27 CEMENT TREATED BASES
27-1 General
27-1.01 General
27-1.01A Summary
Section 27 -1 includes general specifications for placing cement treated base .
27-1.01B Definitions
coarse aggregate: Aggregate retained on a no. 4 sieve. fine aggregate: Aggregate passing a no. 4 sieve.
27-1.01C Submittals
Submit evidence of the cost of cement used for an ordered increase or decrease. Submit cement treated base QC plan.
27-1.01D Quality Assurance
27-1.01D(1) General
27-1.01D(1)(a) General
After the CTB has been spread on the subgrade and before initial compaction, the cement content of the completed mixture of CTB must not vary from the spe cified cement content by more than 0.6 percent of the weight of the dry aggregate when tested under California Test 338. For Class A CTB, compaction is tested under California Test 312 or 231. The relative compaction of CTB must be at least 95 percent. Eac h layer of CTB may be tested for compaction, or all layers may be tested together at the option the Engineer. If all layers are tested together, you are not relieved of the responsibility to achieve the required compaction in each layer placed.
27-1.01D(1) (b) Aggregate
When tested under California Test 301, aggregate for Class B CTB must have (1) an R -value of at least 60 before mixing with cement and (2) an R -value of at least 80 when aggregate is mixed with an amount of cement that does not exceed 2.5 pe rcent by weight of the dry aggregate. Before sand equivalent testing, aggregate samples must not be treated with lime, cement, or chemicals. If the aggregate gradation test results, the sand equivalent test results, or both comply with contract compliance requirements but not operating range requirements, you may continue placing CTB for the remainder of the workday. Do not place additional CTB until you demonstrate to the Engineer that the CTB to be placed complies with the operating range requirements. If the aggregate gradation test results, sand equivalent test results, or both do not comply with contract compliance requirements, remove the CTB or request a payment deduction. If your request is authorized, $2.50/cu yd is deducted. If CTB is paid for by w eight, the Engineer converts tons to cubic yards for the purpose of reducing payment for noncompliant CTB left in place. An aggregate gradation and a sand equivalent test represents up to (1) 500 cu yd or (2) 1 day's production if less than 500 cu yd.
27-1.01D(1)(c) Road-Mixed Cement Treated Base Moisture Content
Just before initial compaction the moisture content of the completed mixture must be at least the optimum moisture content less 1 percent. The moisture content is determined under California Test 226 and optimum moisture content is determined under California Test 312.
27-1.01D(1)( d) Plant-Mixed Cement Treated Base Moisture Content
At the point of delivery to the work, the moisture content of the completed mixture must be at least the optimum mois ture content less 1 percent. The moisture content is determined under California Test 226 and optimum moisture content under California Test 312. SECTION 27 CEMENT TREATED BASE S
27-1.01D(2) Quality Control
27-1.01D(2)(a) General
Reserved
27-1.01D(2)(b) Quality Control Plan
Reserved
27-1.01D(2)(c) Qualifications
Reserved
27-1.01D(2)(d) Quality Control Testing
CTB quality control must include testing the quality characteristics at the frequencies shown in the following table: QC Testing Frequencies Quality characteristic Test method Sampling location Minimum frequency Aggregate gradation California Test 202 modified Stockpiles, plant, transportation units, windrow, or roadway 1 per 500 cu yd but at least one per day of placement Sand equivalent California Test 217 Stockpiles, plant, transportation units, windrow, or roadway R-valuea California Test 301 Stockpiles, plant, transportation units, windrows, or roadway 1 test before starting work and every 2 ,000 cu yd thereafterb Optimum moisture content California Test 312 Plant, transportation units, windrow, or roadway 1 per day of placement Moisture content California Test 226 Roadway 1 per 500 cu yd but at least one per day of placement Cement content California Test 338 Windrows or roadway 1 per 1 ,000 cu yd but at least one per day of placement Relative compaction California Test 312 or 231 Roadway 1 per 2 ,000 sq yd but at least one per day of placement Compressive strengthc California Test 312 Windrow or roadways 1 per day of placement aR-value is required for Class B CTB only . bAdditional R -value frequency testing will not be required while the average of 4 consecutive sand equivalent tests is 4 or more above the specified operating range value. cCompressive strength is required for Clas s A CTB only when specified .
