Utilization of Industrial Solid Wastes for Synthesis of Inorganic Polymer as a Soil Stabilizer

Abstract

Soils need to be stabilized to improve its geo-engineering properties before any construction of infrastructures. Conventional soil stabilizers such as cement and lime have environmental issues and uneconomical. Geopolymers are the new generation binder that has attracted considerable interest in modern construction industries due to their high engineering performance, less environmental impacts and cost-effectiveness. An investigation is made to explore the efficacy of geopolymer prepared by sodium hydroxide activated fly ash-slag in stabilizing the granular soil through a set of experimental studies.
The physical, mechanical and chemical properties of geopolymers are greatly influenced by the synthesis parameters. The fresh and hardened properties such as normal consistency, setting time, soundness, drying shrinkage, flow and compressive strength of the geopolymer paste and mortar are reported. The influence of synthesis parameters on the unconfined compressive strength of the geopolymer; synthesized under different processing conditions is investigated. The microstructural analysis is also made to correlate the reaction products with the observed strength. Statistical analyses are carried out to check the significance of the factors affecting the synthesis process. Also, mathematical relationships are established for factors influencing the mechanical behavior of the synthesized geopolymer. The compaction characteristics, unconfined compressive strength, bearing resistance, permeability characteristics, durability under wetting-drying, freezing thawing cycles and decay under chemical attacks of geopolymer modified granular soil are investigated experimentally in order to assess its suitability as a geotechnical construction material. Also, the effect of delayed compaction on density and strength has also been studied. Microstructural analysis has been carried out and correlated with the strength development.
The test results reveal that the dissolution of alumino-silicates is highly influenced by the alkali content and the reactive component of the source material. The experimental results indicated that the physico-mechanical properties of geopolymer binders are similar to that of conventional cement and are greatly influenced by the composition of the source material, concentration of the activator and processing conditions. The major reaction products were the hydrates of calcium and/or sodium based alumino-silicates and those were intensified with curing temperature and duration. Raw materials are optimized by the design of experiment and the fitted model shows a good relation with the experimental data. Based on the test results of geopolymer stabilized soil, a maximum unconfined compressive strength of about 7 MPa is attained. California bearing ratio ranging from 52 to 416% are obtained at different geopolymer contents and curing conditions. The geopolymer stabilized granular soil showed excellent stability against repeated wetting-drying, freezing-thawing cycles, slaking fluid and aggressive chemical environment. The microstructural developments in geopolymer stabilized granular soil are greatly influenced by the geopolymer content and curing period signifying the formation of hydration and geopolymeric reaction products.