DRY MIXTURES

[:ru]Дубина Э.[:en]Dubina, E.[:] [:ru]кафедра строительной химии, Мюнхенский технический университет, Гархинг, Германия[:en]Chair for Construction Chemicals, Technische Universität München, Garching, Germany[:]

[:ru]Планк Й.[:en]Plank, J.[:] [:ru]проф., доктор техн. наук, зав. кафедрой строительной химии, Мюнхенский технический университет, Гархинг, Германия[:en]prof, Dr. Eng. Sci., Chair for Construction Chemistry, Technische Universität München, Garching, Germany[:]

Alitinform №4-5 (26) 2012 г. 86-99 p.

Abstract

It is well established that the shelf-life of dry mix mortars can be severely affected by improper storage conditions. In particular, fast-setting formulations based on a ternary binder system (OPC/CAC/CaSO₄) are known to be very sensitive. In this study, the behaviour of a self-levelling underlayment (SLU) formulation when exposed to atmospheric moisture and CO₂ was studied. The SLU formulation was stored in moist air for 1 and 3 days at 35 °C and 90 % of relative humidity (RH). The consequences of this ageing were analysed by FTIR-ATR, SEM, in-situ XRD technique and isothermal calorimetry. XRD, FTIR and SEM investigations revealed that the surfaces of the SLU powder exposed to moisture were covered with abundant ettringite crystals.
Also, the performance of tartrate and citrate retarders with the aged SLU powder was tested. In the fresh self-levelling mortar, tartrate provided approximately 3 hrs of workability time while citrate achieved only approximately 0.5 hr. In the aged SLU, the retarding performance of tartrate decreased significantly (approximately 70 %) while that of citrate improved. The dispersing ability of casein superplasticizer was also severely affected as a consequence of ageing. After only 1 day of storage in moist air, the SLU containing casein was no longer fluidized, and after 3 days of storage, a foul odor occurred which indicated substantial decomposition of the biopolymer. Ageing also caused a higher water demand to achieve sufficient flowability, resulting in poor early compressive strength. The study demonstrates that the shelf-life of SLU mortars can be severely affected if stored in inappropriate conditions. High quality packaging is recommended to avoid performance failures.

Key words:

ageing; self-levelling underlayment (SLU); tartrate retarder; citric retarder; casein; polycarboxylate