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. © 1994.

Kothandapani Ganesh Sanjeevi Babu

CEMENT ADDITIVES

Concrete construction

Fly ash

Mortar

Pozzolan

Compressive strength

CONCRETE MIXES

PULVERIZED FUEL ASHES

CONCRETE AGGREGATES

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Efficiency of fly ash in concrete

Cement and Concrete Composites

The corrosion performance of self-compacting concretes with high-volume replacements of fly ash was evaluated by some electrochemical techniques. In this study, eight self-compacting fly-ash concretes of various strength grades were designed at desired fly ash percentages of 0, 10, 30, 50, 70 and 85%, and were compared with five different mixtures of normal vibrated concretes at equivalent strength grades. The corrosion characteristics of the developed concretes were studied through the measurement of resistivity, pH, carbonation depth, half-cell potential and corrosion rate. Results demonstrate that self-compacting concretes at all levels of fly ash replacement performed significantly better than the corresponding normal vibrated concretes. This can be mainly attributed to the pozzolanic activity of fly ash. The carbonation was, however, higher in low- and medium-strength self-compacting concretes compared to the normal concretes.

Magazine of Concrete Research

Corrosion resistance performance of high-volume fly-ash self-compacting concretes

Self-compacting concrete (SCC), a recent addition to the concrete scenario, is gaining popularity worldwide owing to the ease of its placement without any need for compaction. This paper describes the results of an investigation aimed at producing and evaluating SCC mixtures made with high volumes of class F fly ash. Eight fly ash SCC mixtures of various strength grades (20-100 MPa) were designed at the desired fly ash percentages of 0, 10, 30, 50, 70 and 85%, and were compared with five different mixtures of normal vibrated concrete mixtures (20-100 MPa). Tests were carried out on all mixtures to obtain the properties of fresh concretes in terms of viscosity and stability. The mechanical properties of hardened concretes such as compressive strength, splitting tensile strength and elastic modulus were also determined. The different amounts of paste caused differences in the properties of the two types of concrete. Test results indicated that the use of high volumes of class F fly ash in SCC mixtures decreases its 28-day compressive strength. However, the strength results showed continuous and significant improvement at the ages of 90 and 180 days, which was most probably owing to the pozzolanic reaction of fly ash. Self-compacted fly ash concrete mixtures exhibited higher splitting tensile strengths and lower elastic modulus compared with normal vibrated concretes. © 2008 Thomas Telford and fib.

Structural Concrete

Mechanical properties of high-volume fly ash self-compacting concrete mixtures

The use of mineral admixtures is widely accepted, because of several improvements possible in concrete composites and the overall economy. Of these metakaolin is one mineral admixture that appears to have significant potential for the production of high-strength and high-performance concretes. Although available information on metakaolin concretes is limited, the present paper attempts to quantify the 28-day cementitious efficiency of metakaolin in concrete at various replacement levels from the data available in the literature. It was seen that the efficiency of metakaolin in concretes can also be defined through a procedure adopted earlier for other cementitious materials like fly ash, silica fume and ground granulated blast-furnace slag (GGBS). The overall strength efficiency was found to be a combination of two parameters, one depending on the age and the other depending on the percentage of replacement, as is the case with other pozzolans. © 2006 Thomas Telford and fib.

Strength efficiency of metakaolin in concrete

Lightweight concretes can be produced by replacing the normal aggregates in concrete or mortar either partially or fully, depending upon the requirements of density and strength levels. The present study covers the use of expanded polystyrene (EPS) beads as lightweight aggregate, both in concrete and mortar. The main aim of this programme is to study the mechanical properties of EPS concretes containing fly ash and compare the results with these in literature on concretes containing OPC alone as the binder. The effects of EPS aggregate on the green and hardened state characteristics of concretes containing fly ash were evaluated. The compressive strength of the EPS concretes containing fly ash show a continuous gain even up to 90 days, unlike that reported for OPC in literature. It was also found that the failure of these concretes both in compression and split tension was gradual as was observed earlier for the concretes containing plastic shredded aggregates. The stress-strain relations and the corresponding elastic modulus were also investigated. © 2005 Elsevier Ltd. All rights reserved.

Cement and Concrete Research

Properties of lightweight expanded polystyrene aggregate concretes containing fly ash

The utilization of supplementary cementitious materials is well accepted because of the several improvements possible in the concrete composites and due to the overall economy. The present paper is an effort to quantify the 28-day cementitious efficiency of ground granulated blast furnace slag (GGBS) in concrete at the various replacement levels. It was observed that this overall strength efficiency of GGBS concretes can also be defined through a procedure adopted earlier for other cementitious materials like fly ash and silica fume. The overall strength efficiency was found to be a combination of general efficiency factor, depending on the age and a percentage efficiency factor, depending upon the percentage of replacement as was the case with a few other cementitious materials like fly ash and silica fume reported earlier. This evaluation makes it possible to design GGBS concretes for a desired strength at any given percentage of replacement.

Efficiency of GGBS in concrete

RILEM Technical Recommendations for the testing and use of construction materials

FAB 2 Test methods for determining the properties of fly ash in concrete

ACI Materials Journal

Effects of High-Lime Fly Ash Content on Water Demand, Time of Set, and Compressive Strength of Concrete

International Journal of Cement Composites and Lightweight Concrete

Third international conference on fly ash, Silica fume, slag and natural pozzolans in concrete

Mix design for optimal strength development of fly ash concrete

Structural Concrete Incorporating High Volumes of ASTM Class Fly Ash

Journal	Cement and Concrete Composites
ISSN	09589465
Open Access	No