Question

Write a three paragraphs to summarize current efforts and challenges aimed at producing green concrete. (150 words minimum)

Answer 1

Concrete contains four basic ingredients: water, cement, fine aggregate (sand) and coarse aggregates. The manufacturing of traditional concrete using portland cement releases a large amount of greenhouse gases such as CO_2, also the production of portland cement is energy-intensive. The use of supplementary cementitious materials (SCMs), recycled aggregates and other industrial wastes could reduce the environmental impacts of concrete production (Leepch et al.., 2008). The cement produced by using waste material is known as 'green cement'. According to Mannan and Ganapathy (2004) using agricultural and industrial waste as replacement materials in the concrete industr has dual advantage of cost reduction and a better way of waste disposal. They also pointed out that the material recovery from the conversion of these wastes into useful materials benefits both the enviroment and the conservation of natural resources. Extensive studies have been carreid out ot identify waste material that can be used as SCM, for example fly ash, blast-furnace slag and pozzolans (Topcu and Boga, 2010; Bonder et at.., 2011, Limbachiya et al.., 2012).

Although the sustanability of concrete can be improved by using waste material, adding SCMs could impact properties of concrete such as compressive strength, workability etc. which are extremely important for its application. Research on recycled concrete aggregate (RCA) seems promising by recycling waste concrete material from domolition into concrete production. However inferior quality of this type of concrete such as lower strength have been recognized (Limbachiya et al.., 2012). Yang et al.. (2005) found that using crushed oyster shell maintained or improved the compressive strength but decreased the workability The chemical reaction between silica rich glass and the alkali was a major concern when using glass in concrete (Bataynch et al.., 2007). Concrete containing plastic aggregates decreased compressive and tensile strengths (Siqqique at al.., 2008). The industry perception is also conservative in the matter of using green concrete due to the fear of failure (Duxson et al.., 2007).

Therefore it is necessary to advance the understanding of concrete properties when using green raw materials, reduced potential cost in the recycling and reuse process, improve industry standards and educated the industry about the new technologies.