Basic Research of Improving the Mortar Flow by Thermal Stimulation to Superplasticizer

Abstract

Polycarboxylic acid-based superplasticizers are being used for various fields of concrete work, however little has reported on changing basic performance by thermal fluctuation. In this study, heating superplasticizers itself is hereinafter as referred to as “thermal stimulation”, the effect of thermal stimulation and heat retention of superplasticizer on the fresh mortar, moreover the influence of molecular structural changed of superplasticizer by thermal stimulation were investigated. As the result, it was confirmed that improving fluidity of the mortar flow on this condition the highly heat temperature and heat over a long time by thermal stimulation of superplasticizer. In addition, it turned out that this phenomenon was caused molecular structural changed by thermal stimulation, and the result was revealed that the effect of thermal stimulation varies according to the type of polymer.

Effectiveness of Thermal Stimulation of Superplasticizers on Fresh Properties of Cement Mortar

“…This reduction was about 17% for the PCa-type and about 40% for the RMC-type superplasticizer, indicating that thermally stimulating the RMC superplasticizer is more effective in improving its ability to reduce plastic viscosity and increase fluidity. This is related to the fact that thermally stimulating the superplasticizer increased its apparent polymer size and improved flowability, as shown in previous studies (Takigawa et al 2018(Takigawa et al , 2019. The apparent size of the polymer described in previous studies is based on the polymer structure.…”

“…In order to prevent the vaporization of the superplasticizer during heating, it was encapsulated in a small polypropylene bottle and warmed in hot water. The superplasticizer was heated to 60 °C (± 1 °C) over 24 h as in previous studies (Takigawa et al 2018(Takigawa et al , 2019. The rate of temperature increase of the sample was approximately 1.5 °C/min.…”

“…It has also been reported that the rheological properties of mortars with polycarboxylic acid superplasticizers having short side chains improved as the length of the side chains increased (Andreas and Frank 2007;Hamada et al 2006). In light of the hypotheses made in previous studies, it can be inferred that the polymers in superplasticizers that retain slump performance well have long side chains that tend to become entangled, but thermal stimulation causes the entangled polymers to unravel, which not only improves flowability but also affects plastic viscosity (Takigawa et al 2018(Takigawa et al , 2019.…”

“…This is because naphthalene sulfonic acid has a straight-chain-type molecular structure and has a different active mechanism than polycarboxylic acid-based superplasticizers (Ohta 1997;Sugiyama et al 2000). The relevant extant studies (Takigawa et al 2018(Takigawa et al , 2019Nemoto et al 2020;Robert 2004;Ohtsuka et al 2015;Jacek and Janusz 2004;Chandra and Björnström 2002) show that polycarboxylic acid superplasticizers hinder agglomeration of cement particles more than other raw polymer superplasticizers. In addition, thermal stimulation improves the dispersibility of the cement particles, lowering their stiffness since it further reduces their cohesion.…”

“…One previous study formulated a hypothesis that superplasticizers are stimulated by heat, which improves the three-dimensional area of the polymer and the adsorption area of the cement (hereinafter "thermal stimulation") (Takigawa et al 2018(Takigawa et al , 2019. Based on this hypothesis, a superplasticizer was heated at 40 °C to 60 °C for 0.5 h or 24 h. Using mortar flow tests and dynamic light scattering (DLS), the authors showed a change in the fluidity of the mortar and the apparent three-dimensional area of the polymer.…”