Waste and Supplementary Cementitious Materials in Concrete

Characterisation, Properties and Applications

Rafat Siddique, Paulo Cachim

• Publisher: Woodhead Publishing
• Year: 2018
• Print ISBN: 9780081021569
• eBook ISBN: 9780081021576
• Topic: Tecnología e ingeniería
• Subtopic: Construcción e ingeniería arquitectónica

Waste and Supplementary Cementitious Materials in Concrete: Characterisation, Properties and Applications provides a state-of-the-art review of the effective and efficient use of these materials in construction. Chapters focus on a specific type of material, addressing their characterization, strength, durability and structural applications. Sections include discussions of the properties of materials, including their physical, chemical and characterization, their strength and durability, modern engineering applications, case studies, the state of codes and standards of implementation, cost considerations, and the role of materials in green and sustainable construction. The book concludes with a discussion of research needs.- Focuses on material properties and applications (as well as 'sustainability' aspects) of cementitious materials- Assembles leading researchers from diverse areas of study- Ideas for use as a 'one stop' reference for advanced postgraduate courses focusing on sustainable construction materials

Part I

Waste materials

Outline

• 1 Coal bottom ash
• 2 Scrap tires/crumb rubber
• 3 Recycled aggregates
• 4 Waste foundry sand
• 5 Cement kiln dust
• 6 Waste marble powder/dust
• 7 Plastic wastes
• 8 Construction and demolition wastes
• 9 Waste glass
• 10 Wastepaper sludge ash

1

Coal bottom ash

Malkit Singh, Punjab State Power Corporation Limited, Patiala, Punjab, India

Abstract

The use of coal bottom ash (CBA) is an important factor in the economics of power generating utilities. If this by-product of power plants is recycled to beneficial use, then substantial part of amount spent on its safe disposal can be saved in addition to protection of environment. The construction industry has enormous potential for use of CBA as construction material. CBA can be used as replacement of fine aggregate in production of concrete or mortars. Utilization of CBA in concrete will help in three ways: (1) reduction in its cost of production; (2) saving in CO₂ emissions to the atmosphere; and (3) protection of environment from bad effect of CBA disposed on open land. This chapter describes comprehensive overview of properties of CBA as well as critical appraisal of published studies on effect of CBA as partial replacement of fine aggregate on the properties of concrete.

Keywords

Coal bottom ash; workability; bleeding; compressive strength; flexural strength; abrasion resistance; chloride permeability

This chapter describes comprehensive overview of properties of coal bottom ash (CBA) as well as critical appraisal of published studies on effect of CBA as partial replacement of fine aggregate on properties of concrete.

1.0 Introduction

Coal is the dominating fuel source used in thermal power plants for generation of electricity. At the coal-fired thermal power plants, the raw coal is first pulverized to the shape of flour before it is force-fed to the furnace. During the pulverization process, the clay particles entrapped in the cracks of coal get separated from the coal. Then on combustion of coal in furnace, these clay particles and other noncombustible matter result in production of coal ash. The quantity of coal ash produced at coal-fired thermal power plants varies from 5% to 45% depending on the type and source of coal used as fuel in the furnace. The coal ash produced at coal-fired thermal power plants is classified into two types, i.e., fly ash (FA) and bottom ash. During burning of pulverized coal in the furnace, the finer and lighter particles of ash are carried away by the swirling flue gases. These ash particles are extracted from the flue gases in the electrostatic precipitators before entering into the air. The ash collected from the electrostatic precipitators is called FA. It constitutes about 80% of total coal ash. The coarser and heavier particles of ash settle down at the base of furnace. Also some ash particles accumulate on furnace walls and steam pipes. The clinkers so formed build up and when become too heavy, fall to the base of furnace. These clinkers are grounded to the form of fine aggregate before they are sluiced to the disposal site. The ash collected at the base of furnace is termed as coal bottom ash (CBA) and forms nearly 20% of total coal ash. CBA is generally composed of coarser and popcorn-like particles.

FA has been extensively used in production of Pozzolanic Portland cement and in manufacturing of mortar or concrete as cement replacement. It is an established fact that the use of FA as supplementary cementing material in production of concrete improves its strength and durability properties. Whereas, CBA contains coarser and more fused particles compared to FA, as such it shows less pozzolanic activity. Generally CBA is considered as an inert material and unsuitable for use as supplementary cementing material. Since particle size distribution of CBA is similar to that of sand, it attracts to be used as replacement of sand in several civil engineering applications. CBA can be used in embankments construction, as structural fills, unbound or stabilized granular bases and subbases, as a foundation material, in noise barriers, as a capping layer on landfill sites, and as aggregate in asphalt and concrete.

1.1 Uses of CBA

1.1.1 Construction of road base and subbase

CBA can be used as a granular base material in road construction, if it meets specifications for granular base (Edil et al., 2002). Large size or agglomerated popcorn particles are removed from CBA by screening or washing to make it suitable for use as granular base material. Blending with conventional aggregate may also be required. According to published literature, granular base made with CBA having 1.5 times thickness of conventional aggregates achieves a comparable stress level in the underlying subgrade. However, according to study by Ramme and Tharaniyil (2004), the thickness of CBA should be two times the thickness of conventional aggregates to maintain similar deflection at the surface of the base course layer. When CBA is used in construction of stabilized base, the cementitious materials bind the aggregates and provide bearing strength. In such applications moisture control and proper grading...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of contributors
• Preface
• Part I: Waste materials
• Part II: Supplementary cementitious materials
• Index