Analysis Exposition about the Various Soil and Concrete Tests - Case Study Example

Name : xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Tutor :xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Title : Soil and Concrete Test Report Institution : xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Date :xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx @ 2011 Introduction Part 1 – Introduction This report gives an elaborate exposition about the various soil and concrete tests that can be done on a site and building material set a side for making a multi storey building. The place of construction is a brown field site with man made fill and clay layers. Therefore the report is meant to provide the necessary advice for construction on such soil together with the appropriate tests (Wesley 2009 pp. 575-58).This report was compiled in January 2011 by a firm contracted to survey the site and establish the right soil and concrete tests for the construction. Part 2 – Soils Analysis Atterburg Limits This is a test performed to reveal the liquid and plastic limits of fine grained soil. the equipment used include a porcelain or evaporation dish, liquid limit device, a flat grooving tool, gage, moisture cans, glass plate, spatula, balance, wash bottle full of distilled water and an oven for drying at 105°C.setting (Laurence D. Wesley 2009 pp. 575-58). Liquid limit Testing procedure Three quarters of the soil is placed in a porcelain dish. The assumption taken at this point is that the soil has gone through a number 4 sieve, and then air dried and pulverized. The soil is mixed well with a little distilled water to make it into a uniformly smooth paste. The dish is then covered with cellophane to retain the moisture. Next 4 empty cans of moisture are weight plus the lids (Wesley 2009 pp. 575-58.).Their weights and numbers are noted down in a data sheet. The apparatus for the liquid limit is then adjusted through a check on the drop height of the cup. There is a point in the cup that touches the base. This should attain a 10mm height. The block at the grooving tool’s end has a height of 10mm and should serve as the gage. The cup must drop 2 times every second when the right rate of rotating the crank has been determined through practice. A part of the mixed soil will then be put inside the liquid limit equipment cup at the place the cup touches the base. The soil is squeezed down then put in the cup at 10mm depth (Wesley 2009 pp. 575-58). With the grooving tool in a perpendicular position a groove is cut in cup’s centre. No soil should be under the cup and on the apparatus below it. The crank it turned at 2 drops every second and the drops counted. This is the amount of drops taken to bring together the two portions of soil at the groove’s bottom. In case the drops are more than 50 the next step is avoided and the amount of drops not recorded. If less than 50 they are recorded (Wesley 2009 pp. 575-58.). A sample should then be taken on a spatula at all points across the soil pat. The soil is placed in a moisture can, covered then weighed. The lid is removed and the can put in an oven for about 16 hours. The remaining soil in the cup is placed in a porcelain dish before the cup is cleaned and dried. The soil is then mixed in the porcelain and added with little distilled water. A repeat of the 3 last steps is taken two times. One attempt will need 25-35 drops, another 20-30 and the last 15-25 drops. The water content of each trial is then determined Laurence D. Wesley, (2009). Plastic limit testing procedure The remaining cans are weighed together with lids and the weights recorded. Distilled water should be added to the left quarter of the soil sample. The sample of soil should be formed into a mass ellipsoidal in shape then rolled between the glass plate and palm. The mass is again rolled into a thread by use of pressure of 90 strokes a minute. The thread is then deformed to reach 3.2 mm diameter (Laurence D. Wesley 2009 pp. 575-58.). When the right thread diameter is reached it is broken into many pieces. These pieces should be kneaded into masses with ellipsoidal shapes and re-rolled repetitively until it crumbles and cannot be rolled to a thread with 3.2 mm diameter. The crumbled thread portions are then gathered and the soil placed in moisture can and covered. In case the can has less than 6 grams some soil is added. The moisture can with the soil is weighed and its mass recorded, the lid is removed and the can put in the oven for 16 hours. The last 3 steps are then repeated 2 times (Laurence D. Wesley 2009 pp. 575-58.) The water content from all the trials is determined. “The test is done in order to get the consolidated drained shear strength of a sandy to silty soil.” shear strength is a crucial property in soil engineering. The reason is structures depend on the shearing resistance of the soil. Shear strength is necessary in engineering like the determination of slopes’ stability. It is also important in getting the bearing capacity of foundations