This paper reports investigations on the influence of material parameters on electrical conductivity of cement pastes and concrete mixtures. The influence of cement type, water/cementitious materials ratio (w/cm), and the presence of fly ash as a cement replacement material on the conductivity of cement pastes is studied. The electrical conductivity-time relationships of cement pastes and concretes are expressed using a model that facilitates the extraction of initial and final conductivities, and a characteristic time parameter. These terms can be used to derive information about the microstructural changes occurring with time in cement pastes. A fractional factorial experiment scheme consisting of five factors-w/cm, fly ash content, aggregate-cementitious materials ratio (a/cm), aggregate size, and curing condition (saturated or sealed), with each factor at two levels (+1 or À1 corresponding to high and low levels)-is used for concrete mixtures. The experimental results are subjected to a range analysis to isolate the significant factors and factor interactions that influence the initial and final conductivities as well as the time parameter from the conductivity-time model for concrete mixtures. The a/cm exerts significant influence on both initial and final conductivities, whereas the amount of fly ash in the mixture, aggregate size, and curing condition influence the final conductivity of concretes. The w/cm and fly ash content were seen to influence the time parameter. Analysis of variance is conducted on the test results and the prominent two factor interactions that influence the conductivities and the time parameter are determined. The relationship between these responses and the parameters is expressed in terms of a least squares fit equation using the coded values for the variables.
Electrical response of cementitious systems can be used to understand the evolving microstructure, and thus to provide indications of the mechanical and durability performance of such systems. This paper deals with the use of a generalized effective medium (GEM) theory to predict the porosity of cement pastes and concretes containing several cement replacement materials. Methodologies to obtain the pore solution conductivities and an equivalent soild phase conductivity in the case of concretes are outlined. The predicted porosities are found to match well with the experimental values obtained from a vacuum saturation method. It is shown in this paper that the critical exponent in the GEM equation influences the predicted porosities and a universal value for this exponent cannot be used in continuum percolating systems such as cement pastes and concretes. The thermal signature of hydrating cementitious systems, represented using the equivalent age maturity index, is related to a microstructural parameter obtained from electrical impedance. A unique relationship is observed between the equivalent age and the microstructural parameter irrespective of the mixture design parameters thereby providing a crucial link between maturity and microstructure development.
This article proposes an analysis procedure of structural mechanics' problem as integral formulation. The methodology is novel which can be suitably applied for finding the solution of engineering problems with required accuracy either it is linear or nonlinear range (plastic range) of the material behaviour. This methodology, which was proposed as a stress-based analysis procedure, exploits the unfolded part of the structural analysis problems which were not so easy to solve such as geometric and material nonlinearity together with simple integration technique (Gaur and Srivastav, 2021). In fracture mechanics, it has already unfolded the misery of physically exploiting the plastic behaviour of structures before the start of the crack for elastic materials . The formulation is an integral formulation rather than a differential formulation in which whole stress-strain behaviour is utilised in the analysis procedure by using a neural network as a regression tool. In this article, the one-dimensional problem of uniaxial bar, beam bending problem and plane strain axis-symmetric problem of a cylinder subjected to internal pressure is solved. The results are compared with the existing differential formulation or linear theory.
The poor soil properties result in foundation failures of the structure which further causes in cracks of structural elements and walls. To avoid this, it is essential to enhance the soil properties. Soil stabilization is one of the processes to improve the engineering properties of the soil and thus making it more stable. It is required when the soil available for construction is not appropriate for the intended purpose. In this research, for stabilizing clayey soil and to achieve higher strength in minimum time period, gypsum (CaSO4.2H2O) is used as one of the soil stabilizing agents. Experiments were planned to evaluate the properties of clayey soil on the addition of different percentages of Gypsum i.e., 2%, 4%, 6% and 8% to the existing soil. Tests conducted on clayey soil mixed with Gypsum included are, Atterberg’s Limits, Specific Gravity and Standard Proctor Test. A comparison between the properties of clayey soil, clayey soil mixed with Gypsum is done to understand the effect of Gypsum addition on soil properties. It was observed that the soil properties were enhanced for 6% of Gypsum addition to the soil.
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