Description
This item shall goven the treatment of materials in place by adding Portland cement to pulverized soil or aggregate materials,mixing and hydrating,then compact the soil-cement to the required density,as herein specified and in conformity with the sections,lines,grades and thickness as shown on the Drawings or as established by the engineeror designated representative.
Contractor is required to complete mixing and initial compaction of soil-cement within 2 hours of initial cement hydration.Contractor is required to complete final grading and surface finishing within 2 hours of initial compaction.
Submittals
The submittal requirements of this specification item may include:
A) A mix design identifying classification of soil being treated, type of cement proposed, source of water and quantities of cement and water required in the propose application to yield the specified performance requirements.
B) An update in the mix design, if material source or type changes during construction.
C) A plan describing the stabilization equipment proposed to perform the work And identifying the type and condition of each equipment items.
Materials
Soil - Soil to be treated with cement shall be within ≤10 % of the soils Optimum before application of cement. At the engineers discretion the in-situ moisture may be higher for soil-cement mixtures above 5 percent cement content. Soil ure may be higher for soil-cement mixtures above 5 percent cement content. Soil shall not contain rocks or solids other than soil clods larger than 2.5 inches in any dimension.
Soil beneath the soil-cement layer should be moist within 6 inches from the Bottom of soil-cement layer.
Removing and disposing of oversize material or adjusting the in-situ moisture contents by pre-watering or additional cement to reduce excess moisture will be paid for as extra work.
Cement – Portland cement shall conform C 150. The cement shall be protected from moisture until used and be sufficiently dry to flow freely when handled. Cement shall be furnished in bulk and not exposed until applied to soil.
Water - Water shall be free from oils, acids, organic matter or other substance deleterious to the cement treatment of materials. The water shall not contain more than 1000 parts per million of chlorides nor more than 1000 part per million of sulfates as SO4. Water shall be clean and potable and shall be added as needed during mixing, compacting, and finishing operations and the curing period, as required.
Proportioning / Spreading
The cement shall be applied in one operation to the required width, grade and cross section. Cement shall be evenly applied at the designated rate and shall not vary more than 10 percent on any area. The percent cement is based on the in-place dry weight of the soil to be treated or as determined by the engineer. only a calibrated spreader able to provide a uniform distribution of the cement throughout the treatment area shall apply cement. The cement shall be added in a dry state and every precaution shall be taken to prevent dusting outside the treatment area.
Tailgate application of cement will not be permitted. Tailgating is defined as having manual control of the spread rate, rather than automatic. The spreader truck shall demonstrate the ability to maintain a consistent spread rate over variable travel speeds. The contractor will demonstrate the consistency of the application rate by conducting multiple pan tests.
The pan test consists of placing a 3 square foot pan on the grade in front of the spreader truck.After cement has been applied, the cement is weighed to determine the rate of application in pounds per square foot.
No traffic other than the mixing equipment or other related construction equipment will be allowed to pass over the exposed cement until after completion of mixing.
Cement shall nout be spread or mixed/hydrated while the atmospheric temperature is below 350 F or below 1.670 C.
A the engineers discretion,processing will be allowed if temperature is rising
Mixing / Hydrating
Mixing equipment shall be equipped with a visible depth indicator showing mixing depth and an odoment to indicate travel speed. The initial hydration water shall be introduced by means by means of a regulated water additive system integrated into the mixing equipment.
Mixing equipment shall be the type that can mix to the full depth of the desired thickness and leave a relatively smooth bottom of the treated section. Mixing and re-mixing, regardless of equipment used, will continue until the material is uniformly mixed, free of streaks and/or pockets of non-hydrated cement. The soil-cement mixture shall not remain after mixing and before compacting for more than 30 minutes.
The cement to water ratio for hydrating the cement shall be 2 cement to 1 water, plus 2 percent above the optimum moisture content during compaction.
Compaction
Maintain moisture content within allowable range during all compaction procedures. The soil-cement shall be compacted to the project’s minimum relative compaction requirements as determined by ASTM 1557.
The maximum compacted thickness of a single layer may be any thickness the contractor can demonstrate to the engineer that his equipment and method of operation will provide the required compacted density throughout the treated layer.
Initial compaction – Contractor shall achieve the projects minimum compaction requirement during initial compaction operation. Lift thickness of 4 to 8 inches shall be by means of a steel-tired or pneumatic - tired roller. Lift thickness of 8 to 12 inches shall be compacted of a sheepsfoot compactor. Lift thickness greater than 12 inches shall be compacted by a sheepsfoot compactor with an open ring design to prevent bridging of the lower half of section. Areas inaccessible to rollers shall be compacted to the required compaction by other means satisfactory to the engineer.
Final Grading
Surface compaction and finishing shall proceed in such a manner as to produce, in not more than 2 hours, a smooth, closely knit surface conforming to the crown, grade and line indicated and be free of cracks, ridges and loose material. Maintain moisture content of the surface within allowable moisture range during all grading procedures.
All excess material above the grade tolerance specified by the plans should be removed from the grade prior to final surface compaction of the soil – cement section. This excess material can be used in areas inaccessible to treatment equipment, provided the soil-cement is used within the time constraints.
The trimmed and completed surface shall be rolled with steel or pneumatic tired rollers.Minor indentations may remain in the surface of the
finished material as long as no loose material remains in the indentations. Contractor shall take every precaution to avoid sliver or laminated fill ; soil-cement section (layer) should be monolithic.
Curing
After the soil-cement has been finished as specified above , the compacted surface of soil-cement shall be kept moist until cured or covered. In multiple soil-cement layers , the exposed surface of each layer shall be kept moist until covered by a subsequent layer of soil-cement .
Soil-cement cure is defined as soil-cement section meeting the project performance requirement. Cure time is dependent on temperature and rate of hydration throughout the soil-cement section.
If a curing seal is specified, then the curing shall be place on a moist soil-cement surface.
Curing seal shall consist of emulsified asphalt, spread at a rate of 0.10 to 0.25 gallons per square yard.
Curing seal shall not be place when the atmospheric temperature is below 45oF or 5oC.
If the finished soil-cement is to be covered with a base material within 48 hours, the curing seal may be omitted, provided moisture is maintained.
Traffic Loading
Once soil-cement is finished, contractor may be allowed to place subsequent structural layers (with the exception of Asphaltic Concrete) over the soil-cement section provided that the following criteria’s are met :
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The soil-cement section is stable and non-yielding a minimum 10 ton proof-roll.
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The soil-cement section has no evidence of shrinkage or stress cracking.
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The soil-cement section criteria’s have been met, including the soil-cement section thickness, percentage of cement placed, and quantity or volume of soil-cement treated.
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If treated section begins to deflect under repetitive loading, loading must immediately be rerouted and section lelf to heal or reviewed.
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When Asphaltic Concrete (AC) is to be place directly on the Soil-cement section, a minimum of 3 days of curing will be required prior to placement of AC section.