27-1.01D(3) Department Acceptance
The Department 's acceptance testing includes testing the CTB quality characteristics shown in the following table: SECTION 27 CEMENT TREATED BASE S CTB Requirements for Acceptance Quality characteristic Test method Aggregate gradation California Test 202 modified Sand equivalent California Test 217 R-valuea California Test 301 Optimum moisture content California Test 312 Moisture content California Test 226 Cement content California Test 338 Relative compaction California Test 312 or 231 Compressive strengthb California Test 312 aR-value is required for Class B CTB only . bCompressive strength is required for Class A CTB only when specified . The Engineer takes samples for aggregate gradation and sand equivalent from any of the following locations:
1.Plant
2.Truck
3.Windrow, for road -mixed only
4.Roadbed, for road -mixed only
27-1.02 Materials
Cement must comply with section 90 -1.02B(2). Asphaltic emulsion curing seal must be Gra de SS -1 or CSS -1. Aggregate must be clean and free from deleterious substances. Aggregate must be within the percentage passing limits for the sieve sizes shown in the following table: Aggregate Gradationa Sieve size Percentage passing Class A Class B Operating range Contract compliance Operating range Contract compliance 3" -- -- 100 100 2-1/2" -- -- 90–100 87–100 1" 100 100 -- -- 3/4" 90–100 87–100 -- -- No. 4 40–70 35–75 35–70 28–77 No. 30 12–40 7–45 -- -- No. 200 3–15 0–19 3–20 0–24 aCalifornia Test 202 is modified by California Test 105 if the difference in specific gravity between the coarse and fine portions of the aggregate or between the blends of different aggregates is 0.2 or mo re. The aggregate quality characteristics must comply with the requirements shown in the following table: Aggregate Quality Characteristics Quality characteristic Requirement California Test Operating range Contract compliance Sand equivalent (min) 217 21 18 Compressive strength (min, psi)a 312 -- 750 aFor Class A CTB only . Water must comply with section 90 -1.02D. SECTION 27 CEMENT TREATED BASE S
27-1.03 Construction
27-1.03A General
Reserved
27-1.03B Subgrade
Immediately before spreading CTB, the subgrade , must comply with the specified compaction and elevation tolerance for the material involved and be free from loose or extraneous material.
27-1.03C Depositing Aggregate and Mixi ng Road -Mixed Cement Treated Base
27-1.03C(1) General
Reserved
27-1.03C(2) Depositing Aggregate
For road -mixed CTB, deposit enough untreated aggregate on the roadbed to compl y with the depth shown, the depth specifications in section 27 -1.03E, and the grade tolerance specifications in section 27 - 1.03F. Do not mix the aggregate to be treated with roadbed material that is not to be treated. If 2 or more nominal sizes of coarse a nd fine aggregate are deposited on the grade, accurately and uniformly meter each nominal size as it is deposited. Before adding cement, mix the deposited aggregate as many times as necessary to produce a uniform mixture that complies with the specified gr adation. For mixing done from windrows, shape the windrow to a uniform cross section with a sizing device. Do not use a motor grader unless equipped with a sizing device. Aggregate mixed with cement and water before delivery on the roadbed must be deposite d and spread on the prepared subgrade under section 27 -1.03E.
27-1.03C(3) Mixing
Mix road -mixed CTB by either of the following methods:
1.Road -mixed method on the roadbed or at a location off the roadbed
2.Plant -mixed method under section 27 -1.03D except a Class 2 batch plant may be used Use mechanical equipment that uniformly distributes cement and water. Whenever cement is added to windrowed aggregates, flatten or slightly trench the top of the windrow to receive ce ment. If cross -shaft mixers are used, spread cement uniformly over the entire surface of the deposited aggregate. Do not spread cement on aggregate more than 4 hours before the road -mixing operation. The road -mixing machine must introduce water at the time of mixing with a metering device or other authorized methods. Supply the correct quantity of water by means of controls that will produce a completed mixture with a uniform moisture content. Correct water leaks from equipment or excessive amounts of water during application before proceeding. For CTB spread and compacted in 2 or more layers, mix material for each layer separately. If more than 1 pass of the road -mixing machine is required to obtain a unifo rm mixture, at least 1 pass must be made before adding water to the material. Regulate the length of road -mixed sections to comply with section 27 -1.03G.
