Gilson Lomboy - Academia.edu (original) (raw)

Papers by Gilson Lomboy

Examples of microparticle suspensions occur frequently in both industry and nature. For example, ... more Examples of microparticle suspensions occur frequently in both industry and nature. For example, concrete reigns as the most abundant man made material in existence. Yet, the rheology of its key ingredient, cement - a microparticle suspension - , remains poorly understood. Indeed, the simulation of microparticle suspensions, much more simple than cements, present many technical challenges that must be overcome. Such challenges include the need to resolve a broad range of relevant length and time scales. Additionally, many physically relevant model systems are thermodynamically unstable, and particles in this size are expected to make contact. In this talk, we present a first principles approach to studying the rheology of microparticle suspensions: including micro-scale interparticle property measurements, meso-scale simulations of homogeneously sheared suspensions, and comparison with macro-scale rheometer experiments. The systems of interest in this study are suspensions of Port...

The general purpose software XFINAS, which is an eXtended version of FINAS, has been developed on... more The general purpose software XFINAS, which is an eXtended version of FINAS, has been developed on Window Operating system in AIT. The new program to be introduced will enable a powerful nonlinear dynamic structural analysis, taking into account of material and geometric nonlinearity. A large number of numerical testing have been carried out for the validation of XFINAS elements and

Construction and Building Materials, 2014

Thixotropic behavior of cementitious materials is attracting much attention due to its important ... more Thixotropic behavior of cementitious materials is attracting much attention due to its important applications in concrete practice, such as formwork pressure, multi-lift casting, slip form paving, pumping and segregation. This study investigates the influences of nano-sized highly purified magnesium alumino silicate clay (3 nm in diameter, called nanoclay) on thixotropic behavior, particularly, the structural rebuilding of fresh cement pastes. In this study, rheological properties (yield stress, viscosity and thixotropy) of cementitious pastes, with and without nanoclay, were measured at every 15 min after the pastes were mixed. Flow table tests were conducted, and the results were compared with those measured from the rheology tests. Statistical methods were utilized to determine the rates of changes in thixotropy with time. The results indicate that a small amount of nanoclay addition (0.5–1% by mass of cement) significantly facilitates particle re-flocculation or structural rebuilding, and effectively enhances the thixotropy of cement pastes.

Journal of Sustainable Cement-Based Materials, 2014

ABSTRACT The development of self-consolidating concrete (SCC) had revolutionized construction by ... more ABSTRACT The development of self-consolidating concrete (SCC) had revolutionized construction by its ability to achieve full compaction without mechanical vibration and consistency of quality. Use of SCC results in significant reduction in construction time, cost, and noise. With the growing utilization of SCC, the necessity for research to understand and manipulate the fresh and hardened properties of SCC also increases. The paper presents future research needs of SCC in the areas of rheology, construction, and sustainability. Aside from yield stress and viscosity, which are key properties for flowability and stability, the mechanisms behind thixotropy need to be understood. To be able to obtain a better grasp of the mechanisms driving the rheology of cement-based systems, the system needs to be studied at multiple scales. Three research areas in construction using SCC are discussed; pumping, cast-in-place of bridge components, and rock-filled concrete. Finally, the research need for further sustainability is emphasize.

International Journal of Pavement Engineering, 2012

ABSTRACT A new type of self-consolidating concrete (SCC), semi-flowable SCC (SFSCC), has been dev... more ABSTRACT A new type of self-consolidating concrete (SCC), semi-flowable SCC (SFSCC), has been developed for slip-form paving construction. Several field applications of the SFSCC have been conducted. Based on the research results, guidelines for SFSCC mix design, testing, production and construction are developed. This paper provides an overview of the guidelines. In this paper, SFSCC mix design methodology, quality control test methods and special requirements for paving equipment and operations as well as post-placement techniques are presented.

Powder Technology, 2012

ABSTRACT The properties of cementitious materials in their dry state and their influences on visc... more ABSTRACT The properties of cementitious materials in their dry state and their influences on viscosity of pastes were studied. The cementitious materials considered were Portland cement, fly ash, and ground granulated blast furnace slag (GGBFS). Both plain and blended mixes were tested, where plain mixes were made of a single material, while blended materials were made of the Portland cement blended with either fly ash or GGBFS. The properties tested for dry cementitious materials included the compression, recompression, swell indices, stiffness modulus, and coefficient of friction as well as the density and void ratio of gently consolidated bulk materials. Viscosity of the pastes, made with the plain and blended cementitious materials at a water-to-binder ratios (w/b) of 0.45 and 0.55 by weight, were measured. Correlations between the properties of the dry materials and viscosity of the pastes were analyzed. The results indicate that the size, shape and angularity of the cementitious materials greatly affect their dry-state properties as well as the flow behavior of the pastes. Cementitious materials that consolidate well in their dry state will produce a less viscous paste. A decrease in dry coefficient of friction and an increase in stiffness modulus will result in a decrease viscosity of the paste.

