Arkamitra Kar

Characterizations and Quantitative Estimation of Alkali-Activated Binder Paste from Microstructures

Alkali-activated binder (AAB) is recently being considered as a sustainable alternative to portland cement (PC) due to its low carbon dioxide emission and diversion of industrial wastes and by-products such as fly ash and slag from landfills. In order to comprehend the behavior of AAB, detailed knowledge on relations between microstructure and mechanical properties are important. To address the issue, a new approach to characterize hardened pastes of AAB containing fly ash as well as those containing fly ash and slag was adopted using scanning electron microscopy (SEM) and energy dispersive X-ray spectra microanalyses. The volume stoichiometries of the alkali activation reactions were used to estimate the quantities of the sodium aluminosilicate (N–A–S–H) and calcium silicate hydrate (CSH) produced by these reactions. The 3D plots of Si/Al, Na/Al and Ca/Si atom ratios given by the microanalyses were compared with the estimated quantities of CSH(S) to successfully determine the unique chemical compositions of the N–A–S–H and CSH(S) for ten different AAB at three different curing temperatures using a constrained nonlinear least squares optimization formulation by general algebraic modeling system. The results show that the theoretical and experimental quantities of N–A–S–H and CSH(S) were in close agreement with each other. The R2 values were 0.99 for both alkali-activated fly ash and alkali-activated slag binders.

Prediction of Shrinkage of Concrete Containing Fly Ash and/or Silica Fume Using Composite Modeling

Partial replacement of Portland cement by industrial by-products such as fly ash and silica fume (collectively known as mineral admixtures) in the normal concrete diverts the deposition of those by-products from landfills, reduces CO2 emissions, and produces durable and sustainable concrete. Shrinkage strain is a major parameter for concrete durability. No systematic data are available to predict the shrinkage of concrete containing mineral admixtures from paste properties to coupon level. In this study, composite modeling was developed from paste level to coupon level for 10 concrete mixtures containing fly ash, and, silica fume, individually as well as in combination, at two different w/cm ratios. Then a two-step composite model was used; firstly to find the shrinkage of mortar from the paste and then the range of the concrete shrinkages was determined using the shrinkage of the mortar and the Hashin-Shtrikman bounds (1963) with the corresponding elastic modulus. The prediction model agreed well with experimental data. The predicted shrinkages from the ACI 209R and CEB M90-99 were computed and the predicted model was found to be in close agreement with the experimental results.

Experimental Studies on Physical Properties and Strength Response of Construction and Demolition Wastes

There is increasing inclination towards the reuse of construction and demolition wastes (CDWs), primarily containing building derived materials (BDM) in engineering practices such as ground improvement. Currently BDMs are used in the form of recycled aggregates that incur extra cost due to refinements. The present study, thereby, emphasizes on the use of virgin BDM. No previous studies related to its characterization and utilization in ground improvement have been reported till now. Hence, this study focuses on the characterization of BDM and its durability aspects through physical, chemical, and microscopic studies to test their compatibility when used in conjunction with local soil contaminated with aggressive chemicals. Soil composition varies based on the vicinity of a chemical plant, waste processing plant, or a coastal area. Results from this study can be used to encourage the practical use of BDM especially in chemically contaminated soil and developing relevant standard codes.

Effect of Strain Rate on Interface Friction Angle Between Sand and Alkali Activated Binder Treated Jute

The interface friction angle between reinforcement and soil is a significant property that defines the suitability of geotextile for several applications such as reinforced retaining wall and slope stability. However, it is not an intrinsic property and varies with several experimental factors such as relative density of sand and shearing strain at which shear tests are conducted. Recent literature shows the wide application of jute geotextile in geotechnical constructions such as slope stability, river bank protection, and subgrade stabilization. However, its application is limited due to low durability under the soil. Therefore, to improve the resistance of jute geotextile against the biological degradation, it has been treated with the fly ash-based treatment solution. This study makes an attempt to investigate the effect of strain rate on the interface friction angle between sand and alkali activated binder treated jute geotextile. The tests are conducted in large shear box apparatus specifically assembled to determine interface shear properties. The jute geotextile is treated with alkali activated binder of four different water to solid ratios, each of them is cured at the temperature of 40 °C. The results obtained are then collated with those obtained from untreated jute geotextile. This study further delineates the effect of the degree of compaction on the interface friction between the reinforcement and sand. Hence, the interface shear properties apropos to the relative density of sand, shear strain, and treatment composition are compared and the obtained trends along with the optimum values are presented.

