Abstract
Objectives. The aim of this study was to identify variation patterns of the in-series variation coefficient of adhesive strength to base and the dependency of the frost resistance coefficient on the criterion of adhesion on prescription factors of fine-grained concrete obtained from dry building mixtures based on various Portland cements containing various low-modulus inclusions and redispersible polymer powders from 0 to 3%. According to GOST 31357, the main quality indicators of the hardened mixture or fine-grained concrete, in addition to frost resistance, include the indicator of “frost resistance of the contact zone”, which characterises the ability of the hardened concrete to maintain adhesion to the base during normal separation following a certain number of freeze-thaw cycles.Method. The tests of the main samples were carried out after 75 freeze-thaw cycles in accordance with GOST 31356. The marks of the frost resistance of the contact zone are set from FKZ25 to FKZ100. The number of freeze-thaw cycles is taken as a mark, after which the adhesion strength to the base, determined according to GOST 31356, is at least 80% of the strength of the control samples. The arithmetical average is taken at between at least 5 values, while the variation coefficient measured across a series of adhesion strength values is not considered.Results. The average values of the variation coefficient of adhesion strength were: following 75 cycles of freezing-thawing – 0.224 (in a range from 0.058 to 0.616); following 25 cycles of freezing-thawing – an average of 0.129 (in a range from 0.016 to 0.352). The variation coefficient of adhesion strength can exceed the variation coefficient of compression strength by approximately 2.5 to 3 times. When introducing the redispersible powders into the structure of fine-grained concrete, there is no unambiguous pattern of change in the values of the variation coefficient of adhesion to base and it is possible to increase or decrease this value, while the values of the variation coefficient of adhesion can vary by an order of magnitude.Conclusion. For all concretes, there is a tendency of increase of the coefficient of frost resistance with a decrease in the adhesion variation coefficient both after hardening under normal conditions as well as during cyclic freezing and thawing. When conditions VF/V28A<1 are met, the coefficient of frost resistance of adhesion, determined when considering the variation coefficient, will satisfy the requirements of GOST 31356.
Highlights
31356 проведены на мелкозернистых бетонах (МЗБ) различных составов [9], в т.ч. с низкомодульными включениями (НМВ) на базе75 циклов
Notes: 1 - In the numerator after 28 days of hardening under normal conditions (NU), in the denominator after 75 cycles of freezingthawing, 4 - after 25 cycles of freezing-thawing; 2 - in the numerator - without taking into account the in-series coefficient of variation of adhesion strength, in the denominator - taking into account the in-series coefficient of variation in adhesion strength; 3 - AF / A0
В соответствии с ГОСТ 31356 можно представить коэффициент морозостойкости прочности сцепления с основанием в виде kF,A
Summary
Несветаев Г.В.1, Долгова А.В.2, Постой Л.В.3, Хаджишалапов Г.Н.4 1Донской государственный технический университет, Ростов-на-Дону, 1344000, г. 1, Россия, 2Ростовский государственный университет путей сообщения, Ростов-на-Дону, 2344038, г. Цель исследования состояла в выявлении закономерностей изменения внутрисерийного коэффициента вариации прочности сцепления с основанием и зависимости коэффициента морозостойкости по критерию прочности сцепления от рецептурных факторов мелкозернистых бетонов, полученных из сухих строительных смесей на основе различных портландцементов с содержанием различных низкомодульных включений и редиспергируемых полимерных порошков от 0 до 3%. За марку принимается количество циклов замораживания-оттаивания, после которого прочность сцепления с основанием, определяемая по ГОСТ 31356, составляет не менее 80% от прочности контрольных образцов.За прочность сцепления принимается среднее арифметическое не менее 5 значений, при этом коэффициент вариации измеренных в серии значений прочности сцепления не учитывается. Ключевые слова: морозостойкость контактной зоны, прочность сцепления, коэффициент вариации, коэффициент морозостойкости, мелкозернистый бетон, сухие строительные смеси
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