304.01 Description
This work is producing and placing one or more courses of a mixture of water, hydraulic cement, and aggregate or soil on a prepared surface in conformity with the lines, grades, and thicknesses established in the contract.
304.02 Materials
304.02.1 Cement
Furnish Type I or II Portland cement listed on the QPL, in accordance with Subsection
551.02.1 Blended hydraulic cement that conforms to one of the following may be substituted:
AASHTO M 240 Type IL, Type IP, or Type IP (MS) ASTM C1157 Type GU or Type MS Fly ash may be used to replace a maximum of 25% of the cement by weight. Furnish fly ash in accordance with AASHTO M 295, Class C requirements. Mixtures with fly ash must meet all of the requirements of cement treated base (CTB).
304.02.2 Water
Furnish water in accordance with Subsection 713.01 requirements.
304.02.3 Aggregate
Obtain aggregates from sources in accordance with Section 106 requirements to produce aggregates in accordance with Subsection 701.02.9 requirements. Stockpile aggregates in accordance with Subsection 303.03.
304.02.4 Blending Material
Blending material, consisting of selected natural or crushed mineral aggregate may be combined with the produced aggregate to meet gradation requirements. For fine aggregate passing the No. 40 (0.425 mm) sieve; the liquid limit may not exceed 30, and the plasticity index may not exceed 7, tested in accordance with AASHTO T 89 and AASHTO T 90.
304.02.5 Composition and Proportioning
Develop and submit a proposed CTB or Cement Treated Pulverized Base mix design for approval. Develop a mix design with cementitious materials content that: • Ensures a 7-day unconfined compressive strength of 500 – 1,500 psi (3,450 – 10,350 kPa) in accordance with MT 216 , and • Is a minimum of 4.5% the weight of the dry aggregate. Include the following items as part of the mix design submittal:
1.Cement and fly ash certifications.
2.Optimum moisture content and maximum density determined in accordance with AASHTO T 134.
3.Aggregate gradations determined in accordance with MT 202 ;
4.Soil-cement losses, moisture changes, and volume changes (swell and shrinkage) produced by the repeated wetting and drying of hardened soil-cement specimens determined by AASHTO T 135. 304 – CEMENT TREATED BASE 2020 EDITION V5.1 304-2
5.Soil-cement losses, moisture changes, and volume changes (swell and shrinkage) produced by the repeated freezing and thawing of hardened soil-cement specimens determined by AASHTO T 136. The maximum freeze/thaw weight loss is 14%.
6.7-Day compressive strength tests determined in accordance with MT 216.
7.Atterberg limits determined in accordance with AASHTO T 89 and AASHTO T 90; and
8.Sand equivalent determined in accordance with AASHTO T 176 alternate method No. 2 using stock solution with formaldehyde. Acceptance of the mix design will be based on a review of the submitted results for all the above testing procedures. Do not place CTB until the submitted mix design has been approved.
304.03 Construction Requirements
304.03.1 Aggregate Production, Testing, and Acceptance
A.General. Perform all work meeting the approved job-mix target values within the specified tolerances. Sample and test aggregates during production to control gradations.
B.Acceptance Sampling and Testing. The Project Manager will randomly select samples of the stockpiles taken by the Contractor and witnessed by an Inspector, for acceptance of the aggregate’s physical properties, excluding combined gradations. Aggregate gradation samples will be taken before hydraulic cement and water are added to the mixture. Provide aggregate samples as directed by the Project Manager using an aggregate sampling device, just before the aggregate enters the pug mill mixer. The approximate quantity represented by each sample is 1,500 tons (1,500 MT). Additional samples may be taken and tested. The quantity represented by 5 samples will represent a lot whenever production schedules and material continuity permit. The Project Manager may establish a lot consisting of a quantity represented by 3 to 7 consecutive samples when there are short production runs, significant material changes, or other unusual characteristics of the work.
C.Acceptance. CTB is evaluated for gradation requirements on a lot-by-lot basis. Acceptance is determined in accordance with Subsection 105.03.2 .
304.03.2 Weather Limitations
Do not mix or place CTB when the ambient temperature is below 40 °F (4 °C) or the ground temperature is below 35 °F (2 °C). Do not mix or place cement treated base when the weather forecast for the project site includes a predicted temperature of 25 °F or below for the following night. Do not incorporate frozen aggregate in the CTB or place on a frozen subgrade.
304.03.3 Subgrade Preparation
Prepare the subgrade in accordance with Section 203 . Trim the subgrade to the thickness tolerances in accordance with Subsection 304.03.4.
