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10 czerwca 2023

Specific Gravity of Metals and Non-Metals Used in Construction: Properties and Applications

Introduction

Specific gravity is a fundamental property of soils and other construction materials. This dimensionless unit is the ratio of material density to the density of water and is used to calculate soil density, void ratio, saturation, and other soil properties. Applications include the foundation design for structures, calculations for the stability of slopes and embankments, and determination of the bearing capacity of soils.

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Specific gravity is also used to identify and classify different types of construction materials based on their composition, quality, and suitability for various purposes. For example, specific gravity can help distinguish between similar-looking gems, metals, or rocks; check the progress of chemical reactions and the concentration of solutions; and test the quality of battery fluid and antifreeze.

In this article, we will explore the specific gravity of common construction materials, both metals and non-metals, and how they affect their properties and applications. We will also learn how to measure specific gravity using different methods and instruments.

Specific Gravity of Common Construction Materials

The specific gravity of a substance is characteristic; it is the same for different samples of a substance (if pure, the same in composition, and free from cavities or inclusions) and is used to help identify unknown substances. The specific gravity of most organic compounds containing only carbon, hydrogen, and oxygen is less than one.

The usual standard of comparison for solids and liquids is water at 4 C (39.2 F), which has a density of 1.0 kg per litre (62.4 pounds per cubic foot). Gases are commonly compared with dry air, which has a density of 1.29 grams per litre (1.29 ounces per cubic foot) under so-called standard conditions (0 C and a pressure of 1 standard atmosphere ). For example, liquid mercury has a density of 13.6 kg per litre; therefore, its specific gravity is 13.6. The gas carbon dioxide, which has a density of 1.976 grams per litre under standard conditions, has a specific gravity of 1.53 (= 1.976/1.29).

Because it is the ratio of two quantities that have the same dimensions (mass per unit volume), specific gravity has no dimension. However, it can be expressed in various units depending on the context. For example, specific gravity can be expressed as grams per cubic centimeter (g/cm3), kilograms per cubic meter (kg/m3), pounds per cubic foot (lb/ft3), or pounds per gallon (lb/gal).

To measure specific gravity of solids and liquids, there are several methods and instruments available. Some common ones are:

The pycnometer method: A pycnometer is a glass flask with a narrow neck and a stopper that has a capillary tube. The flask is filled with a liquid of known density (usually water or alcohol) and weighed. Then, the flask is emptied, dried, and filled with the material to be tested and weighed again. The difference in weight divided by the density of the liquid gives the volume of the material. The specific gravity is then calculated by dividing the weight of the material by its volume.

The hydrometer method: A hydrometer is a glass tube with a bulb at one end and a graduated stem at the other. The bulb is weighted so that the hydrometer floats upright in a liquid. The stem is marked with different scales for different liquids, such as water, alcohol, or oil. The specific gravity of a liquid is read from the scale at the level of the liquid surface. The specific gravity of a solid can be measured by immersing it in a liquid of known density and reading the change in the hydrometer reading.

The Archimedes' principle method: This method is based on the principle that a body immersed in a fluid experiences an upward force equal to the weight of the displaced fluid. The specific gravity of a solid can be measured by weighing it in air and then in water (or another liquid of known density). The difference in weight divided by the weight in water gives the specific gravity. Alternatively, the specific gravity can be calculated by dividing the weight in air by the loss of weight in water.

Specific Gravity of Metals

Metals are commonly used in construction for their strength, durability, conductivity, and resistance to corrosion. However, not all metals are suitable for every purpose, and some metals have advantages over others depending on the application. One of the factors that affects the performance and suitability of metals is their specific gravity.

Specific gravity is highest in rocks rich in iron, magnesium oxide, and the heavy metals and lowest in those rich in alkalies, silica, and water. Metals with higher specific gravity tend to be denser, harder, stronger, and more resistant to deformation than metals with lower specific gravity. However, they also tend to be heavier, more expensive, and more difficult to work with than metals with lower specific gravity.

The following table shows some common metals used in construction and their specific gravity values:

Table 3: Specific Gravity of Metals Metal Specific Gravity --- --- Aluminum 2.55 - 2.8 Brass 8.4 - 8.7 Copper 8.89 Iron 7.03 - 7.9 Lead 11.35 Aluminum

Aluminum is a light-weight metal with a low density and a high strength-to-weight ratio. It has good corrosion resistance, electrical conductivity, thermal conductivity, and reflectivity. It is also easy to form, weld, and recycle. Aluminum is widely used in construction for roofing, siding, windows, doors, frames, panels, bridges, railings, and other applications where lightness, durability, and aesthetics are important.

Brass

Brass is an alloy of copper and zinc with varying proportions of other elements such as tin, lead, nickel, or iron. Brass has a yellowish color and a high resistance to corrosion by water, saltwater, air, and many chemicals. It also has good electrical conductivity, thermal conductivity, ductility, malleability, and machinability. Brass is used in construction for plumbing fixtures, valves, fittings, pipes, tubes, wires, cables, hinges, screws, nails, and decorative elements.

Copper

Copper is a reddish-brown metal with excellent electrical conductivity, thermal conductivity, ductility, malleability, and corrosion resistance. It is also biostatic, meaning that it inhibits the growth of bacteria and fungi on its surface. Copper is used in construction for electrical wiring, plumbing, roofing, cladding, gutters, downspouts, and ornamental features.

Iron

Iron is a grayish-white metal with high strength, hardness, rigidity, and magnetic properties. It has moderate corrosion resistance, electrical conductivity, and thermal conductivity. Iron is rarely used in its pure form in construction, but rather as an alloy with other elements such as carbon, manganese, nickel, chromium, or molybdenum. The most common iron alloys used in construction are steel and cast iron.