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

Abstract

Polycarboxylic acid-based superplasticizers are used in various types of concrete work. Wide variations in environmental temperatures are known to affect how well chemical admixtures perform as superplasticizers, influencing the properties of the concrete. However, little has been reported on changes in performance caused by thermal variations. Previous studies have reported that heating superplasticizers change the polymer structure, improving and sustaining cement particles' dispersibility. Moreover, the improved fluidity from thermal stimulation is not temporary. The effect has been observed to remain for about seven days, with the residual characteristics differing depending on the superplasticizers used. Therefore this study evaluates mortar stiffness when using thermally stimulated superplasticizers and evaluates how the stimulation affects construction performance using measures such as the flow and rheological properties (plastic viscosity) of fresh mortar, vane shear tests, blade viscometer tests, and mortar vibration box tests. Mortar's fluidity was found to improve by about 25% when using thermally stimulated additives, with plastic viscosity dropping by up to 45% and the stress likely to be needed for pumping also being reduced by about 16%. Filling speed was also found to increase by about 26%. Thus, thermal stimulation improves mortar and concrete construction performance, and it may be possible in the future to carry out the construction with fewer workers utilizing this technology’s benefits. The study indicates a need for further investigation of how thermal stimulation affects polymer molecules’ adsorption efficiency with cement to elucidate the mechanism at full scale and propose ways to adopt thermal stimulation at actual construction sites.

Performance Change in Superplasticizers after Thermal Stimulation

“…The amount of superplasticizer added was set so that the value of 0 tamp flow without thermal stimulation was 120 ± 10 mm for each formulation. In Case 1, the dispersion performance was different between LSC and MSN, and the sand to cement ratio (S/C) could not secure the prescribed fluidity under the same conditions as in the previous studies [15,16,17]. Therefore, by setting the S/C to 1.5, it was possible to confirm the fluidity improvement due to thermal stimulation of the in this study.…”

“…In our various studies [15,16,17] to verify that when a superplasticizer is stimulated by heat (hereafter, referred to as "thermal stimulation"), the polymer molecule's stereoscopic projection area in the superplasticizer changes, and the region that adsorbs cement particles expands. Based on the results, it was confirmed that the fluidity and construction performance was improved by thermal stimulation.…”

“…Therefore, it is considered that the degree of adsorption of polymer molecules and cement particles in the superplasticizers also differs depending on the effect of thermal stimulation. Moreover, although the effects have been verified for polymer molecules [15,16], but the relationship between the degree of entanglement and the effect of thermal stimulation has not been investigated.…”