Alternative shrinkage-compensate admixture using an Al-based waste for Ordinary Portland Cement

Reference	Presenter	Authors (Institution)	Abstract
04-090	Elisângela Guzi de Moraes	Souza, M.T.(Universidade Federal de Santa Catarina); Correa, B.(Universidade Federal de Santa Catarina); Onghero, L.(Universidade Federal de Santa Catarina); Repette, W.L.(Universidade Federal de Santa Catarina); Raupp-Pereira, F.(Universidade Federal de Santa Catarina); Novaes de Oliveira, A.P.(Universidade Federal de Santa Catarina); Guzi de Moraes, E.(Universidade Federal de Santa Catarina);	Cement-based materials undergo volumetric changes (mainly shrinkage) during hydration process. When restraint prevents length change, tensile stresses are originated and, if these stresses exceed the strength of the material, cracking occurs. Several methods have been suggested to reduce the shrinkage cracking in Portland cement based concrete, including optimization of mixture design, to change the cure practices, relieves the stresses by proper placement of contraction joints and the incorporation of fibers to improve the crack-arresting mechanisms. It is also common the use of chemical admixtures to reduce or compensate the cement shrinkage of OPC, named as shrinkage-reducing (SRAs) or shrinkage-compensating (SCAs) admixtures. These admixtures are relatively expensive, limiting their uses for projects where the reduction of the shrinkage is highly beneficial or necessary. In this work, we proposed an alternative and low-cost shrinkage-compensating admixture (SCA) based on the use of an Al-rich waste from the aluminum anodizing industry (AAW). Cement pastes with 10wt% of AAW and additional gypsum were investigated by DSC/TG, ICC, SEM, expansion/shrinkage and mechanical assays. The admixtures leaded to an early-age expansion (between 1 and 3rd day) in hydrated cement pastes, enough to compensate the natural shrinkage of the cement matrix (evaluated up to 7th) an act, successful, as a SCA. The expansion mechanism are straight related to the additional ettringite formation with expansive character formed from the use of the SCA.
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