Development of Non-Clinker Based Cement for Hazard Reduction

Northwestern University, Evanston IL

Investigators

Abstract

Concrete has been the material of choice for the nation's $1.4 trillion infrastructure. The rapid growth of human population, industrialization, and urbanization has led to more cement being used in concrete materials to meet the increasing needs of infrastructure. As a result, the environmental concerns related to portland cement clinker production, such as greenhouse gas (carbon dioxide, CO Z) emission and disposal of cement kiln dust (CKD), a by-product of cement manufacturing, have become increasingly important. The United States cement industry generates about 80 million tons of CO 2 and 5 million tons of CKD every year. The disposal of waste CKD is not only associated with the problem of land use but also with the contamination of ground water from leaching of chemicals (especially heavy metals) in the material. Similarly, another industrial by-product, fly ash, collected from the stack gases of power plants burning pulverized coal, is also commonly considered an extensive waste material. About 59 million tons of fly ash are generated annually in the United States and 80% is placed in landfills. The goal of the proposed research is to explore an effective way to substantially utilize CKD and fly ash by developing an environmentally friendly, sufficiently performing, and cost effective cementitious product (without portland cement clinker) for future concrete materials. CKD and fly ash have been used as a supplementary cementitious material in concrete in small amounts. Usage is limited due to deficiencies of the two materials. For example, CKD contains an excessive amount of fine particles and a high alkali content, which often impart a,,,,erse effects on concrete workability and durability. Most fly ash hydrates slowly and some contain a high unburned carbon content. These inadequacies are unacceptable for strength development and volumetric stability of cement and concrete materials. However, if the two materials are blended together, the alkalis from CKD may activate hydration of fly ash. The proposed research involves properly blending CKD with fly ash to create a cementitious material in which the material deficiencies will be converted into benefits. The proposed research program includes six major tasks: (1) raw material characterization, (2) statistical design and optimization of blend proportions, (3) the grinding process, (4) testing and evaluation for effectiveness of chemical and mechanical activation of the blends, (5) developing criteria for acceptance of new products, and (6) testing and evaluation for performance of concrete made with the new products. Task 2 contains four successive steps: design, preliminary optimization, refinement, and conformation, thus developing optimal blends orderly. A series of chemical, physical, and mechanical experiments will be used to evaluate product performance at each step of optimization, thus leading to the next optimal step of blend proportioning continuously. A systematical study of different grinding processes and their affect on alkali activation and cement hydration will be conducted along with the curing conditions that promote such hydration. Thus, four key issues, (a) alkali activation, (b) high-energy grinding, (c) proportion optimization, and (d) product performance, are brought together into the proposed development of a non-clinker CKD-fly ash cement. The new product performance is engineered by tailoring the chemistry, microstructure, and manufacturing process. An interdisciplinary collaborative research team has been formed, consisting of members from the Center for Advanced Cement-Based Materials (ACBM) at Northwestern University (NU), Evanston, Illinois, and Construction Technology Laboratories, Inc. (CTL ), Skokie, Illinois. The team members have complementary strengths needed for the proposed research, with expertise in the areas of concrete material science, statistical design and analysis, cement chemistry, manufacturing, guideline development, and concrete testing and properties. Working together, they expect the successful conversion of CKD and fly ash from a current environmental burden and industrial profit "thief' into a viable construction material.