Reaction kinetics, gel character and strength of ambient temperature cured alkali activated slag–fly ash blends

Abstract

h i g h l i g h t sSlag/fly ash ratio and activator modulus show synergetic effects on reaction. Activator modulus has a more significant influence on early age reaction. Gel structures remain stable regardless of activator modulus and slag/fly ash ratio. Slag content shows a dominating effect on compressive strength. a r t i c l e i n f o t r a c tRoom temperature cured alkali activated slag/fly ash blends have shown their advantages in field applications. Given that alkali activated materials are extraordinarily sensitive to the composition of the starting materials, identifying their influences is essential for their application. This paper focuses on the effects of two compositional factors: activator modulus (SiO 2 /Na 2 O from 1.0 to 1.8) and slag/fly ash mass ratios (between 90/10 and 50/50) on reaction kinetics, gel characters and compressive strength. The results show that when lowering the activator modulus, the early age reaction is significantly accelerated with a higher reaction intensity, and increasing the slag content also leads to an increased reaction rate, especially at low activator modulus. Regardless of the two influential factors, the main reaction products are chain structured C-A-S-H gels with similar water contents and thermal properties, and no typical N-A-S-H type gels are formed in the system. Slight differences in terminal SiAO bonds and crystallization temperature are caused by the activator modulus and slag/fly ash mass ratios, respectively. The compressive strength results show that the optimum activator modulus changes with the slag/fly ash mass ratio, and higher slag/fly ash mass ratios prefer higher activator moduli in general, while either too high or too low activator modulus has detrimental effect on strength. Understanding the reaction, gel structure and strength changes are fundamental for determining key manufacturing parameters and tailoring the properties.

Characterization of alkali activated slag–fly ash blends containing nano-silica

“…on reaction kinetics, gel characters, mechanical properties and durability issues were also intensively investigated [16][17][18][19][20][21]. The recent progresses in understanding the blended system provide solid basis for further investigations and those modified properties demonstrate a promising future for the application of alkali activated materials.…”

Characterization and application of municipal solid waste incineration (MSWI) bottom ash and waste granite powder in alkali activated slag

“…The most widely applied activator solutions are sodium hydroxide modified with sodium silicate, and the commonly used starting solid materials are slag, fly ash and metakaolin. Besides, the effects of key synthesizing factors on reaction kinetics (Gao et al, 2015), gel characteristics (Li et al, 2010), mechanical properties and durability issues (Bernal et al, 2012) for the alkali activated systems were intensively investigated; also their ability to bind heavy metals was also observed (Zhang et al, 2007).…”

Evaluation of hybrid steel fiber reinforcement in high performance geopolymer composites

“…The main reaction products in the blended system are stably coexisting C-(A)-S-H and N-A-S-H type gels [12][13][14]. Besides, the influences of key synthesizing factors on reaction kinetics, gel characteristics, mechanical properties and durability were intensively investigated [15][16][17][18][19][20][21]. The recent understandings on the blended alkali systems provide solid theoretical support for the further researches.…”