89 Figure 4.7 Variation of plastic limit of different soil-fly ash mixtures with increasing lime content (for 1 day conditioning period). 255 Figure 8.5 Change in hydraulic conductivity of the soil-fly ash-lime mixtures with the variation of (a) fly ash content (b) lime content.
NOTATIONS
ONE INTRODUCTION
- THE CONTEXT
- RESIDUAL LATERITIC SOIL
- FLY ASH: A NEW RESOURCE MATERIAL
- Need for Bulk Utilization of Fly Ash
- Fly Ash Stabilisation of Soils
- THE PRESENT STUDY
- OBJECTIVES OF THE PRESENT STUDY
- THE APPROACH
However, very few attempts have been made to understand the effects of fly ash and lime on the residual behavior of mined laterite soils. Therefore, the entire research was primarily aimed at understanding the plasticity, compaction, stress-strain strength and leaching behavior of soils modified with fly ash and lime.
TWO LITERATURE REVIEW
INTRODUCTION
RESIDUAL LATERITIC SOIL .1 Origin and Formation .1 Origin and Formation
- Distribution of Lateritic Soils in India
Prusza (1983) Taiji (1979) Taiji (1979) Taiji (1979) Similar to the effects of drying on index properties, drying lateritic soil by in situ moisture content can also change the compaction characteristics of lateritic soils. Several authors (Foss, 1973; Vargas, 1973; Fooks, 1990; Barksdale and Blight, 1997; Rao and Revanasiddappa, 2002) have reported the collapse behavior of soil structure in lateritic soils after saturation.
FLY ASH
- Production, Storage and Disposal
- Classification of Fly Ash
- Physical and Chemical Characteristics of Fly Ash
- Geotechnical Properties
Color is useful for estimating the calcium oxide content and organic content of fly ash. They observed that the static resistance to liquefaction of fly ash was higher than that of the cyclic resistance to liquefaction.
LIME MODIFICATION OF SOIL AND FLY ASH .1 Modification of Soil .1 Modification of Soil
- Modification of Fly Ash
The UCS of the soil-fly ash mixtures increased with the increase in fly ash content. The permeability character of the soil was noticeably affected by the addition of lime fly ash mill.
LEACHING MECHANISM AND CONTROLLING FACTORS
Several investigators have studied the leaching properties of metals from fly ash and soil-fly ash mixtures. Chichester and Landsberger (1996) investigated the leaching dynamics of metals from municipal waste incinerator (MSWI) fly ash. Test results showed that the concentration of most pollutants is higher for fly ash than soil.
The barium concentration of all the soil-fly ash mixtures was much lower than that of fly ash alone.
CONCLUSIONS
The ability of fly ash to retain ions increases with the increase in initial concentration up to a maximum and then remains constant. It was also observed that the reaction time required by the fly ash to retain metal ions to its maximum capacity is 72 hours. Leaching research on fly ash and fly ash stabilized materials has been the focus of many researchers due to the presence of a number of toxic contaminants in the fly ash.
More importantly, leaching studies have become important because of the nature of some fly ash-stabilized materials that can retain such contaminants to later leach under favorable conditions.
THREE PHYSICAL AND CHEMICAL PROPERTIES OF
THE FLY ASH AND THE SOIL
- EXPERIMENTAL FLY ASH
- Physical and Chemical Properties
- EXPERIMENTAL RESIDUAL LATERITIC SOIL
- Physical Properties of the soil
- Chemical Composition
- Mineralogical Composition
- Grain Size Distribution
- EXPERIMENTAL LIME
- METHOD OF SOIL-FLY ASH-LIME MIXTURE PREPARATION
- MIX DESIGNATIONS FOR PRESENT INVESTIGATION
- CONDITIONING AND CURING
- SUMMARY
The mineralogical composition of the fly ash was obtained by X-ray diffraction studies (SEIFERT, Model-XRD 3003), using a graphite monochromator and Cu-Kα radiation (scanned from 2θ ranging from 10˚ to 80˚). For the determination of specific gravity, IS: 2720 (Part III) recommends drying the soil in the oven before the experiment. Grain size analysis of the soil was done by wet sieving method, using undried soil in natural state.
The percentage of lime added was indicated as a percentage of the weight of soil-fly ash mixture.
FOUR PLASTICITY CHARACTERISTICS OF
THE SOIL-FLY ASH-LIME MIXES
INTRODUCTION
TEST PROGRAM
The testing program, experimental details and results of this research are presented, together with a discussion of the mechanisms known to control the plasticity characteristic of different soils.
EXPERIMENTAL DETAILS .1 Initial Investigation on the Soil .1 Initial Investigation on the Soil
- Sample Preparation and Test Procedure for Mixes
After thorough mixing, the samples were packed in polyethylene bags, sealed and conditioned for a period of time according to the test program. After conditioning, the samples were initially tested using the Casagrande method for liquid limit determination according to ASTM D a). As difficulties were encountered in cutting the required groove for certain samples, especially for 35FA and 50FA samples, the cone penetration method according to BS Test 2A (British Standard Institution, 1975) was used for all samples.
Using parts of the above samples, the plastic limit was determined according to the standard method according to ASTM D.
MECHANISMS CONTROLLING PLASTICITY CHARACTERISTICS
Whenever reported, the mean liquid limit value is averaged from two separate flow curves. This results in a higher liquid limit due to the greater amount of water trapped within the void spaces. For kaolinitic soils, Sridharan et al. 1988) observed that the liquid limit is not a function of the thickness of the dispersed bilayer and has no correlation with the percentage of clay fraction.
