Crushed Edwards Limestone Base

There is no better indicator of construction materials’ effectiveness and success than the materials’ service history. Crushed Edwards Limestone Base has been used extensively in the Austin Texas area since the mid 1940’s. At the time E. B. Snead (1904-1982) founded Texas Crushed Stone in 1947, the primary road building material being used in the Austin area was pit run gravel stabilized with emulsified asphalt.

With the introduction of Crushed Edward’s Limestone Base into the Austin market in the 1940’s. road builders soon began to appreciate the unique properties of this excellent road base. Crushed Edward’s Limestone Base was inexpensive, easily placed, and resulted in long lasting, smooth riding roads. The only equipment required to place crushed stone base is a motor grader, water truck and compaction roller. By the mid 1950’s, this crushed base material was the standard road building base material in the Austin area.

Because of the excellent results had been achieved on many projects, crushed Edward’s Limestone base was chosen for use on the interstate highway as it was built through Austin. Crushed Limestone base was chosen in the Austin area in spite of the fact that concrete paving was being used on much of the interstate system. The decision to build Interstate Highway 35 out of crushed limestone base with a relatively thin asphalt surface turned out to be a wise choice. While much of the interstate system has been rebuilt numerous times, the sections built over Crushed Edward’s Limestone have only required periodic resurfacing with hot mix asphalt. Other areas of the country were not blessed with a local material with the properties of the Edward’s Limestone.

To be economical, a construction material must be close to the point of use. In the Austin Texas area, just west of Interstate Highway 35, lies a band of Edward’s Limestone. This limestone was formed 120 million years ago when much of Texas was covered by a shallow sea. This Edward’s Limestone has several characteristics which make it an excellent road base material. First, it is soft enough to be easily crushed, yet tough enough to be a durable building material. When crushed into a well graded mixture of rock fragments ranging in size from golf ball size to microscopic crushed particles, it can be packed into road base layer that is almost as strong as the original solid rock. A well graded mixture means that there is a rock of the proper size to fill every void.

A good road base should perform well in both dry and wet weather. Since limestone base is made up of broken particles of solid rock, it performs well even in wet weather. A road base’s function is two fold. First, it must provide a roof over the underlying soil. Soils are strong when they are dry and weak when they are wet. Edwards Limestone has a characteristic of adhesion to itself. This stickiness and the fact that there is a crushed rock to fill every void, allows the crushed limestone base to form a dense impervious mat that sheds water. Second, a road base must spread the concentrated load of vehicles using the road to a large area of the weaker soil below. Once properly packed into place, the limestone base is itself strong enough to support the largest rubber tire wheel load. The limestone base layer then spreads the load over a large are of soil below.

Crushed Limestone Base is easy to apply, but the sub grade must be prepared. The steps to preparing a sub grade are to first insure that the roadway is well drained. Next, the sub grade must be dried or wet to optimize moisture and compacted. When the sub grade is ready, then the base can be dumped on the sub grade, spread, and compacted.

Both the sub grade and limestone base should be compacted at optimum moisture. Optimum moisture is the amount ofmoisture that will allow a material to be compacted to maximum density. This number is determined in the laboratory. Experienced construction personnel can usually get very close to optimum moisture, however, by observing the appearance of the materials. Many people experienced in placing limestone base will intentionally get the base a little too wet and then let it dry back as they compact the base.

For more than 60 years Edwards Crushed Limestone Base has been the primary base material for road building used in the Austin area. With over 300,000,000 tons of base in service this unique material has proven to build economic, smooth riding roads that last a long time with minimal maintenance.