27-1.03D Proportioning and Mixing Plant -Mixed Cement Treated Base
27-1.03D(1) General
Mix plant -mixe d CTB at a central mixing plant by either of the following:
1.Batch type mixing using either of the following: 1.1. Revolving blade 1.2. Rotary drum mixers
2.Continuous type mixing SECTION 27 CEMENT TREATED BASE S In all mixing plants, proportion aggregate, cement, and water by weight or volume. The Engineer must be able to readily verify the amount of water per batch or the flow rate for continuous mixing. The time of the addition of water o r the points where it is introduced into the mixer must be authorized. In all mixing plants, add cement in such a manner that it will be uniformly distributed throughout the aggregates during the mixing operation.
27-1.03D(2) Batch Mixing
If different agg regate sizes are used, the aggregates must be blended as they enter the mixer. Weigh cement for each batch on scales that are separate and distinct from the aggregate batching scales. Each cement scale graduation must be approximately 1/1 ,000 of the total scale capacity. The total capacity of the scale must not exceed the capacity of the smallest commercially available scale that is capable of weighing twice the amount of cement when the plant is operated at full capacity. No scale is required to have a tot al capacity less than 1 ,000 lb or graduations less than 1 lb. Mixing plants must be Class 1 unless Class 2 is specified. Class 1 batch mixing plants must be equipped with:
1.Enough paddles arranged to produce a uniform mixture
2.Mixer platform large enou gh to provide safe and convenient access to the mixer and other equipment
3.Timing device accurate to within 2 seconds that indicates the end of the mixing period by an audible or visual signal For Class 1 mixing plants, the mixing period begins after al l the ingredients are in the mixer and ends when the mixer is half empty. Mix until a homogeneous mixture with uniformly distributed and properly coated aggregates, that do not change appearance, is produced and testing indicates the cement content consist ently complies with section 27 -1.01D(1). The mixing period must not be less than 30 seconds. Class 1 mixing plants must be equipped with automatic sampling devices actuated by operation of a push button or similar device. When a sampling device is actuated it must simultaneously deliver a representative sample of each size of aggregate or the combined aggregates to adequately sized receptacles. Each sample must weigh from 55 to 65 lb. Locate receptacles safely clear of plant operations with convenient acces s. Class 2 mixing plants must comply with the specifications for a Class 1 mixing plant except (1) a timing device to signal the end of mixing is not required and (2) automatic sampling devices are not required. Class 2 mixing plants must provide safe and convenient access to sampling facilities for obtaining representative samples of aggregate and the mixture.
27-1.03D(3) Continuous Mixing
Draw aggregate from storage facilities by a feeder or feeders that continuously supply the correct amount of aggregat e in proportion to cement. If different aggregate sizes are used, arrange feeders such that the proportion of each aggregate size can be separately adjusted. Storage facilities for fine aggregate must be equipped with a device that effectively vibrates the side walls of the feeder preventing hang -up of material while the plant is operating. The plant must be equipped with a control system that automatically closes down the plant when the material in any storage facility approaches the strike -off capacity of the feed gate. The plant must not be operated unless the automatic control system is in good working condition. The aggregate feeder must be mechanically or electrically driven. Mechanically driven feeders must be directly connected to the cement feeder d rive. The drive shaft on the feeder must be equipped with a revolution counter that reads to 1/10 revolution with sufficient capacity to register the total number of revolutions in a day's run. Electrically driven feeders must be actuated by the same circu it that provides power to the cement feeder motor. For electric power obtained from a noncommercial source, a frequency meter must be connected SECTION 27 CEMENT TREATED BASE S to the cement feeder motor circuit. The meter must have a minimum range from 57 to 63 Hz and must be graduated i n 1 Hz increments or less. A voltage regulating transformer must be installed in the circuit of vibratory aggregate feeders. The transformer must maintain the voltage to the feeder motors to within 1 percent of their nameplate voltage. A voltmeter must be connected to the secondary of the voltage regulating transformer. The meter must have a range from -10 to +10 percent of the motor nameplate voltage and must be graduated in increments of 1 percent of the nameplate voltage, or less. For plants equipped with electrically actuated aggregate feeders, the power must have a frequency of 60 ± 1 Hz. Continuous mixing plants must be equipped with an automatic sampling device specified for Class 1 plants in section 27 -1.03D(2) that allows samp ling when the plant is in full operation. The cement feeder and aggregate feeders must be equipped with devices that allow the feed rate to be determined when the plant is in full operation.
