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2016SpringShotcreteEMag

Sustainability An Approach for Improving the Sustainability of Shotcrete By Ezgi Yurdakul, Klaus-Alexander Rieder, and Diego Granell Nebot According to the World Commission on Environment and Development,1 sustainability is defined as “meeting the needs of the present without compromising the ability of future generations to meet their own needs.” Based on this definition, it is clear that the construction industry is showing weakness on sustainability because cement production is one of the most energy intensive of all manufacturing industries2 and it contributes 5% of total global carbon dioxide (CO2) emissions,3 as shown in Fig. 1. These numbers are more drastic in the United States as a result of being the third largest cement producer in the world.4 With the increased rate of industrialization and urban development globally, construction business is significantly growing, which further increases the demand on cement production followed by higher energy consumption and CO2 emissions. In the last decades, the cement industry has already significantly reduced the amount of CO2 per ton of cement produced by reducing the amount of clinker while maintaining 28-day strength. Considering shotcrete applications, where a typically high amount of cementitious materials are used and often 20 to 30% of batched concrete is lost during the spraying process as a result of rebound, there is certainly a need to improve the sustainability of shotcrete. Therefore, the aim of this paper is to propose a few methods for greener shotcrete with the aid of the latest advancements in chemical admixture technology. Proposal 1—Reduction of Cementitious Materials Content The production of each ton of portland cement clinker emits approximately 1 ton (900 kg) of carbon dioxide. Therefore, in an era of global warming and climate change, either a reduction in the production or a more efficient use of carbonintensive materials is desirable to meet the future needs of society. Although the production of structures that are highly sustainable is still challenging to accomplish, the industry has shown progress by motivating alternative solutions such as using recycled aggregates, binary and ternary mixtures with high levels of supplementary cementitious materials, and alternative binders with different chemistries with lower carbon footprints than portland cement.7-10 Among all these available options, a simple approach for improving sustainability of shotcrete would be to use cementitious materials more efficiently without sacrificing the shotcrete performance. Furthermore, considering that cementitious materials such as ordinary portland cement and silica fume are the most expensive mixture components in shotcrete, minimizing the cementitious content will not only lead to a more sustainable method of shotcreting but also reduce the project cost. Researchers11 have studied the minimum paste content requirement for optimum pumpability in shotcrete, and found out that a minimum of 34.2% of real paste content is needed to achieve the desired pumpability (10.2% of paste is required Fig. 1: Global CO to form a lubricating layer and 24% is required to 2 production5,6 32 Shotcrete • Spring 2016


2016SpringShotcreteEMag
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