Los Angeles Abrasion Test & Polyvinyl Chloride (PVC) Properties
Determination of Wear on Aggregates Using the Los Angeles Abrasion Machine
The attrition rate of an aggregate is related to its resistance to abrasion by mechanical means and also to the resistance capacity of the concrete manufactured with it. This is particularly important in aggregates used in concrete pavement.
The Chilean Standard NCh 1369.of 78 outlines the procedure for determining the wear resistance of gravel with normal real density.
This document summarizes the most useful aspects directly related to laboratory procedures.
The Los Angeles Abrasion Test involves analyzing a dry aggregate, preparing a test sample, subjecting it to abrasion in the Los Angeles machine, and expressing the wear as the mass loss rate of the sample with respect to its initial mass.
1. Electrical Devices
a. Los Angeles Machine: A steel drum of 710 ± 6 mm internal diameter and 510 ± 6 mm in length, mounted horizontally with an axial tilt tolerance of 1 in 100. It has a pulley for engine coupling, an opening for sample introduction with a securely fixed cap, and a removable steel plate projecting radially inward 90 ± 3 mm. The distance between the fin and the opening is equal to or greater than 1.25 m. The rotation speed is between 30 and 33 revolutions per minute.
b. Scale: Capacity exceeding 10 kg and accuracy greater than or equal to 0.1%.
c. Screens: Wire mesh with square openings.
d. Oven: With airflow and adjustable temperature for test conditions.
e. Spheres (Abrasive Charge): Steel balls 45 to 50 mm in diameter with a mass of 440 ± 50 g each.
2. Test Sample
The original sample size should be ≥ 2 DN kg, where Dn = max. nominal gravel size in mm. This amount exceeds 50 kg for grades 1 through 5 and 25 kg for grades 6 and 7.
3. Procedure
a. Determine the original sample size distribution by sieving using the following series of sieves (in mm): 80, 63, 50, 40, 25, 20, 12.5, 10, 6.3, 5, 2.5.
b. Choose the test grade that most closely matches the original sample’s particle size distribution.
c. For aggregates without selection or treatment, process the sample to compose the appropriate grading band and choose the corresponding test grade.
Test
a. Weigh the fractions for the chosen test grade and record the initial total mass (mi).
b. Place the material in the machine and test according to the chosen grade.
c. After the cycle, remove the material and sieve it through 2.5 mm and 1.6 mm meshes.
d. Wash and dry the retained material to a constant mass and cool to ambient temperature.
e. Weigh and record the mass of the final retained material (mf).
f. Calculate the wear of the gravel as the mass loss rate of the sample using the formula: LA = (mi – mf / mi) * 100 (approximated to 0.1%).
Polyvinyl Chloride (PVC) Properties and Applications
Polyvinyl chloride (PVC) is a white material that softens around 80°C and decomposes above 140°C. It is a polymer resin resulting from the polymerization of vinyl chloride or chloroethylene. PVC has excellent electrical resistance and flame retardancy.
The chlorine atom bonded to each carbon atom gives PVC its amorphous characteristics, hindering recrystallization. The strong dipole moments caused by the chlorine atoms contribute to high cohesion between molecules and polymer chains. This also creates steric hindrance, reducing the flexibility of the polymer chains. Therefore, additives are often incorporated to achieve the desired end product.
Types of PVC
Rigid PVC: Used in packaging, windows, and pipes, often replacing iron due to its superior oxidation resistance.
Flexible PVC: Used in cables, toys, footwear, flooring, coatings, and stretch ceilings.
Key Features of PVC
- High resistance to abrasion
- Low density (1.4 g/cm3)
- Good mechanical strength and impact resistance
- Dimensional stability and environmental resistance
- Recyclable
- High halogen content
- Ductile and tough
With the use of additives like stabilizers and plasticizers, PVC can be made rigid or flexible, making it suitable for various applications.
Applications of PVC
PVC is widely used in sanitation-critical applications like catheters and blood bags due to its stability and inertness. It is also commonly used in drinking water pipes.
PVC products are highly durable, lasting over sixty years in applications like water pipes and window frames.
Due to the chlorine in its polymer structure, PVC is not easily flammable and self-extinguishes when the heat source is removed. This makes it suitable for electrical cable insulation.
PVC is readily recyclable, minimizing waste in landfills. It is also inert and does not contribute to the formation of toxic gases or leachates.
Benefits of PVC
- Made from abundant natural resources (oil and salt)
- Lightweight, easily transportable, and inexpensive
- High energy value (can be used for energy recovery in waste combustion)
- Economical with low installation and maintenance costs
Polymerization of Vinyl Chloride
or chloroethylene. It has a very good electrical resistance and flame. The chlorine atom bonded to each carbon atom gives mainly amorphous features and impeding their recrystallization, high cohesion between molecules and polymer chains of PVC are mainly due to strong dipole moments caused by the chlorine atoms, which in turn give some steric hindrance ie molecules that repel the same charge, creating electrostatic repulsion that reduce the flexibility of the polymer chains, this difficulty in the structural conformation, in most applications, requires the incorporation of additives to be obtained a product desired end.
In industry there are two types: Rigid: packaging, windows, pipes, which have largely replaced the iron (which is oxidized more easily.) Flexible cables, toys, footwear, flooring, coatings, stretch ceilings. Among its features are its high content of halogens. It is ductile and tough, has dimensional stability and environmental resistance. It is also recyclable by several methods.
It features high resistance to abrasion, along with a low density (1.4 g/cm3), good mechanical strength and impact, making it ideal for common and building and construction.By using additives such as stabilizers, plasticizers, among others, the PVC can become a rigid or flexible material, a feature that allows it to be used in many applications. It is stable and inert so it is used extensively where sanitation is a priority, such as catheters and blood bags and blood products are made with PVC, and many drinking water pipes. It is a highly resistant material, PVC products can last more than sixty years as seen in applications such as pipes for drinking water supply and sanitary according to the state of the facilities expected of a long duration as well as with PVC door frames and windows. Because the moleculeschlorine as part of the PVC polymer, does not burn easily or burn by itself and ceases to burn once the heat source is removed. It is used effectively to isolate and protect electric cables in the home, offices and industries because it is a good electrical insulator. PVC profiles used in construction for coverings, ceilings, doors and windows, is due to the low flammability presents. Readily recyclable, which facilitates the conversion of PVC into useful items and minimizes the chances that objects are made of this material dumped in landfills. Since PVC is inert there is no evidence that contributes to the formation of toxic gases or leachates. When made from natural raw materials: oil and salt. Common salt is an abundant and virtually inexhaustible resource. The PVC production process used oil (or natural gas) very efficiently, helping to conserve fossil fuel reserves. It is also a lightweight, easily transportable and inexpensive.High energy value. When power is restored in modern waste combustion, where emissions are closely monitored, the PVC to provide energy and heat for industry and households.
Economical. Low installation cost and virtually zero maintenance cost in its life.
The polymerization of vinyl chloride is polymerized via commercially radical en bloc, suspension and emulsion. The solution polymerization methods are less commercial importance, at least in Europe. While not providing details of the process, according to a patent type, vinyl chloride is polymerized with 0.8% benzoyl peroxide, based on weight of monomer. The operation is performed at 58 ° C for 17 hours in a rotating cylinder, inside which there are stainless steel balls. Because the polymer is insoluble in the monomer, polymerization block is heterogeneous. The reaction is difficult to control and leads to a slight decrease in the insulating properties and transparency. The shape and particle size and size distribution can be controlled by varying the dispersal system and stirring speed.