K. Ganesh Babu

BEHAVIOUR OF LIGHTWEIGHT EXPANDED POLYSTYRENE CONCRETE CONTAINING SILICA FUME

Abstract Lightweight concrete can be produced by replacing the normal aggregate with lightweight aggregate, either partially or fully, depending upon the requirements of density and strength. The present study covers the use of expanded polystyrene (EPS) beads as lightweight aggregate both in concretes and mortars containing silica fume as a supplementary cementitious material. The main aim of this project is to study the strength and the durability performance of EPS concretes. These mixes were designed by using the efficiency of silica fume at the different percentages. The resulting concretes were seen to have densities varying from 1500 to 2000 kg/m 3 , with the corresponding strengths varying from 10 to 21 MPa. The rate of strength gain for these concretes shows that an increase in the percentage of silica fume increases the 7-day strength. This was observed to be about 75%, 85%, and 95% of the corresponding 28-day strength at the silica fume replacement levels of 3%, 5%, and 9%, respectively. The results of absorption, at 30 min and the final absorption, show that the EPS mixes made with sand have lower levels of absorption compared to the mixes containing normal aggregates. Further, the absorption values were seen to be decreasing with increasing cementitious content. The performance of these concretes, in terms of their chloride permeability and corrosion resistance, even at the minimal silica fume content level was observed to be very good.

Efficiency of fly ash in concrete with age

Abstract Research efforts over the past many decades towards an effective utilisation of fly ash in concrete do not seem to have led to a quantitative understanding of the efficiency of fly ash as a mineral admixture, particularly because of the vast variation in the grades of concrete and the different levels of replacements adopted. This paper is an effort directed towards a specific understanding of the efficiency of fly ash in concrete, considering the strength to water cement ratio relations, age and percentage of replacement. The “overall cementing efficiency” (k) of fly ash was established through a “general efficiency factor” (k e ), dependent on the age and a “percentage efficiency factor” (k p ), dependent on the replacement percentage. This information will allow designers to evaluate the strength of well designed fly ash concretes at any age and at the different percentages of replacement.

Efficiency of silica fume in concrete

Abstract The use of silica fume as a mineral admixture for the production of high strength high performance concretes is gaining importance in recent years. The present paper is an effort towards a better understanding of the efficiency of silica fume in concrete. It was observed from an evaluation of the data available in literature that the efficiency of SF in concrete was not a constant at all percentages of replacement. It was proposed that the “overall efficiency factor” of SF can be assessed in two separate parts, the “general efficiency factor” — a constant at all the percentages of I replacement and the “percentage efficiency factor” — varying with the replacement percentage. A comparison of the efficiencies obtained from the earlier data with studies on a “Lower Grade Silica Fume” in the laboratory show that the proposed values of efficiency are of lower bound and it is possible to achieve even higher efficiencies with proper mix proportioning.

Efficiency of fly ash in concrete

Earlier efforts towards an understanding of the efficiency of fly ash in concrete has led to the introduction of rational methods. Based on the results available on some of the more recent pulverised fuel ashes, the authors evaluated the efficiency of fly ash in concrete over a wide range of percentage replacements (15–75%). It was clearly shown that the overall efficiency of fly ash cannot be adequately predicted using a single efficiency factor at all percentages of replacements. The overall efficiency factor (k) has been evaluated at all percentages of replacements considering the general efficiency factor (ke) and the percentage efficiency factor (kp). This study resulted in a quantitative assessment of the behaviour of fly ash in concrete, especially for the 28 day compressive strength at different percentages of replacement.

Early strength behaviour of fly ash concretes

Abstract The strength of concrete at early ages has assumed a considerable significance in recent years due to the several specific requirements of the modern construction industry, like the early striking of forms, early transfer of prestress etc. However, fly ash concretes are known to have a lower early age strength and there have been many efforts to predict and/or to improve this in recent years, so that these concretes can be utilized appropriately. Thus a quantitative understanding of the early age strength behaviour of fly ash concretes will help in designing the concrete for any specific requirement. This investigation, assumed on the most recent results available, predicts the same through the efficiency concepts at the different percentages of fly ash replacement.

Track Modulus Analysis of Railway Track System Using Finite Element Model

With the development of ever faster trains, the problem of excessive ground vibrations has increased. Dealing with ground vibration from surface and underground trains is a challenging issue for the railway industry. In the present work, the analysis of a typical Indian railway track system has been done with special emphasis on “track modulus” for Prestressed Concrete (PSC) sleepers and Wooden (WOOD) sleepers. The track consists of two rails of standard length, rail pads and sleepers with constant sleeper spacing, ballast and subgrade covering the length of the rails as per the Indian Railways standards. Finite Element models have been developed for computer simulation of the dynamic behaviour of the railway track system for 52PSC, 60PSC, 52WOOD and 60WOOD track. In this model, subgrade, ballast and rail pad parameters have been considered for parametric analysis of the track modulus. Finally the track system is excited harmonically over a range of frequencies to predict the dynamic variation in the track modulus.

Unit Cell Approach as a Multi Scale Modeling Technique for Predicting the Behaviour of Fiber Reinforced High Strength Concrete Under Compression

Fiber reinforced concrete has been identified as a particulate composite consisting of hardened cement paste, fine aggregates, coarse aggregates, particulate fibers etc. and each constituent plays a significant role in the combined quasi brittle behaviour of the material. From the view point of a numerical modeler, a two phase model consisting of a matrix phase and a coarse aggregate phase is simple and sufficient enough to take care of the heterogeneity without affecting the capability of the model to predict the material behaviour as reported by Ghouse et al [1]. Thus the unit cell under consideration is modeled as a square with an inner circle (Fig. 1), the square representing the total volume fraction of combined properties of cement paste, fine aggregates, particulate fibers and water. The inner circle represents the total volume fraction of coarse aggregates in the material. This representative volume fraction is assigned with periodic boundary conditions to ensure uniformity in deformation and to avoid any discontinuities in the material once the unit cell has been repeatedly arranged to build up the macro sized material and has undergone deformation in elastic range. Ghouse et al [1] could identify only slight variations in the compressive strength of normal low strength concrete with varying aggregate volume fractions. A comparatively decreasing trend in compressive strength has also been observed initially when glass fiber reinforced high strength cement composite (GFRCC) was analyzed by Sunir et al [2]. Investigations proceed in the direction of predicting the material behaviour by replacing the glass fiber and its volume fraction with polypropylene fibers considered by Pavan [3] as being significant in improving the mechanical characteristics of the macro composite under consideration. An analysis of polymer fiber reinforced high strength concrete (PFRC) with similarly varying aggregate volume fractions could predict significantly decreasing trends in compressive strength for lower volume fractions. In future, the ease with which the unit cell approach predicts the behaviour of fiber reinforced plain mortar is also to be investigated in a similar manner.Copyright

Probabilistic model for wave forces acting on a cylinder in random waves

Abstract Generally, the sea-state (random waves) is best described by a wave spectrum. A number of statistical models for wave spectra has been well established and a sea-state can be specified. Once the specified sea-state is established, the corresponding model for wave forces acting on a single cylinder or a group of cylinders can be formulated. Since peak force is of more practical value, a multivariate or joint probability density function for wave forces has been developed for the peak force distribution of wave forces. This theoretical force model derives the tri-variate probability density function P(F, F′, F″) , where F is the peak force defined by Morison equation. This model is of wide-band in nature and is tested by wave flume experiments.