Mechanics of Advanced Materials and Structures, 2007

A nonlinear resultant shell element is developed for the solution of problems of composite plates... more A nonlinear resultant shell element is developed for the solution of problems of composite plates and shells undergoing nonlinear static and nonlinear dynamic behavior with progressive layer failure. The formulation of the tangent stiffness is defined on the mid-surface and is efficient for analyzing thick laminated plates and shells by incorporating bending moments and transverse shear resultant forces in the

Journal of Materials in Civil Engineering, 2011

ABSTRACT Shrinkage behavior and fracture properties of five semiflowable self-consolidating concr... more ABSTRACT Shrinkage behavior and fracture properties of five semiflowable self-consolidating concrete (SFSCC) mixes are studied, and their results are compared with those of conventional pavement concrete. In the study, prism tests were employed to evaluate concrete free shrinkage behavior. Restrained ring tests were performed to assess concrete cracking potential. In addition, unrestrained ring tests were conducted and compared with the restrained ring tests. Compressive strength, splitting tensile strength, elastic modulus, and notched beam fracture properties of the concretes were tested at 1, 3, 7, 14, and 28 days. The results indicate that the rates of shrinkage of SFSCCs are generally higher than those of conventional pavement concrete. Compressive strength, splitting tensile strength, and critical stress intensity factor of SFSCCs are comparable to those of conventional pavement concrete, but elastic modulus of SFSCCs is lower than that of conventional pavement concrete. With a higher shrinkage stress-to-fracture strength ratio, SFSCC mixes have higher potential for shrinkage-induced cracking than conventional pavement concrete. The use of a clay additive, purified magnesium alumino silicate, further increases the rate of SFSCC shrinkage. DOI: 10.1061/(ASCE)MT.1943-5533.0000249. (C) 2011 American Society of Civil Engineers.

International Journal of Structural Stability and Dynamics, 2008

Abstract: In this paper, we investigate the natural frequencies and buckling loads of functionall... more Abstract: In this paper, we investigate the natural frequencies and buckling loads of functionally graded material (FGM) plates and shells, using a quasi-conforming shell element that accounts for the transverse shear strains and rotary inertia. The eigenvalues ...

International Journal for Numerical Methods in Engineering, 2003

Quasi-conforming formulations of 4-node stress-resultant shell elements are presented. The elemen... more Quasi-conforming formulations of 4-node stress-resultant shell elements are presented. The element formulations use interrelated displacement-rotation interpolations. The formulation also includes drilling degrees of freedom, which improves membrane behavior and allows the modeling of sti ened plates and shells. The proposed treatment for bending provides very good results in the 4-node shell element. The sti ness matrices for the present elements are explicitly expressed and the stresses are taken accurately at the nodal points. Compared to elements using Gauss integration, where the stresses are most accurate at the integration points, the extrapolation procedure needed for post-processing is eliminated in the present shell element. A lot of numerical tests were carried out for the validation of the present 4-node shell element and the results are in good agreement with references.

Computer Methods in Applied Mechanics and Engineering, 2006

A co-rotational, quasi-conforming formulation of a 4-node stress resultant shell element is prese... more A co-rotational, quasi-conforming formulation of a 4-node stress resultant shell element is presented for non-linear analysis of plate and shell structures. The tangent stiffness matrix in this quasi-conforming formulation is explicitly integrated. This makes the element computationally efficient in incremental, non-linear analysis. It includes drilling degrees of freedom, which improves membrane behavior and allows the modeling of stiffened plates and shells. It is also free of shear locking behavior. The formulation of the geometrical stiffness is derived using the full definition of Green strain tensor. The inclusion of the bending moment and transverse shear resultant forces in the geometric stiffness allows effective analysis of stability problems of moderately thick plates and shells. The stresses are accurately taken at the nodal points without extrapolation. The plasticity is traced by applying the von Mises yield condition and Prandtl-Reuss flow rule to discrete points through the thickness. The multi-layered approach is based on equally spaced stations, including extreme fibers. A modified trapezoidal rule is used for the numerical integration of the constitutive relation in the plasticity part. Numerous tests are carried out for the non-linear validation of present 4-node shell element and the results are in good agreement with references.

