Cementitious Blends of Portland Cement with Calcium Sulphate, Fly Ash and Cupola Slag.
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Cementitious Blends of Portland Cement with Calcium Sulphate, Fly Ash and Cupola Slag. Yared E. Rodríguez-Mendoza1, Antonio F Fuentes, J Iván Escalante-García1 1
Cinvestav IPN Unidad Saltillo, Mexico
ABSTRACT This investigation is on alternative cementitious materials of low cost, energy and environmental emissions. Portland cement (PC) was replaced by different types of calcium sulphate (hemihydrate HH, or anhydrite AN), fly ash (PFA) and cupola slag (CS) from an iron foundry. Pastes of blends of (HH or AN) – CS – PC and (HH or AN) – PFA – PC were characterized. The compositions varied within the ranges of 0 – 35% PC, 15 – 80% HH or AN, 10 – 80% CS and 10 – 80% PFA. The water/solids ratio was kept at 0.45 for HH blends and 0.37 for those of AN. The pastes were cured in dry and for some time under water. Selected blends of CS were repeated with blast furnace slag (BFS) for comparison. CS showed better results over PFA and less than BFS, perhaps as derived from its chemical composition, phase configuration and physical characteristics. These and other results of microstructural characterization will be discussed. This work is part of a broader research on the development of alternative environment friendly hydraulic composite cements of Portland cement highly replaced by calcium sulphate and industrial byproducts.
INTRODUCTION Research on the use of alternative regional cementitious materials to reduce the use of Portland cement (PC) is of interest due to the energy consumption and CO2 emissions associated to its production. Moreover, is well known energy and CO2 emissions derived from the construction materials are less than 10% of those derived from the operation of a building during its lifespan [1]; thus, alternative cements in nonstructural concretes could be exploited in properties such as thermal mass and thermal insulation, together with passive solar architectural design, to further reduce energy consumption and CO2 emissions [2, 3]. Gypsum is a widely used binder, regarded as low-energy binder as its processing requires low temperatures and develops strength rapidly [4]; however its solubility in water limits its applications to dry environments, unless special procedures are applied [5]. Calcium sulphate can be combined with other cementitious materials, resulting in the formation of additional water insoluble hydration products and a microstructural reconfiguration that enhances the strength and hydraulic character [6, 7]. Different types of calcium sulphate can be used for this purpose, in which the crystallization habits and setting of gypsum change depending on the hydration level of the starting material (hemihydrate or anhydrite); when hemihydrate is used, rheology modifiers or organic acids may be employed to delay setting [8]. Cupola slag (CS) and blast furnace slag (BFS) are byproducts of iron production. The granulated slags have latent hydraulic properties; however, mechanical and chemical activation is needed. Studies on BFS as a PC replacement are widespread due to its chemical composition
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