as well as the calculation of pressure of soil on retaining walls (Laurence D. Wesley 2009). Fig. 1: The shear box, Laurence D. Wesley, (2009) Fig 2: The shear box, Laurence D. Wesley, (2009) Testing procedure The soil mass in the pan is weighed. The height and diameter of shear box is weighed then the diameter computed in millimeters. The shear box is then assembled then placed in the shear device. A filter paper and porous stone is placed in the shear box. The sand should be put in the shear box and the top leveled. On the sand to there should be placed a top plate with a ball, porous stone and filter paper. The alignment screws are then removed from the shear box (Laurence D. Wesley 2009 pp. 575-58.). The gap between the shear box halves is then opened to 0.025 inches by use of gap screws. The pan of soil is then weighed and the mass of soil used is computed. The assembling of the direct shear device should then be completed and the three gauges initialized to zero Laurence D. Wesley (2009). Next the vertical load is set then the bladder valve is closed. The load should then be applied to the soil specimen when the toggle switch is raised. The motor should be started with a chosen speed in order to have a selected constant rate of shearing. ‘The shear gage load readings and the horizontal displacement gauge should be taken and recorded.’ The readings should be taken continuously until the peak of the horizontal shear load is reached or the diameter of the horizontal displacement gets to 15% Laurence D. Wesley, (2009). Fig 3: Shear box in use Laurence D. Wesley, (2009) Tri-axial compression test The first thing is to put the specimen inside the chamber then the tri-axial chamber is assembled. The piston is aligned with the cap by bringing the axial load piston to touch the specimen cap a number of times. A deviator stress of over 0.5% of the compressive strength should not be applied to the specimen. If this is to happen then the piston is fastened in position over the cap of specimen upon checking the alignment and seating. It should remain locked until when chamber pressure is applied. The chamber should then be put in the in its place inside the axial loading equipment (Wesley 2009 pp. 575-58.). Fig 4: Tri-axial compression test apparatus Laurence D. Wesley, (2009) Carefully align the axial loading device, the axial load-measuring device, and the tri-axial chamber to prevent the application of a lateral force to the piston during testing. The device to measure and maintain pressure is then attached. Next the chamber is filled with a confining fluid to a certain level (Wesley 2009 pp. 575-58).The device for measuring and maintaining pressure is adjusted until the right pressure in the chamber is attained and then pressure is applied to the chamber fluid. In case of the device measuring the axial load being out of the tri-axial chamber then an upward force is produced in the chamber to the piston which reacts on the axial loading equipment Laurence D. In such cases the test should be started when the piston is over the specimen cap and also before they come into contact with each other. The upward thrust and piston friction is measured and the axial load corrected. Otherwise the device for measuring the axial load is adjusted so that it can compensate for the thrust and friction load. If the device for measuring the axial load is within the chamber correcting or compensating for the upward force that acts on the piston friction or axial loading device is unnecessary. In both cases the reading on the deformation indicator should be recorded when the specimen cap is in contact with the piston Laurence D. Wesley, (2009). Fig: 5 Tri-axial compression apparatus in use Laurence D. Wesley, (2009) At about 10 minutes after chamber pressure has been applied start applying the axial load in order to produce axial strain at a rate of about:1% per minute for plastic materials and 0.3% per minute for brittle materials that achieve maximum deviator stress at about 3 - 6% strain. The deformation and load values should be recorded at a strain of about 0.1, 0.2, 0.3, 0.4, and 0.5% (Wesley 2009 pp. 575-58). Recording should also be done at increments of approximately 0.5 % strain, 3% then every 1%. Deformation and load can be recorded at 2% strain increments for strains of over 10%. Adequate readings that can give the stress-strain curve should be taken. This may require frequent readings in initial stages of test Laurence D. Wesley, (2009). The loading must be carried on to a strain of 15%. When deviator stress peaks and drops 20% then loading can stop. Otherwise it can be stopped when a 55 axial strain is reached after the deviator stress peaks Laurence D. Wesley, (2009). The shear box test is a better option to the others for soil testing because of its elaborate and easy procedure. It is bound to produce more accurate results due to its simple and easy to follow instructions. Part 3- Wet and Hard Concrete Testing Wet stage concrete testing Concrete slump test is