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Hydration and strength evolution of air-cured zeolite-rich tuffs and siltstone blended cement pastes at low water-to-binder ratio

Abstract:

This contribution is the second part of an in-depth study on the hydration and strength evolution of blended cement pastes at a water to binder (W/B) ratio of 0.3, cured by two different methods. The blended cement pastes showed significant hydration up to 7 days, when almost all of the hydration products had already formed; thereafter, carbonation played an important role up to, and possibly beyond, 91 days. Likewise, the hydration of alite (tricalcium silicate, Ca3SiO5, C3S) proceeded up to 14 days and then started to slow down. However, the hydration of belite (dicalcium silicate, Ca2SiO4, C2S) was affected most strongly, as it nearly ceased, under the air-curing conditions. During hydration, some of the blended cement pastes had a larger calcium hydroxide (CH) content than the unblended (plain) ones. The accelerating effects of the addition of supplementary cementitious materials (SCMs), the air-curing conditions and the low W/B ratio may explain these unusual results. Under these experimental conditions, the water incorporated into hydrates was about 50% of the total amount of water used during full hydration of the cement pastes. The pozzolanic reaction predominated during the early ages, but disappeared as time passed. In contrast, the carbonation reaction increased by consuming ∼45% of the total amount of CH produced after aging for 91 days. Only one blended cement paste reached the compressive strength of the plain cements. The blended cement pastes containing 5% of the zeolitic tuffs, Zeo1 or Zeo2, or 10% of the calcareous siltstone, Limo, developed the greatest compressive strength under the experimental conditions used in this study.