Instead, the arrangement of particles (clay fabric), which is regulated by attractive and repulsive forces between particles, plays a dominant role in influencing the fluid boundary.
RESULTS AND DISCUSSION
- Plasticity Behaviour of Experimental Soil
- Plasticity Behaviour of Soil – Fly Ash – Lime Mixes
- Variation of Liquid Limit
- Variation of Plastic Limit
The effect of lime content and conditioning period on soil liquid limit is shown in Fig. It can be noted that adding only fly ash lowers the liquid limit of the soil. The observed continuous decrease in the liquid limit of the mixtures confirms that the dilution effect of the fly ash is dominant.
For a conditioning period of 1 day, the plastic limit of the soil without any additive is 37.1%.
CONCLUSIONS
Most of the change is effected in the first 28 days of conditioning, and after this period the rate slows down considerably. The short-term change in plasticity characteristics of the soil-fly ash-lime mixtures appears to be controlled by both cation exchange and flocculation. However, in view of the complex nature of plasticity changes as well as early onset of pozzolanic activity in the present case, the specific contribution of each of these mechanisms is not clear at this stage.
FIVE COMPACTION BEHAVIOUR OF THE
SOIL-FLY ASH-LIME MIXES
INTRODUCTION
A preliminary study was also carried out to understand the compaction behavior of the test soil before the above tests were carried out.
COMPACTION TEST PROGRAMME
EXPERIMENTAL DETAILS .1 Initial Investigation on the Soil .1 Initial Investigation on the Soil
- Test Procedure for the Mixes
- Test Procedure for Successive Re-Compaction Test
The separation was carried out with the aim of maintaining the uniformity of the grain size distribution of the soil part that would be used for studying the variation of the compaction properties when mixed with fly ash and lime. A fresh sample was used each time to obtain each compaction point of the compaction curve. Based on the results of the preliminary tests, it was decided to air dry the soil and limit the maximum grain size to 2 mm.
At the end of the specific conditioning period, compaction tests were carried out as per IS: 2720 part (VII).
RESULTS AND DISCUSSION
- Compaction Behaviour of the Soil
- Effect of Fly Ash and Lime
- Effect of Re-Compaction
- Effect of Delay in Compaction
The addition of lime and fly ash also has a significant effect on the OMC of the soil, as clearly shown in the figure. compaction is shown in fig. Changes in MDD due to delay in compaction of soil and fly ash mixtures after the addition of 2% and 4% lime are shown in the figure.
The changes in OMC due to compaction delay of the mixtures by addition of lime are illustrated in Fig.
CONCLUSIONS
The addition of lime to soil and fly ash mixtures leads to a decrease in MDD and an increase in OMC. Re-compaction can significantly change the MDD and OMC of soil, fly ash and lime mixtures. Even if only fly ash is added to the soil, MDD and OMC do not change appreciably with time lag.
When lime is added to the soil – fly ash is mixed, MDD decreases gradually with delay.
SIX STRESS–STRAIN–STRENGTH CHARACTERISTICS
UNCONFINED COMPRESSION TEST)
INTRODUCTION
SIX CHARACTERISTICS OF STRENGTH-TENSION-STRENGTH .. c) effects of time-dependent hardening reactions and subsequent changes in density and unconfined compressive strength of mixtures for different compression delay periods,. To understand the effects of soil texture on soil strength and to study the suitability of the soil for compaction purposes, several UC tests were also conducted on the undisturbed and remoulded soil specimens.
TEST PROGRAMME
Unlike the conventional oven-drying process, which is usually used to pre-dry soil before sample preparation, this study was performed entirely with air-dried soil, taking into account the water required for lime hydration and moisture loss due to drying due to an increase in the plasticity limit after the addition of lime. In the second regime of tests, consisting of a further five series, the samples were prepared similarly to the first regime, except that the samples were soaked for another 2 days after curing for 0, 3, 28 and 480 days. In the third test regime, which consisted of an additional three batches, the conditioning period of the uncompacted hand-mixed samples was varied from 0, 12 h, 24 h and 72 h.
EXPERIMENTAL DETAILS .1 Sample Preparation .1 Sample Preparation
- Curing
- Testing
- Tests on Undisturbed and Remoulded Soil
After extrusion, the ends of the specimens were trimmed exactly flat to a length of 76 mm using a split die. The ratio of the diameter of the sample to the maximum particle size of the samples in the present study is 19. In the case of tests without soaking, the specimens were tested immediately after the end of the curing period.
In cases of soaked unconfined compression tests, specimens were soaked in distilled water after completion of the specified curing period.
RESULTS AND DISCUSSION
- Behaviour of Soil and Fly Ash in Different States
- Stress-Strain Behaviour of Soil-Fly Ash Mixes
- Stress-Strain Behaviour of Soil-Fly Ash-Lime Mixes
- Unconfined Compressive Strength (UCS) of Soil-Fly Ash Mixes
- Unconfined Compressive Strength (UCS) of Soil-Fly Ash-Lime Mixes
- Soaked Unconfined Compression Tests
The addition of lime to soil-fly ash mixtures causes a substantial change in the stress-strain characteristics of the treated material. In Fig. UCS values and corresponding failure strains of soil-ash mixtures are summarized in Table 6.3.
The changes in UCS of the mixtures with increasing fly ash content and curing time are shown in Fig. 6.12 & 6.13 that the compressive strength of the mixtures increases steadily with increasing curing time. The effects of curing time and lime content on UCS of different mixes are shown in Fig.
