CMT - Particle Size Distribution Analysis of Coarse Aggregate

Summary

This video explains the particle size distribution analysis of coarse aggregates, also known as sieve analysis. The process involves sieving a dry sample, weighing the retained materials, and plotting the results on a semi-logarithmic graph. The analysis is crucial in evaluating the gradation of aggregates and determining parameters like the fineness modulus, coefficient of uniformity, and coefficient of curvature. These factors influence concrete workability, reducing the need for cement and fine aggregates. The video guides viewers through the necessary equipment, testing procedure, and calculations, including the creation of a grain size distribution curve.

Takeaways

• 🧪 Particle size distribution analysis, also called sieve analysis, is used to determine the size distribution of coarse aggregates.
• 📊 The results are plotted on a semi-logarithmic graph, with grain size on a logarithmic scale and percent finer on an arithmetic scale.
• 🛠 Sieve analysis is performed to evaluate the grading of coarse aggregates, affecting concrete's workability by influencing the water-cement ratio.
• 🔬 The sieve test also helps determine the fineness modulus, coefficient of uniformity, and coefficient of curvature, providing insights into the properties of the aggregate.
• 📉 A well-graded aggregate requires less fine aggregate and cement, resulting in denser and more cost-effective concrete.
• 🌡 To prepare the sample, oven-dry the aggregate at 105°C for 24 hours to remove moisture.
• 🧩 Sieve the sample for 10 minutes using stacked sieves with progressively smaller openings from top to bottom.
• ⚖ Weigh and record each sample fraction retained on each sieve to determine cumulative mass, cumulative percent retained, and percent finer.
• 📈 Plot the grain size distribution curve on a semi-logarithmic graph to classify the sample as well-graded, poorly graded, or gap-graded.
• 🧮 Use provided equations to calculate fineness modulus, uniformity coefficient, and coefficient of curvature to classify aggregate properties.

Q & A

What is sieve analysis and why is it important?

Sieve analysis, also known as particle size distribution analysis, is the process of sieving a dry sample and weighing the particles retained on each sieve. It helps in evaluating the grading and particle size distribution of coarse aggregate, which is crucial for the workability and quality of concrete mixes.

How is the result of a sieve analysis represented?

The results of a sieve analysis are plotted on a semi-logarithmic graph, with grain size on the logarithmic abscissa (x-axis) and percent finer on the arithmetic ordinate (y-axis).

What does a sieve test help to determine in terms of concrete mix?

A sieve test helps evaluate the gradation of aggregate and provides information on key parameters such as the fineness modulus, coefficient of uniformity, and coefficient of curvature. These factors influence the concrete's workability and strength by affecting the water-cement ratio and aggregate distribution.

What is fineness modulus and what does it indicate?

Fineness modulus is an index that indicates the fineness or coarseness of aggregates. It gives insights into the texture and grading of the aggregate, which affects the mix proportions and performance of concrete.

What is the significance of the coefficient of uniformity and coefficient of curvature?

The coefficient of uniformity and coefficient of curvature are used to classify aggregate as well-graded or poorly graded. A well-graded aggregate improves concrete density and reduces the amount of fine aggregate and cement required, enhancing concrete strength and workability.

How does aggregate gradation affect concrete mixes?

Aggregate gradation affects the workability, water-cement ratio, and packing density of concrete mixes. Properly graded aggregates result in denser concrete with better strength, requiring less fine aggregate and cement.

What is the procedure for preparing coarse aggregate samples for sieve analysis?

Coarse aggregate samples are oven-dried at 105°C for 24 hours before testing. The nominal maximum size of the aggregate is determined, and the sample is weighed based on this size.

What are the steps involved in conducting a sieve analysis?

The sieves are stacked in order of decreasing sieve opening size, with the largest at the top and a pan at the bottom. The aggregate is placed on the top sieve, and sieving is conducted for 10 minutes using lateral and vertical motions. The mass of particles retained on each sieve is then weighed and recorded.

How is the cumulative mass and percent finer calculated in sieve analysis?

Cumulative mass is calculated by summing the mass retained on all larger sieves, including the sieve in consideration. The cumulative percent retained is found by dividing the cumulative mass by the total weight. Percent finer is determined by subtracting the cumulative percent retained from 100.

How is the grain size distribution curve used to classify aggregate gradation?

The grain size distribution curve is used to classify aggregate as well-graded, poorly graded, or gap graded. A well-graded aggregate shows a smooth curve over a wide range of sizes, while poorly graded aggregate has a straight vertical portion, indicating a deficiency in certain sizes. Gap-graded aggregates show two or more well-graded portions.