UTILIZATION OF WASTE MATERIALS IN SUBGRADE OF PAVEMENT

Abstract

A shortage of construction materials and the subsequent rise in their rates has lead to an increase in the cost of road construction in many folds. The shortage of construction material is across the country due to a ban on mining and scarcity of open land for borrows areas. On the other hand, construction of flexible pavement demands enormous quantities of raw materials including soils. In the coming decades the design, construction and maintenance of roads will face a range of new challenges and as such will require a number of new approaches. Such challenges will result from a growing number of interconnected environmental, social, and economic factors, which are set to apply significant pressure on the future of roads. Natural materials are exhaustible in nature. Hence, their quantity is declining gradually day by day. Concerned about this, highway engineers and scientists have started looking for alternative materials for highway construction, and waste product is one such category. Enormous quantities of domestic, industrial, agricultural and mining wastes are generated annually in the world. Therefore, authorities face the challenges of reinforcing their available infrastructure for efficient waste management and ensuring a scientific disposal of the wastes. If these materials can be suitably utilized in highway construction, the pollution and disposal problems may be partly reduced. Huge amount of construction materials are required to meet the demands of the increasing road network in India. The use of conventional material like soil for a large road network may result in scarcity of naturally available materials; hence an alternative is required to fulfill these demands. Use of locally available materials, including marginal and industrial waste materials could be one of the possible solutions to reduce the consumption of conventional materials. Studies have been conducted in several forms using waste materials in subgrade construction. However, the use of new waste materials and technologies is not becoming popular owing to certain procedural constraints as well as lack of awareness and therefore appropriate steps may have to be taken for popularizing the waste materials for building sustainable roads. This may also result in the conservation of natural resources, thus protecting the environment. iv One of the major causes for flexible pavement failure is the weak foundation due to the presence of soft clay particles in soil subgrade. In recent time, one of the topics that have recently received much attention from highway engineers is the study on problematic soils. Basically, a soil is problematic when it exhibits an unexpected behavior under specific conditions and this unpredicted behavior will, in many cases, cause problems during road construction. As clay soils are highly expansive in nature in presence of moisture; clay soil is considered among these problematic soils. India is one of the countries where expansive soil is prevalent in most of its region. Therefore, more of such problems are frequently encountered during construction of highways. Hence, with the perspective to upgrade clayey soil as a construction material using various waste materials like fly ash, bagasse ash, rice straw ash, rice husk ash, bagasse fiber, and recycled fines obtained from demolished concrete slabs to explicitly recommend the most suitable stabilizers in terms of their effectiveness and economy, the present research work has been taken up. It is more important as India produces a huge amount of waste materials as byproducts from different sectors like industrial, agricultural, construction etc. The quantities of wastes (such as cement and lime kiln dusts, quarry waste, slags, fly ash, construction & demolition wastes, rice husk ash bagasse ash, etc.) accumulating throughout the world are causing disposal problems that are both financially and environmentally expensive. To deal with the growing disposal problem of such waste materials is an issue that requires co-ordination and commitment on the part of all parties involved such as government agencies, companies, the public and professionals. One of the most effective ways to overcome such problem is by recycling and utilizing these waste materials in the construction of highways. Therefore, the present research is aimed at investigating the soil engineering properties with and without stabilizers to check their suitability and make maximum utilization of these waste materials in highway construction. In the present study, the influence of different waste materials on the geotechnical characteristics of soil were investigated by conducting various laboratory tests. Tests were performed for various combinations of soil-waste materials as 0, 5, 10, 15, 20, 25, 30, & 35% of fly ash (FA), bagasse ash (BA), rice straw ash (RSA), rice husk ash (RHA) & fines obtained from demolished concrete slab (FDCS) and 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, & 3.5% of bagasse fiber (BF). The tests were conducted in accordance with IS and ASTM standard codes. v Chosen additives were subjected to the thermo gravimetric