Limerock Bearing Ratio Technician Training Course

Transcription

1 Limerock Bearing Ratio Technician Training Course Module 3: Preparation August 2017 LBR Technician Release 10, Module This section will cover the preparation of materials for LBR testing. Preparation is covered by AASHTO T 180 section 8 (in method C), as well as FM 1-T 180 section 4. August

2 Preparation AASHTO T 180 section 8.2: Materials dried until friable upon trowel Oven maybe used for drying at a maximum of 140 F (60 C) Break up aggregations of materials to the natural size of the particle FM 1 T 180 section 4: Replace section of AASHTO T 180 with the following August 2017 LBR Technician Release 10, Module Preparation of materials for LBR testing is found in FM 1-T 180. Since LBR is a continuation of the modified Proctor method (FM 1-T 180) it make sense that the preparation method will follow that outline in the Proctor method. - Technicians with CTQP Aggregate Base Testing Technician qualification are qualified to complete the preparation and compaction portions of this training. Those without that qualification will not be qualified to perform those tasks. For those individuals without this qualification, the preparation and compaction portions of this training will be for information only to better understand the origin of LBR samples. - Natural Size of particles is defined as: the smallest size the aggregate can be broken down into with mechanical alteration of the particle (i.e. limerock, shell, sand, clay/silt). A 1 ball of clay is not in it s natural size. It should be broken up to a smaller size. Limerock (although it may be in a variety of size fractions) is generally in it s natural size because you cannot break it up any further without using mechanical tools (i.e. crushers, pulverizers, hammers, etc.). - For Base materials (as we will see) we will use a Jaw Crusher to reduce the materials to a smaller size (this is the only exception) August

3 FM 1 T 180 section 4.1: Preparation of Base Materials Pass entire sample through Jaw Crusher (maximum opening of 3/4 inch (19 mm), under tolerance inch (3.175 mm)). DO NOT SEPARATE COARSE MATERIAL BEFORE CRUSHING. Discard materials > 3/4 inch that remain after one crushing pass. Do not re crush any portion of the sample. Pass entire sample over #4 sieve and record mass retained on sieve and mass passing sieve. Keep plus #4 and minus #4 materials separate. There should not be ANY 3/4 inch or larger sized material in the sample after crushing and sieving. August 2017 LBR Technician Release 10, Module The ENTIRE sample should be passed through the jaw crusher in it s combined form. DO NOT separate the coarse materials from the fine before crushing. This changes the gradation of the total mass of the sample. - AFTER crushing ONCE, remove any particles still larger than ¾. This would include flat elongated pieces that slipped through the crusher sideways. - Sieve the entire sample over a #4 sieve. This can be done manually but it is recommended to use a sieve shaker. - BE SURE TO USE BREAKER SIEVES OR SIEVE INCREMENTALLY SO TO NOT OVERLOAD A SIEVE. - Keep the material retained on the #4 sieve separate from the material that passed the #4 sieve so they can be properly portioned into subsamples later. - All material should be smaller than ¾ once preparation is completed. Anything larger than ¾ after crushing should be removed and discarded after the one pass through the jaw crusher. August

4 Preparation of Base Materials Calculate percent retained/passing. Remember, when working with percent you need to mathematically express them correctly to get the right answer. Examples: 2% of 50 7% of % of X 50 = X 100 = X 300 = 36 August 2017 LBR Technician Release 10, Module Masses retained and passing #4 sieve will be converted into percentages (of the total sample after crushing). Those percentages will be used to proportion subsamples for compaction. - Convert a percentage to a decimal by moving the decimal place two digits to the left. - 2% % of 50 = 0.02 x 50 = 1-7% % of 100 = 0.07 x 100 = 7-12% = % of 300 = 0.12 x 300 = 36 August

5 Preparation of Base Materials Calculate percent retained/passing example: #4 retained = 84 lbs. + #4 passing = 43 lbs. Total mass = 127 lbs. 84 / 127 = 0.66 X 100 = 66% 43 / 127 = 0.34 X 100 = 34% What are the percentages for the portions on the plus #4 and the minus #4 assuming we are using 12 lb. samples? August 2017 LBR Technician Release 10, Module Add the masses retained and passing the #4 sieve to get the total sample mass. - Divide the mass retained on #4 sieve by the total sample mass to get the percentage (in decimal form). Multiply by 100 to get the percent! - Do the same for the mass passing the #4 sieve. - Your percentages should add up to 100%. (66% + 34% = 100%) August

6 Preparation of Base Materials Calculate the mass of each proportion for a 12 lb sample: #4 retained = 66% #4 passing = 34% 12 X 0.66 = 7.92 lbs. 12 X 0.43 = 4.08 lbs. Total mass = lbs. A 12 lb. sample should consist of: 7.92 lbs. of plus #4 material lbs. of minus #4 material. August 2017 LBR Technician Release 10, Module Using the percentages obtained on the previous slide, calculate the mass needed from both the plus #4 and minus #4 portions to get a 12.0 lb. subsample - By calculating the percentages and using them to portion smaller samples for testing you ensure the smaller portions are fully representative of the gradation of the sample (after crushing). - Since limerock is a relatively soft material it is likely to be broken down by roller compactor (or another mechanical compaction device) during construction. We crush materials before testing to simulate that construction impact so the test results are better representative of what materials will actually be compacted on the construction site. August

