Preparation of a Rice Husk Composite and Effects of Cold Pressing on the Flexural Strength Properties

The study of composites made from residual organic materials and polymeric resins, has a great projection due to the use of new raw materials and the good physical, mechanical and aesthetic characteristics these materials present in the construction industry. The manufacturing processes of these composites include the necessary pressure application to generate an efficiently compact material, where matrix and reinforcement bonding are efficient. This study defines how the compaction force influences the flexural strength of composites made from polyester resin as polymer matrix, and rice husk as reinforcement material. This is achieved by testing different series of specimens, made by applying different compaction forces in a cold process, to analyse the relationship between compaction and flexural strength. Specimens are made varying only the compaction force, from 2, 5, 8, 11, 14, and 17 tons. The results show that, when the compaction force increases, the flexural strength in the composites also increases, however, there is a pressure range where the flexural strength values are very close, conditioning the use of pressure in relation to the decrease in the specimen section.

The Influence of Water on the Heat Loss of Hot Mix Asphalt

Compaction of hot mix asphalt (HMA) is a process of altering the internal structure of the material and, as a consequence, also its performance characteristics. The process should ensure the adequate viscosity of binder, a property depending on the temperature and the material-specific property (hardness) of the binder (in the case of HMA). One of the external factors that can affect the process of compaction is the presence of water quickly decreasing the HMA temperature. This paper presents a theoretical model for determining the HMA temperature variation under the effect of water. One of the model parameters is the heat transfer coefficient α for the outward flow of heat. Its value varies strongly in the interfacial zones of the HMA layer (i.e., near the top and bottom surfaces) due to the effect of external factors. The paper presents the attempt to estimate the average value for the whole paving process depending on the precipitation rate (amount of water involved in the process). The temperatures obtained from the model were verified experimentally on laboratory specimens cooled with water. The temperature was measured on the surface and across the specimen section. The drop of temperature of HMA was almost instantaneous on the surface—due to the thermal processes involving water (boiling and evaporation)—and much slower across the layer thickness.

Estimation of Credibility of the Results of Measuring Temperature within Specimens of Wood Columns Obtained During Fire Tests

Analysis of the results of experimental studies of wood columns mode of behaviour both having fire retardant coating based on OSB slabs and without any coating under standard time – temperature curve fire conditions was realized. An assumption was made that thermocouple wires could be positioned along isotherm at a distance of at least50 mmfrom measuring thermojunctions (otherwise disturbance of the structure of isotherm itself possible). Due to specific features of thermocouples positioning within the specimen, this assumption calls in question of credibility of the obtained results of temperature indices measuring. Bearing this in mind we prepared calculation scheme of the specimen of wood column under study. We have composed finite elements scheme of specimen under study for heat engineering calculations. We simulated temperature distributions within the wood column specimen section at various moments of time and substantiated the obtained results. It was revealed in the course of the study conducted that the obtained results were adequate for relative error was as small as ca. 4.5% and Fisher test did not exceed appropriate tabulated value. Thus, assumption made does not affect in general credibility of the results of measuring thermal values within the layers of specimens obtained during fire tests.

Repulsive interaction between coplanar cracks in the double–cantilever geometry

Experiments on thin mica sheets are used to demonstrate that coplanar cracks in double-cantilever beam specimens do not universally attract each other, as conventionally portrayed, but, at long range, actually repel. An elasticity analysis explains the repulsion in terms of a compression zone, ≍0.35 times the beam half-thickness ahead of the crack tip, generated by bending moments from the cantilever arms on the remaining specimen section.