Portland and Belite Cement Hydration Acceleration by C-S-H Seeds with Variable w/c Ratios

Abstract

The acceleration of very early age cement hydration by C-S-H seeding is getting attention from scholars and field applications because the enhanced early age features do not compromise later age performances. This acceleration could be beneficial for several low-CO2 cements as a general drawback is usually the low very early age mechanical strengths. However, the mechanistic understanding of this acceleration in commercial cements is not complete. Reported here is a contribution to this understanding from the study of the effects of C-S-H gel seeding in one Portland cement and two belite cements at two widely studied water–cement ratios, 0.50 and 0.40. Two commercially available C-S-H nano-seed-based admixtures, i.e., Master X-Seed 130 and Master X-Seed STE-53, were investigated. A multi-technique approach was adopted by employing calorimetry, thermal analysis, powder diffraction (data analysed by the Rietveld method), mercury intrusion porosimetry, and mechanical strength determination. For instance, the compressive strength at 1 day for the PC (w/c = 0.50) sample increased from 15 MPa for the unseeded mortar to 24 and 22 MPs for the mortars seeded with the XS130 and STE53, respectively. The evolution of the amorphous contents was determined by adding an internal standard before recording the powder patterns. In summary, alite and belite phase hydrations, from the crystalline phase content evolutions, are not significantly accelerated by C-S-H seedings at the studied ages of 1 and 28 d for these cements. Conversely, the hydration rates of tetracalcium alumino-ferrate and tricalcium aluminate were significantly enhanced. It is noted that the degrees of reaction of C4AF for the PC paste (w/c = 0.40) were 10, 30, and 40% at 1, 7, and 28 days. After C-S-H seeding, the values increased to 20, 45, and 60%, respectively. This resulted in larger ettringite contents at very early ages but not at 28 days. At 28 days of hydration, larger amounts of carbonate-containing AFm-type phases were determined. Finally, and importantly, the admixtures yielded larger amounts of amorphous components in the pastes at later hydration ages. This is justified, in part, by the higher content of amorphous iron siliceous hydrogarnet from the enhanced C4AF reactivity.

Recent Advances in C-S-H Nucleation Seeding for Improving Cement Performances

“…To investigate the possible role of the w/c ratios, Figure 4 shows a calorimetric study for a CEM I 42.5 R paste at two relevant w/c ratios (0.50 and 0.40), from [ 71 , 78 ]. In these works, the pastes were seeded with 2 wt% of different Master X-Seed admixtures (≈0.50 wt% referring to the solid contents).…”

“…However, at 28 d, the situation is reversed and the improvements in mechanical properties of blends are larger than in plain PCs. In this sense, the synergy of C-S-H nucleation seeding and alkanolamine addition (to enhance calcium aluminate hydration) seems to be a very promising strategy to have improved mechanical strengths at 28 days and later [ 71 , 77 , 78 , 82 , 86 , 87 ].…”

“…Symbols (lines and arrows) as in Figure 2 . Replotted from data of the authors of this work originally reported in references [ 71 , 78 ].…”

Activation of LC3 binders by C‐S‐H nucleation seeding with a new tailored admixture for low‐carbon cements

“…For the seeded samples, the CH content is slightly smaller than that for the corresponding unseeded samples at all the selected ages and in all the series. As it was previously reported [15,16], for the PC reference sample, this could be due to the smaller reactivity of the C3S phase, a larger Ca/Si ratio of the resulting C-S-H gel, or because of the formation of the amorphous phases such as AFm-Hc which consume portlandite. Moreover, for the LC 3 series, the smaller CH contents could be a sign of enhanced pozzolanic reaction but the nuances listed above also apply.…”

Fracture Performance of Cementitious Composites Based on Quaternary Blended Cements

“…The obtained test results of the mechanical parameters can be explained by the fact that the FA additive, used in small amounts, is able to additionally produce a larger amount of more compact C-S-H phase, which makes the material more airtight by filling the material’s pores [ 82 , 83 ]. However, the presence of FA in the composition of the cement matrix implies a slight reduction in the strength parameters of the composite through the heterogenization of its structure and reduced pozzolanic activity in the initial curing period of materials with these additives [ 84 , 85 , 86 ].…”