As an unskilled worker, I was one of the shovel hands. I started the day lifting and tossing asphalt as I copied the workers who had been doing the work for years. By 9 a.m. the shovel’s wide arc became smaller; by 11 a.m. I could barely lift the shovel load of hot mix 6″ off the ground and dump it on the mat. I was nearly dragging it. It was a small parking lot and mercifully finished by 2 in the afternoon. I was so glad to shuffle into my house. I still stand by my opinion that women can do anything that men can do if they aren’t a short woman who believed weight lifting is limited to lifting a can of Coors from table to mouth. A little strength training might have helped.
Both the strength and the cost of local roads have increased considerably over the past 35 years. Oil, a petroleum product, has increased like gasoline; transportation cost between San Antonio and Corpus Christi drives up the cost of limestone rock. The first time I sorted hot mix tickets for our bookkeeper as our paving company’s receptionist, the cost of hot mix asphalt was $10/ton. It’s about $75/ton today. The quality of roads has increased with their lifespan over the years, too. That’s my opinion based on years of observation. I am not an engineer. But years of working in the civil construction industry have given me enough experience to surmise knowledgeably. I know when I don’t know since I know what I know.
(If you want an engineered opinion, you can check out http://texasasphalt.org website for the Texas Asphalt Pavement Association.)