Thaumasite Non-Sulphate Attack at Ambient Temperature and Pressure

Abstract

One of the products of concrete sulphate corrosion, besides gypsum and ettringite, is thaumasite. The thaumasite is a very dangerous, non binding crystalline phase, which is forming at the expense of C-S-H phase. There was a conviction that the conditions required for the formation of thaumasite in concrete are: source of calcium silicate, sulfate ions, carbonate ions and a very wet, cold (below 15°C) environment. The corrosion of concrete caused by the external source of sulphate ions during which thaumasite is formed was called thaumasite sulphate attack (shortly TSA). While the TSA is recognized, the thaumasite non-sulphate attack (T n S A) must be highlighted, because is also possible. The purpose of this work is to show that thaumasite, or solid solutions of Ett-Th (ettringite with thaumasite) are able to form in hardened cement paste without external source of sulphate ions, at ambient temperature and pressure (25±2°C (298.15 K) and 102±1 kPa). The experiment appeared on thaumasite formation in corroded specimen made of CEM I (Portland cement) and of CEM III (slag cement) after 4 days of immersion in saturated water solution of NH 4 Cl.

The Impact of Chloride and Sulphate Aggressiveness on the Microstructure and Phase Composition of Fly Ash-Slag Mortar

“…XRD tests indicated the presence of Friedel’s salt for only one of the specimens, and probably only a small amount of it ( Figure 5 ). This, we believe, resulted from the pore liquid model pH, since Friedel’s salt is decomposed at pH < 12 [ 30 , 31 ]. Furthermore, the source literature contains the information [ 25 , 32 ] that the formation of Friedel’s salt will be limited by the total available Al content in the binder, and not by the very content of AFm phases, since all aluminate hydrates will be transformed at a similar range of concentrations as Friedel’s salt.…”

Mechanical evaluation and hydration kinetics of cement pastes with dolomitic filler

“…It is important to note that the thaumasite identified in this paper does not refer to sulfate attack thaumasite (SAT). Słomka-Słupik and Zybura [36] propose a new term for this formation, called TnSA (thaumasite non sulfate attack), which means thaumasite without sulfate attack. Also, by analyzing the results obtained, the formation of brucite and hydrotalcite was not detected in the mixtures, reinforcing the study of Barsi et al [37].…”

Analysis of Concrete Corrosion of Manhole Located Near Source of Odorous Emission

“…In the first stage of corrosion of concrete, hydrogen sulphide can react directly with calcium components of concrete, in particular with Ca(OH) 2 creating calcium bisulfite [2,3]. In the next stage of corrosion resulting from the interaction of sulfuric acid, ettringite 3CaO Al 2 O 3 3CaSO 4 32H 2 O is formed, and then gypsum CaSO 4 2H 2 O, because of lowering pH [24,25]. In several cases, a fine plastic, mushy mass was also observed, which was associated with a drop in adhesion and strength of the concrete [3,18].…”

“…8. Near the gypsum and the highly decalcified C-S-H phase, next phase present in the tested material in small amounts was probably calcium carbonate, which accompanied gypsum in the strong concrete decalcification conditions [24,25,26,27]. The research on identification of microorganisms groups present in fragments of corroded cast iron manhole plate is presented in Table 4.…”