27-1.03E Spreading Treated Mixture
Transport materials mixed at a location off the roadbed as a uniform mixture. Cover the mixture during transport to avoid moisture loss, if ordered. Deposit the mixture on the roadbed at a quantity that provides the specified compacted thickness without spotting, picking up, or shifti ng the mixture. Just before depositing plant -mixed or spreading road -mixed CTB , moisten the area to be covered. The area must be kept moist, but not excessively wet. Avoid material segregation. CTB must be free from p ockets of coarse or fine material. Spread the mixed materials in widths of not less than 2 lanes, insofar as the width of the CTB to be spread permits. Sections with 3 -lane width may be spread as a 2 -lane width and a 1 -lane width. Spread materials with 1 s preader or with several spreaders operating in a staggered position across the subgrade, unless traffic conditions limit spreading to less than a 2 -lane width. If traffic conditions limit spreading to less than a 2 -lane width, spread the remainder of the 2 -lane section within 2 hours. For traffic conditions that prevent placement of CTB in adjacent lanes within 2 hours, a longer time may be authorized. Longitudinal construction joints must be within 1 foot of lane line delineation. For areas inaccessible to mechanical spreading equipment, spread CTB in 1 layer using an authorized method. After spreading, thoroughly compact the mixture with pneumatic tampers or other compacting equipment that obtains the degree of compaction specified in section 27 -1.03F to t he required lines, grades, and cross section. Do not mix or place CTB while the atmospheric temperature is below 35 degrees F. Do not place CTB on frozen ground. Apply curing seal to completed CTB before the atmospheric temperature falls below 35 degrees F . Comply with one of the following types of spreading operations:
1.For Type 1 spreading operation, spread CTB with a self -propelled mechanical spreader in 1 operation. The CTB must be ready for compaction without further shaping. Equipment not propelled by the unloading equipment is considered self -propelled. The spreader must be equipped with a screed that strikes off and distributes the material to the full width being spread and within the specified surface tolerance. The screed must be adjustable to p roduce the required cross section. Screed action includes any cutting, crowding , or other practical motion that produces a finished surface texture of uniform appearance. The mechanical spreader must be equipped with fully automatic screed and grade sensin g controls that control the longitudinal grade and cross slopes of the screed. Screed controls must be able to automatically compensate for differences from the slope and grade established by the Engineer.
2.For Type 2 spreading operation, comply with Typ e 1 except automatic screed controls and grade sensing controls are not required.
3.For Type 3 spreading operation, spread the treated mixture with any equipment that will consistently finish the base within the tolerance specified in section 27 -1.03F wit hout material segregation. SECTION 27 CEMENT TREATED BASE S If a spreading type is not specified, use Type 3 on ramps and Type 1 at all other locations. Except as otherwise specified in section 27 -1.03F, do not use motor graders for spreading and compacting operations. To finish the base within the specified tolerance, motor graders may be used to trim the edges and surface of CTB after initial compaction. A motor grader is considered a self -propelled mechanical spreader if:
1.It is equipped with end wings on the blade
2.Blade is locked in a position perpendicular to the direction of travel
3.It is equipped with cross slope and automatic grade controls that comply with the requirements for the specified type of spreading operation
27-1.03F Compacting
Compacting equipment must produce the required compaction within the operation time limit specified in
27-1 03g.
