Papers by Keyword: Impact-Echo

Abstract: Testing methods used for assessment of buildings considered as a cultural heritage are focused mainly on non-destructive testing methods. Old buildings are usually sensitive to destructive in-situ testing, and a variety of non-destructive techniques (NDT) are frequently used. One of the most commonly used sensors are accelerometers, which can measure vibrations of different part of structures. These can be used in either continuous monitoring or in short-time assessment. Impact-Echo is a well-known method which can locate defects, caverns, or damaged parts not only in industry-level structures, but also in preservation of cultural heritage. This type of measurement requires attaching a sensor to the surface of the observed element. This is in most cases done by adhesives which can damage the more porous structures. In this paper a comparison of two different sensor types in testing of reference concrete elements is presented: contact piezoceramic accelerometer; non-contact MEMS type microphone. Signals recorded by each sensor type are assessed by the statistical method of feature extraction.

Abstract: Production of Portland cement is relatively environmentally demanding (high CO₂ emissions, extraction of raw materials for its production). Alkali-activated materials are an alternative to conventional Portland cement in the production of concrete. For alkali-activated binder concretes, their ability to withstand corrosive environments and their ability to protect steel reinforcement must be assessed. It is also necessary to know the suitability of non-destructive methods for monitoring the degradation process of these concretes. The paper deals with the carbonation monitoring of concrete with alkali-activated binder (slag) by the impact-echo method. Slag activated by sodium hydroxide (NaOH) was used as a binder. The specimens were tested by the non-destructive method (Impact-echo, ultrasound velocity). We focused on the shift of the dominant frequency obtained by the Impact-echo method.

Abstract: The impact-echo method is commonly used for detection of flaws in concrete elements based on the shift in the thickness frequency of a plate-like member. However, there is a need to develop this efficient technique for other applications. This paper investigates the feasibility of using the impact echo-method for identifying corrosion of steel reinforcement in concrete structures. For this purpose, 180 reinforced concrete cubes were cast and tested. The main parameters studied were the amount of recycled aggregate (i.e. 0%, 25%, 50% and 100%), nanosilica (1.5% and 3%) and the steel bar diameter (12 and 20mm). Different levels of corrosion were electrochemically induced by applying impressed voltage technique for 2, 5, 10 and 15 days. The impact-echo results were correlated against the actual corrosion levels obtained by the mass loss method. The experimental results showed that the response of impact echo in terms of frequency peaks is found to be sensitive to the high and moderate levels of corrosion. However, no clear trend was observed at the initial stage of corrosion. It is demonstrated that the impact-echo testing can be effectively used to qualitatively detect the damage caused by corrosion phenomenon in reinforced concrete structures.

Abstract: The paper presents the results of experiments carried out on test samples made from reinforced concrete. Within this experiment, concrete beams with steel reinforcement in the middle were made. The concrete samples were tested by a non-destructive acoustic Impact-echo method before and after high temperature loading (after cooling to room temperature). We focused on the dominant frequencies shift in the frequency spectra obtained by this method. The aim was to assess the ability of aforementioned acoustic method to detect the thermal damage of steel reinforced concrete.

Abstract: The paper presents the results of the experimental work which was focused on the use of the Impact-echo method for testing of concrete specimens damaged by high-temperature. The test specimens were heated to 600 and 800 °C for sixty, one hundred twenty and three hundred minutes. After heating, the samples were continuously cooled to room temperature and tested by Impact-echo method.

Abstract: 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.

Abstract: This paper first introduces the basic concept of the CSG (cemented sand and gravel) dam construction. It then puts forward a new quality control method by inspecting the in-situ P-wave speed of CSG as an alternative to the conventional specimen compression tests. Through an extensive experimental program, it is found that there is a good correlation between the compressive strength and P-wave speed of CSG, which makes the P-wave speed measurement potentially an effective and efficient quality control measure to evaluate the CSG strength on site.

Abstract: The application of Impact-echo acoustic method to evaluate the degradation and the composition of mortar composites modified with rubber aggregates and EVA polymer binder degraded at high temperatures was studied. Specimens were prepared by using a type CEM I Portland cement and siliceous sand, as well as by substituting 25% of sand with shredded automobile tires and by adding of EVA polymer binder (10% w/w to cement mass). The samples were subjected to high-temperature treatment in the temperature range of 200-400 °C. The results of non-destructive testing of such samples by acoustic methods confirmed the differences in the structure of mortar specimens. Addition of rubber aggregates in samples caused absorption of lower frequency as compared to reference specimens. A significant decrease of the absorbed frequencies was observed depending on the temperature. The largest decrease happened after exposure of samples at 200-300 °C. It indicates that the effect of heat treatment was reduced when the EVA binder was added.

Abstract: The aim of this paper is to evaluate the corrosion of reinforced concrete structure. To assess the state of corrosion we used frequency signal analysis, where we observed the changes in dominant frequencies and growth of damping factor λ. Tension pulse was produced in axis of the rod at one end and detected in axis at opposite end of rod. Diameter of steel rod was 8 mm. The article presents the results of measurements obtained during 24 months controlled degradation in aqueous NaCl solution.

Abstract: The use of impact-echo acoustic method to test cement-based mortar composites modified with rubber aggregates and EVA polymer binder and degraded at high temperatures was studied. The specimens were prepared by using a type CEM I Portland cement and siliceous sand, as well as by substituting 25% of sand with shredded automobile tires and by adding EVA polymer binder (10% w/w to cement mass). The specimens were subjected to high temperatures (200-400 °C). The results of non-destructive testing confirmed the different structure of mortar specimens. The partial substitution of sand with rubber aggregates led to absorption of lower frequencies as compared to the reference specimens. A significant decrease of the absorbed frequencies was observed, depending on temperature. The largest decrease occurred after the specimens exposure at 200-300 °C. The effect of heat exposure to the decrease of frequencies was mitigated when the EVA polymer was used.