useful in measuring the workability of concrete in a consistent manner. Workability is crucial since the concrete will flow and fill the form well without leaving voids on the face of the form and totally surrounds the rebar to form bonds. Non destructive test for hardened concrete The real strength of a structure may need to be tested. The concrete and the reinforcing bars will therefore be tested for strength. The non destructive quality test is important for testing quality, determination of form removal time and assessment of the quality of concrete structures. ‘There are various methods used for measuring various qualities. Surface hardness methods require that the surface be impacted using a mass and then the size of the resultant indention be measured Mohan Malhotra and Nicholas J. Carino 2004). Its accuracy is 20-30%. Rebound hardness test is the commonest non destructive method. In this method a steel hammer is hardened then impacted on concrete using a spring. The rebound is then measured. The outcome depends on content of moisture, surface finish, rigidity, and temperature and impact direction. It is good in testing concrete uniformity. Penetration resistance measures the concrete’s resistance. A steel probe is driven and the amount of energy used is measured (Malhotra and Nicholas J.2004 pp.561-565). Another test is the pull out test which measures the force needed to pull out a steel insert embedded inside the concrete at the time of casting. The ultra pulse velocity depends on the relationship of sound with the elasticity modulus. The equipment has an accuracy of + 1%. The results can be affected by the position taken by testing equipment. The test will be affected by smoothness of surface, pulse’s travel path, moisture content, concrete age, and steel bars present (Carino 2004 561-565). Rebound hammer A rebound hammer’s plunger is pressed on the concrete’s surface. A constant energy mass controlled by a spring is used to hit the surface of the concrete as it bounces back. The level of rebound which determines the hardness of the surface is reflected on a marked scale. The value recorded is noted as rebound index. When concrete has low stiffness and strength it absorbs a lot of energy and gives out a low value of rebound (Carino 2004 561 565). Rebound hammer in operation, Mohan Malhotra and Nicholas J. Carino (2004) This test helps in determination of concrete strength depending on the hardness at or near its surface. The hammer is calibrated periodically by use of standard anvil. If a construction with concrete is new the calibration is done on concrete test cubes (Carino 2004 561-565). Procedure Before a test starts, testing should be done on the rebound hammer with the test anvil, to get reliable results, for which the manufacturer of the rebound hammer indicates the range of readings on the anvil suitable for different types of rebound hammer.” Light pressure should be applied on the plunger to remove it from its locked position so that it can take the position needed for testing (Carino 2004 561-565). The plunger should then be placed against the concrete surface with the instrument in a perpendicular position to the surface Mohan Malhotra and Nicholas J. Carino (2004). A gradually growing pressure is applied till an impaction of the hammer is observed. In the process of plunger depression the button must not be touched. If it proves hard to note the reading of the rebound the button can be pressed after impact. About 15 readings should be taken on overage (Carino 2004 561-565).The rebound hammer method for testing hardened concrete is easy to follow. It is therefore easy to attain the desired results when the procedure is taken carefully. It is therefore the best method to apply in testing the hardened concrete. Conclusion In conclusion both soil testing and concrete testing are necessary for the construction to continue successfully. The soils need to be analyzed because the place a brown field site and the soils are made of man made fill and clay layers which are not suitable for construction of a storey building. The concrete tests should also be carried out appropriately since mixing will be done on the site. Both wet and hard concrete tests should be performed (Carino 2004 561-565).The recommended test for wet concrete is the Slump test to BS EN 12350 – 2:2000 while the hard concrete can best be tested using the rebound hammer method. References Neville, A. M., Properties of Concrete, 5th Edition, Addison-Wesley Longman, UK, 1995, 844 pp.245 V. Mohan Malhotra and Nicholas J. (2004) Handbook on Nondestructive Testing of Concrete, New York: CRC Press LLC,ch. 3. 561-565. K. W. Nasser, "New and Simple Tester for Slump of Concrete", ACI Journal, Oct. 1976, pp. 561-565. Nasser K (1994) A New Method for Evaluation of the Slump of Concrete", ACI Journal Special Publication, SP 144-27pp. 575-58 Laurence D. Wesley (2009).Fundamentals of Soil Mechanics for Sedimentary and Residual Soils. Amazon Publishers New York City. pp. 575-58. Read More