Immediately following the spreading operation, compact the CTB with at least 1 complete coverage. After initial compaction, wherever the finished surface is higher than the specified tolerance, trim off high spots to within tolerance. Do not fill low areas by drifting or hauling trimmed material . Follo wing trimming, the trimmed areas must be compacted with 1 complete coverage such that the entire layer of CTB complies with the specified compaction requirements. Perform final compaction in such a manner that no loose material remains on the surface and t ear marks are eliminated. If CTB is spread and compacted in more than 1 layer, compact each layer to the required degree of compaction before placing the next layer. Trim only to comply with the specified layer thickness. The compacted thickness of any 1 l ayer must not exceed 0.50 foot or be less than 0.25 foot. When placed in more than 1 layer, keep the compacted material moist until covering with the next layer or applying curing seal. Apply curing seal to the surface of a lower layer that will not be cov ered with the next layer on the same day. The finished CTB surface must be uniform and must not deviate at any point by more than 0.03 foot from the bottom of a 12 -foot straight edge laid in any direction. The finished CTB surface must be within 0.05 foot above or below the grade established by the Engineer, except wherever concrete pavement will be placed on CTB, the finished CTB surface must not extend above the grade established by the Engineer. The surface must be kept moist at all times until the curing seal is applied. Wherever the surface of hardened CTB is lower than 0.05 foot from the grade established by the Engineer, remove the base and replace it with CTB or if authorized fill low areas according to the pavement material as follows:
1.For H MA pavement, fill low areas with HMA that complies with the specifications for the lowest layer of pavement. Do not fill low areas concurrently with the paving operation.
2.For concrete pavement, fill low areas with pavement concrete concurrent with the p aving operation. If CTB is paid for by the cubic yard, a deduction will be made if there are areas that are deficient in thickness and the deficient thickness has not been compensated for by filling of low areas. The deduction will be computed as the product of:
1.Deficient thickness less allowable tolerance
2.Spread width
3.Longitudinal distance of the deficient thickness
4.$28.00 per cubic yard or the item bid price, whichever is higher For determini ng areas of deficient thickness, the longitudinal distance between thickness measurements will not exceed 1,000 linear feet for each direction of travel. Whenever requested, the Engineer will make SECTION 27 CEMENT TREATED BASE S additional measurements at the Engineer's discretion to def ine the area of deficient thickness at your cost. Excess material may be placed as aggregate for shoulder construction if:
1.Shoulder subgrade is prepared as specified.
2.Hardened chunks of trimmed material are removed or reduced to the maximum size spec ified for shoulder aggregate.
3.Trimmed material incorporated into the shoulder does not exceed 25 percent of the planned volume of shoulder aggregate per foot of shoulder. If trimmed material exceeds this limit, it must be removed and placed in other are as under the 25 percent limit.
4.Excess material is uniformly distributed in the shoulder area before spreading additional shoulder aggregate. Excess material may be used in other work if the material complies with the applicable specifications. The rela tive compaction of CTB must be at least 95 percent.
27-1.03G Operation Time Requirement
Complete initial compaction before trimming within 2 hours of adding water to the aggregate and cement. Complete final compaction after trimming within 2 -1/2 hours of adding water to the aggregate and cement.
27-1.03H Contact Joints
Construct a contact joint at the end of each work day and whenever CTB operations are delayed or stopped for more than 2 hours . Contact joints must be constructed in thoroughly compacted material, normal to the roadbed centerline, with a vertical face. Do not place additional CTB until the contact joint is accepted. Where CTB has been fin ally compacted for more than 1 hour, construct longitudinal joints by cutting vertically into the existing edge approximately 3 inches deep. Moisten the face of the cut joint in advance of placing adjacent base. Material from cutting may be used as excess material as specified in section 27 - 1.03F.
