Question

a 10 pages report about (Sieve analysis and hydrometer). introduction - body - conclusion

Answer 1

{1} Sieve Analysis

(A) Introduction

A sieve analysis is a practice or procedure used to assess the particle size distribution of a granular material by allowing the material to pass through a series of sieves of progressively smaller mesh size and weighing the amount of material that is stopped by each sieve as a fraction of the whole mass.

The size distribution is often of critical importance to the way the material performs in use. A sieve analysis can be performed on any type of non-organic or organic granular materials including sands, crushed rock, clays, granite, feldspars, coal, soil, a wide range of manufactured powders, grain and seeds, down to a minimum size depending on the exact method. Being such a simple technique of particle sizing, it is probably the most common.

This test is performed to determine the percentage of different grain sizes contained within a soil. The sieve analysis is performed to determine the distribution of the coarser, larger-sized particles.

The sieve analysis technique involves the layering of sieves with different grades of sieve opening sizes.

The finest sized sieve lies on the bottom of the stack with each layered sieve stacked above in order of increasing sieve size. When a granular material is added to the top and sifted, the particles of the material are separated into the final layer the particle could not pass.

Commercial sieve analyzers weigh each individual sieve in the stack to determine the weight distribution of the particles. The base of the instrument is a shaker, which facilitates the filtering.

Sieve analysis is important for analyzing materials because particle size distribution can affect a wide range of properties, such as the strength of concrete, the solubility of a mixture, surface area properties and even their taste.

Sieve analysis uses sieves of various types, depending on the sieve hole size range.

A few sieve types and their nominal aperture ranges are as follows:

Woven wire mesh sieves: 20 μm – 3.6 mm
Perforated plate sieves: 1 mm – 125 mm
American standard sieves: 20 μm – 200 mm
With the sieve type chosen, the actual sifting process can be carried out using various methods, such as:

Throw-action sieving methods involve applying a vertical force along with a circular motion to rotate granules and reorient them to pass through a sieve hole.
Horizontal sieving methods uses horizontal circular motions and is the preferred method for long fibrous sample types.
Tap sieving also uses a horizontal circular motion, but adds regular vertical taps, much like sieving would be performed by hand.
Air jet sieving uses an air stream to disturb the material during the process.
In cases where fine powders are present that may clog the system, wet sieving may be used for the sieving process and each layer of the stack is dried and weighed in a secondary step.
After the sieving process, the weight percentages of each section of the stack are analyzed by percentage of weight retained and then percentage of weight passed.

From this data the distribution of granule size can be displayed graphically. The distribution, called a gradation, can be described as one of the following:

1.) Dense gradation
2.) Gap gradation
3.) Narrow gradation
4.) Open gradation
5.) Rich gradation
Sieve analysis works well for large granules that are approximately spherical in shape. Shapes that deviate strongly from spherical, such as a rod shape, or granule sizes that are very small can cause errors to occur in the sieve analysis process.

(B) Body

Test Procedure:

Sieve Analysis:
(1) Write down the weight of each sieve as well as the bottom pan to be
used in the analysis.
(2) Record the weight of the given dry soil sample.
(3) Make sure that all the sieves are clean, and assemble them in the
ascending order of sieve numbers (#4 sieve at top and #200 sieve at
bottom). Place the pan below #200 sieve. Carefully pour the soil
sample into the top sieve and place the cap over it.
(4) Place the sieve stack in the mechanical shaker and shake for 10
minutes.
(5) Remove the stack from the shaker and carefully weigh and record the
weight of each sieve with its retained soil. In addition, remember to
weigh and record the weight of the bottom pan with its retained fine
soil.
Data Analysis:

Sieve Analysis:
(1) Obtain the mass of soil retained on each sieve by subtracting the
weight of the empty sieve from the mass of the sieve + retained soil,
and record this mass as the weight retained on the data sheet. The
sum of these retained masses should be approximately equals the
initial mass of the soil sample. A loss of more than two percent is
unsatisfactory.

