306 – CEMENT TREATED BASE
300-19 If the mix is stiff (can be slip-form ed), determine the standard density by averaging the 3 most recent field
molded densities using plant mixed base material. Compact one standard mold (using plant mixed material with the proper moisture content) for each day’s operation as specified in KT-37. If the mix is fluid (requires forming), determine the Standard Dry Density by averaging the 3 most recent consolidated unit weight test results (K T-20). It will be necessary to convert the unit weight (wet density) into a standard dry density which also requires the percent of moisture (KT-11 (4) ) to be known. Use Equation 1 to determine the standard dry density. Equation 1: 100]) / [%Moisture (1 y Wet Densitty Dry Densi Standard Determine the density of the CTB within 1 day of the compaction operations. The Engineer may verify the Contractor’s density test results by conducting density tests at random. If the comparison is not favorable, the DME will investigate to determine the cause and may suspend production until corrective action is taken.
e.Trimming and Finishing the CTB. Trim and recompact the CTB within 2½ hours of the time the water and cementing agent is added to the aggregate. Trim and compact the CTB to the grades, lines and typi cal cross sections shown in the Contract Documents. Dress the edge slopes and joints between sections. Use automatic grade control equipm ent to trim the surface of the CTB to line grade and cross section. Keep the surface of the CTB moist during all finishing operations. Perform the finishing and compac ting operations to produce a smooth, dense surface, free of surface compaction planes, cracks, ridges or loose material. If required, lightly scarify the surface of the CTB to l oosen any imprints left by the trimming and compacting equipment. Recompact the surface of the CTB. At the end of each day’s operations, construct a straight transverse construction joint by cutting back into the completed work to form a vertical face. Place a protectiv e covering of earth on the ne wly constructed CTB a distance back of the joint for turning of equipment used on the following day’s work. Upon satisfactory performance, the Engineer may approve the use of equipment that combines the placing, compacting and finishing operations.
f.Protection and Curing. Keep the surface of the CTB moist until the curing material is applied. Apply the curing material immediately after completing the trimming and finishing. Protect the CTB against the loss of moisture for a curing period of 7 days (unless the Contractor’s mix design test results justify a different curing period). Protect the CTB against freezing during the curing period. Apply a wax-based liquid membrane-forming compound for the curing material. The minimum application rate for wax-based liquid membrane-forming compound is 0.12 ga llons per square yard. Use an enclosed spray system that minimizes wind influence and obtains the proper applicat ion rate. Keep all traffic and construction equipment off the CTB. The only exception is the equipment used to appl y the curing material. Cover the surface and edges of the CTB with a complete, uniform coverage. Us e a hand sprayer in inaccessible areas. If the wax-based liquid membrane-forming compound will be in place for more than 30 days, reapply a single coat at the single application rate within 7 days of placing the pavement. At locations where it is necessary to carry traffic acro ss the CTB, place a layer (8 inches or greater, compacted depth) of stable earth (sand-clay) over the CTB. The Contractor may place portland cement concrete pavement (PCCP) on the CTB after a minimum of 24 hours, provided all traffic and construction equipment is kept off the CTB. The Contractor assumes the risk of 7-day compressive strength requirements when PCCP is placed early. To promote cracking through the full depth of the base, score or cut the finished CTB surface to coincide with the pavement joint locations, in a parallel manner and within 1 foot: if the 7-day compressive strength exceeds 1600 psi. (Note: This does not apply if the CTB has developed cracks at regular intervals prior to placing the PCCP.) if the Contractor opts to place the PCCP over th e CTB before the 7-day compressive strength is determined. The Engineer may waive this requirement when the Contractor’s control charts for CTB shows a history that the 7-day compressive strength is below 1600 psi. 306 – CEMENT TREATED BASE
300-20 g. Compressive Strength Determination. Using random numbers, select and obtain sampled material at the
plant. Make and cure compression test specimens to represent each sublot. Make and cure compression test specimens, and determine the 7-day compressive strength of the CTB according to Part V. Sulfur cap compression test specimens in accordance with AASHTO T 2 31. When additional test specimens are taken for early determination of the compressive strength, the specimens are for information only. Perform the 7-day compressive strength testing. Maintain records of all sampling and testing. The Engineer will witness all compressive strength tests and initial the Contractor’s documentation. A percent within limits ( PWL ) analysis shall be made on a lot-by-lot basis and shall be based on Contractor quality control test results on all quality control samples representing the lot of the completed CTB. The PWL result shall be determined as specified under Computation of Pay Factor. Compute the pay adjustment as shown in Equation 2. It shall be based on the compressive strength values within each lot and the lower specification limits (LSL). KDOT will use a spreadsheet program to calculate pay adjustments for compressive strength and to compare the Contractor’s QC and KDOT’s verification test results. If the comparison fails, KDOT’s value will be used to calculate the pay adjustment for that lot. The lot comparison is based on KDOT’s verification result falling within the Contractor’s mean, plus or minus 2 times th e Contractor’s sample standard deviation. When the Contractor’s sample standard deviation is less than 260 psi, then 260 psi shall be used for the sample standard deviation during lot comparison with KDOT’s value. When there are 3 or more tests in a lot and when the lot comparison between Contractor and KDOT tests pass, the Contractor’s actual standard deviation will be used to calculate the compressive strength pay factor. When reques ted, KDOT will provide a copy of this program to the Contractor. It is the Contractor’s responsibility to obtain the software required to run this program. Values computed using equations referenced in this specification may vary slightly from the spreadsheet values due to the rounding of numbers. In such cases , the numbers computed by the spreadsheet shall take precedence. A typical lot is defined as a normal day’s placement. At the beginning of the project, estimate the quantity to be placed during a normal day and submit to the Engineer for approval. Once approved, break the quantity into 4 equal parts (each part represents a sublot). Determine a random location for sampling w ithin each sublot. When the total quantity for the day deviates from expectations, adjust the number of sublots based on TABLE 306-1 . TABLE 306-1: SUBLOT BREAKDOWN OF A NORMAL DAY’S PRODUCTION Number of Sublots % of Daily Quantity 4 75-115 3 50-74 2 25-49 1 1-24 Adjust the quantity of the last sublot to accommodate any minor chan ges in production, and adjust the random location for sampling based on the size of the sublot. When there is only 1 test in a lot, the pay factor will be automatically calculated by the KDOT spreadsheet using a sample standard deviation of 260 psi and n of 3. When there are 2 tests in a lot, the pay factor will be calculated by the KDOT spreadsheet using a spreadsheet calculated standard deviation and n of 3. When there are 3 or 4 tests, the lot stands on its own. Regardless of the number of Contractor tests in a lot, the lot comparison between Contractor and KDOT tests will apply. When the quantity exceeds 115% of the normal daily quantity, in crease the number of sublots and restrict the 4 th sublot to a maximum of 100% of the established normal daily quantity. Each sublot added may have a maximum of 25% of the normal daily quantity. Compute the sample standard deviation as shown in Section 5.2.1-Statistics, Part V. Calculate the Compressive Strength Quality Indices ( QL) for each lot as shown in Section 5.2.1-Statistics, Part V. Use the following definitions, and round to the nearest hundredth. Where: X is the average measured compressive streng th of all QC samples representing a lot, rounded to 1.0 psi. LSL is the lower specification limit for compressive strength, defined as 650 psi. S is the sample standard deviation of the compressive strength of all QC samples representing a lot, rounded to 0.1 psi.
Source: Kansas Standard Specifications for State Road and Bridge Construction, 2015 Edition. Pages 165–166 of 978.