304.03.4 Mixing and Placing
Mix the CTB in a central plant. Proportion the aggregate and cement by weight. Water may be proportioned by weight or by volume. 2020 EDITION V5.1 CEMENT TREATED BASE – 304 304-3 Use weigh systems and meters accurate to within ± 0.5% of the total quantity batched and are equipped to indicate the total quantity of each ingredient batched between one-half and 10 hours. Calibrate the feed system before production mixing begins. Periodically verify the mix ingredient proportions from the weigh indicators. Produce CTB having a minimum of 4.5% cementious materials. Maintain cementious content to within ± 0.5% of the job mix target at any periodic check and within ± 0.3% for each day’s production. Mixing will be suspended until corrections are made if the cement content is not maintained within the above tolerances. Do not lower cement content during production that will result in freeze/thaw losses exceeding 14% based on mix design testing. Uniformly mix aggregate, cement, and water. Modify mix procedures when evidence of a non-uniform mix is identified. Place CTB in 4 to 8-inch (100 to 200 mm) compacted lifts. Place all lifts required to achieve full depth within 48 hours. Replace any partial depth section damaged prior to placement of successive lifts as directed by the Project Manager at Contractor expense. Keep the compacted material of previous lifts moist until placement of successive layers. Keeping lower layers moist or furnishing and applying curing seal to partial depth layers is incidental to the CTB.
304.03.5 Compaction
Compact the CTB to 98% of the maximum dry density within 2 hours of mixing. The moisture and density relationship are determined in accordance with AASHTO T 134 using samples taken from the aggregate stockpiles before starting mixing operations. If a moisture and density test varies from the running average (as determined in accordance with MT 216) during production, a new moisture-d ensity relationship will be determined. Moisture and density tests will be taken in accordance with MT 212 on the roadway approximately every 750 cubic yards (575 m3). Five tests will represent one lot of production. Remove and re-process any un-compacted sections where the weather or contractor operation has increased the average moisture content above optimum by more than 1%. Removed mix may be re-processed as aggregate for producing CTB. If the density of any section is less than or equal to 95% of the maximum dry density, 2 additional tests will be taken in that section and the average of all 3 test results will represent the section. The average density for the 3 tests must be at least the specified density, with none of the 3 tests less than 93% of the maximum dry density. Remove any section with an average density less than or equal to 95% of the maximum dry density. Removed mix may be re- processed as aggregate for producing cement treated base. CTB with densities between 95% and 98% is evaluated on a lot-by-lot basis in accordance with Subsection 105.03.2 .
304.03.6 Finishing
Shape the compacted surface to the specified lines, grades, and cross sections. Finish and compact to produce a smooth, dense surface free of compaction planes, cracks, irregularities, or loose material. Complete the surface finishing within 2 hours of compaction. Scarify and re-compact surface deformations in the base caused by equipment. Do not permit the moisture content to fall below the specified optimum during finishing. Apply water in a uniform fog spray. 304 – CEMENT TREATED BASE 2020 EDITION V5.1 304-4
304.03.7 Construction Joints
Construct straight vertical-faced transverse joints at the end of each day’s work and when CTB operations are delayed or stopped for more than 2 hours. Do not place additional material until the transverse joint has been approved by the Project Manager. Construct straight vertical faced longitudinal joints in compacted material that has been in place for more than one hour by cutting vertically approximately 3 inches (75 mm) from the existing edge. Dispose of the cut material in accordance with Subsection 304.03.12 . Moisten joints prior to placing adjacent CTB material. Repair all construction related damage to finished sections of the CTB at Contractor expense.
304.03.8 Protection and Curing
When the CTB is finished to grade, apply the specified bituminous curing seal at 0.15 to 0.25 gallons per square yard (0.68 to 1.13 L/m2). Keep the CTB surface moist between the final compaction and application of the curing seal. Apply the curing seal within 48 hours of finishing the cement treated base to grade. Before applying the curing seal, ensure the base surface is tightly knit, free of all loose material, and has sufficient moisture to prevent asphalt penetration. Apply the specified blotter material at approximately 15 pounds per square yard (8.2 kg/m2) when directed. The actual application rate of curing seal and blotter may be adjusted by the Project Manager. Remove CTB areas that have absorbed the curing seal, down to a hard, clean surface, within 24 hours of the curing seal application. Re-moisten and patch the area with approved cement treated material. Re-apply the curing seal as directed by the Project Manager. Apply the curing seal and blotter material in accordance with Section 409.
304.03.9 Curing Period
Do not perform any work on the CTB for 3 calendar days after the curing seal is applied. Do not place pavement on the CTB until the compressive strength reaches 400 psi (2760 kPa).
304.03.10 Maintenance
Maintain the finished surface and seal before placing the wearing course. Make all repairs or patches to the full depth of the base. Repair damage to the curing seal or cement treated base as directed by the Project Manager at the Contractor’s expense. Remove any loose material from the CTB surface prior to paving operations.
304.03.11 Surface Smoothness and Thickness Requirements
Finish CTB in accordance with Subsection 105.08 .
304.03.12 Use of Trimmed Material
CTB trimmings may be used for shoulder construction in lieu of aggregate, subject to the following:
1.The shoulder subgrade is prepared in accordance with Subsection 304.03.3.
2.Hardened material is reworked to the maximum size specified for aggregate placed on the shoulder.
3.The trim material does not exceed 25% of the shoulder aggregate depth.
