The effect of redispersible polymer powders and holding conditions on the shrinkage of building mortars
Abstract
The effect of redispersible polymer powders and holding conditions on the shrinkage of building mortars
Incoming article date: 10.10.2023The influence of the type and dosage of some redispersible polymer powders on the shrinkage deformation of building mortars obtained from dry building mixes, including for underfloor heating, after exposure at a temperature of 70 ° C in accordance with GOST R 56387-2018 was investigated. The introduction of admixtures 4042N, E06RA, 5603 into the mixtures did not lead to an increase in shrinkage deformations when maintained according to GOST R 56387-2018 relative to the additive-free standard, regardless of the type and dosage of the admixture, while with these admixtures, regardless of their dosage, within 1-3%, the values of shrinkage deformations were less than 1.5 mm / m. The greatest influence of the type and dosage of the redispersed polymer powders on the shrinkage change is manifested at the heating stage, which is due to their influence on the kinetics of dehydration and the magnitude of the E-modulus. Depending on the type of cement, type and dosage of the admixture, the moisture loss values by the end of heating to 70oC ranged from 0.114 to 0.629 relative to the total moisture loss by the end of holding. Naturally, a change in shrinkage by the end of heating from 0.027 to 0.595 relative to complete shrinkage by the end of aging was noted, while a proportional relationship between moisture loss and shrinkage was revealed. In some formulations, an expansion of up to 0.469 mm/m was recorded by the end of heating. For a comprehensive assessment of the degree of influence of admixtures on changes in the deformation and strength properties of mortar at a holding temperature of 70 ° C according to GOST R 56387-2018, an indicator of the conditional stress level is proposed, varying depending on the holding stage, type of cement, type and dosage of the additive in the range from 0.489 to 3.05.
Keywords: Shrinkage, building mortars, dry building mixes, redispersible polymer powders, underfloor heating