27-1.03I Curing
Cover the completed CTB with asphaltic emulsion curing seal. Dilute and thoroughly mix asphaltic emulsion for curing seal at a ratio of 1 part water to 1 part asphaltic emulsion. The water must not cause premature separation of the emulsion. Uniformly apply the diluted curing se al at a rate between 0.20 to 0.30 gal/sq yd of CTB surface. The Engineer determines the exact rate. Apply curing seal on the same day as completion of final compaction and as soon after final compaction is practicable. Keep the surface moist until curing s eal is applied. Do not allow traffic or equipment on the CTB for 72 hours after application of the curing seal. After 72 hours, limit traffic and equipment on the CTB to that used in paving operations or placing additional layers of CTB.
27-1.04 Payment
If excess material is placed in an area in which the item is measured by the ton, payment as the item where placed is not made unless applicable measurement specifications for the item where placed are complied with. If cement treated base is paid for by th e ton, the payment quantity for cement treated base does not include the quantity of excess material except for the quantity of excess material used in shoulders. If cement treated base is paid for by the cubic yard:
1.The payment quantity for cement trea ted base is the volume determined from the dimensions shown .
2.The payment quantity for cement treated base does not include the volume of any cement treated base placed below the grade established by the Engineer. SECTION 27 CEMENT TREATED BASE S
3.If an increase or decrease in the spe cified quantity of cement is ordered, the quantity of cement subject to increased or decreased payment is the difference between the specified theoretical quantity of cement and the theoretical quantity of cement ordered. The theoretical quantity of cement is determined from the following formula: Wc = 1686 C x V(D − M) 100 + C where: Wc = Theoretical quantity of cement in lb V = Pay volume of cement treated base in cu yd C = Percentage of cement in the mix D = Average in -place wet density in g/cc M = Average in -place moisture in g/cc If cement treated base is paid for by the ton:
1.Payment quantity of cement treated base is the sum of the weight of the aggregate used in the mix and the weight of cement to b e added to the mix.
2.Weight of aggregate for road -mixed cement treated base that is mixed on the roadbed is measured before delivery to the roadbed under section 9 -1.02 except the weight to be paid for is determined by deducting from the weight of the ag gregate, the weight of the water in the aggregate at the time of weighing in excess of 3 percent of the dry weight of the aggregate.
3.Weight of cement for road -mixed cement treated base that is mixed on the roadbed to be included in the payment quantity of road -mixed cement treated base is the product of the specified percentage of cement to be added to the mix and the weight of dry aggregate.
4.Weight of plant -mixed cement treated base or road -mixed cement treated base that is mixed by the plant -mixed m ethod is measured after mixing under section 9 -1.02 except that moisture in excess of 3 percent of the dry weight of the mixture is deducted from the weight of the combined aggregate, cement, and water. When the specified quantity of cement is increased in plant -mixed cement treated base or road -mixed cement treated base mixed by the plant -mixed method, the weight of cement for which increased compensation is made, as specified in section 27 -1.04, is deducted from the combined weight of aggregate and cement . If an increase or decrease in the specified cement content is ordered, payment is adjusted based on the cost of cement per ton, FOB from the cement mill, including sales tax plus the freight cost per ton for delivery from the mill to the plant. In deter mining the cost of cement, any cash or trade discount offered or available is credited to the Department even if the purchaser did not take the discount. Maintain records that allow a clear determination of the cement costs associated with the increase or decrease. Submit evidence of the cost of cement used for the increase or decrease. If your records show an excessive cost for the increase or decrease of cement or you furnish inadequate evidence for the cost, the Engineer determines the cost to be the low est wholesale price that the cement was available for in the quantities delivered to the point of production less any available discounts. The quantity of cement subject to increased or decreased compensation will be the difference between the specified th eoretical quantity of cement and the theoretical quantity of cement ordered. The Department does not adjust payment for variations in the cost of work resulting from the change in the quantity of cement.
27-2 27-10 Reserved
Source: California Standard Specifications, 2024 Edition. Pages 411–420 of 1,372.