Abstract
The aim of work is to describe and to complement the existing knowledge on the effect of redispersible polymer powder on the setting time of cement mortar as measured by means of ultrasonic apparatus. The mortars were simple mixtures of filler in the form of quartz sand, Portland cement CEM I 42.5 R as binder and methyl hydroxyethyl cellulose. The mortar additives were two commercially available redispersible polymer powders in an amount of 0-5% of total weight. The chosen polymers had different chemical structure: styrene-acrylic copolymer (SA), vinyl acetate-ethylene copolymer (ET), and minimum film forming temperature (MFFT). The amount of water was constant and equal to 20% of the total weight of the mortar. Conclusions: - even the small amount of redispersible polymer powder added to the cement mortar has a significant influence on mortar’s initial and final setting time and this effect strongly depends on the percentage of the additive, - the chemical structure of the studied redispersible polymer powders did not influence the behaviour of the whole chemical system, - the further studies on technical properties, such as mechanical strength and permeability are planned in order to find more information on the structure of hardened mortar.
Highlights
The consequence of development in architecture and construction engineering is the constant increase of technical requirements for construction products, including thin-bed mortars based on cement
The comparison of kinetic traces for the „00” and „0” samples unequivocally shows the influence of methyl hydroxyethyl cellulose on retardation of setting of cement mortars (Figure 1)
The retardation is visible for the final setting time – the addition of Methyl hydroxyethyl cellulose (MHEC) resulted in approx. 2.4-fold retardation of setting time; including the 1% of styrene-acrylic redispersible polymer powders (RDP) in the sample lead to 1.2-fold further prolongation of the final setting time compared to 1.1-fold increase of setting time for 1% of vinyl acetate polymer powder
Summary
The consequence of development in architecture and construction engineering is the constant increase of technical requirements for construction products, including thin-bed mortars based on cement. The increase of the requirements regards mainly technical parameters such as mechanical strength or durability for which the expectations are presented in the standards. Fulfilment of these high requirements by building mortars, which are simple mixtures of cement binder and mineral filler, is impossible for many applications. Application of chemical additives is based rather on macroscopic observations and empirical evaluation of their influence on the technical parameters. For this reason, each analysis of the effect of single chemical additive on the performance of building mortars is a valuable complementation of knowledge and has high application potential
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