Minutes-long creep tests on young cement pastes provide access to creep properties relevant for ageing creep with a duration of 2 days

摘要

Cementitious materials are particularly creep active at early ages. We here perform an ageing creep test on a cement paste sample exhibiting an initial water-to-cement mass ratio amounting to w/c = 0.50. The sample is conditioned to 20 °C. The creep test is started 24 hours after production and runs for 48 hours. The loading amounts to 15 % of the uniaxial compressive strength of the material at the time instant of loading. Inspired by a recently developed new testing protocol consisting of hourly-repeated three-minutes long creep tests, we exploit force and deformation readings recorded during the first three minutes of our 2-days creep test, i.e. we identify Young's modulus and power-law creep properties. Given that the chemical hydration process does not progress significantly during the analyzed three minutes, the identified creep properties refer to non-ageing creep. The identified properties are combined with measurements of autogenous shrinkage, in order to predict the strain evolution over the entire 2-days runtime of our ageing creep test. When fitting of the creep function targets, through an appropriately chosen weight functions, the end of three minutes creep interval, in terms of both absolute creep strain and creep strain rate, then the resulting creep function remarkably well predicts creep up to a time period of 2 days.