4.The trim material is uniformly distributed in the shoulder area before spreading additional shoulder material. 2020 EDITION V5.1 CEMENT TREATED BASE – 304 304-5
304.03.13 Cement Treated Pulverized Base
When required by the Contract, process the existing plant mix surfacing with the existing base course and/or add crushed aggregate course and cementitious material as needed to restore the roadway section to the grade and dimensions shown in the Contract.
A.Requirements. Use equipment capable of pulverizing and mixing road sections to the depths shown in the plans. The equipment must be able to utilize a water spray or injection system capable of uniformly mixing the water, pulverized material, and cementitious material together. Meet the construction requirements of Section 304 with the following exceptions:
1.Begin production at the mix design targets for cementitious material and moisture content. Adjust cementitious material and moisture content as directed by the Project Manager to get compressive strengths between 500 and 1500 psi (35 and 104 KPa) as tested in accordance with MT 216. Changes in the amount of cementitious material used must be approved by the Project Manager.
2.Immediately suspend operations due to detrimental weather conditions (e.g., wind and/or rain).
3.Spread cementitious material uniformly on top of the pulverized surface. The spreading operation cannot exceed 1000 feet (300 m) ahead of the pulverizing operation.
4.Perform mixing of cementitious material and pulverized base with pulverizing equipment.
5.Shape the compacted surface to the specified lines, grades, and cross sections meeting the requirements of Subsection 105.08.
6.Do not perform any subsequent work on the completed roadway sections until accepted by the Project Manager. Water must be introduced at the mixing stage. Water added after mixing and prior to compaction will not be allowed. Complete compaction within 2 hours after re-mixing is complete.
B.Sequencing.
1.Pulverize the road to the specified depth and width as shown in the plans.
2.Uniformly place cementitious material across the width of the roadway section on top of the pulverized base.
3.Re-mix the pulverized sections and cementitious material with the pulverizing equipment.
4.Compact the re-mixed and completed sections.
5.Shape completed sections to the specified grade.
6.Apply the curing seal and blotter.
304.03.14 Testing and Acceptance of CTB
Samples for determining the compressive strength will be taken in accordance with MT 201 . Test method MT 216 will be used to mold cylinders for strength testing. The approximate quantity represented by each sample is 750 cubic yards (575 m3). Additional samples may be taken and tested. The compressive strength tests will be conducted at 7 days and the material represented will be accepted or rejected in accordance with Table 304-1. Any corrective action is at Contractor expense. The Contractor may make additional cylinders to determine strength gain and to maintain quality control. 304 – CEMENT TREATED BASE 2020 EDITION V5.1 304-6 TABLE 304-1 PAY FACTORS FOR CTB Lot Acceptance Strength, x psi (1 psi = 6.9 kPa) Strength, x (psi) Strength Pay factor, PF x > 2000 PF = 0.90 2000 ≥ x ≥ 500 PF = 1.0 500 > x ≥ 400 PF = 1.0 - 0.50 (500 - x) / 100 x < 400 PF = 0, remove and replace
304.04 Method of Measurement
304.04.1 Cement Treated Base
CTB is measured by the cubic yard (m3) of in-place volume. CTB placed outside the lines and grades shown in the contract or established by the Project Manager is not measured for payment. No measurement is made of the width required for forms or equipment operations. Gravel used in trimmings and lateral support sections outside the planned typical section dimensions is not measured for payment. Blending material is not measured for payment.
304.04.2 Curing Seal
Curing seal is measured by the gallon (L) or by the ton (MT) in accordance with Subsection
409.04 1.
304.04.3 Blotter Material
Blotter material is measured by the square yard (m2) based on the length and width of CTB placed and accepted.
304.04.4 Cement Treated Pulverized Base
Cement Treated Pulverized Base is measured by the square yard (m2) based on the designated width shown in the plans. Crushed Aggregate Course is measured by the cubic yard (m3) as a predetermined pay quantity as described elsewhere in this contract. Portland cement is measured by the ton (MT) in accordance with Subsection 109.01. Fly ash, if included, is measured by the ton (MT) and the quantity added to the measured quantity of Portland cement.
304.05 Basis of Payment
304.05.1 Cement Treated Base
Payment for the completed and accepted quantities is made under the following: Pay Item Pay Unit Blotter Material Square Yard (m2) Cement Treated Base Cubic Yard (m3) Curing Seal Gallon (L) or Ton (MT) No separate payment will be made for cement, fly ash, blending material or surface preparation. Include the cost in the unit price bid for CTB. 2020 EDITION V5.1 CEMENT TREATED BASE – 304 304-7
304.05.2 Cement Treated Pulverized Base
Payment for the completed and accepted quantities is made under the following: Pay Item Pay Unit Blotter Material Square Yard (m2) Cement Treated Pulverized Base Square Yard (m3) Cement Ton (metric ton) Crushed Aggregate Course Cubic Yard (cubic meter) Curing Seal Gallon (L) or Ton (MT) No separate payment will be made for blending material or surface preparation. Include the cost in the unit price bid for CTPB.
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Source: Standard Specifications for Road and Bridge Construction, 2020 (v5.1) Edition. Pages 217–224 of 611. View official source ↗