K Ramamurthy

This paper discusses water penetration resistance studies on conventional brick/block masonry for variations in construction types and materials adopting ASTM E 514-90 procedure. The behaviour of interlocking block masonry for the influence of type of bedding (dry-stacking, thin-jointing, and mortar-bedding), surface finishes (stucco/plaster finish) have been investigated. Also the relative performance of solid as well as hollow interlocking block masonry system developed by the authors, with conventional masonry is reported. © 2003 Elsevier Science Ltd. All rights reserved.

Use of ductless split air conditioners in small workspaces leads to accumulation of carbon dioxide due to the absence of fresh air entry. Additional mechanical ventilation is required to meet the ASHRAE standard. Providing constant-rate ventilation would reduce the CO2 concentration but would lead to high energy consumption when there is variation in occupant density. Instead, demand-controlled ventilation, that is, ventilation rate linked with the occupant density, can reduce energy consumption and maintain adequate indoor air quality. The purposes of this study were to quantify the temporal variation of CO2 in a workspace, to determine the factors influencing the demand-controlled ventilation strategy, and to assess its performance in workspaces with flexible work environment (varying occupant density with time). A parametric study on demand-controlled ventilation design indicates that the ventilation cycle time depends significantly on the occupant density and the range of threshold levels of CO2. The occupants can decide the lower CO2 threshold level based on the requirements. Use of a lower CO2 threshold limit of 700 ppm in a typical workspace with varying occupant density resulted in an energy saving of around 90% when compared with the ventilation rate required by ASHRAE 62.1. The assessment would be helpful in identifying the workspaces that do not require external ventilation. The ventilation design strategy thus developed would help the building managers in improving indoor air quality and lowering energy costs when compared with the constant rate ventilation system.

Most of the investigations on foam concrete in the past have been confined to neat cement paste, cement paste with partial replacement with admixtures and to cement-sand mixes. This paper reports the results of a systematic study to ascertain the influence of filler type (i.e., sand and fly ash) and the particle size of sand on the properties of moist cured foam concrete. This study shows that the consistency of mixture, for achieving pre-formed foam concrete of design density, mainly depends on the filler type. The flow behaviour of foam concrete is mainly influenced by the foam volume. A reduction in particle size of sand caused an improvement in strength of foam concrete. For a given density, replacement of sand with fly ash resulted in higher strength. Finer filler resulted in a higher ratio of strength to density. © 2005 Elsevier Ltd. All rights reserved.

Coral islands are tiny and are scattered in deep seas throughout the world, hundreds of kilometres away from the mainland. For construction activities in these islands, coral shingles and coral sand are the main locally available materials. A review indicates that only a few investigations have been undertaken on the properties of coral aggregates and concrete made with them. This paper discusses the results of a systematic investigation of the physical, chemical and mechanical properties of coral shingles and coral sand. Their suitability as aggregate for concrete making has been studied through comparison with the results of tests on conventional crushed granite aggregate and river sand. The workability, density and compressive strength characteristics of different nominal mixes of conventional aggregate concrete and coral concrete with various water-cement ratios have been compared and discussed.

Selection of the surfactant has an impact on many of the foam properties as it affects the surface tension and gas-liquid interfacial properties. The objective is to produce stable aqueous foam of required density. These two characteristics are influenced by the type of surfactant, its concentration and foam generation pressure. This study compares the density and stability of foam produced using four synthetic surfactants namely sodium lauryl sulfate, sodium lauryl ether sulfate, sulfanol and cocodiethanolamide through a systematic experiment design based on response surface methodology. The relative performance has also been assessed in terms of their suitability for use in foamed concrete production based on ASTM test method. The effect of surfactant concentration has relatively lesser effect on foam density for sodium lauryl sulfate and sulfanol irrespective of foam generation pressure adopted. The drainage is proportional to the initial foam density for all the surfactant concentration for ionic surfactants at different foam generation pressures. For all the four surfactants under the optimum foam generation pressure, a stable foam with drainage less than 12% in 300 s (by considering economy as a factor) is achieved. From the foam stability test based on ASTM C 796-97, it is observed that all the four surfactants are suitable for use in foamed concrete production when optimized foam production parameters are adopted. © 2010 RILEM.

