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Influence of alkali-activated materials placement during curing on their dynamic parameters
(EDP Sciences, 2020-04-16) Plšková, Iveta; Matysík, Michal; Topolář, Libor; Bílek, Vlastimil
The production of Portland cement has a considerable environmental impact. Its replacement with alkali-activated binders can contribute to reducing the environmental burden of building production. The paper presents partial results from our experimental research carried out on test specimens made of alkali-activated slag mortar (activated by sodium carbonate). The specimens of dimensions 40x40x160 mm differed in the manner of placement after 28 days of curing in water. The samples were tested by non-destructive methods at different ages. We observed the effect of sample storage on ultrasonic pulse velocity, dominant frequency shifts and dynamic modulus of elasticity as well as changes of these parameters over time.
Pulse-Echo Ultrasonic Verification of Silicate Surface Treatments Using an External-Excitation/Single-Receiver Configuration: ROC-Based Differentiation of Concrete Specimens
(MDPI, 2025-08-11) Topolář, Libor; Kalina, Lukáš; Markusík, David; Cába, Vladislav; Sedlačík, Martin; Černý, Felix; Skibicky, Szymon; Bílek, Vlastimil
This study investigates a non-destructive, compact pulse-echo ultrasonic method that combines an external transmitter with a single receiving sensor to identify different surface treatments applied to cementitious materials. The primary objective was to evaluate whether treatment-induced acoustic changes could be reliably quantified using time-domain signal parameters. Three types of surface conditions were examined: untreated reference specimens (R), specimens treated with a standard lithium silicate solution (A), and those treated with an enriched formulation containing hexylene glycol (B) intended to enhance pore sealing via gelation. A broadband piezoelectric receiver collected the backscattered echoes, from which the maximum amplitude, root mean square (RMS) voltage, signal energy, and effective duration were extracted. Receiver operating characteristic (ROC) analysis was conducted to quantify the discriminative power of each parameter. The results showed excellent classification performance between groups involving the B-treatment (AUC 0.96), whereas the R vs. A comparison yielded moderate separation (AUC 0.61). Optimal cut-off values were established using the Youden index, with sensitivity and specificity exceeding 96% in the best-performing scenarios. The results demonstrate that a single-receiver, one-sided pulse-echo arrangement coupled with straightforward amplitude metrics provides a rapid, cost-effective, and field-adaptable tool for the quality control of silicate-surface treatments. By translating laboratory ultrasonics into a practical on-site protocol, this study helps close the gap between the experimental characterisation and real-world implementation of surface-treatment verification.
Experimental assessment of steel fibre reinforced concretes with different concentrations of fibres
(IOP Publishing, 2018-07-16) Komárková, Tereza; Láník, Jaromír; Topolář, Libor; Štoller, Jiří; Stoniš, Patrik
At present, steel fiber reinforced concrete can be classified as a composite material commonly used for load-bearing building structures. Adding steel fibers to fresh mixture improves its mechanical properties in comparison to plain concrete. The problem is, however, the production technology, which has not been standardized by regulations so far, and thus, proposals for the amount of steel fibers added to the mixture are still based on the long-term experience and performed tests. The paper describes an experiment focused on the determination and assessment of mechanical properties of steel fiber reinforced concretes with high concentrations of fibers. To better understand the behavior of test specimens during the three-point bending test, the acoustic emission method was used, which is able to capture active defects.
Rupture Strength and Irregularity of Fracture Surfaces
(IOP Publishing, 2017-11-28) Ficker, Tomáš
Textural irregularities of fracture surfaces of cement-based materials seem to be an interesting source of information on some mechanical properties. Besides compressive strength, the flexural strength is strongly correlated with height irregularities (i.e. roughness) of fracture surfaces of hydrated cement pastes. This correlation has been a subject of experimental study. An analytical relation between flexural strength and height irregularities has been inferred. The formula contains height parameters, which represent basic descriptors of surface irregularities of fracture surfaces of cement pastes. These irregularities are governed by the capillary porosity of cement pastes with different water-to-cement ratios. The relation yields values that are in agreement with the empirical formula published in the technical literature.
Properties of concrete intended for further testing measured by the Impact-Echo and the ultrasonic pulse method
(IOP Publishing, 2018-07-16) Balkanský, Ondřej; Dvořák, Richard; Čairović, Iva; Schmid, Pavel
The aim of the paper is non-destructive measurement of differently degraded specimens by high temperature intended for further testing of joints of stainless steel helical reinforcement glued into the groove and differently degraded concrete. Measurement intended for determination of possibilities of estimation of future properties of named joints is performed by the Impact-Echo method and by the ultrasonic pulse velocity method on specimens of dimensions 400 × 100 × 100 mm made of concrete of the C20/25 strength class degraded by different elevated temperature. Five sets of specimens were manufactured - four sets of specimens were heated in the furnace at temperatures of 400 °C, 600 °C, 800 °C and 1000 °C and one set was kept intact as reference. Specimens will be afterwards additionally strengthened at the tensile side of specimens and broken by four-point flexural strength test. The non-destructive measurement aims to evaluate the residual physical-mechanical properties of plain concrete in terms of resonance frequency of test specimen, and sound velocity in tested specimen before and after the temperature degradation. This assessment will serve as material information basis for interpretation of the expected behaviour of used helical reinforcement for a retrofitting process and the thermally damaged concrete reaction to such intervention.

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