Historically speaking:

Getting out of the mud

text by Michele Regenold, photos courtesy of the Iowa DOT historic photo collection

In the early days of automobiles, many roads were made of earth. When those roads got too wet, they turned into mud pits and were practically impassable. People tried all sorts of different ways to make roads better.

Wooden planks were one temporary solution on dirt roads.

Rock was another solution, but traffic tends to make the rock fly around. In this photo, a horse-drawn tank wagon is spraying tar or sealer on gravel. The man in the back of the wagon is manually controlling the spray nozzles.

Brick was a paving material in the early days of automobiles when vehicles weighed less than 3,000 pounds. Today’s 18-wheel semi-tractor trailers are too heavy for those original brick streets.

Smooth, hard pavements made of asphalt or concrete became more desirable as more automobiles hit the roads. In this photo, a steam-powered portable concrete mixer is being manually loaded with sand and cement. The horse-drawn wagons are delivering sand. Notice the wooden boards, called forms, along the edges of the road bed. Forms had to be built along the whole route and later removed.

Building fixed forms made concrete road construction a slow process. James “Jimmy” Johnson, who worked as the lab chief at the Iowa Highway Commission from 1922 to 1966, invented a way to build concrete roads without fixed forms. This photo shows the first prototype slipform paver circa 1947. It could lay a slab of concrete 18 inches wide and 3 inches deep.

In 1948, Johnson built and tested a larger model that was big enough to pave a 3-foot wide sidewalk that was 6 inches deep.

In 1949, a full-size slipform paver that could pave a 10-foot wide strip of concrete was ready for testing. The wet concrete would be dropped in front of the paver and come out the back. This photo shows the front of the paver (without any concrete ready for paving). Behind the paver is a stretch of nicely formed concrete.

Over the next few years, several companies developed their own versions of the slipform paver. The development and adoption of slipform pavers in road construction helped speed up paving. Using fixed forms, construction crews used to lay about 1,000 feet of concrete per day. With modern slipform pavers, crews can lay a mile or more of pavement per day in widths of 12 to 50 feet and depths up to 19 inches.