Influence of cellulose pulp fiber addition on the hydration of cementitious pastes with silica fume
The use of natural fibers in cementitious materials can provide multiple benefits on both the issue of reducing the environmental impact and the mechanical behavior, while enhancing the toughness and post-cracking resistance. However, to be able to use these materials in various areas of engineering it is necessary to better understand its behavior in the fresh, hardening and hardened state. The present study aimed at investigating the influence of cellulose fibers (eucalyptus and pine) on the hydration of cement pastes containing silica fume. For this goal, composites were produced with volumetric fiber fractions of 0, 0.25, 0.50 and 1.0%. The matrix was composed of cement, silica fume, silica sand, water and superplasticizer. The ratio of materials was 1: 1: 0.55 (cementitious blend: silica sand: water/cementitious blend). The ratio of the cement blend was: 0.65 :0.35 (cement :silica fume). Hydration was studied from tests using ultrasonic pulse velocity, adiabatic calorimetry, electrical conductivity, isothermal calorimetry. The evolution of the compressive strength with time for the mixtures under consideration was determined until the age of 180 days. From the results, it was observed that the dormant stage period was not affected by the presence of pulps, but once commenced, a retardation of the hydration reactions occured. Furthermore, an inclination in the rate of hydration during the acceleration period developed that could be associated with the kinetics and the formation of various hydration products, including pozzolanic C-S-H. Through adiabatic calorimetry tests, it was concluded that pine fibers cause a larger reduction in total heat release than eucalyptus fibers. This is due to the fact that pine fibers contain more hemicellulose, lignin and extractives than eucalyptus fibers. Finally, comparing non-destructive testing results with the compressive strength results, a reduction in the ultimate strength (after 180 days) appeared, which is in agreement with the lower formation of hydrated products indicated by the adiabatic and isothermal tests.