Effect of TIPA on Chloride Immobilization in Cement‐Fly Ash Paste

Abstract

Utilization of sea sands and coral aggregate for concrete in ocean construction is increasingly attracting the attention all over the world. However, the potential risk of steel corrosion resulting from chloride in these raw materials was one of the most concerned problems. To take this risk into account, chloride transporting to the surface of steel should be hindered. e formation of Friedel's salt in hydration process is widely accepted as an effective manner for this hindrance. In this study, an attempt to hasten the formation of Friedel's salt by adding triisopropanolamine (TIPA) was done in the cement-fly ash system, with intention to chemical bind chloride, and the chloride-binding capacity at 60 d age was examined. e results show that TIPA can enhance the chloride-binding capacity of cement-fly ash paste at 60 d age, and the reason is that the formation of Friedel's salt can be accelerated with addition of TIPA. e mechanism behind is revealed as follows: on the one hand, the accelerated cement hydration provides more amount of calcium hydroxide to induce the pozzolanic reaction of fly ash, which can hasten the dissolution of aluminum into liquid phase; on the other hand, TIPA can directly hasten the dissolution of aluminum in fly ash, offering more amounts of aluminum in liquid phase. In this case, the aluminum/sulfate (Al/S) ratio was obviously increased, benefiting the formation of Friedel's salt in hydration products. Such results would expect to provide useful experience to promote the chloride-binding capacity of cement-fly ash system.

Effect of Nanosilica on Impermeability of Cement‐Fly Ash System

“…e hydration products were characterized with 29 Si MAS NMR. It was reported that six peaks were found in NMR spectrum of hydrated cement-FA paste [12,38,39]; Q 1 and Q 2 represented the chain-end Si-O tetrahedrons and middle-chain Si-O tetrahedrons in hydration products; Q 2 (1Al) denoted the middle-chain groups where one of the adjacent tetrahedral sites was occupied by Al 4+ ; Q 0 , Q 3 , and Q 4 represented the Si-O tetrahedrons in unhydrated cement minerals and Si-O tetrahedrons in FA, respectively. A Bruker Advance III400 spectrometer was adopted to carry out 29 Si-NMR (solid-state nuclear magnetic resonance), operating at 79.5 MHz, with rotation frequency of 5 kHz and the delay time of 10 s. Tetramethylsilane was used as 29 Si standard.…”

“…where C is a constant; P i and V i stand for the mercury pressure and intruded pore volume at step i; and D stands for the fractal dimension of the pore surface [45][46][47][48]. erefore, equation 9is expressed as equation (12). e fractal dimension of the pore surface can be obtained by the slope of the curve log (V 1/3 n /r n ) versus log (W n /r 2 n ).…”

“…e mechanical performance could be deteriorated, and under load, the cracks occurred; thereafter, sulphate ions were easier to go into the inside of concrete structure along the cracks and the more serious corrosion would happen [9][10][11]. Chloride ions could easily permeate into the inside of the matrix and migrate to the surface of steels and then cause steel corrosion probably [12,13]; finally, volume expansion happened and the concrete structure was destroyed. In the process of various external erosions, one precondition is that corrosion ions need to penetrate through the surface and go into the inside of the concrete.…”

Free and bound chloride relationships affecting reinforcement cover in alkali activated concrete

“…Cement particles have surface charges which causes them to flocculate when in contact with water while the addition of chemical admixtures into the fresh concrete mix releases the trapped bound water within the gel matrix [22,23]. However, other research reports that the effect of these chemical admixtures is to increase the amount of bound chloride when chloride diffusion into hardened concrete occurs from external sources [30,31]. This is due to the greater surface area of the hydration products produced by the flocculation of cement particles and release of bound water caused by the admixtures [30,31].…”

Comparative Study on Chloride Binding Capacity of Cement-Fly Ash System and Cement-Ground Granulated Blast Furnace Slag System with Diethanol-Isopropanolamine

“…One was to promote the formation of FS or KS to chemically bind chloride ions; the second was to hasten the hydration to produce more amount of C-S-H gel to physically adsorb the chloride ions; the last was to improve the pore structure to hinder the migration of chloride ions. For example, one reason for supplementary cementitious materials (SCM), such fly ash (FA) and ground granulated blast furnace slag (GGBS), to promote the binding capacity was that the dissolution of aluminates could be facilitated in the process of pozzolanic reaction, which could expedite the formation of FS or KS, thereby promoting chemical binding [ 12 , 13 ]. The other reason was that pore structure and the hydration degree were also improved, which promoted the migration resistance and physical binding.…”