Use Of Excavation Soil As Fine Aggregate In Construction Industry
About the Practice
Concrete is the second most used material by mankind after water. As aggregates comprise a major portion of it, depletion of river sand worldwide has made a great impact on the construction industry. Aggregate is said to be the largest volume of solid material extracted globally. Depletion of natural resources causes scarcity in of good quality raw materials, posing problems to the upcoming infrastructural developments. Indirect estimation of aggregate consumption can be made through cement production which is 4.2 billion tonnes in 2016. This suggests that aggregate consumption could be 25.2 to 29.4 billion tonnes could be the aggregate consumption in 2016. In addition to this, aggregates are also used in applications like road embankments, asphalt pavements and other industries. All together this estimate could exceed 40 billion tonnes per year which is more than twice the sediments carried by world rivers annually. Due to the increase in cost of raw materials and the continuous depletion of natural resources, use of waste materials has become a potential alternative. In 2016, Ministry of Environment, Forest and Climate Change of India released the ‘Sustainable Sand Mining Management Guidelines’. This guideline stresses on controlled mining of river sand and use of alternatives such as fly ash, crushed stone, slag and so on. Added to the problem of river sand depletion, the transportation of aggregate from source to the site location increases the cost of the projects. These issues highlight the need for identification of alternative materials that can be a potential replacement for aggregates in construction. The main disadvantage of most alternative fine aggregate materials is the presence of excessive fines or deleterious materials. Though properties of concrete produced with alternative fine aggregates could match the properties of concrete with river sand, use of alternative fine aggregate is mostly done as partial replacement. However, the main aim of this study is to maximize utilization of other natural resources, recycled materials and by-products to reduce the river sand depletion. Hence, there should be treatment methods to enhance the properties of these alternatives to increase their replacement level in concrete. On the other side, dumping of excavation soil should be looked-up as a matter of environmental concern than an economical issue. Mine soil or overburden, the major source of excavation soil is the material that lies above the area of economic or scientific interest of mining. In India, for every 1 million ton of coal extracted by surface mining method damages a surface area of 4 hectares, which results in huge volume of mine spoil being dumped near the mining area. This gives a clear picture of the intensity of the problem in disposing excavation soils from different sources. Some of the negative effects of mines overburden include environmental pollution, loss of biodiversity, and problems to the nearby occupants. Similar effects can be expected in various sources of excavation soil that affect the environmental equilibrium. Raw earth or soil is widely used in various applications based on the quality of the material. It is mainly used in backfilling, if the soil does not contain any expansive clay. Rammed earth, stabilized blocks and adobe are made of raw earth; however, poor resistance to moisture restricts their usage. Plastering with soil as fine aggregate is possible by maintaining the proportion of soil to lime as low as possible and the application is restricted to interior walls and needs a proper maintenance plan. However, the presence of fines and clay is an important drawback in considering materials such as excavation soil as a fine aggregate in mortar/ concrete. Hence, a systematic study was done on treatment methods of excavation soil which helps in transforming the soil to a potential alternative to river sand.
Detail:
Excavated soils are globally available materials which have not been well explored for their use as fine aggregate in concrete. Excavation soils cannot be directly used in cement mortar as they cause excessive shrinkage and poor strength due to the presence of excessive fines (with clay). However, the unprocessed excavation soils can be used as fine aggregates in geopolymer mortar, as alkali activation of reactive Si Al in the clay particles helps in the formation of alumina-silicate inorganic polymers. Hence, as an initial step the excavation soils without any treatment were used as fine aggregate in fly ash based geopolymer mortar. Mortar with clayey fine aggregates helps to achieve better compressive strength at a lower dry density range. It was observed that all the three types of soil could be used as a fine aggregate material in the geopolymer mortar. Using excavated soil in geopolymer mortar as fine aggregate may be the simplest application for the direct use of untreated excavated soil. However, geopolymer is not widely used and hence, as a next step the performance of treated excavation soil in cement mortar was evaluated. Initially, dry sieving has been done using 600 μm size sieve to remove clay and fines. Even after dry sieving, particles < 75 μm (silt + clay) were still present in the soil. Hence, stabilization which is a common treatment method used for improving poor quality soil in geotechnical engineering applications, was employed. Stabilization using lime/ GGBS were tried as treatment methods on unprocessed and sieved soil samples, for observing its effectiveness in reducing the plastic characteristics of soil. The treated soils were then used as fine aggregate in cement mortar. Though there was improvement in mortar properties, shrinkage values were high owing to the presence of fines content and reaction products in mortar with dry sieved and stabilized high plastic soil. To further improve the properties of cement mortar, clay and fines were eliminated from excavation soil using wet sieving method. Wet sieving of excavation soil resulted in three products namely, sand (>75 μm), wash water and fines (< 75 μm). Low (LP) and medium plastic (MP) soil were used in the wet sieving process. Wet sieving method was difficult to be applied for high plastic soil which has more than 50% of fines including 41% of clay sized particles that clogs the sieve. The wet sieved sand retained in 75 μm sieve was used as fine aggregate in mortar preparation. With wet sieving process, properties of mortar with excavation soil reached values similar to those of mortar with river sand. This resulted in a zero-wastage technology for the treatment and usage of excavation soil as river sand replacement material. Though wet sieving method was effective in LP and MP soils, it was not suitable for soil with high clay content and results in removal of most of the material as residual clay. Hence, thermal treatment was adopted to study its effectiveness on medium and high plastic soil. The influence of temperature (200 to 1000°C) and duration (30 mins to 180 mins) of thermal treatment of soil on cement mortar properties were studied. From the different treatment methods adopted for excavation soil of low, medium and high plasticity, dry sieving can be applied to low plastic soil to remove the non-reactive clay and silt. Wet sieving with 75 μm sieved should be restricted to soils of low and medium plasticity. Stabilization with calcium compounds can be applied to any type of soil. However, it does not help in reducing the fines content. In such cases, thermal treatment can be a better option. These treatments make the excavation soil a potential replacement for fine aggregate (river sand) in cementitious systems.
About the Innovator
Address: Room no:BSB210, Building Science Block, Civil Engineering department, IIT-MADRAS, Chennai-42
City: Chennai
State: Tamil Nadu
PIN Code 600042
Email: mail2pridha@gmail.com
Contact No: 9962140402.0
Practice Details
Link: Excavation soil generated from earth works of mining industries, tunneling and large volume excavation for construction contains basically sand particles with clay and fines. Though these are sand equivalent materials, presence of fines and clay makes them deleterious to mortar production. The problem of excess fines and clay in excavation soil can be avoided to some extent if replaced partially for fine aggregate. However, the aim is to conserve depleting river sand and use the available alternatives in larger volume. Hence, treatment methods to enhance the properties of alternative fine aggregates will be the better solution, to use them as complete replacement for river sand in cementitious composites. Though there exist few studies addressing such issues of fines on fine aggregate alternatives, there is a need for a systematic study on different treatment methods and their relative effectiveness on different soil types. There is also lack of understanding in the effect of processed material on properties of mortar. Hence, an attempt is made to study the influence of unprocessed and processed excavation soil as a complete replacement for fine aggregate in mortar. This also helps in identifying the adaptability of different treatment methods based on the properties of excavation soil.
Problem Scale: Worldwide
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