Abstract
The purpose of the study: to identify the effect of the dose of redispersible polymer powders and the type of low-modulus inclusions on the frost resistance of dry adhesives mixes made using Portland cement with the concrete base. Methods of research: The research was carried out on the basis of 75 freezing-thawing cycles. The following parameters were determined: compressive and flexural strength on samples 40x40x160 mm in accordance with GOST 30744; bond strength to the concrete base after 28 days hardening and after 75 cycles of freezing and thawing in accordance with GOST 31356. The dynamic modulus of elasticity was determined by the value of the ultrasonic pulse velocity on samples of 40x40x160 mm. The influence of prescription factors on the ratio of these values after 75 freeze-thaw cycles relative to the values after 28 days hardening under normal conditions was studied. Main results: The coefficients of frost resistance of the contact zone of the adhesive mortar made using dry mixes after 75 cycles of freezing and thawing exceeds the values of the coefficients of frost resistance according to the criteria of strength or dynamic elastic modulus. Dry adhesives mixes of class C1 with a dosage of redispersible polymer powder from 1 to 3% and an air-entraining admixture after 75 freezing cycles may be corresponded to class C2. The coefficient of variation in the compressive strength of mortar inside a series of samples after 28 days of hardening under normal conditions is not appropriate to consider as an indicator of the homogeneity of the mortar structure, potentially having a high resistance to cyclic freezing-thawing.
Highlights
Cement binder dry mixes are widely used in modern construction for producing various types of building mortars, including various adhesives [1-8]
Due to the limited information on the quantitative effect of various factors on the frost resistance of the contact zone [14], the purpose of this study was to identify the dependence between the frost resistance of the contact zone of adhesives mortar obtained from dry adhesives mixes made with various Portland cements and the content of various low-modulus inclusions and different redispersible polymer powders (RPP) with dosage from 0 to 3%
From the presented in table. 1 data obviously: - most of the adhesive mortars corresponding to class C1, irrespective of the conditions of testing; - mixes of class C2 can be produced with all the studied cements, it is necessary to select the appropriate dosage of RPP; - air entraining admixture has a positive effect on the increasing of the bond strength to the concrete base after 75 cycles of freezing and thawing; - the fly ash microsphere as a low-modulus inclusion is not effective for obtaining mixes corresponding to class C2
Summary
Cement binder dry mixes are widely used in modern construction for producing various types of building mortars, including various adhesives [1-8]. In accordance with GOST R 56387-2018 "Dry-mix construction cement based adhesives. Specifications» dry adhesive building mixes of classes C1 and C2 are used for indoor and outdoor using. Bond strength of this adhesives with concrete base must be more than 0.5 and 1.0 N/mm[2], respectively. Resistance to such influences is normalized by the “frost resistance” indicator
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