Soil stabilization with lime in road construction
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Published: Mon, 5 Dec 2016
Soil Stabilization with lime
Lime is another fundamental soil material that has been widely used as soil stabilizer for road pavement construction. Limestone is a soil material that discovered from sedimentary rock combining of high levels of calcium and magnesium carbonate composition as other small amounts of minerals. This is the extraction of underground mines and quarries all around the world. Therefore, the lime can be very cheap, it can be found everywhere in many countries. There is no transportation between long distances and it normally used to create a capping layer of road pavement from appropriate in- situ soils. In some road pavements, lime is considered to be a subbase layers that appeared the first part of a two part construction process using ordinary Portland cement and ground blast furnace cement.
In general, the plasticity of soil material can be decreased by treating the performance of fine-grained soils. Once, the characteristic or physical property been changed, an improvement of workability needs to be made and also the volume of the material needs to be reduced. in addition, the strength of lime is basically depended on many elements such as curing time, curing temperature, water content and percentage of lime content.
Types of lime.
There are many types of lime have been introduced as soil stabilizer for road pavement. However, several types of lime have been commonly used there are dolomitic lime, calcitic quicklime, dolomitic quicklime and hydrated high-calcium lime respectively.
The high calcium hydrated lime is used more often, this is because the hydrated lime is much less caustic than quicklime, the high calcium hydrated lime is a dry powder that made by a chemical reaction of quicklime with water to ensure natural affinity of the quicklime for moisture content. Easy to form the hydrated lime that is suspended or mud, often the process of pumping a variety of positions within the industrial plant. The alkaline as a result, having a pH of 12.4. Most hydrated limes have a combination of 75 percent cao and 25 percent H2O.Hydrated lime is used in a variety of industrial applications including water treatment, as an anti-stripping agent in asphalt, and in soil stabilization. Some hydrated limes are sold into the food grade market as well.
The advantage of using lime as a soil stabilizer is basically concerned with many reasons such as reduced construction or operational cost during process of the project especically, reduce water use energy consumption and a reduction of Co2 emissions as well as saving time of operational processes.
Stabilization with Lime-Fly Ash (LF) and
Lime-Cement-Fly Ash (LCF).
There is little for coarse-grained soils in soil stabilisation that can be achieved by the use of a combinations of LF or LCF. Lime -Fly Ash is also known as Coal ash which is a part of mineral residual from the burning of crushed coal. It is a combination of aluminum and silicon compounds. Once mixed with water anf lime, the mixture of soil can be created a strengthened cementitious mass accomplished of containing high compressive strengths. A combination of lime and fly-ash can also be used comomly as a soil stabiliser for stabilizering grainy materials when the lime can react with the fly-ash produced a agent. The combination of LF or LCF as a soil stabilisation is suitable for road base and sub-base materials.
In gerneal,the appearance of Lime-Fly Ash or Lime-Cement-Fly Ash both them looks almost the same to the appearance of cement. When Fly Ash appear as circular particles that looks like a ball bearing while cement appears angular that looks like a crushed rock more. In addtion, Fly Ash contains strengthened cementitious quality so it can be used to replace the cement in a cement mix.
Fly Ash can easily replace the cement in the concrete mixes that is good for saving costs during a soil stailisation process. There is another problem that needs to be considered once Fly-Ash as a soil stabiliser. The compressive strength of concrete mix with Fly-ash is approximately the same to the compressive strength of concrete without Fly-ash. There may be a slight decrease in compressive strength in the first, and then there is a slight increase after the first two weeks.
Types of fly ash
There are two different types of Fly-ash have been introducted to soil stabilisation or construction industry, type C and type F respectively. Type C Fly-ash is come from the combustion of lignite or subbituminous coal and the type C Fly-ash is also called as “high lime ash”this is because a high percentage of lime is contained in type C Fly-ash. The type C Fly-ash is a pozzolanic substance, when it is self-reactive with water . Type F Fly-Ash is produced from the combustion of anthracite or bituminous coal and sometimes it is known as “low lime” ash.It is required the addition of lime to make a reaction to produce a pozzolanic substance.
