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This study addresses the application of polyvinyl alcohol (PVA) fibers to improve the performance of lightweight cement composites with pozzolans. Blended cement mixes based on expanded glass granules were modified with PVA fibers (Type A: Ø40 µm, L = 8 mm and Type B: Ø200 µm, L = 12 mm). The following research methods were used to analyse the effect of the fibers on the structure of cement matrix and physical-mechanical properties of lightweight composite: SEM, XRD, DTG, calorimetry tests, and standard test methods of physical and mechanical properties. Results from the tests showed that a denser layer of hydrates was formed around the PVA fiber and the amounts of portlandite, CSH, and CASH formed in the specimens with PVA were found to be higher. PVA fibers of Type A accelerated hydration of the cement paste, slightly increased the compressive strength of the lightweight composite, but had no significant effect on the values of density, ultrasonic pulse velocity and flexural strength. The shrinkage of cement composite was significantly reduced using both types of PVA fiber and both types of PVA fibers increased the fracture energy of lightweight cement composite with expanded granules.

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This article describes equations derived to predict the duration of local pyrolytic charring under standard fire conditions. The equations consist of five variables: electrical capacity, electrical conductivity, calorific value, depth and rate of char. The equations are split up into two groups: one for the formation of non-impregnated carbonaceous residue, and one for impregnated carbonaceous residue during pyrolysis. This means that before predicting the local duration of charring, it is necessary to determine whether the wood has been impregnated with a fire retardant solution before the fire. Electrical conductivity and electrical capacity measurement methods were used for this purpose. The temperature of standard fire local exposure is calculated by predicting the duration of local pyrolytic charring according to the standard temperature and the time dependence of fire.