This article discusses the results of tests regarding mechanical properties of polymer-cement repair mortars which were cured at a lowered temperature. The assessment was based on compressive strength tests of three PCC repair mortars available on the market. The tests were performed on samples cured at a temperature of 21°C and 8°C and following designed variable-temperature cycles. The tests showed a negative impact of lowered temperature present during curing of concrete repair mortars on these mortars’ compressive strength. Repairing concrete structures during lowered temperatures may cause a drop in parameters considerably lowering the product’s class. Extending the cure time for mortars applied and cured at low temperatures will cause these parameters to increase, but will not always allow to achieve values equal to those of samples cured in laboratory conditions.

This paper presents research dealing with the evaluation of the efficiency of concrete repairs with polymer-cement mortars made at low temperatures with two types of cement and modified by copolymer acrylic-styrene. The low temperature used for the tests, of about 8 °C, is representative for Central Europe, and was established based on the analysis of mean temperatures in Poland during the last 45 years. A comparative analysis of the basic properties of the mortar tested, important from the point of view of repair efficiency, was performed, i.e., flexural and compressive strength, modulus of elasticity, adhesion to the substrate, and porosity for mortars applied and cured at 8 °C and 21°, respectively. The studies were conducted using standard methods and supported with an assessment of microscopic images (1000× magnification). It was shown that when the temperature of polymer-cement composite (PCC) mortar application is lowered to values slightly exceeding the minimum film-forming temperature (MFT) temperature of the polymer modifier, the type of cement determines the effectiveness of the repair. Only for PCC mortar with CEM I sulfate-resistant types of cement was it possible to achieve the same strength parameters as at 21 °C, during 28 days of mortar curing, and at a lowered temperature. Starting from day seven of setting at both above-mentioned temperatures, a relation between the values of the flexural and compressive strength expressed as a quotient of these values, amounting to ca. 0.14–0.19, was found.

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