Stabilization of Expansive Black Cotton Soils with Alkali Activated Binders

The black cotton soil is mainly composed of clay minerals of Smectite group and is highly expansive when exposed to moisture. The present paper proposes a method of geo-polymerizing the black cotton soil with alkali activated binders (AAB). AAB is produced by the reaction between an aluminosilicate precursor (primarily Class F fly ash and/or slag) and an alkali activator solution of sodium hydroxide and sodium silicate. The water to solids ratio is maintained at 0.3. Mineralogical and microstructural characterizations through X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) are carried out for both untreated and treated soil to identify the changes in chemical composition and surface morphology. The index properties, compaction characteristics, unconfined compressive strength (UCS) and swelling characteristics of both untreated and treated soil are carried out. It is observed that the AAB reduces the plasticity index and free swell of black cotton soil by 15–25%, while the UCS values are increased by 10–12%. Recommendations on practical implementation of this technique for stabilization of expansive soils are proposed based on the findings of this study.

Performance of alkali-activated binder-treated jute geotextile as reinforcement for subgrade stabilization

AbstractGeotextiles are widely used for reinforcing soil, improving drainage, controlling soil erosion and embankment construction. Existing research recommends the improvement of soil in an econom...

Characterization of building derived materials for partial replacement of pavement subgrade layer

This study investigates the potential of BDM in its virgin state for enhancing the geotechnical and mechanical properties of soft non-swelling soil with low shear strength. A series of material and geotechnical tests carried out on soil replaced with different percentages of BDM include specific gravity, water absorption, standard Proctor’s test, permeability test, aggregate impact test (AIV), Los Angeles abrasion test, and large shear box test. The results indicated that an optimum of 18–23% of BDM by weight can be added to soil to improve its mechanical and geotechnical properties such as shear strength and compaction. This study also evaluates the compatibility of BDM in soils from sites surrounding chemical plants. For this purpose, the BDMs are exposed to sulfuric, hydrochloric, and nitric acid solutions to identify the effects of these acids on the BDM behavior. It is observed that the strength of BDM decreases after their exposure to these solutions, with maximum effect manifested by nitric acid and least by hydrochloric acid. The results of AIV and LA abrasion test on BDM exposed to chemicals show that the performance of the BDM deteriorates in the presence of chemicals. The results obtained from the proposed study can be used to promote the practical use of BDM in geotechnical applications. However, necessary precautions must be adopted for their practical application in ground improvement based on soil conditions.

Experimental Investigations on Building Derived Materials in Chemically Aggressive Environment as a Partial Replacement of Soil in Geotechnical Applications

Construction and associated demolition processes produce huge amount of solid waste, generally termed as construction and demolition waste (CDW). Management and proper disposal of these wastes is an area of prime concern for modern civil engineers. About 90% of all CDW is composed of building derived materials (BDM) obtained from concrete, bricks, and tiles from structural and non-structural elements of a building. The present study emphasizes on the use of virgin BDM, which conserves natural aggregate, reduces the impact on landfills, saves energy, and thus can provide significant cost benefit. Five types of BDM—crushed lightweight concrete (T1), crushed marble tiles (T2), crushed high strength concrete (T3), crushed normal portland cement concrete (T4), and crushed bricks (T5)—are characterised to assess their compatibility when used in conjunction with local soil. The soil, BDM and soil–BDM mixes are characterized from physical, mechanical, mineralogical, microstructural, and chemical aspects. These tests are then repeated for the aforementioned soil-BDM mixes after immersion in acids. Aggregate impact value (AIV) results on the five types of BDM indicate that T1 and T5 are poorly resistant to impact loads. However, T2, T3, and T4 show relatively better resistance to impact loads and satisfy the requirements for sub-base material standards. Shear strength studies show that the average optimum replacement of soil by BDM is in the range of 17–23% by mass. In order to test the compatibility of BDM in soils containing aggressive chemicals, the properties mentioned above are re-evaluated after exposing the BDM to aggressive chemical environments. The results indicate that the internal angle of friction (ϕ) of virgin BDM is found to vary significantly due to acid attack. The results of AIV after exposing the BDM to acids show that BDM are highly susceptible to chemically aggressive environment. The performance of all types BDM are affected by the presence of acids and appropriate measures must be adopted while using BDM in such chemically aggressive environment. These standards can be used as guidelines in the present study in the absence of specific standards for BDM applications.

Durability evaluations of bridge deck high-performance concrete

Although several information are available on various aspects of durability of high-performance concrete (HPC), no systematic information is available on durability of HPC used for bridge decks. In this study, 12 HPC mixtures were prepared with different combinations of fly ash, slag, and silica fume with three different w/cm ratios: 0.40, 0.35, 0.30 to study the durability primarily concerning bridge deck. Results show that at higher w/cm ratio, both rapid chloride penetration and chloride diffusion depend mostly on supplementary cementitious materials. A combined freezing and thawing/salt-scaling test for a properly made test specimen is representative of real-life situation for bridge deck slab. The physical sulphate attack is minimal for HPC with low w/cm ratios. The present experimental study serves to establish a basis for the future optimisation of HPC mixture proportions as well as test methods through critical durability evaluations.