Mukesh Limbachiya

Use of recycled concrete aggregate in high-strength concrete

The results of a test programme to study the use of recycled concrete aggregate (RCA) in high-strength, 50 N/mm2 or greater, concrete are described. The effects of coarse RCA content on the ceiling strength, bulk engineering and durability properties of such concretes have been established. The results showed that up to 30% coarse RCA had no effect on concrete strength, but therafter there was a gradual reduction as the RCA content increased. A method of accommodating the effects of high RCA content, involving simple adjustment to water/cement ratio of the mix is given. It is shown that high-strength RCA concrete will have equivalent engineering and durability performance to concrete made with natural aggregates, for corresponding 28-day design strengths. The practical implications of the study for concrete construction are discussed.RésuméSont décrits ici les résultats d’une série d’essais destinés à étudier l’utilisation de granulats provenant du recyclage d’éléments en béton (RCA) dans des bétons de haute résistance (50 MPa et plus). Les effets de la teneur en gros granulats recyclés sur la résistance des plafonds et des bâtiments, ainsi que les propriétés de tels bétons ont été établis. Les résultats ont montré qu’une teneur allant jusqu’à 30% en gros granulats recyclés n’a pas d’effet sur la résistance du béton, mais qu’au dessus de 30%, la résistance diminue progressivement à mesure que la teneur en gros granulats recyclés augmente. Une méthode visant à accommoder les effets dus à une forte proportion de RCA, nécessitant un simple ajustement du rapport eau/ciment dans le mélange, est proposée. Il est prouvé que le béton RCA de haute résistance aura des qualités de résistance et de durabilité équivalentes à celles de bétons constitués de granulats naturels, pour les résistances mécaniques à 28 jours prévues. Les implications pratiques de l’étude sur la réalisation d’ouvrages en béton sont présentées.

PERFORMANCE OF RECYCLED AGGREGATE CONCRETE

Waste arising from construction and demolition (C & D) constitutes one of the largest waste streams within the European Union (EU) and many other developed countries. Of this a large proportion of potentially useful material disposed of as landfill. The environmental and economic implications of this are no longer considered sustainable and, as a result, the construction industry is experiencing more pressure than ever before to overcome this practice. On the other hand, in recent years the wisdom of continued wholesale extraction and use of aggregates from natural resources has been questioned at an international level. This is mainly because of the depletion of quality primary aggregates and greater awareness of environmental protection. The results of an extensive experimental programme aimed at examining the performance of Portland-cement concrete produced with natural and coarse recycled aggregates are reported in this paper. The effects of up to 100% coarse recycled concrete aggregate on a range of fresh, engineering and durability properties have been established and assessed its suitability for use in a series of designated applications.

Performance of Portland/Silica Fume Cement Concrete Produced with Recycled Concrete Aggregate

This paper shows how the use of recycled aggregate in the concrete industry has a great potential in reducing the demand for natural aggregate and the amount of solid waste dumped at landfill sites. The main objective of this paper is to design a concrete made with different proportions of coarse recycled concrete aggregate (RCA) having a similar 28-day design strength to corresponding natural aggregate concrete. Recycled coarse aggregates, obtained by crushing concrete debris from various sources, were used in three proportions of 30, 50, and 100% (by weight) in order to produce concrete with various water-cement ratios (w/c) and different compressive strength grades. The key mechanical properties and durability performance of concrete produced with portland silica fume (PSF) and RCA were investigated in the paper. The RCA used showed inferior mechanical properties (crushing and impact values) than the natural aggregates (NA) and, hence, RCA concrete exhibited slightly lower performance than NA concrete. The results presented in the paper showed that up to 30% coarse RCA had no major effect on the compressive strength of concrete and, thereafter, a gradual reduction in strength with an increase in RCA content was observed. Reducing the w/c of concrete treated with the RCA has led to an enhanced compressive strength, higher resistance to carbonation, and chloride ion ingress. It was also found that, when properly designed, portland cement silica fume (PC-SF) concrete made with different proportions of coarse RCA as substitute of NA may contribute to enhance the durability performance of concrete.

Effect of initial curing on chloride diffusion in concrete repair materials

Abstract This paper presents the results of an experimental investigation on the effect of initial curing on chloride diffusion in three generic repair materials and a concrete mix of similar grade. Two field conditions of initial curing were simulated as follows: (1) exposure to a chloride environment after 24 h of casting to simulate repair situations, for example in the tidal zone of marine structures where repairs cannot be protected from tidal exposure for long periods; and (2) 28 days of curing at 20°C, 55% relative humidity to simulate field conditions where the repair patches are exposed to the ambient environment without any prolonged protected curing. For comparison purposes identical specimens were cured in water at 20°C for 28 days before exposure to the chloride environment. Chloride concentration profiles in the materials were determined after 28, 90, and 180 days of exposure. Regression analysis of the experimental data was carried out applying Ficks second law of diffusion to determine the diffusion coefficients (DC) and chloride concentration on the surface (C0). Based on the results obtained, an analytical expression for the long-term prediction of chloride concentration in repair materials is given. The results show a high rate of chloride diffusion in the cementitious repair materials containing polymer latex additives relative to plain concrete. The effect of inadequate initial curing on chloride penetration (e.g., exposure to chlorides after 24 h of casting or 28-day air curing) is more pronounced in concrete mixes than in generic repair materials.