- Provide sulfate resistance of cement equal to or better than Type V cement.
- Effectively controls heat gain during concrete curing.
When type C fly-Ash adds into the concrete mixes, it will contains a early strengths this is becuuse it contains its own amount of lime. Under this circumstance, it requires pozzolanic reaction to be started reacting eailer.
There are many advantages of using Fly-ash that concerned with the manufacturing of concrete pipe which contains a greater density of the concrete.the peremebility of a construction project can be improved by using a more dense concrete mix and reduce the probability of infiltration. Finaly, the workability of the project can also be improved by using Fly-ash material.
A fly ash concrete mix will generally gain strength more slowly at early ages. After about seven days, the rate of strength gain of fly ash concrete exceeds that of conventional concrete, enabling equivalent strength at 28 days. This higher rate of strength gain continues over time enabling fly ash concrete to produce higher ultimate strength than can be achieved with conventional concrete.
Stabilization with Bitumen
Soil Stabilization with Bitumen which is an aggregate contains bitumen. It has a big difference in appearance when it compared to cement and lime soil stabilisation. The mechanism of bitumen is basically concerned with fine-grained soil that is a sealing or waterproofing phenomenon. The bitumen is coated by soil particles that can reduce the strengths of
Soil by slowing down the penetration of water. In some construction project, the bitumen for soil stabilisation is widely used for bitumen bound pavement that is normally less than any other purpose of using. Normally, the bitumen for soil stabilisation will contain approximately about 4-8% of the soil without any water content.
TYPES OF BITUMEN.
- Sand bitumen: a mixture of sand and asphalt, of which the sand particles cemented together, provide a more stable material.
- Bitumen with aggregate: asphalt mixture gradation and a good gravel or artificial aggregates, after compaction, provides a highly stable sub-base or water quality based on the quality of course.
- Bitumen with lime: a mixture of lime, soil and bitumen after a soil compaction, the compacted soil mixture may has characteristics of the bitumen treated materials that will contains a high PI value.
In general, there are several types of bitumen used for soil stabilization. The type of bitumen which is to be used that based or depended on the different type of soil need to be used as a stabilizer, the processing for a road pavement construction and operational or weather conditions. Frost areas, tar as a binder, should be kept away because of its high temperature sensitivity. The asphalts substance can be slightly influenced by a change in temperature. According to a specific soil experiment, a good result can be perfectly achieved by the soil mixed quickly with liquid asphalt which is the stickiest one. One of the higher qualities for soil mixture that used for a central plant, the sticky grade asphalt cement should be used.
There are many soil bituminous stabilization needs to be operated in a place where the bitumen material can be used directly for the soil and soil compaction can also easily be done during construction process. Emulsion is highly recommended to use in a soil stabilization construction, because of energy limitation and reduction of pollution control efforts. For a road pavement project, the engineer needs to decide what kind of the type of bitumen would be used that is based on operational or weather conditions and the cost of the project as well as the different types of equipment in the construction. There are several types of bitumen are introduced as below that would be used for the soil gradation indicated:
- Rapid- and medium-curing liquid asphalts RC-250, RC-800, and MC-3000.
- Medium-setting asphalt emulsion MS-2 and CMS-2.
Well-graded aggregate with little or no material passing the No. 200 sieve
- Rapid and medium-curing liquid asphalts RC-250, RC-800, MC-250, and MC-800.
- Slow-curing liquid asphalts SC-250 and SC-800.
- Medium-setting and slow-setting asphalt emulsions MS-2, CMS-2, SS-1, and CSS-1.
Aggregate with a considerable percentage of fine aggregate and material passing the No. 200 sieve
- Medium-curing liquid asphalt MC-250 and MC-800.
- Slow-curing liquid asphalts SC-250 and SC-800.
- Slow-setting asphalt emulsions SS-1, SS-01h, CSS-1, and CSS-lh.