Computational Mechanics, 2003

The formulation of a nonlinear composite shell element is presented for the solution of stability... more The formulation of a nonlinear composite shell element is presented for the solution of stability problems of composite plates and shells. The formulation of the geometrical stiffness presented here is exactly defined on the midsurface and is efficient for analyzing stability problems of thin and thick laminated plates and shells by incorporating bending moment and transverse shear resultant forces. The composite element is free of both membrane and shear locking behaviour by using the assumed natural strain method such that the element performs very well as thin shells. The transverse shear stiffness is defined by an equilibrium approach instead of using the shear correction factor. The proposed formulation is computationally efficient and the test results showed good agreement. In addition the effect of the viscoelastic material is investigated on the postbuckling behaviour of laminated composite shells.

Cement and Concrete Research, 2013

Millions of metric tons of cementitious materials are produced, transported and used in construct... more Millions of metric tons of cementitious materials are produced, transported and used in construction each year. The ease or difficulty of handling cementitious materials is greatly influenced by the material friction properties. In the present study, the coefficients of friction of cementitious materials were measured at the microscale and macroscale. The materials testedwere commercially-available Portland cement, Class C fly ash, and ground granulated blast furnace slag. At the microscale, the coefficient of friction was determined fromthe interaction forces between cementitious particles using an Atomic Force Microscope. At the macroscale, the coefficient of friction was determined from stresses on bulk cementitious materials under direct shear. The study indicated that the microscale coefficient of friction ranged from 0.020 to 0.059, and the macroscale coefficient of friction ranged from0.56 to 0.75. The fly ash studied had the highest microscale coefficient of friction and the lowest macroscale coefficient of friction.

Cement and Concrete Research, 2011

A method for determining Hamaker constant of cementitious materials is presented. The method invo... more A method for determining Hamaker constant of cementitious materials is presented. The method involved sample preparation, measurement of adhesion force between the tested material and a silicon nitride probe using atomic force microscopy in dry air and in water, and calculating the Hamaker constant using appropriate contact mechanics models. The work of adhesion and Hamaker constant were computed from the pull-off forces using the Johnson-Kendall-Roberts and Derjagin-Muller-Toropov models. Reference materials with known Hamaker constants (mica, silica, calcite) and commercially available cementitious materials (Portland cement (PC), ground granulated blast furnace slag (GGBFS)) were studied. The Hamaker constants of the reference materials obtained are consistent with those published by previous researchers.

Archives of Computational Methods in Engineering, 2009

Abstract The quasi-conforming technique was introduced in the 1980&amp;#x27;s to meet the... more Abstract The quasi-conforming technique was introduced in the 1980&amp;#x27;s to meet the challenge of inter-elements conforming problems and give a unified treatment of both conforming and nonconforming elements. While the linear formulation is well established, ...

A cell-based smoothed three-node Mindlin plate element (CS-MIN3) based on the first-order shear d... more A cell-based smoothed three-node Mindlin plate element (CS-MIN3) based on the first-order shear deformation theory (FSDT) was recently proposed for static and dynamics analyses of Mindlin plates. In this paper, the CS-MIN3 is extended to geometrically nonlinear analysis of functionally graded plates (FGPs) subjected to thermo-mechanical loadings. In the FGPs, the material properties are assumed to vary through the thickness by a simple power rule of the volume fractions of the constituents. The nonlinear formulation is based on the C0-type high-order shear deformation plate theory(C0-HSDT) and the von Kármán strains, which deal with small strains and moderate rotations. In the analysis process, both thermal and mechanical loadings are considered and a two-step procedure is performed including a step of analyzing the temperature field along the thickness of the plate and a step of analyzing the geometrically nonlinear behavior of the FGPs subjected to both thermal and mechanical loadings. The accuracy and reliability of the proposed method is verified by comparing its numerical solutions with those of available other numerical results

This paper presents the rheological properties of self-consolidating concrete (SCC), semi-flowabl... more This paper presents the rheological properties of self-consolidating concrete (SCC), semi-flowable selfconsolidating concrete (SFSCC), and normal concrete (NC) and their relation to formwork pressure decline. IBB and Brookfield rheometers were used to determined rheological properties of concrete and mortar at 15-90 min after mixing. Formwork pressures were measured using a 200 mm (8 in.) diameter form. Setting time, hydration temperature and compressive strength development of the concretes were also evaluated. SCC displayed shear thickening behavior, and Bingham model became insufficient to describe such rheological behavior of SCC. The initial viscosity and yield stress of SFSCC and NC mortars are similar, but SFSCC mortar has a much higher thixotropy. In concrete mixtures, yield torque increased with time while flow curve slope and thixotropy did not. SCC had the fastest decrease in formwork pressure, followed by SFSCC, then by NC. This correlates with the rate of thixotropy increase of mortar.