Effect of Delaying Addition of Heat Stimulated Superplasticizer on Fresh Properties of Mortar

Abstract

To assure the quality and required workability of mortar or concrete, various types of superplasticizers are used. There are many factors affecting the performance of superplasticizers explicitly, type and dosage of the superplasticizers, type of cement, temperature and mixing procedure, as well as the addition times of the superplasticizers. Some researchers investigated the effect of delaying the addition time of superplasticizer to mortar or concrete, but there is not enough data about the effect of external temperature on performance of superplasticizers and consequent influences on fresh properties of mortar or concrete. In this research the effect of delaying the addition time of superplasticizers and influence of external temperature, namely, heat stimulation of superplasticizers, on fluidity, fresh density and air content of fresh cement mortar was investigated. Two types of Precast and Ready-Mix of Polycarboxylic acid-based ether superplasticizers with Ordinary Portland Cement was used. Delaying the addition time of superplasticizers enhanced the fluidity, slightly decreased the fresh density and increased the air content of mortar in comparison with simultaneous addition time with both heated and non-heated Superplasticizers.

Effect of Thermal Stimulation on Various Characteristics of Superplasticizer

“…There result concluded to estimate that polymer relax and straighten by thermal stimulation. Moreover, in previous studies [7]- [10], when the more contained amount of slump keeping polymer, it was recognized that the polymer was relaxing for thermal stimulation. However, it is thought that by cooled slowly it will return to the size and geometric structure of stable polymer molecules in the state before thermal stimulation.…”

“…As these results, it was confirmed that the effect of thermal stimulation and its sustainability will be improved as the content of SK type in the superplasticizer increases. In the previous studies [7][8][9][10], only fluidity of the mortar right after mixing were investigated, in this study, the effect of thermal stimulation after mixing had been evaluated. Moreover, it was confirmed that even if the initial dispersion performance improves by thermal stimulation, slump keeping performance can be maintained.…”

“…Fresh test of the mortar was conducted in accordance with the JIS R 5201 "Physical testing methods for cement". And also, in Case 2 the effect of thermal stimulation the value of mortar flow compared with presence or absence of thermal stimulation by the index shown in Equation (1) [7]- [10].…”

“…In this study, heating superplasticizers itself is hereinafter as referred to as "thermal stimulation". Fig.1 shows the image of polymer structures changing by thermal stimulation [8]- [10], [17]- [19]. Hypothesis about thermal stimulation that increase dispersion performance of cement because of increased adsorbed sites with cement hence superplasticizer was given to thermal stimulation.…”

“…In addition, the paper by Takigawa et al [8], [9] clearly indicated that three-dimensional structure of polymer in the superplasticizers will be changed by thermal stimulation. Other researchers [10]- [14] have reported that polycarboxylic acid-based and etheric polycarboxylic acids are relevant to Hydrophobic backbone, type of hydrophobic grafts, length, arrangement and functional group [3], [4]. More it has reported that the dispersion efficiency of cement increases in step with the number and length of hydrophobic grafts, and polymer molecular of hydrophobic grafts adsorb onto the surface of cement particles.…”