Interaction of TEOS with cementitious materials: Chemical and physical effects

Abstract

This study explored the effectiveness of tetraethyl orthosilicate (TEOS) as a Portland cement mortar consolidant to verify whether it meets the requirements for use in cultural assets. TEOS was found to raise cement mortar strength, lower its porosity and permeability and occasion minimal alteration in its appearance, an indication of its suitability to conserve heritage mortar works.FTIR and 29 Si MAS NMR studies supported the notion that TEOS interacts with the hydrated phases of the cement, portlandite and C-S-H gel. The reaction product between portlandite and TEOS was C-S-H gel and between TEOS and C-S-H gel was a gel with longer chain.

Carrageenan–Silica Hybrid Nanoparticles Prepared by a Non‐Emulsion Method

“…The 29 Si MAS NMR and CP/MAS NMR spectra of the SiO 2 and SiO 2 /SiCRG‐1 particles are shown in Figure 4 (b and c), respectively. The silicon sites are labeled according to the usual NMR spectroscopy notation: Q n represents Si atoms quaternary oxygen linked, that is, bond to (4 – n ) OH groups 41,47,48…”

“…Therefore, Q 4 symbolizes the internal siloxane‐type Si atoms in Si(OSi) 4 , whereas Q 2 and Q 3 represent the surface Si atoms bound to hydroxyl groups Si(OSi) 2 (OH) 2 and Si(OSi) 3 OH, respectively 41,47,48. The resonances at approximately δ = –91, –101, and –110 ppm are assigned to Q 2 , Q 3 , and Q 4 Si sites, respectively, in accordance with the literature 47.…”

Use of nanosilica- or nanolime-additioned TEOS to consolidate cementitious materials in heritage structures: Physical and mechanical properties of mortars

“…Recent studies on the consolidation of cement-based materials, less intensely researched to date [18,19,20], have assessed the effect of TEOS on the physical properties of mortars with promising results: mechanical strength and durability (reduction of chlorides and carbonation depth) were enhanced with no significant alteration of surface colour or gloss. Nonetheless, TEOS has been shown to penetrate compact materials in depth [19] and in early age (1 day) cements the formation of alcohols during TEOS hydrolysis retards hydration and favours the formation of a more porous, weaker structure [21].…”

“…Nanosilica (nano-SiO2, NS)-based surface consolidating treatments [22], on the grounds of the reactivity of two of the main products of Portland cement hydration, portlandite (Ca(OH)2) and C-S-H gel [10,20,23], and their ability to fill the pore systems, have been attempted, with varying success on hardened concrete and cement mortars, for whilst they can densify these materials, their penetration capacity is lower than in TEOS. In fact, NS compared with a variety of organic or inorganic surface treatments has been found to be less effective in reducing water absorption [24], chloride migration or CO2 penetration [19; 24] or in raising mechanical strength [25].…”

Lanthanum-Silica Sol-Gel Coatings for Protecting Metallic Materials in Museums: Approaches to Copper, Bronze, Lead and Steel

“…Much research has been carried out on sol-gel formulations applied as consolidants for Heritage materials, e.g., different kinds of stones, Portland cement mortars, ceramic tiles, stained glasses, etc. In stones, sol-gel preparations were developed with the aim of reducing cracks inside the stone and/or to modify its hydrophobic character or porous size distribution [6][7][8][9]. The results seem to be promising, although some improvements are still needed.…”