Advanced Materials Research Vol. 1124

Abstract: NDT impedance spectroscopy method was used to characterize a Cetris wood-cement chipboard. Dry specimen pre-stress and post-stress cycle tan δ (f) spectrum variances were observed. Effects of potential dielectric losses and the predominance of the polarization and conductivity components in various regions of the impedance spectrum of samples after frozen stress cycle are described. The method reproducibility has been verified by multiple measurements.

Abstract: Impedance spectroscopy (IS) is a non-destructive testing (NDT) method ranking in the electrical engineering measuring method group. It outputs data providing information on material electric and dielectric properties. Microscopically inhomogeneous materials are frequently used in the building industry. Unfortunately, the impedance spectroscopy results and their characterization on the basis of this method are not unambiguous. The frequency spectrum behavior of Cetris-basic specimens was studied by means of the NDT impedance spectroscopy method for various water content values. A stress cycle with defined absolute water content values is described. Influences of potential dielectric losses and the predominance of the polarization and conductivity components in various regions of the impedance spectrum are described for various water content values.

Abstract: Reinforced and pre-stressed concrete have been used increasingly for various kinds of complex structures in the past decades. The structures assembled from panels belong into this group. The current design methods rely on linear elastic analyses based on empirically derived material laws assuming homogeneous and isotropic material. Practical experience and various investigations however have indicated that majority of structures and structural elements are in fact stressed beyond the range of linear elastic behavior. In addition, long term effects may have a significant influence on the structural behavior of this category of structures and structural members.

Abstract: The acoustic emission phenomenon is directly associated with nucleation of cracks in building materials, therefore the changes result from the volumetric expansion causing formation micro and macro cracking in structure, which we can recognize. The main aim of the article is to compare four ways of curing alkali activated slag mortars by method of acoustic emission. A comprehension of microstructure−performance relationships is the key to true understanding of material behaviour. The results obtained in the laboratory are useful to understand the various stages of micro-cracking activity during the hardening process in quasi-brittle materials such as alkali activated slag mortars and extend them for general practice

Abstract: Almost all reinforced concrete structures which are exposed to weather effects are threatened by corrosion. The corrosion of steel elements in structures has an influence on lifetime these constructions and adversely affects their properties. However, the steel in concrete structures is protected against corrosion due to the properties of concrete such as high pH or impermeability, but if the concrete is of poor quality and his protective properties are insufficient the corrosion can occur. A problem causes the action of carbon dioxide which has the effect of lowering the pH below the critical value and thereby accelerating the corrosion.Non-destructive methods such as Impact-echo method offer the possibility of easy and quickly detection of initial damage of structure and thus can prevent the occurrence of permanent damage to the whole construction.This article describes the development of corrosion which is caused by carbonation of the concrete and supported by action of chlorides by using Impact-echo method. The paper presents results obtained on the reinforced concrete samples with one steel rod passing through the center. After carbonation concrete the samples were exposed accelerated controlled degradation in aqueous NaCl solution for 4 months.

Abstract: This paper reports the analysis of acoustic emission signals captured during three-point bending fracture tests of concrete specimens with different mixture composition. Acoustic emission method is an experimental tool well suited for monitoring fracture processes in material. The typical acoustic emission patterns were identified in the acoustic emission records for three different mixtures to further describe the under-the-stress behaviour and failure development. An understanding of microstructure–performance relationships is the key to true understanding of material behaviour. The acoustic emission results are accompanied by fracture parameters determined via evaluation of load versus deflection diagrams recorded during three-point bending fracture tests.

Abstract: This paper examines the analysis of acoustic emission signals captured during three-point bending fracture tests of concrete specimens with similar water-cement ratio, but one set of specimens was prepared from aerated concrete. The acoustic emission method is an experimental tool well suited for monitoring fracture processes in material. The typical parameters of acoustic emission signals were identified from the acoustic emission records for two different concrete mixtures to further describe the under-the-stress behaviour and failure development. An understanding of microstructure–performance relationships is the key to true understanding of material behaviour. The crack growth was continuously monitored using four acoustic emission sensors mounted on the specimen. The acoustic emission results are accompanied by selected fracture mechanical parameters determined via evaluation of load versus displacement diagrams recorded during three-point bending fracture tests.

Abstract: This article presents a new direct testing method and device for evaluation of response of blast-absorption materials against direct blast wave and its ability to absorb energy generated during this type of loading. This is a second step of characterization of blast energy absorption materials which take place after standard and most common characterization using Split-Hopkinson pressure bar. The principle of the method is an assessment of longitudinal stress process in standard rod after the explosion of testing blast charge. Stress amplitude reduction in standard rod caused due to energy-absorption of sample material will directly lead to absorption capability of tested sample material.

Abstract: This article deals with the measurement system and the use of special cement composites with carbon particulates. The type of carbon particulates consequently determines the electrical properties of cement composite material. These materials can be used for electric heating, electromagnetic shielding or stress measurement. Strain properties can be used to measure the deformation of concrete structures (bridges, beams, pillars) or for weighing-in-motion of road vehicles. This article describes novel laboratory equipment which is designed for multichannel dynamic and long-period material stability measurements.

Abstract: Usage of hydroinsulating gels in order to create injection screens in various building materials to deny rising wetness is nowadays one of the most widespread methods of remediation of damaged structures. One of the biggest advantages of this method are its low impact on the building statics, relatively quick and easy application and low final cost. The main focus of this article is observation effectiveness and final functionality of various types of hydroinsulating gels in samples of aerated concrete.