(2) Calculate the percent retained on each sieve by dividing the weight
retained on each sieve by the original sample mass.
(3) Calculate the percent passing (or percent finer) by starting with 100
percent and subtracting the percent retained on each sieve as a
cumulative procedure.
For example: Total mass = 500 g
Mass retained on No. 4 sieve = 9.7 g
Mass retained on No. 10 sieve = 39.5 g
For the No.4 sieve:
Quantity passing = Total mass - Mass retained
= 500 - 9.7 = 490.3 g
The percent retained is calculated as;
% retained = Mass retained/Total mass
= (9.7/500) X 100 = 1.9 %
From this, the % passing = 100 - 1.9 = 98.1 %

For the No. 10 sieve:
Quantity passing = Mass arriving - Mass retained
= 490.3 - 39.5 = 450.8 g
% Retained = (39.5/500) X 100 = 7.9 %
% Passing = 100 - 1.9 - 7.9 = 90.2 %
(Alternatively, use % passing = % Arriving - % Retained

For No. 10 sieve = 98.1 - 7.9 = 90.2 %)
(4) Make a semilogarithmic plot of grain size vs. percent finer.

Tables of standard sieve sizes can give the appearance of offering a precision of separation down to a micron or so, which is unjustified.
Firstly, because woven wire sieves are an industrial product and subject to tolerances of around ± 5 μm for new sieves and probably much more for old sieves which have been in use for several years. Secondly, the aperture in a woven wire sieve is a complex 3D shape formed by four crossing wires to select the passage or retention of irregular particles. Consequently it is an illusion to use a too close range of sieve sizes. The principal size range of each sieve standard is adequate in most circumstances.

Powder to be analysed is put on the top sieve of a stack of 5 to 10 sieves in descending aperture size with a lid on top, a collecting pan at the bottom, and the stack shaken for up to about 30 min before separation and weighing of the amount retained on each sieve. Several types of mechanical shaker are available for handling sieve stacks using vibration, tapping, stop–start movements, etc. The aim is to move the material over the sieve surfaces to present the particles to the apertures, at the same time clearing oversize material from the sieve surface to limit sieve blinding. Standard practice suggests putting no more than a couple of millimetres depth of powder on a working sieve, and using sieving times of around 30 min. General size separation is usually achieved in 30 min or so even though there will always be a continual slow passage of near aperture size material for a long time. A working limit to sieving time can be established by stopping when the weight on a given sieve changes by less than 0.5% in 5 min.

Hand sieving can be used for more accurate work. Here a single sieve with lid and bottom pan is shaken, tapped and rotated by hand until there is no noticeable change in the pan weight. It is good practice to first separate the fines from the bulk using the sieve with the smallest aperture, then to separate the coarse particles using the sieve with the largest aperture. The remaining sieves are then used one by one in descending aperture size. In some circumstances it may be advantageous to use wet sieving by washing the powder through sieves. This is especially useful with very fine powders where particles tend to clump together, but subsequent caking after drying may bring more difficulties.

(C) Conclusion

In this laboratory exercise Sieve Analysis of Fine and Coarse Aggregates, I conclude that to conduct a sieve analysis,sample are oven dried for at least 24 hours. The soil is placed and shaken through a stack of sieve with opening of decreasing size from top to bottom. The mass of particles retained in each sieve is determined. If an Aggregates are good to be used in a construction of structures and buildings is that we have to sieve an amount of gravel and sand from coarse down into fine pieces wherein different sizes will be separated and we will see if the sieved aggregates are well balanced wherein our graphs with percentage of each sieve size will show which have more and less amount.

Aggregates that are to be used in constructions must consist the different sizes (fine and coarse) because it will help our structure to be stronger and though.I conclude that we have succeed and reached the objectives of this exercises, and learned how to use and separate different sizes of aggregates through sieving and graph them to see if percentages of each sizes are connected and good to be used in constructing different structures. We may apply it in the field of engineering most especially in construction of structures like buildings, roads and bridges.

{2} Hydrometer Test

(A) Introduction

Grain size analysis is widely used for the classification of soils and for specifications of soil
for airfields, roads, earth dams, and other soil embankment construction. The hydrometer
analysis determines the relative proportions of fine sand, silt and clay contained in a given soil
sample. A knowledge of the range of moisture content over which a soil will exhibit a certain
consistency is beneficial to the understanding of how a soil might behave when used as a
construction material.

