PART 1. Measurement of liquid and plastic limits of a material
Introduction
The lab is performed to test the plastic and liquid limits of soil. The liquid limit is arbitrary referred to as the water content in percentage at which a part of the soil in a standard cup by a groove of standard measurements flows together at the base of this groove for about a half-inch (13 millimeters) when subjected to twenty-five shocks from the standard cup being dropped ten millimeters in a standard liquid limit apparatus that is operated at a rate of 2 shocks/second. Plastic limit is referred as the water content in percentage at which the soil cannot be deformed further by rolling into one-eighth inch (3.2 millimeters) diameter threads without crumbling.
The plastic limit is the point at which the moisture content that defines where soil changes from the semi-solid state to plastic (flexible) state. In the liquid limit, the soil changes from the plastic viscous fluid state. A broad range of engineering properties is correlated to liquid and plastic limits. The seven limits of consistency, as classified by Swedish soil scientist Albert Atterberg, are crucial to the classification of fine-grained soil about the Unified Soil Classification system.
Approximately three-quarter of the soil is placed in the evaporating dish. The soil is thoroughly mixed with water to form a paste. The dish is covered to prevent the escape of the moisture. Moisture cans are weighed and their masses recorded. Also, a portion of the posted soil is placed into the liquid limit apparatus. It is squeezed to remove air pockets and spread into the cup with a depth of 10mm. A clean straight groove is cut down the center of the cup. The crank of the apparatus is turned at two drops per second. The number of drops taken to make double halves of soil pat come into contact with the bottom of the groove was counted as N.
Samples are taken using a spatula and placed in a moisture can. The moisture can hold the samples is weighed immediately, the mass is recorded and the lid removed. The moisture can is left in the oven for 16 hours. The entire sample is remixed in the porcelain dish and a distilled water added. The whole process is done with three more trials.
On the other part, the Plastic limit is as easy as a liquid limit: Empty moisture cans are weighed together with their lids. Distilled water is added to the remaining one-quarter soil sample until the soil is capable of rolling without sticking on hands. The soil is rolled between fingers and glass plate using enough pressure using 90 strokes per minutes into a uniform diameter. A diameter of 3.2 mm must be attained.
The soil threads are broken down into smaller ellipsoidal masses. The portions are gathered and placed in moisture can. The cans are left in the oven for 16 hours. Five other trials can as well be done using this method. The water content of the soils is measured.
Results
Liquid limit tests
Plastic Limit
Calculations
Liquid limit of the soil is 21
Plastic limit =
Plastic index (PI) = Liquid Limit (LL) – Plastic Limit (PL)
21.0-18.3 = 2.3
Discussion
The experiment is aimed at finding the liquid limit as well as the plastic limit of fine soil. The difference between the two figures results to plastic index, for instance;
Plastic Index (PI) = Liquid Limit (LL) – Plastic Limit (PL)
The plastic index yields an indication of a reduction in moisture content needed to convert the soil from liquid to semisolid state. The plastic index is considered as the measure of cohesion possessed by the soil. To obtain PI of the soil, LL and PL must be determined. The soil must not be sandy. If PL is equal to LL, the plastic index is non-plastic.
Conclusion
The method used to determine liquid and plastic limits of the soil was simple. The objectives of the lab experiment were achieved. Arguably, the exercise was successful.
References
Cripps, J. C., Reeves, G. M., & Sims, I. (2006). Clay materials used in construction. London, The Geological Society.
Germaine, J. T., & Germaine, A. V. (2009). Geotechnical laboratory measurements for engineers. Hoboken, N.J., John Wiley.
Lamoreaux, P. E., Assaad, F. A., & Hughes, T. H. (2003). Field methods for geologists and hydrogeologists. New York, Springer-Verlag.
Olson, G. W. (1977). Soil survey interpretation for engineering purposes. Rome, FAO.
Part 2
Bulk density test and sieve analysis
Introduction
This experiment is aimed at determining the bulk density of aggregates by passing them through a sieve. Bulk density is the mass per unit volume of a material at a particular temperature (including both permeable and impermeable voids). Bulk density is dependent on the density of powder particles and spatial arrangement of particles. It’s expressed as grams per cubic centimeter.