7 Preparation of Subgrade Materials FM 1 T 180 section 4.2: Pass entire sample over a 2 inch, 3/4 inch, and #4 (50 mm, 19 mm, 4.75 mm) sieve. Ensure all material is reduced to natural size of particles (i.e. no clay balls). Record mass retained on each sieve. Discard material on 2 inch sieve. Remove material on 3/4 inch sieve (and passing 2 inch sieve). Replace with equivalent amount of material in 3/4 to #4 size fraction. Record mass passing #4 sieve. Keep plus #4 and minus #4 materials separate. There should not be ANY 3/4 inch or larger sized material in the sample after removing and replacing with smaller size material. August 2017 LBR Technician Release 10, Module Subgrade preparation is similar to the base except you do not crush any materials, instead remove anything over 2 inches, and remove and replace anything between 2 inches and ¾ inches with smaller sized material. - As with base, once preparation of subgrade materials is completed there should be NO material ¾ or larger in the plus #4 sized portion. August

8 Preparation of Subgrade Materials Calculate percent retained/passing example: 2 retained = Discarded ¾ retained = 17 lbs. replaced #4 retained = 20 lbs. ( ) / 136 x 100% = 0.27 X 100 = 27% #4 passing = 99 lbs. 99 / 136 x 100% = 0.73 X 100 = 73% Total mass = 136 lbs. What are the percentages for the portions on the plus #4 and the minus #4 assuming we are using 5440 g. samples? August 2017 LBR Technician Release 10, Module Same as with base except you add the mass retained on the ¾ sieve to the mass retained on the #4 sieve. The physical material that is retained on the ¾ sieve is discarded. - 2 inch size material is not used and is discarded before recording any other size materials retained. August

9 Preparation of Subgrade Materials Calculate the mass of each proportion for a 5440 g. (12 lb.) sample: #4 retained = 27% #4 passing = 73% 5440 X 0.27 = g X 0.73 = g. Total mass = g. A 5440 g. sample should consist of: g. of plus #4 material g. of minus #4 material. August 2017 LBR Technician Release 10, Module Since we added the plus ¾ to the plus #4 inch, when you portion the samples you will be using only materials smaller than ¾ sized (plus #4 and minus #4) g = 5.44 kg = 12 lbs. August

10 FM 1 T 180 Note: Preparation of Materials If the material retained on the #4 (4.75 mm) sieve is seven percent (7.0 %) or less of the total sample mass, the material may be added back into the sample and thoroughly mixed with no correction. August 2017 LBR Technician Release 10, Module This Note applies to both base and subgrade materials. Materials added back in should be thoroughly mixed before portioning into subsamples. August

11 Preparation of Materials FM 1 T 180 section 4.3: For LBR testing, recombining plus #4 and minus #4 materials into a minimum of 5 portions weighing at least 12 lbs. (5.44 kg, g). Using gradation percentages obtained in sections 3.1 and 3.2. Keep extra material separated in case additional portions are needed to define compaction curve. FM 1 T 180 section 4.4 / AASHTO T 180 Note 6: Should be applied for LBR samples. Each portion shall be soaked in a container that is sealed to prevent moisture loss. Soaking times for materials based on AASHTO M 145 gradations (Table 1.) August 2017 LBR Technician Release 10, Module 3 11 To meet the requirements of compaction (per AASHTO T 180), a minimum of 5 portions is needed. You should have a compaction curve that is represented by two points under the optimum moisture, one at or near optimum, and two above optimum. This will also provide an LBR value that is well defined. Additional portions should be prepared in the event a point does not fall on the compaction curve, or the optimum is between two points and cannot be determined because of conditions in Section 7.2 for FM 5-515, A reported passing LBR shall not be extrapolated from a plot unless at least two points are above 90 percent of the minimum required specification value for the intended material use. Note 6 says to pull a moisture sample from the mixing bowl immediately before beginning compaction. This is vital to LBR testing since the compacted specimen will need to be retained for penetration testing and you will be unable to slice a moisture sample out of it. Table 1 represents the soaking time prior to compaction. If classification is unknown samples should be soaked a day before compaction so to meet the minimum soak time requirements (these are minimum soaking times). Be sure to soak materials in a container seals in the moisture. August

12 FM 1 T 180 Table 1 Preparation of Materials August 2017 LBR Technician Release 10, Module 3 12 Again, these are minimum soak times, so if the classification is unknown, err on the side of conservative and all portions to soak overnight (12 hours minimum). No harm is done letting sample soak longer. Not soaking them long enough can result in improper hydration of the aggregates and a lower than expected density. August

13 ANY QUESTIONS? August 2017 LBR Technician Release 10, Module 3 13 August