A hydrometer analysis is required to determine the particle size distribution for that portion of
the soil which passes through a No. 200 sieve (0.075 mm). The test is conducted on that
fraction of a soil sample which passes through a No. 10 sieve (2 mm) however the sand
particles in excess of 0.075 mm settle almost immediately and thus little information about
their size and relative proportion is obtained during this test. Mechanical sieve analyses are
commonly used to determine the relative distribution of soil particles greater than 0.075 mm.
When both the mechanical and hydrometer methods are performed on the same soil, the
analysis is said to be a combined analysis.
The hydrometer method depends on Stoke’s equation for the terminal velocity of a falling
sphere. Stoke’s equation was developed for perfect spheres whereas most silt and clay
particles are platey shaped. Furthermore, clay particles have a tightly bound layer of
adsorbed water which remains on the particle as it falls through the water column, resulting in
a greater resisting surface than that of the clay particle alone. Notwithstanding these
discrepancies, the hydrometer method is accepted as being of value in attempting to learn
the diameter and proportion of the smallest soil particles.
2
Prior to the conduct of the hydrometer test, the hydrometer bulb (151 H) is calibrated to the
dispersing solution and prevalent test temperatures. This is simply accomplished by obtaining
hydrometer readings in a 5g/l sodium hexametaphosphate solution at two or more
temperatures. The 151 H hydrometer bulb is manufactured to provide a reading of 1.000
when placed in pure distilled water at 21 oC. Because the sodium hexametaphosphate
solution has a specific gravity greater than 1, a hydrometer reading in excess of 1.000 will be
obtained. The difference between this reading and unity is considered as a composite
correction factor which is applied to all subsequent hydrometer readings of the soil-water
suspension.
To provide reasonably accurate results, a soil sample must be completely broken down into
individual soil grain prior to testing. This is accomplished by thorough wetting and mixing of
the soil in a dispersing agent. A concentrated solution of water and sodium
hexametaphosphate (40g/l) is used for this purpose. After complete dispersion, the soil-water
suspension is introduced into a 1 litre settlement tube and diluted with distilled water such that
the resulting sodium hexametaphosphate solution a concentration of 5g/l. Successive, timed
measurements of the specific gravity of the soil-water suspension, using a calibrated
hydrometer bulb, provides an indication of the maximum size of a soil particle still in
suspension and the proportion of soil fines still in suspension. These values are then used to
compute the percent of soil by weight finer than a given diameter.

(B) Body

Hydrometer
Glass measuring cylinder (jar), 1000ml
Rubber bung for the cylinder (jar)
Mechanical stirrer
Weighing balance, accuracy 0.01g
Oven
Deflocculating agent.
Desiccator
Evaporating dish
Conical flask or beaker, 1000ml
Stop watch
Wash bottle
Thermometer
Water bath
75 µ Sieve
Scale

Procedure of Hydrometer Test
Part – 1: Calibration of Hydrometer
Take about 800ml of water in one measuring cylinder. Place the cylinder on a table and observe the initial reading.
Immerse the hydrometer in the cylinder. Take the reading after the immersion.
Determine the volume of the hydrometer (VH) which is equal to the difference between the final and initial readings. Alternatively weigh the hydrometer to the nearest 0.1g. The volume of the hydrometer in ml is approximately equal to its mass in grams.
Determine the area of cross section (A) of the cylinder. It is equal to the volume indicated between any two graduations divided by the distance between them. The distance is measured with an accurate scale.
Measure the distance (H) between the neck and the bottom of the bulb. Record it as the height of the bulb (h).
Measure the distance (H) between the neck to each marks on the hydrometer (Rh).
Determine the effective depth (He), corresponding to each of the mark (Rh) asEffective depth Formula (Note: The factor VH/A should not be considered when the hydrometer is not taken out when taking readings after the start of the sedimentation at ½, 1, 2, and 4 minutes.)
Draw a calibration curve between He and Rh. Alternatively, prepare a table between He and Rh. The curve may be used for finding the effective depth He corresponding to reading Rh.

(C) Conclusion

Sodium hexametaphosphate has been found to ineffective when dealing with certain highly flocculated soils. In such cases dispersion may be carried out by adding N-sodium hydroxide solution at the rate of 4 ml per 10 g of soil.

The suspension should be kept out of direct sunlight and away from any local source of heat. Evaporation should be retarded by keeping a cover on the measuring cylinder between the readings.

The specific gravity should he determined for the fraction of the sample passing 75 micron sieve.

This method shall not applicable if less than 10% of the material passes the 75 micron IS Sieve.

The hydrometer makes use of Archimedes' principle

a solid suspended in a fluid is buoyed by a force equal to the weight of the fluid displaced by the submerged part of the suspended solid. The lower the density of the fluid, the deeper a hydrometer of a given weight sinks; the stem is calibrated to give a numerical reading.