For many road pavement design, the engineer use the bituminous stabilization which is the application of liquid to construct surface of an unbound aggregate road. There are SC-70, SC-250, MC-70, and MC-250 are respectively applied to the slow and medium curing liquid bitumen.
Gradations for soil stabilization
There are several soil gradations which is highly recommended to used for sub-grade base or sub-basematerial as show below in two tables
Recommended gradations for bituminous stabilized sub-grade materials
Recommended gradations for bituminous-stabilized base and sub-base materials
In many soil stabilizations with a sub-grade material, there is one equation that needs to be applied for identifying the groundwork quantity of falloff asphalt. The equation as shown below:
p = ((0.02(a) + 0.07(b) + 0.15(c) + 0.20(d))/(100 – S)) X 100
p = percent cutback asphalt by weight of dry aggregate
a = percent of mineral aggregate retained on No. 50 sieve
b = percent of mineral aggregate passing No. 50 sieve and retained on No. 100 sieve
c = percent of mineral aggregate passing No. 100 and retained on No. 200 sieve
d = percent of mineral aggregate passing No. 200
S = percent solvent
The initial number of emulsified asphalt
Once soil stabilization with sub-grade materials need to be involved in a road construction. The initial quantity of emulsified asphalt also needs to use for the sub-grade materials that can be determined by a table as shown below:
Emulsified asphalt requirements
For the final design stage the content of emulsified asphalt that need to be chosen based on the experimental results of the Marshal Stability testing. The test is used to determine the Marshall stability of bituminous mixture. There is a minimum requirement of Marshall Stability which required for sub-grade is 500 pounds. Once, the recommended quantities of bituminous materials need be added, if appearance of increased Marshall Stability is not shown for the soil particles, the soil gradation would be identified with more details or another type of bituminous materials need to be applied as a soil stabilizer.
STABILIZATION WITH LIME-CEMENT AND LIME-BITUMEN
In a road pavement construction project, the advantage of using combination stabilizers is that one of the stabilizers does not perform its effectiveness properly, the other one is able to compensate when treating a specified characteristics of a given soil. For example, lime has been used frequently with stabilizers such as asphalt or Portland cement in order to provide base courses for clay areas.
Since plastic clays is not totally compatible with asphalt or Portland cement and the lime cannot corporate into the soil to make it friable, therefore, asphalt and the cement can be effectively mixed. Stabilization practice might be more expensive than conventional single stabilizer methods, but it could be still reasonably priced at places where base aggregate costs are high. There are many different types of cement as a soil stabilizer. But in this case study, two combinations of cement particle are concerned with lime-cement and lime-asphalt respectively.
Lime can be used as an initial additive with Portland cement or the primary stabilizer. The main effects lime gives is to reduce the plasticity of the soil. The main approach is to add enough lime I order to reduce the plasticity index to satisfactory levels.
Lime can be used as an initial additive with asphalt or the primary stabilizer. The main effects lime gives is to act as an anti- stripping agent. In the layer capacity, the lime acts to neutralize acidic chemicals in the soil or aggregate which tends to interfere with bonding of the asphalt. 1-2 percent lime is basically needed for this objective.
LIME TREATMENT OF EXPANSIVE SOILS.
In a road pavement, the surface of an expansive soil is defined as those exceeding three percent expansion in the exhibition. The expansion of soils is concerned with a road pavement construction, when water is influenced in clay minerals. The plasticity characteristics of a soil particle can be used as an indicant for the swell potential of a soil which is shown as below:
Swell potential of soils
A treatment with lime would be introduced to determine the well potential of a soil. The lime can be used to reduce swell. For an expansive soil, A more or less degree of expansive soil may be present activities of the clay minerals. Once, the lime needs to be added that requires a minimum amount of the lime, it can reduce swell to acceptable limits. There is an experimental process for conducing swell test which can be found in ASTM D 1883. The depth of lime should be incorporated into the soil, in general, the equipment used by the construction of a limited. In general, A maximum required depth need to be calculated with 2 to 3 feet that can be treated directly without removal of the soil.
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