In this paper, the factors influencing the properties of aerated geopolymer concrete using low calcium fly ash through sodium-based alkali activation at a range of curing temperature is discussed. The parameters and their influence are statistically studied using design of experiments. The initial rate of reaction in the aeration process is controlled by using the alkaline solution (viz., sodium hydroxide (NaOH) and sodium silicate (Na-Si)) which is cooled to a lower temperature. The conditioning of solution at lower temperature helped in achieving uniform mixing and to increase the placing time without hindering aeration. The factors influencing and their interaction effects on fresh density, dry density, compressive strength and water absorption were studied. Compressive strength of aerated geopolymer paste is 55% higher than mortar for the given range of parameters.

Design of concrete hollow block masonry subjected to lateral loading is controlled by appropriate permissible tensile stresses developed with respect to bed joints, ie, either normal or parallel to the bed joints, depending upon the direction in which the wall spans. There are wide variations between code provisions and many parameters have not been accounted for adequately, revealing the need for systematic investigation. As a first step, tests for flexural strength normal to bed joints of concrete hollow block masonry prisms in running bond have been carried out. The influences of full mortar bedding using conventional mortar mixes, the influence of plastering and grouting were investigated by using a bond wrench apparatus. Results show that the flexural bond strength increases with the richness of the bedding mortar mix proportion adopted, and observed to be higher than those specified by IS 1905. The plastering and grouting have significant effect in contributing to the flexural strength of masonry, and hence, these aspects need to be included in the design provisions.

Numerous types of concrete hollow blocks with varied geometries are being used in practice all over the world. As the masonry is constructed in stretcher bond, use of blocks with different geometries result in different behaviour and leads to different load bearing capacities. Therefore, the use of a single table of permissible stresses as per IS : 1905 will result in either underestimation or overestimation depending on the type of blocks used. This paper deals with an experimental investigation carried out on the compression behaviour of three - course high concrete hollow block masonry (CHBM) prisms using one type of block geometry. Five block and five mortar strength combinations have been considered. The study indicates that the design of hollow block masonry as per the provisions of IS : 1905-1987 is conservative. The table of masonry basic compressive stresses formulated based on the present study, for different block-mortar strength combinations, could be used for a more rational design approach for CHBM which would result in cost-effective use of the material.

This paper discusses the performance evaluation of anidolic concentrators in an overcast sky condition. The concentrators were designed, with acceptance angles of 60°, 70° and 80°, first by maintaining the profile of the concentrator's uniform and secondly by keeping the height uniform. Studies were done using these concentrators with a model light pipe and the performance was compared with that of an acrylic dome and a profiled Fresnel collector. For a given condition, the illuminance ratio (ratio of illuminance measured at the base of the pipe to external illumination) increased with the acceptance angle. For a given acceptance angle, the concentrator with uniform height and variation of entrance aperture, performed better than a concentrator having a uniform profile.

Singly curved or doubly curved shells, most commonly used in large span structures, are analyzed using flat plate/shell/plate-shell. Depending on their structural actions and stresses generated, sometimes they are also prestressed. If the prestressing is in a direction where the curvature of the shell is negligible or zero, the shell structure could be analyzed using surface elements (e.g. cylindrical shells prestressed longitudinally). If the prestressing is in a direction where the structural element has a curvature (e.g. cylindrical shells prestressed along the curved axis), it introduces circumferential forces and hence may introduce stress gradients in direction normal to the curved axis viz., in the thickness direction, which cannot be idealised using surface elements. Analysis of such shells using ADINA code is presented in this paper. The results show that for a prestressing cable placed somewhere within the thickness of the shell and sufficiently away from the boundaries, the variation of normal radial stress changes from tension above the cable profile to compression below the cable profile, clearly indicating the existence of radial tension. The magnitude of the radial tension is influenced by the parameters like radius, semi-central angle, rise of the shell and thickness. The radial stress varies inversely with radius and directly with rise, while change in thickness and semi-central angle do not affect its behaviour at the apex.