فعال سازی شیمیایی سیمان پرتلند مخلوط شده با اسلگ Chemical activation of slag-blended Portland cement

1. Introduction Cement industry is faced with serious environmental problems. The production of Portland cement (PC) in the cement industry not only consumes raw materials and large amounts of energy, but also as one of the primary industrial producers of carbon dioxide, contributes to the greenhouse effect and causes acid rain. Actually, this industry generates greenhouse gases (GHGs) both directly through the emission of CO2 when clinker is produced and also through the consumption of energy [1-4]. On the other hand, the severity of environmental regulations is enhanced progressively and has forced the industries to put in a great effort to reduce their pollutants [4]. One of the interesting approaches for reducing environmental problems and also gaining technological and economic advantages is the increasing usage of industrial byproducts and wastes [1-6]. Among the industrial wastes, only slags have latent cementing property and have been converted to an important research area [5, 7, 8]. In fact, the production of slag cements and slag-blended Portland cements results in resource conservation, reducing energy consumption and minimizing emission of GHGs, especially CO2 [2]. Blast furnace slag (BFS) as one of the industrial solid wastes is formed in a molten state simultaneously with iron in a blast furnace. The chemical composition of the slag is originated from silicate and oxide components of the raw materials used in the smelter feed [9]. The slag exhibits primarily latent hydraulic activity, but may show some pozzolanic character as well. Nevertheless, BFS adversely affects the early-age strength of PC when used at high replacement levels [10] and as a supplementary cementing material, it is necessary to tailor its reactivity by auxiliary activation techniques [10-12] such as thermal, chemical, and mechanical as the most common activation techniques [11, 12]. Thermal activation or curing at elevated temperatures can improve strength development [12], but at the same time may decrease the ultimate strength [13]. Mechanical activation results from compound effects of particle fracture and other bulk and surface physicochemical changes [14, 15], dislocations and other defects induced by the milling [14, 16]. Mechanical activation of solid dispersed materials leads to accumulation of mechanical energy that is used for enhancement of the specific surface energy of a dispersed material [17, 18]. In mechanical activation, physicochemical properties of solid materials are varied during grinding process [16, 17]. Chemical activation refers to the use of some chemicals to impart cementing properties and/or to activate latent hydraulic properties [11, 18]. There are two types of alkali-activation, including (1) activation with strong alkaline activators that are suitable both for imparting cementing properties to aluminosilicate materials exhibiting no cementing properties and activating industrial slags with latent hydraulic properties, and (2) activation with mild alkaline activators that are applicable only for industrial slags exhibiting some cementing properties [19, 20].