The paper is concerned with the technical aspects of the appraisal and retrofitting process of fire damaged reinforced concrete structures. The assessment of fire damaged structures is carried out along lines similar to those of the appraisal of existing structures. In practice, constructions are most often assessed by destructive tests in-situ and on core bore specimens. In addition to destructive tests, damaged structures are also assessed by non-destructive ones. The present paper shows the use of non-destructive methods of measurement using the acoustic-emission and impact-echo methods. Acoustic emission provides valuable data on the structural integrity of a material. This method has a significant potential to be used for in-situ monitoring and evaluation of the current state of structures. An impact-echo method is based on impact-generated stress waves that propagate through concrete and are reflected by internal flaws and external surfaces. Impact-echo can be used to determine the location and extent of flaws such as crack delamination, voids, honeycombing and deboning in plain, reinforced, and post-tensioned concrete structures. The paper presents a possible rehabilitation plan based on the potential results obtained by these non-destructive methods.
The paper describes an experiment focused on observing the development of the elastic modulus and compressive strength in a polymer-cement mortar during the first 28 days of aging. The specimens (aged 3 and 28 days) were tested for the static and dynamic modulus of elasticity using two methods – the ultrasonic pulse velocity test and the resonance method. During the test of the modulus of elasticity in compression the mortar’s behaviour was also examined by means of the acoustic emission method, which is based on the recording of mechanical pulses caused by dilation waves generated by microcracks that form during loading. The outcome of the experiment is an evaluation of the polymer-cement mortar’s behaviour in terms of the development of its elastic modulus and compressive strength as well as in terms of the material’s acoustic response during loading.
This paper describes an experiment focused on monitoring the development of the modulus of elasticity and the compressive strength of composites that are based on alkali‑activated slag (AAS) during the first 28 days of ageing. The test specimens were tested at the age of 3 and 28 days using two non-destructive methods (ultrasonic pulse and resonance methods) to determine the value of the dynamic modulus of elasticity. Subsequently, the same specimens were used to determine the static modulus of elasticity using compressive stress test, during which the behaviour of the composite was monitored by equipment for recording the acoustic emission in the material. The result of the experiment is the evaluation of the behaviour of the AAS composite in regard to the development of its modulus of elasticity and compressive strength, as well as in regard to the acoustic emission method during loading.
The obtained physico-mechanical properties (mainly flexural and compressive strength) of cement-based composite materials depend on various factors (type of mixture, its composition, standard hardening process, proper testing, handling during transportation, etc.). Important properties to be tested include in particular properties of materials in the fresh, still plastic, state, since accurate identification of defects in building materials/structures at the early stage will allow early elimination and minimization of their future consequences. The aim of this paper is the application of the acoustic emission (AE) method for the detection of high-frequency elastic waves created by physical and chemical processes accompanying setting and hardening of cement pastes. The experiment was conducted on cement pastes produced from different cements but with the same water/cement ratio. Since there are many possible sources of AE and the identification of the individual sources is difficult, the monitoring of the setting cement paste was conducted simultaneously with measurements of the internal temperature. The results of these experiments can be used to expand the understanding of the various processes occurring at the early stage of setting and hardening of cement-based materials.
Non-destructive testing is a process of inspecting, testing, and evaluating materials, components or assemblies for discontinuities, or differences in characteristics without destroying the serviceability of a system or its part. The acoustic non-destructive methods are concerned with the state-of-the-art situation in the field of experimental studies of the physical properties of engineering materials. In this paper, the acoustic emission method was used for classification of cracks recorded during the cyclic loading of the reinforced concrete beam. Acoustic emission is a phenomenon of stress wave radiation caused by the dynamic reconstruction of material’s structure that accompanies processes of deformation and fracture. Crack propagation is one of the macroscopic sources of acoustic emission. Acoustic emission signals generated by different loading patterns can provide valuable information concerning the structural integrity of a material. Load levels that have been previously exerted on a material do not produce acoustic emission activity.
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