Effect of drying method on compressive strength of straw-based thermal insulations

Most of the thermal insulations in the construction industry market based on fossil raw material or need a huge amount of production energy. Nowadays, sustainable thermal insulation products are more popular, and the demand for these products on the market is increasing. Some of them reach the main material properties of artificial ones but usually not all. Today the reaction to fire is another big challenge in this field. In many cases, producers use chemicals that can increase fire resistance, but on the other hand, increase the environmental impact of insulations too. It is also hard to find a binder which provides proper mechanical parameters and durability and is environmentally friendly too. During our scientific research on environmentally friendly thermal insulation materials, which is running for 4 years, we found that silicate-based adhesives meet many of these criteria mentioned above. In this article, the mechanical properties of straw-based insulation bonded with silicate binder were investigated. The effect of conventional and microwave drying on compressive strength were compared to found the optimal hardening process of binders. During the experiments, straw was applied in a natural state, natural stem length distribution and without microstructure and surface modification. The used binder is a simple silicate-based binder (potassium silicate) without any modification agent. Conventional drying needs a longer time, and during it, many cracks form in the early age of the hardened binder. It is because of shrinkage and the differences in the rigidity of the binder along its cross-section. Besides, the straw stems swell when exposed to moisture (from binder), and after drying they shrink, which decreases the quality of the bond between stems and binder. The microwave drying evenly heats the various points of the specimen, so it is not generated such big differences in shrinkage. The contact between stems and binder are also better. Due to these effects, the microwave dried specimens reached the limit required for step resistance, and they had three-time higher average compressive strength than we got by the conventional drying of the same raw material.

Static analysis of bond between prestressing strand and UHPC exposed to elevated temperatures

This article deals with the numerical analysis of the bond of a prestressing strand with UHPC heated to elevated temperatures and subsequently cooled. Numerical analysis was performed with experimentally determined material properties of UHPC at a reference temperature of 20 °C and further after heating to temperatures of 200, 400 and 600 °C and subsequent annealing to normal temperature. The resulting deflection depending on the pulling force from the numerical analysis were compared with the experimental results. The results are used to configure the cement composite model for more demanding simulations of structures and load cases.

Buckling length of reinforced concrete columns in non-sway constructions

The paper presents a comparison of methods of determining the buckling length of reinforced concrete columns in non-sway frames. The comparison was made on the basis of guidelines issued by Poland some EU countries, USA and India. Differences in approaches and values of buckling length coefficients of columns calculated according to these guidelines are shown. An example of the calculation of column buckling length coefficients on selected multi-span, multi-storey non-sway frames is given.