Length changes of fine-grained cement-based composites specimens in early stage of ageing: correction reflecting temperature variations

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The paper deals with the numerical analysis of the experimental data obtained from the measurement of relative length changes during the ageing of cementitious composites. Two fine-grained composites based on the Portland cement, with different water to cement (w/c) ratio and amount of plasticizer, were prepared for the experiment. The quartz-aggregate with maximum grain size of 2 mm was used for both mixtures. The measurement procedure was designed to record simultaneously the relative length changes (measured along the longitudinal axis of test specimens), weight losses, temperature inside the test specimens and ambient temperature and relative humidity. Test specimens were manufactured in special moulds with dimension of 100 × 60 mm in cross section and 1000 mm in length which allows to measure the length changes very early after their filling. The moulds were placed on a special weighing table and a thermal sensor was embedded at the end of the test specimens. The relative length changes, weight losses and temperature changes were continuously measured in the moulds until the specimens were ca 72 hours old. The upper surfaces of test specimens were not protected from drying. During whole time of ageing all test specimens were stored in laboratory at the temperature of (21 ± 2) °C and relative humidity of (60 ± 10) %. The ambient temperature and relative humidity were continuously measured over the whole time of measurement. The experimental data were further used for numerical approximation aimed at the elimination of the temperature variation which affected the development of the relative length changes values during the whole time of cementitious composites’ ageing. The rate of thermal affection depends on the actual value of the coefficient of thermal expansion which depends on the materials’ composition and also on their actual degree of solidification or amount and redistribution of water. The most visible effect of the thermal changes under isothermal conditions can be observed at the early age (mostly within first 24 hours) when the hydration heat is reaching its maximum value which can lead to the expansion of the test specimens. This early expansion can be further strengthened by the water reabsorption in the case of composites with a high w/c ratio.

length change, cement-based composite

KUCHARCZYKOVÁ, B.; FRANTÍK, P.; ŠIMONOVÁ, H.; ODSTRČIL, Š.; KUBEŠ, P.; KERŠNER, Z.

4. 9. 2017

Societa editrice esculapio

Bologna

978-889-385-041-4

Proceedings 20th International Conference on Composite Structures

180

180

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