# Novel Processing Methods of Low-Clinker Multi-Component Cementitious Materials--A Review
## 2 Ultrasound Treatment (US-T) Methodology
#### US-T of Cementitious Materials/Concrete and SCMs  
In concrete construction engineering, US-T waves are conventionally employed for the nondestructive diagnostics of structural conditions, including flaw detection or damage development [40; 41; 42; 43; 44; 45]; for early-age hardening monitoring to aid technological processes like formwork removal, aggregate exposure, etc. [45; 46; 47; 48; 49; 50; 51; 52]; and also for concrete demolition works. Applications of power US-T in construction material processing include the sonochemical activation of natural pozzolans [53]. Power US-T has proven highly beneficial in crystallization procedures, playing roles in seeding, crystal formation, and growth. Cavitation bubbles act as building blocks for crystal development while disrupting the medium and releasing more seeds and nuclei into the solution. Studies involving synthetic calcium silicate hydrate (C-S-H) or nanomaterials in cementitious systems have explored these effects [54; 55]. Investigations on CaCO\({}_{3}\) precipitation by Nishida [56] found that US-T enhanced the speed of calcium carbonate precipitation in a supersaturated solution. The most important consideration in these events was macrostreaming, rather than microstreaming, which is typically associated with cavitation. The presence of SCMs agglomerates led to the formation of C-S-H, with a significantly higher calcium-to-silicate (Ca/Si) molar ratio than typical cementitious composites due to microstructural and chemical reactions [57]. US-T application can overcome challenges in the particle hydration of PC and SCMs in concrete technology and cement chemistry, including aggregation/agglomeration, packing density control, and hydration rate control. Hydration mechanisms in PC systems are complex [58], and pore structure has a significant impact on the mechanical characteristics and durability of hardened cement materials [58; 59]. The penetration/dissolution of anhydrous phases during hydration plays a crucial role in controlling cementitious materials' early age and long-term properties [58; 59; 60]. US-T accelerates the heat release rate during the hydration acceleration phase but does not affect the total heat release [30] (Figure 2). The accelerated strength development in sonicated cement suspensions, observed for the first 16 h, is likely due to rapid cement hydration [30]. Figure 1: The acoustic cavitation methodology (with permission from [37]). [PERSON] et al. [61] introduced a novel method for 3D concrete printing composition using a US-T dispersion apparatus (ultrasonic processor with water-cooled transducer, Figure 3). This method achieved an fc of 1 MPa at 20 min of hydration and 50 MPa after 28 days, with the freshly prepared mixture transported to the ultrasonic dispersion device within 5 min to avoid premature setting. Ultrasonic dispersion equipment accelerates hydration, making shorter transport times acceptable. [PERSON] et al. [62] showed that after 60 days of curing, mortar containing sonicated Silica Fume (SSF) (a mineral admixture for the PC system) exhibited a significantly higher fc (over 38.9 MPa compared to non-sonicated SF) and a more than 20% reduction in total capillary porosity with diameters larger than 10 \(\upmu\)m. Ultrasonic processing altered the particle size distribution, favoring smaller sizes, resulting in SSF with an average particle size of 3.85 \(\upmu\)m, volume content of sub-micrometric particles of 56.9%, and a d\({}_{50}\) of 0.72 \(\upmu\)m. The particle size that corresponds to a 50% cumulative frequency is known as the d\({}_{50}\). SSF also demonstrated enhanced pozzolanic reactivity, as evidenced by increased consumption of portlandite during paste hardening. Pastes containing SSF exhibited 68% consumption of portlandite after 28 days of curing, compared to 28% for pastes containing Densified Silica Fume (DSF).