Repair material properties for effective structural application

Abstract Strength and engineering properties of three generic repair materials which are likely to influence long-term performance of repaired concrete structures were studied. Measured properties include strength, stiffness, shrinkage and creep deformations, together with the complete compressive stress-strain characteristics including post-cracking behaviour. The repair materials considered in this investigation are commercially available and widely used. These included a high performance non-shrinkable concrete, a mineral based cementitious material with no additives or coarse aggregate size particles, and a cementitious mortar containing styrene acrylic copolymer with fibre additives. Performance comparisons are also made between these materials and plain concrete mixes of similar strength and stiffness, suitable for repair applications. The results show that shrinkage of the repair materials was significantly greater than the shrinkage of normal concrete. Moreover, the shrinkage of those modified with a polymer admixture was found to be very sensitive to the relative humidity of the exposure compared to normal concrete. The post-peak strain capacity of the material modified with a polymer admixture was markedly improved leading to a more pronounced falling branch of stress-strain curve. The ultimate stress level (at a maximum load) of specially formulated repair materials varies significantly, the lowest ultimate stress being recorded for the porous mineralbased material. The inclusion of aggregates improves the mechanical properties and dimensional stability of repair materials.

Compaction assessment of recycled aggregates for use in unbound subbase application

AbstractStudy was recently conducted at Kingston University to assess the suitability of using recycled concrete aggregate (RCA) and reclaimed asphalt pavement (RAP) in unbound subbase mixtures. The results showed that the use of 100% recycled aggregates increased the optimum moisture content and decreased the maximum dry density of the sub-base materials in comparison with natural aggregates. Moreover, the replacement of RCA by reclaimed asphalt pavement by 50% decreased the optimum moisture content and increased the maximum dry density in proportion to 100% RCA. The effects of physical properties on 0% air void and compaction curve were discussed for each type of subbase. The CBR values of the subbase materials prepared with 100%RCA is lower than subbase mixture with 100% natural aggregates. The CBR further decreased for replaced subbase with RAP so that 50%RCA + 50%RAP is not suitable for unbound subbase from the point of CBR view. In each mix the trend of CBR value was investigated in terms of water c...

Water Absorption Study Recycled Aggregates for Use Pavement Material

Water absorption properties of recycled materials play an important role in pavement performance. The performance of aggregates changes after absorbing water, then it affects highways layers such as base, subbase, capping. This is why these materials must comply requirements of codes and standards. With regard to the increasing trend of application of recycled aggregates in highways layers, this issue needs more investigation. This research is only a part of our large research programme on three different purposed mixes of unbound subbase mixture below: 1) 100% Recycled Concrete Aggregate (RCA); 2) 100% Lime Stone (NA); 3) 50% RCA + 50% Re-claimed Asphalt Pavement (RAP). Water absorption for each mix has been performed in different size fraction with pyknometer and wire basket methods. The relationship between density, grading and water absorption and its comparison for mixes would be indicating the changes in behaviour of aggregates and future performance of subbase. Laboratory testing showed that 100% Lime Stone had the higher densities than other mixes and water absorption value of 100% RCA was about 40% higher than 50% RCA + 50% RAP in 31.5 mm - 4 mm fraction.

Integrated Advance Data Storage Technology for Effective Construction Logistics Management

This paper presents a study on applying an integrated application of RFID, GPS and GSM technology for mobile, pervasive and ubiquitous tracking and locating of any objects in construction supply chain and logistics. Accurate and timely identification and tracking of resource are vital to operating a well managed and cost efficient construction project. RFID integrated with the GPS provides an opportunity to uniquely identify materials and to locate and track them in a real time basis using minimal or no worker input where transmission of data from the system to the central database will be carried out with the help of standard cellular phone communications networks technology such as GPRS and SMS. In this research GIS will be used for analyzing and representing collected data. The authors believe that full automation of the construction supply chain and logistics can increase the efficiency and productively and lead to reductions in project costs and time.

Simultaneous Design Characteristics Optimization in an Earth Retaining Structure

The aim of this paper is to present a method for simultaneous optimization of the design characteristics of an earth retaining structure design using quality tools. The design characteristics examined in this paper are safety factor, total displacements and cost. The methodology for the multi-response optimization used is the desirability analysis which gives the appropriate combinations for the design variables. Through standard experimental runs, we process the results for this optimization. The experimental measurements are calculated via finite elements analysis. The designs used are taken from two real-life case studies. This methodology is intended as a guide tool for civil and geotechnical engineers to predict the values of the design variables as long as they can be named and take discrete values. The uniqueness in this study is that approved experimental methodology can simultaneously optimize the design characteristics of an earth retaining structural design, which were until now calculated empirically.

Real-time landslides monitoring and warning using RFID technology for measuring ground water level

Across the world, economic and social landslide losses have increased as human development has expanded into unstable onto hill slopes. Every landslide catastrophe produces a significant loss to infrastructures, services and buildings as well as resulting in large numbers of casualties and fatalities. Although ground water level is often a primary controlling factor in landsliding, modeling of ground water is difficult due to the complex internal geology in most landslides. There are different approaches to locate the ground water table. Field observations are vital. This research has focussed on the utilization of integrated applications of Radio Frequency (RF) technologies such as Radio Frequency Identification (RFID), with ultrasonic sensors for accurate and timely identification and monitoring of ground water level in slopes and landslide susceptible areas. RFID integrated with ultrasonic and temperature sensors provide an opportunity to monitor groundwater in landslide susceptible areas on a real-time basis. The transmission of data to the central database can be carried out with the help of Global System for Mobile Communications (GSM), and the collected data can be used for slope stability analysis.