A simplistic definition of sieving is the separation of fine materials from the coarse ones using a meshed or perforated aperture. According to Astm Committee E-29 On Particle Size Measurement (1985), a sieve is a series of gages that reject or pass present particles in the aperture. This theory dates back in the old Egyptians days when grains were sized with various sieves of woven reeds and grass. Sophistication sieving tests have increased with rising in industrial revolution; sophisticated methods of classifying materials have also come to replace the old ones. Woven wire cloth has provided alternative for greater accuracy and durability.
Woven wire cloth for Sieve Analysis has a variety of sizes ranging from 125mm (5-inch) openings to 20-micrometer openings. The mesh sizes are governed by both national and international standards. The urge to analyze fine-sized particles prompted the development of electrodeposited sieves (electroformed or micro mesh) that are produced by finer openings as fine as 3 micrometers. Sieve analysis is one of the methods of particle size analysis that escaped modernization; modernization has not changed the actual hardware of sieving, only that application, and utilization of existing equipment has proceeded (Merkus, & Meesters, 2016).
Results
During the analysis, the total mass of soil retained is 822 grams.
Mass loss during sieve analysis = (Wt-W10/Wt = (824-822)/824*100 = 0.2
When a graph of percentage finer is plotted against particle diameter, the following relationship is seen.
Discussion
In bulk density test with sieving analysis, the following terms are frequently used. Agglomerate – is the tendency of the particles to clump together or ball together. Materials that have high moisture or have fats or oils content agglomerate easily. Blinding (pegging) is plugging of screen openings with particles the same size as the openings of the sieve or by fine particles building up in the wire mesh to close off the openings. A cover is a stamped or a spun lid that tightly covers the sieve top to prevent the material from loss during sifting and mechanical agitation.
The experiment presents the understanding of how percentage finer of materials depends on the size of the opening as the data above show. It is clear that the relationship is decaying as the size of the aperture increases meaning that the bigger the hole size, the lower the finer percentage of the particles. Also in sieve analysis, apart from bulk density, tapped density is obtained by mechanically tapping the graduated cylinder with powder sample. The volume and mass readings are recorded until a change in further volume and mass is noted (Landers, Schmidt, & Seymour, 1945). Due to the interparticulate interactions affecting bulk properties of the powder are as well the interactions that interfere with the flow of the powder, the comparison of bulk and tapped densities yield the relative importance of that particular powder. The comparison is used as the index of the capability of the powder to flow (Compressibility Index/Hausner Ratio).
Compressibility index = and Hausner Ratio =
Where Vo is the unsettled apparent volume and Vf is the final tapped volume.
Compressibility index is, therefore, the measure of the propensity of the powder to be compressed. In a free-flowing powder, the interactions are of less importance, bulk and tapped densities are almost equal. In poor flowing materials, greater frequent interparticulate interactions occur. There is a greater difference between the bulk and tapped densities (Crawford, 1993).
Conclusion
The practical is aimed at measuring the bulk density of particles using sieve analysis method. The method is simply such that any person can perform with minimum supervision. The data collected is first hand. Generation of curve and calculation of values are simple. Arguably, the exercise was successful.
References
Astm Committee E-29 On Particle Size Measurement. (1985). Manual on test sieving methods. Philadelphia, Pa, American Society for Testing and Materials.
Crawford, R. J. (1993). Rotational molding. Shawbury, Shrewsbury, Shropshire, U.K., Rapra Technology Ltd.
Landers, W. S., Schmidt, L. D., & Seymour, W. (1945). Control of bulk densities in the coke ovens: studies on coal used at three byproduct-coke plants. Washington, D.C., U.S. Dept. of the Interior, Bureau of Mines.
Merkus, H. G., & Meesters, G. M. H. (2016). Production, handling and characterization of particulate materials. Available at: http://search.ebscohost.com/login.aspx?direct=true&scope=site&db=nlebk&db=nlabk&AN=1104020[retrieved on 14th March 2016]
