Cement, Energy and Environment

Prospects of Geopolymeric Cements in Environmental Sustainability M MAli Ashwani Pahuja R S Gupta National Council for Cement and Building Materials Ballabgarh- 121004, India Abstract The geopolymeric cements prepared utilizing industrial wastes such as fl y ash, blast furnace slag and calcined clay are emerging as alternative to the Portland cements to produce building components and can play significant role in reduction of C0 2 emissions in addition to conservation of energy and natural raw materials.Such green cement products are derived from alkali activation of aluminosilicates treating with adequate concentration of sodium/potassium ions under optimum curing conditions to achieve geopolymerization associated with desirable microstructural developments. Investigations have been reported on high performance and improved durability characteristics of structures based on such cements and even when exposed to aggressive and high temperature conditions. The present article provides an insight into various technological milestones achieved so far with their constraints and prospects for sustainable constructions by utilizing available industrial wastes. Introduction: Global warming and consequent climate change has posed a threat to the present habitat on the earth. It is known that Portland cement manufacture is responsible for about 6 percent of total global anthropogenic C0 2 emissions adding to environmental hazard. Besides ,the conventional cement manufacturing practices are leading towards depletion of good quality limestone and fuels deposits due to their continuous and increased consumption. Further the quantum of unutilized fly ash has increased many fold due to high jump in its production protocol by coal based power plants in lndia..The manufacture of cements utilizing large amount of supplementary materials such as fly ash and blast furnace slag has contributed significantly in addressing the issues. However in last two decades there has been seen focus on research for development of cold process cements utilizing these wastes.The emerging geopolymeri c cements are produced by alkali activation of materia ls rich in Si0 2 and Al 2 0 3 such as fly ash, slag and metakaolin.These are considered suitable alternatives with improved performance characteristics and wide range of applications . The attack of alkali on aluminosilicates by using concentrated alkali hydroxide/ silicate solution results in producing alkaline aluminosilicate polymers which are considered as zeolitic precu rsors or analogues to zeolites and on hardening could achieve excellent mechanical properties , fire and acid resistance. These properties make them suitable for special applications requiring higher durability. It has been found that the performance characteristics of geopolymers prepared from different aluminosilicate sources may vary widely and are controlled by parameters such as dose and type of alkaline activator, pH, and curing conditions etc.The conversion of gel to crystalline phases with microstructural developments affects the physical properties of geopoplymeric materials. Formation of Geopolymers: The alkali metal ion in alkaline solution attacks the aluminosilicates resulting in dissolution of silica and alumina which are available as aluminate and silicate ions.Dissolution process of aluminosilicates is rapid at high pH and quickly creates a supersaturated aluminosilicate solution. This results in the formation of a gel. The time for the supersaturated aluminosilicate solution to form a continuous gel varies considerably with raw 9