309In-Place Cement Treated Subgrade

309.01 DESCRIPTION. In-Place cement treated subgrade is primarily

used for existing roadway reconstruction, typically for subgrade soils with a Plasticity Index (PI) not exceeding 20, unless otherwise specified. The design compressive strength criteria for in-place cement treated subgrade shall be 100 psi as determined in accordance with DOTD TR 432, Method B or C. Treat subgrade soil materials with portland cement, blended hydraulic cement, or as directed. These specifications set forth the minimum requirements for construction of the treated subgrade; however, construct a treated subgrade that will provide adequate support for construction equipment and processes. Submit a dust control plan to address weather, sight clearance, operational procedures, traffic control, and any other project specific concerns. Failure to maintain sight clearance will result in the engineer stopping contractor operations. The Department will identify dust sensitive areas in the plans. In these specific areas, the dust control plan must also include environmental requirements. Quality assurance requirements shall be as specified in the latest edition of the Department’ s publication titled Application of Quality Assurance Specifications for Embankment and Base Course.

309.02 Materials.

Materials shall comply with the following sections and subsections: Portland Cement 1001.01 Blended Hydraulic Cement 1001.02 Water 1018.01

309.02.1 Determination of Cement Rate

309.02.1 1 Predetermined (Plan Specified): For portland

cement, mix the roadbed material with the rate of cement by volume as shown on the plans.

309.02.1 2 Non-Predetermined: If the percent cement has not

been predetermined, the rate will be provided by the engineer. The District Laboratory may determine the percent of cement by volume in accordance with DOTD TR 432, Method B or C from materials sampled in-place on the project from isolated random areas selected by the engineer. Depending on the materials to be treated, normal testing time to determine the required cement content may require up to 21 calendar days.

309.02.1 3 Contractor Selected Cement Type: When the

contractor elects to use blended hydraulic cement the rate of cement shall be determined in accordance with 303.02.1.3 at no expense to the Department.

309.03 EQUIPMENT. Furnish and maintain equipment necessary to

produce a finished product meeting specification requirements in accordance with 303.03. The equipment will be approved prior to use.

309.04 Construction Requirements

309.04.1 Treatment and Pulverization: Treat subgrade soils by

mixing with portland cement in accordance with Section 303. Compact and finish treated materials in accordance with Section 203. When traffic conditions warrant, and an adequate rolling pattern has been established that demonstrates density and pulverization as achieved, the engineer may reduce density frequency testing requirements to expedite construction. A change in subgrade materials will require testing at the original frequency until a new rolling pattern is established. Make reasonable efforts to conform to the compaction requirements above. When field conditions make this impractical or detrimental, such as a yielding subgrade, establish an optimum rolling pattern to the satisfaction of the engineer. The engineer has the option of increasing or decreasing the percentages of cement based on field conditions. Determine optimum moisture of the mixture in accordance with DOTD TR 415 or TR 418. Increase the cement content by one percent by volume for every 3 percent of moisture content above optimum. After treatment the pulverized mixture shall conform to the gradation requirements in Table 309-1. Table 309-1 Gradation Requirements for In-Place Cement Treated Subgrade

309.05 MEASUREMENT. The quantities of in-place cement treated

subgrade for payment will be the design areas as specified in the plans and adjustments thereto. Design quantities are based on the horizontal dimensions of the completed in-place cement treated subgrade shown on the plans. Design quantities will be adjusted if the engineer makes changes to adjust to field conditions, plan errors are proven, or design changes are necessary. DOTD TR 602 measurements for width and thickness will not be made, but the width and thickness will be checked by the engineer during construction.

309.06 PAYMENT. Payment for in-place cement treated subgrade will

be made at the contract unit price per square yard, which includes cement, cement treatment, and water. If the actual required percent of cement differs from that required by the contract documents, payment will be increased or decreased based on the difference in required quantity of cement at the price of cement shown on paid invoices (total of all charges). The contractor shall provide copies of paid invoices for this determination. If the contract documents do not specify a percent cement, 6 percent will be used for treated subgrades for bid purposes. Payment will be made under: Item No. Pay Item Pay Unit 309-01 In-Place Cement Treated Subgrade ___in Thick Square Yard PART IV—SURFACE COURSES Section No. Page No. Section 401 Aggregate Surface Course ............................................................................. 153 Section 402 Traffic Maintenance Surfacing ........................................................................ 157