analysis (TGA) in a dry air atmosphere by maintaining heating rate of 10°C/min. Samples weighing 80 mg were heated at preselected heating rates from ambient temperature to 850°C in a Mettler thermal analyzer. The TGA curve showed that the mass loss for FA & RHA was 1.0-1.5% even after heating at a temperature of 650°C, whereas in case of BA & RSA it was 8-10%. Initially, physical and chemical properties of clayey soil and waste materials were analyzed and compared. Then wet grain size analysis was conducted for clayey soil to accrue the details of particle size distribution, and soil classification was done in accordance with IS: 1498. Tests like Atterberg limits, shrinkage limits; maximum dry density (MDD) & optimum moisture content (OMC), California bearing ratio (CBR), unconfined compressive strength (UCS), static triaxial and cyclic triaxial tests were conducted to study the soil engineering properties with and without waste materials (stabilizers). Also, investigations on microstructures of clay soil and stabilized soils were carried out to elucidate their changes in relation to consequent improvement on engineering properties such as strength and permeability. Effort was also made to study the deformation behavior of different compacted layers of pavement in a model tank under repeated applications of load. Admixing of FA, BA, RHA RSA and FDCS increased the shrinkage limits remarkably. This increase was more pronounced for RHA and FA admixed with soil samples. Similar behavior was also observed for soil admixed with BA and RSA, BF and FDCS. Highest CBR value was observed for FDCS admixed soil sample amongst all the selected soil mixtures irrespective of days of curing. No significant improvement on CBR was observed for BF reinforced soil sample. However, BF reinforced soil sample produced remarkable unconfined compressive strength irrespective of days of curing and which has proven to be the best in all the additives used. Reinforcing BF into clayey soil not only improved split tensile strength but also improved the modulus of subgrade reaction and ultimate strength considerably. However, as far as modulus of subgrade reaction is concerned, FDCS is more effective by offering the highest kvalue in comparison to the rest of the mixes. vi Based on the cyclic triaxial test, substantial improvements in resilient modulus were noted on admixing of FA, BA, RHA, RSA, FDCS and BF irrespective of confining pressure applied. Resilient modulus increased with the percentage increase of additives. In overall, lower permanent strains were observed on admixing of FA, BA, RHA, RSA, FDCS and BF in comparison to clayey soil. However, the least permanent strain was observed for BF admixed soil sample followed by FDCS, RSA, RHA, BA and FA admixed soil samples respectively. SEM micrographs were determined to analyze the significant changes in mineralogical phases of stabilizers in presence of moisture. Calcium silicate hydrates (CSH) developed at early stage in case of the RHA, RSA, FA and BA admixed soil. Whereas in case of BF admixed soil, fibrous materials tend to reinforce the soil mass. Efforts were made to establish correlation between different strength parameters, additives content and days of curing for FA, RSA, RHA, BA, FDCS and BF. The correlation between strength parameters, percent additives and curing days was developed by multiple linear regression analysis using 7, 14, 28 & 56 days results. The validation of the developed relation was done using the results of 128 days strength parameters results. Validation results were compared between the predicted values from developed equation and results obtained in laboratory. The behaviour of pavement under repeated load has been studied by model tank test which was constructed with a subgrade (natural and treated stabilized soil), sub base, base layer of wet mix macadam (WMM), dense grade bituminous macadam and bituminous concrete (BC). The total deflection on surface of specimen was determined and vertical stress was evaluated at each interface of layer and bottom to better understand the dynamic behaviour of a portion of natural soil subgrade and treated soil subgrade by LVDT and pressure cell. In same manner, the vertical stresses at each interface of layer and bottom of subgrade were determined by KENPAVE software. Three magnitude of pressure 0.57 MPa, 0.40 MPa and 0.20 MPa were applied to determine stress and strain for model tank test as well as KENPAVE analysis. vii For the cost benefit analysis of the stabilized soil by different types of additives, it is pertinent to evaluate the pavement thickness reduction in different layers based on its CBR value. The pavement structure was designed based on the CBR value and the cost analysis was done to compare the cost of flexible pavements having stabilized and non-stabilized subgrade. The total thickness of pavement was 805 mm with natural subgrade soil and minimum value was 555 mm after admixing of FDCS or RSA. This reduction in thickness leads to reduction in cost by 30.90%. It was seen that all waste materials used for subgrade soil at their optimum content of admixing not only improve the strength but also reduce the total cost of pavement.