Research and Development – Nano Mechanics and Engineering
Recently Completed Projects
Molecular dynamics simulations to investigate the performance of nano-engineered composites
Cementitious composites are multiphase heterogeneous materials with distinct dissimilarity in strength under compression and tension (high in compressive and very low in tensile). At macro scale, the phenomenon can be well-explained as the material contains physical heterogeneity and pores. But, it is interesting to note that this dissimilarity initiates at molecular level where there is no heterogeneity. In this regard, molecular dynamics based computational investigations are carried out on cement clinkers and calcium silicate hydrate (C-S-H) under tension and compression to trace out the origin of dissimilarity. It has been identified that certain type of molecular interactions and the molecular structural parameters are responsible for causing the dissimilarity in behaviour.
Atomic structure of Tobermorite a) With extra inter-layer calcium atoms b) With less calcium atoms
Nano-engineering of materials has proven to enhance the performance of conventional materials. However, the improvement in the properties mainly depends on the compatibility and extent of interaction of nanoparticles with matrix. In view of this, MD studies have been carried out to investigate the interaction of filament type nano materials such as Carbon Nanotube (CNT) with different types of epoxy polymers. Pull out simulations were also carried out in order to ascertain the efficiency of load transfer between CNT and epoxy polymers.
Simulated pull-out test on CNT engineered epoxy using Molecular Dynamics
Multiscale modeling of cementitious composites
Cementitious materials are of unique kind of materials since they have multiple phases at multiple length scales during different hydration ages. In depth understanding of the properties of each of the phases at different length scales and how their properties are transferred to the next higher scale is necessary to use the material optimally. In this regard, a methodology has been established to determine the mechanical properties using hybrid technique. An analytical hydration model has been used to obtain the microstructural arrangement of different phases within the cement paste. This microstructural arrangement is then used to determine the mechanical properties at macro-level using different analytical and numerical techniques. This study will also be extended further to investigate the influence of addition of foreign moieties on its micromechanical properties.
Before Hydration 3 days 28 days
Microstructures obtained from hydration model
Development of micro-engineered concrete
The brittleness of concrete has been its bottleneck for many decades, and it’s low tensile strength and ductility are the primarily reasons for frequent repair and rehabilitation of concrete structures. The addition of fibers has reduced the brittleness and improved the fracture toughness, but still, it is not deemed to be fit during earthquakes. There is increasing interest to improve the concrete behaviour under tensile loading and to incorporate the strain hardening behaviour. Micromechanics based composite optimization can be employed to develop the cementitious composites exhibiting strain hardening behaviour by using optimum fiber content. Further, the scientifically designed fiber reinforced cement composite can provide tensile strain capacity and the important feature of composite materials like FRC is that the overall mechanical properties can be controlled by adjusting the micromechanical parameters of their constituents. In the present study, experimental studies using the Poly Vinyl Alcohol (PVA) fibers is carried out for different microstructural parameters. The difference in composite mechanical behaviour is studied by varying the fiber length, fiber volume fraction and water to cement ratio. The restricted crack growth due to bridging of fibers is evident. The results of this study demonstrate the significance of understanding the mechanics of fiber reinforced composites to developing new class of engineered cement composite (ECC).
Crack bridging and strain hardening of PVA ECC
Development of low cement concrete
One of the main focuses of this group is to develop concrete by significantly reducing the cement content. Cement production is one of the major sources of CO2 emission as production of one tonne of cement emits approximately 0.8 tonne of CO2. In view of this, attempt is made to replace cement upto 80% and found that the replacement of cement to the extent of 60% is possible by incorporating the industrial waste such as fly ash. However, loss in strength due to high volume replacement of cement is regained by adopting suitable and feasible chemical intervention through incorporation of various sources of calcium carbonate (CC) in this study as waste lime sludge can be one of the many potential sources for CC (ball milled to obtain the micro or nano size). Further, suitable nano activation was done for an effective replacement of cement upto 60% and to achieve a strength of 30 MPa (most used for common structures). The procedure of developing the low cement concrete is given in form of a schematic diagram.
Schematic diagram for developing low cement concrete
This group is also aiming at determining the early age properties of engineered cementitious composites using micro-analytical and wave propagation techniques. It is aimed at development of the new class of concrete with various criteria such as low cement, strain hardening, high-strength-high ductility etc. and evaluate their performance in structural components under various types of loading scenarios.
Performance evaluation of newly designed- and deficient- structural sub-assemblages under seismic type loading
Seismic performance of sub-assemblages of reinforced concrete (RC) structure designed and detailed based on the provisions of various national Standards at different stages of their evolution was evaluated. Performance of the sub-assemblages designed and detailed according to the three different stages of codal evolution (gravity load designed, ‘Nonductile’ and ‘Ductile’) was evaluated through analytical formulations and experimental investigations. In the analytical study, shear and flexural failure of members of sub-assemblage and shear failure of the joint were considered as possible modes of failure of the sub-assemblage. For evaluating the shear strength of the joint region, a soften strut and tie model was used. Analytically obtained strengths based on the failure criteria of different components of the specimens were first validated with experimental results and then, used to determine the strength of the specimens. It is found that the provisions for ductile detailing of RC structures under seismic type loading are not adequate and there is a wide room for improvement using mechanics based approaches such as compression field theory, strut and tie models, etc. to first calculate the available strength hierarchy of the structural component and then to stipulate the detailing requirements based on the strength hierarchy. This unified approach provides not only the better detailing for the structures under seismic type loading, but also the quantification of level of upgradation required for under-designed structures.
Failure pattern of NonDuctile and Ductile specimens
Piezo –resistive cementitious composites for structural health assessment
Smart material reinforced non-destructive structural health monitoring technique has been evolving as the most predominated route for assessing the performance of the civil structures. In view of this, in this study, multiwalled nanotubes (MWNT) were suitably incorporated into the cement matrix, which act as actively embedded sensor for monitoring real-time flaws in structures. Micromechanics based analytical investigations were carried out to identify the influence of geometry of CNT on the conductivity and to assess the effective electric percolation network in cement matrix. Also, the role and effect of concentration of ionic surfactant (SDBS) and various parameters of ultrasonication for synthesis of the nano-composite had been established. The electrical conductivity of MWNT incorporated cement system, as developed in the present study, was measured using four probe method. Piezo-resistivity of the oven dried samples was measured to evaluate the change in potential drop under cyclic loading regime. Thus, the material can be used as embedded sensor for health monitoring (real-time) and identifying initiation of any damage in reinforced concrete structure.
Fabrication of piezo-resistive cementitious composites
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