Masonry Magazine May 1964 Page. 11
One of the means of securing limestone is that of quarrying. Pictured is one of these quarries in the midwest.
Lime -
This article on lime is a continuation of Masonry's effort to acquaint the readers with the materials the contractor uses in his everyday work. The bricklayer and masonry contractor know that lime is used in mortar, but they may not be familiar with its manufacture and its uses in other allied industries.
All limestones are formed when calcium carbonate crystallizes out of solution. There are two types of limestone formations. One is formed without the aid of organisms. This type was deposited by the evaporation of calcium carbonate salts from the oceans that once covered parts of the earth. The second type is formed by organisms such as urchins, oysters, clams, and other shell-forming organisms. When these organisms die, their shells are deposited on the ocean floor and subsequently become layers of limestone. As a result of these depositions, limestone is found in areas where millions of years ago oceans covered the earth. Now 300 to 500 million years later we use this limestone as a building block of our civilization.
Limestone can be either mined or quarried. If there is very little covering of dirt, clay, or unsound stone (this is called "overburden"), then the limestone is quarried. If the limestone is deep in the ground, removing the overburden would be too expensive; thus a mining operation must be employed.
When the stone is quarried, the overburden covering the rock must be removed to expose the high purity stone. A predetermined pattern of holes is drilled in the exposed stone by rotary bits. These holes are then filled with explosives which shatter tons of rock into fragments that can be picked up with power shovels or endloader equipment. The stone is then moved to crushers and screening equipment to be reduced to the proper size for burning.
Mining the stone is the most effective means when large amounts of overburden cannot be removed economically. In the mining operation a ramp or roadbed is first blasted out to level the rock to be removed. When the stone is exposed, horizontal holes are drilled into the face. Areas 15 to 20 feet high and 20 to 40 feet wide are blasted out leaving pillars to hold up the roof. The thickness of the limestone deposit determines the height of the ceiling. Some mines have ceilings of 90 to 100 or more feet in height. With these types of mines, the floor goes deeper in lifts. Normally mines are developed from the upper strata of stone downward (or from the ceiling down). The floor is removed by blasting out approximately 20 feet of rock at a time; this is called a "lift". As in quarrying, the stone is removed to crushing and screening equipment for sizing and further processing.
Limestone is burned in a furnace at high temperature to make lime. This furnace is called a kiln, or calciner. Lime is one of the oldest products known to man, dating possibly as far back as the cave-man era and the discovery of fire. Primative kilns which are believed to have been used for preparing lime during the stone age have been excavated. Lime plaster, still in good condition, has been found in some pyramids built more than 4500 years ago in Egypt.
The early American shaft kiln consisted of a vertical brick stack. The stone was sized to about 4 to 6 inches in diameter and then dumped into the top of the stack. These kilns were usually built against a hill or bluff and the stone was conveyed in a wheelbarrow to the top and dumped into the kiln. A wood or coal fire was built in the bottom of the kiln and kept burning from two to four days. The stone slowly changed into lime by the heat going up the (Continued on next page)
MASONRY
May, 1964
11