2. MATERIALS
2.1 Fly Ash
Fly Ash shall be a Class C Fly Ash, meeting the requirements of ASTM C 618, and shall also have a minimum compressive strength of 1000 psi when tested in accordance with ASTM C 593.
2.2 Water
Water shall be free of industrial waste and other objectionable material. Do not use salt water.
2.3 Base Material
The base material shall be crushed calcium sulfate. The binder shall be material obtained from the crushing operation and from the fines intermixed with the material. The base material shall consist of hard, durable particles or fragments of calcium sulfate, free from objectionable matter and shall not contain an excessive amount of flat or elongated pieces. The method used hi production of the crushed material shall be such that the finished product is uniform.
2.4 Physical Requirements
The processed material, when properly sampled and tested by standard laboratory procedures, shall meet the following requirements:
2.4.1 The crushed calcium sulfate material shall be within the following gradation:
3. PROPORTIONING OF MIXES
4.1 Preparation of Underlying Course
The underlying course shall be proof rolled in accordance with Tex Dot Item 216. Soft areas shall be repaired or replaced before compaction to required density as directed by Engineer. The sub grade shall be compacted to 95% standard density (ASTM D698) or as directed by engineer. The surface of the sub grade shall be tight bladed by a maintainer or trimmer to match grades on plans. Attention should be given to the modifications of excessively plastic or organic soils with stabilizing agents. Proper drainage of the underlying course and base are necessary.
4.2 Base Course Placement
The fly ash stabilized base shall be placed in uniform layers on the prepared sub grade to produce the depth specified on the plans. The depth of layers shall be as approved by the Engineer. But not in lifts of less than six inches (6") with the fly ash stabilized base. Construction joints between new fly ash stabilized base and fly ash stabilized base that has been in place four (4) hours or longer shall be vertical. The plane of the joint may be formed by a header which shall be removed immediately prior to placing the subsequent base or the base placed first may be cut to an vertical face, free of loose and shattered material before placing subsequent base.
Fly ash stabilized base shall not be placed when the air temperature is below 40° F and is falling, but may be placed when the air temperature is above 35° F and is rising. Fly ash stabilized base shall be mixed or placed only when weather conditions in the opinion of the Engineer is stable for such work.
4.3 Base Course Compacting and Finishing
Compaction shall be carried out under the Controlled Density method as outlined below and as shown on the plans. The moisture content of the mixture before and during compaction operations shall be maintained within a range of + or - 2% of the optimum moisture content. A testing Lab and Engineer should determine this.
The compaction shall be completed within four (4) hours of the time water is added to the mixture. No vibratory compaction should be done after two (2) hours from the time moisture is added and compaction starts. If any reshaping needs to be done; scarify the base material to full depth maintaining optimum moisture and re-compact to achieve maximum density. This has to be done within the four (4) hours after the time moisture is added. Final grade should be approximately 1/4" inch above grade. Immediately after compaction, the surface of the base should be tight bladed with a maintainer to a depth of approximately 1/4 ", removing all loosened materials. The loosened materials shall be disposed of at a location approved by the engineer. The surface shall then be rolled with a pneumatic tire roller, adding increments of water as needed during rolling. A testing Lab should determine 95% modified density as per ASTM D1557. Drainage of the base and underlying sub grade should be maintained at all times.
4.4 Curing
The fly ash stabilized base shall be kept wet for a period of seventy-two (72) hours after completion of compaction. The fly ash stabilized base shall be opened to traffic as specified on the plans or as directed by the Engineer. Asphalt should not be placed on the base before being cured at least 72 hours.
4.5 Re-Working
Unlike cement-stabilized material, the fly ash stabilized materials can be re-worked. Before reusing, proper aggregate sizing and moisture must be added to achieve maximum density. The Type C Fly Ash used in GS-200 has the ability to react a second time as long as the material is at optimum moisture or above. Repairs to fly ash stabilized base shall be done by replacing the base for its full depth rather than by adding a thin layer of fly ash stabilized material to the base in need of repair. All joints where the fly ash stabilized base is removed shall be vertical joints before new base is added.
The same compacting and finishing methods should be used as discussed in 4.2,4.3 and 4.4. NOTE: Some strength will be lost, but in most cases it will still meet GS-200 specifications.
4.6 Stockpiling
Stockpiling stabilized base is not recommended, but if it is necessary for a short period not exceed 36 hours, care must be taken to assure that the stockpile is stacked in its loose state. Additional moisture will be necessary to obtain optimum density (ASTM D1557) when material is placed for compaction. Use the same methods as discussed in 4.2,4.3 and 4.4.
Note: Some strength will be lost, but in most cases it will meet GS-200 specifications. A testing lab and engineer should determine this.
5. MEASUREMENT
The amount of accepted base material measured as specified will be paid for at the unit contract price per ton of "Fly Ash Stabilized Base Material, ITEM GS-200". This price shall be full compensation for all labor, materials, equipment, and incidentals necessary to complete the work.
