Performance of Class F Pulverised Fuel Ash and Ground Granulated Blast Furnace Slag in Ternary Concrete Mixes

Jhon Kamau,Joseph Kangwa,Ash Ahmed,Paul Hirst

doi:10.24018/ejeng.2017.2.6.363

Abstract

Cement is the most utilised material after water, and the processes that are involved in making it are energy intensive, contributing to about 7% of the total global anthropogenic carbon dioxide (CO2). Energy efficiency can however be achieved by using Supplementary Cementitious Materials (SCMs) such as Pulverised Fuel Ash (PFA) and Ground Granulated Blast Furnace Slag (GGBS) which demand less process heating and emit fewer levels of CO2. This work examined the advantages of substituting cement using PFA and GGBS in ternary (2 SCMs) concrete at steps of 0%, 5%, 7.5%, 10%, 15%, 20%, 25%, and 30%. It was found that PFA increased the workability of GGBS, whereas GGBS improved the strength of PFA. The densities of the resultant concrete were below those of the 0% replacement as well as those of individual binary (1 SCM) concretes. The tensile strengths of the ternary concrete were lower than those of the binary concretes, whereas the gains in compressive strengths over curing time were higher at lower replacements for the ternary concrete compared with the 0% replacement and the binary concretes, but lower at higher replacements. The findings indicate that PFA and GGBS could be used together to improve the properties of concrete where each falls short.

Highlights

It has been argued that cement is one of the most notorious contributors to global anthropogenic CO2 [1]
There is growing consensus in literature that the use of Supplementary Cementitious Materials (SCMs) in concrete mixes under optimum conditions of blending, transportation, placing and curing improves the strength and durability of hardened concrete, with researchers agreeing on replacements of up to 35% for Pulverised Fuel Ash (PFA) and 65% for Ground Granulated Blast Furnace Slag [GGBS] [5]
A constant Water Cement Ratio (WCR) of 0.5 with no superplasticisers was used for all mixes in a bid to achieve a good balance of workability and strength in line with Abram’s law, which states that the strength of a concrete mix is determined by the WCR, with lower WCRs spelling higher strengths and vice-versa [15]

Summary

Introduction

It has been argued that cement is one of the most notorious contributors to global anthropogenic CO2 [1]. Being the main ingredient in concrete, it has been described as the most utilised construction material in the world, its global consumption only seconding that of water [2], [3]. It accounts for about 7% of the total global CO2 loading in the atmosphere [2]. It appears that the global emissions which result from its production could be higher than those associated with aviation, which were only estimated at 2% by [4]. There is growing consensus in literature that the use of Supplementary Cementitious Materials (SCMs) in concrete mixes under optimum conditions of blending, transportation, placing and curing improves the strength and durability of hardened concrete, with researchers agreeing on replacements of up to 35% for Pulverised Fuel Ash (PFA) and 65% for Ground Granulated Blast Furnace Slag [GGBS] [5]

Methods

Results

Conclusion