5.3
Análisis de tamices y curvas de clasificación
El análisis granulométrico es un método que se utiliza para determinar la distribución del tamaño de las partículas de los materiales agregados. Este…
El análisis de tamices de agregados se lleva a cabo utilizando un conjunto de tamices apilados en orden descendente de su tamaño de apertura de arriba a abajo.
Los tamaños de los tamices varían para agregados gruesos y agregados finos.
Una muestra de agregados secados al aire se pesa y se tamiza a través de los tamices, ya sea agitándolos mecánica o manualmente durante un tiempo específico.
En el proceso, cada tamiz retiene partículas más gruesas que su tamaño de malla, al tiempo que permite que las partículas más finas pasen al siguiente tamiz.
El peso de las fracciones retenidas en cada tamiz se registra, expresado como porcentaje de la masa total, y se representa en una tabla.
Comenzando desde el tamiz más fino y subiendo hacia arriba, se calcula el porcentaje acumulado que pasa por cada tamiz y se redondea al uno por ciento más cercano.
Además, se utiliza un gráfico semilogarítmico para representar el porcentaje de paso en el eje y y las aperturas de tamiz en el eje x a escala logarítmica.
En este gráfico, se representa el porcentaje de paso acumulado correspondiente a cada tamaño de tamiz para obtener la curva de clasificación, que indica la distribución de las partículas agregadas en función de sus tamaños.
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Q1: How is sieve analysis performed on aggregate samples?
Sieve analysis begins with weighing an air-dried aggregate sample, then passing it through a stack of sieves arranged in descending order of aperture size from top to bottom. The sieves are shaken mechanically or manually for a specified time, allowing finer particles to pass through while coarser particles are retained. The weight of material retained on each sieve is recorded and expressed as a percentage of total mass.
Q2: What is the purpose of calculating cumulative percentage passing in sieve analysis?
Cumulative percentage passing is calculated from the finest sieve moving upward to establish the foundation for grading curve development. This calculation, rounded to the nearest one percent, represents the proportion of aggregate particles finer than each sieve size. These values are plotted on the y-axis of a semi-logarithmic graph to visualize particle size distribution.
Q3: Why is a semi-logarithmic graph used to represent grading curves?
A semi-logarithmic graph is used because sieve apertures are plotted on a logarithmically scaled x-axis while cumulative passing percentages are plotted linearly on the y-axis. This scaling approach effectively displays the wide range of aggregate particle sizes and produces a grading curve that clearly indicates the distribution of particles across different size ranges.
Q4: What information does a grading curve provide about aggregates?
A grading curve visually simplifies the distribution of particle sizes within an aggregate sample by plotting cumulative passing percentages against sieve apertures. This graphical representation is essential for ensuring that aggregates meet required grading specifications for construction projects and helps engineers assess whether the material is suitable for specific applications.
Q5: How do sieve sizes differ between coarse and fine aggregates?
Sieve sizes vary for coarse aggregates and fine aggregates to accommodate their different particle size ranges. Coarse aggregates require larger mesh openings, while fine aggregates use smaller mesh sizes. The specific sieve stack selected depends on the aggregate classification and the particle size distribution being analyzed.
Q6: What does the weight retained on each sieve represent in sieve analysis?
The weight retained on each sieve represents the mass of particles coarser than that sieve's mesh size. This weight is recorded after sieving and then expressed as a percentage of the total sample mass. These percentages are essential for calculating cumulative passing values and constructing the grading curve.
Q7: Why must aggregate samples be air-dried before sieve analysis?
Air-drying the aggregate sample ensures consistent and accurate results by removing surface moisture that could affect particle behavior during sieving. Moisture can cause particles to clump together or stick to sieves, leading to incorrect weight measurements and inaccurate particle size distribution data.