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Greencrete: A Project on Environmentally Friendly Concrete

Abstract

Students are tested in their knowledge of “green” concrete through a course project that requires the development of Greencrete. Greencrete is similar to a commercially available product called Quikcrete 5000©. Quikcrete 5000© is a ready-mix bag of concrete available in 80 pound bags that will attain a compressive strength of 5000 psi by 28 days of age. Each bag consists of cement, gravel, and sand. For the project, students are divided into groups of 4 or 5, and each group must develop their own Greencrete mixture. Each mixture must contain slag cement and fly ash, both recycled materials. Their mixture can not cost more than Quikcrete 5000© and must also have a 28 day compressive strength greater than 5000 psi. Students are also required to research yearly sales of Quickcrete 5000©, and determine how the use of their product, Greencrete, would benefit the environment.

Introduction

Protecting the environment is becoming a ubiquitous mandate and, more frequently, civil engineers will be called to meet infrastructure demands in ways that are less harmful to the environment and sustainable into the future. One way to meet such demands is by producing and using “green” or environmentally friendly concrete. Supplementary cementing materials (SCMs) such as fly ash, silica fume, and slag cement are frequently employed in concrete mixtures for performance and economic reasons. However, there are environmental reasons for incorporating SCMs. SCMs are mainly industrial byproducts that, in most cases, would otherwise be headed for landfill disposal but now are used to improve concrete performance. Also, the use SCMs extend the current supply of cement. Cement production is energy intensive and emits carbon dioxide (CO2), a greenhouse gas. Reducing the amount of cement in a concrete mixture through the use of SCMs also benefits the environment by decreasing the amount of energy required to produce a concrete structure.

Background

Slag cement and fly ash are two industrial byproducts that have cementitious properties when introduced into the proper environment. These waste products are typically disposed of in landfills, but many state departments of transportations (DOTs) are allowing the use of slag cement and fly ash as building or construction materials for use in transportation structures.

Fly ash is waste from coal-burning energy plants. Slag cement is created from fluxes, lime- based inorganic sources, and iron ore combined and heated to a molten state in the production of iron. The fluxes absorb the impurities from the iron ore and are rich in lime, silica, and alumina. When the slag is rapidly cooled by water, glassy granules are formed and then ground to cement sized particles. Both fly ash and slag cement have the proper chemistry to achieve cementitious properties. The chemical compositions for the slag cement and fly ash used in the project are shown Table 1.

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Becknell, N., & Hale, M., & Freyne, S., & Durham, S., & Lamanna, A. (2006, June), Greencrete: A Project On Environmentally Friendly Concrete Paper presented at 2006 Annual Conference & Exposition, Chicago, Illinois. 10.18260/1-2--675