Resistance of Young Concrete on Frost Action at Early Age Part 1 – Compressive Strength

Abstract

Concreting at winter time and in cold weather regions causes technological problem by production of fresh mix prevented from temperature below 0°C. Generally problem concerns fresh mix as well as young concrete. Apart from higher costs of mix appears durability of this concrete. Young concrete is prevented from single freezing if its strength obtains minimum 3,5MPa according to ACI 306R-16 but based on other publications the range of compressive strength can be much wider. Nevertheless, standards do not precise how investigate and how looks in reality the durability of concrete, which was subjected to freezing at early age. High compressive strength of concrete after 28 days and 90 days cannot be an indicator for its durability. Admittedly, high early strength cannot lead to unambiguous statement, that durability was reached. The destructive mechanism differs from freeze-thaw resistance of hardened concrete and depends on free water content, which remains after 22each freezing and initial curing temperature. Used measurement technic can also play significant role by describing of results. This paper presents part of doctoral thesis entitled “Resistance of young concrete on frost action at early age”, scope and parameters of freezing test base instead on analysis and long-standing author’s practice on building sites. The objective of the paper is to evaluate compressive strength loss after cyclic freezing of young concrete in different air conditions with different material modification and its effectiveness. It was considered change in modification of concrete mainly standard air entrainment, polymer microspheres and cement replacement. Concrete series with microspheres reached on the one hand the lowest reference compressive strength on the other hand has shown resistance on freezing at early age, but not in all cases. Modified concrete series by sulphate aluminate as replacement in 10% of Portland cement showed lack of resistance on freezing. Air entrained concrete and self-compacting concrete have shown different behavior depending on cycles and initial curing temperature. Frozen samples independently for strength increment in time revealed different strength loss after 28 days and 90 days. It is interesting, that cyclic freezing at early age must not influence on strength increment, however concrete loses its permeability in almost all cases.