Concreto celular de diferentes densidades: efeito da goma xantana como estabilizador de espuma e de fibras de polipropileno

Abstract

Cellular concrete is a cementitious material with a porous structure and low density, resulting from the hardening of a mixture composed of binders, fine aggregates and air pores. One way of inserting the air pores is through a preformed foam. Foam is composed of air bubbles, which influences the behavior of foamed cellular concrete both in the fresh and in the lasting state. Recent work has proposed the use of Xanthan Gum (XG) as a foam thickening agent, and found that XG increased its stability and quality, as well as implemented improvements in the performance of cellular concrete in the resisted state. However, the functioning of XG and different dosages is still unclear. Likewise, some researchers have suggested the insertion of fibers in order to provide better mechanical behavior and durability to foamed cellular concrete. Among the synthetic fibers used to reinforce cementitious materials, Polypropylene (PP) fiber stands out. PP provides some benefits, such as increased flexural and tensile strength, better post-cracking behavior and reduced drying shrinkage. However, the use of PP leads to the generation of additional pores, causing greater connectivity between the pores, as well as favoring the formation of fragile transition zones between the matrix and the fiber. However, it is not clear how PP behaves at different densities. Thus, this work presents a study of the influence of Xanthan Gum on the quality of preformed foam, as well as on the physical and mechanical properties of foamed cellular concrete in the hardened state. Furthermore, this study verifies whether the stability provided by Xanthan Gum minimizes the difficulties encountered as a result of the use of PP in cellular concrete.Samples with two different densities, 800 Kg/m3 and 1200 Kg/m3 were evaluated. The Xanthan Gum content was evaluated according to the content of the foaming agent used to manufacture the foam. The composition that provided better foam quality was 2% XG. In cellular concrete, the addition of XG proved to be more efficient for the sample with a target density of 800 kg/m3, because due to the greater stability provided to the foam, there was a lower void ratio, as well as a greater distribution of smaller pores , smaller interconnected and tending to a circular shape. Likewise, Xanthan Gum promoted an increase in density, resulting in a greater average resistance to compression and traction in flexion, with a small increase in thermal conductivity and shrinkage on drying. Regarding the addition of PP, it was also more relevant for samples with a target density of 800 kg/m3, as it reduced drying shrinkage and provided greater mechanical strength through the stress bridge effect, but provided pores of irregular shapes the mixture. Finally, when using XG and PP together, it is evident for the 800 Kg/m3 samples that they promoted a greater distribution in smaller pores, tending to a circular shape, which consequently allowed better physical and mechanical properties to cellular concrete.