Development of High Volume Fly Ash and/ or Slag Modified Concrete and Geopolymer Concrete as Sustainable Construction Materials

Although cement constitutes only about 10% to 15% of the total weight of concrete, it accounts for 6% of global CO2 emissions. The other emissions from cement plants are: particulate matter, CO, NOx, SOx, total hydrocarbon, and the major wastes are cement kiln dust and water. Unfortunately cement is also an energy intensive material as 1 metric tonne of cement requires 1 million MJ of energy. Therefore, a large reduction in cement content in concrete by replacing it with other cementitious materials can make concrete a greener and sustainable material. Industrial by-products such as fly ash and ground granulated blast furnace slag (slag) are routinely used as cement replacement materials; but the replacement typically does not exceed 40% (by mass of cement). Also, recently fly ash produced from coal-fired power plants has been proposed to be declared as a hazardous waste under Resource Conservation and Recovery Act (RCRA) of Environmental Protection Agency (EPA), restricting its disposal as landfill. Considering all these factors, we produced and evaluated a number of high-strength and durable concretes by replacing cement by large volumes of fly ash from 40% to 70%; and also a group of concretes using 100% fly ash, 100% slag, and 50% fly ash+ 50% slag (no portland cement) all with geopolymer binder. The objective of this study is to evaluate the effects of the beneficial use of including 40% to 100% fly ash and/or slag to produce sustainable, green, and durable concretes.;This study included evaluations of compressive strengths from 3 days to 90 days; and durability parameters such as freeze-thaw, free shrinkage, and rapid chloride permeability. Isothermal calorimetry test was conducted to characterize the early hydration reaction of these materials up to 96 hours per ASTM C 1679-09. Leaching tests were performed according to EPA TCLP 1311 on pure fly ash, pure slag, sand, limestone, crushed concretes containing fly ash and/or slag, geopolymer concretes containing fly ash and/or slag at to examine the effectiveness of containment of the heavy metal ions present in fly ash and/or slag within these concretes. The Ecological Toxicity potential was calculated and compared among different concretes. Finally, BEES 4.0 software was used to conduct the life-cycle cost (LCC), life-cycle assessment (LCA) of these concrete products.;Results showed that properly designed high volume fly ash and/or slag modified concretes and geopolymer modified concretes can produce high-strength and durable materials. The leaching tests showed that these concretes also can effectively contain the toxic heavy metal ions within their structures. The LCC and LCA results indicated that concrete products containing high volume fly ash and/or slag as replacement of cement are much more sustainable, green, and energy-efficient compared to concrete without cement replacement