Kamil Zalegowski

The aim of the present research was to empirically prove that the non-destructive ultrasonic direct method is an effective scientific tool for measuring the maturity of polymer concretes (PC). Maturity is understood as obtaining a stabilised, maximally homogeneous, and dense microstructure of the composite, which is closely related to its mechanical strength. The direct ultrasonic method was used to assess the homogeneity, and thus the quality, of the microstructure of the composites shortly (14 days) after production and after 9 and/or 9.5 years. Different values of the ultrasonic pulse velocity were computed for "young" and several-year-old composites of identical compositions. This study confirmed the authors’ thesis that particular types of PC (with vinyl-ester matrix saturated with finely ground rocks and fossil fuel combustion by-products) show maturation extended up to several years and an additional increase in mechanical strength, despite the long-standing widespread view that polymer concretes obtain their full potential within several days. This indicates the necessity of a thorough examination of the microfiller morphology before its application in PC because it may affect the curing process and strength development. This leads to the second conclusion, that the design rules for PC with microfillers with more developed specific surface areas should be revised because the designed values may be underestimated in relation to the actual values but obtained after a longer time. Graphical abstract

The study investigates the influence of an air-entraining admixture on the properties and pore structure of ordinary concrete. The aim was to examine how modifications to the concrete mix affect compressive strength, ultrasonic pulse velocity, and resistance to freeze–thaw cycles. Concrete samples with varying admixture dosages (0.00–1.50% of cement mass) were tested for mechanical properties and pore structure. Freeze–thaw resistance was assessed using both direct (PN-B-06265) and indirect methods (EN 480-11), while pore characteristics were evaluated via computer-aided image analysis. Results show that increasing the admixture dosage enhances freeze–thaw resistance by refining the pore structure—particularly by increasing the content of micropores below 0.3 mm—while simultaneously reducing compressive strength and ultrasonic velocity. Statistical analysis revealed that pore parameters such as total air content, specific surface area, and spacing factor significantly correlate with concrete performance. The regression models confirmed that compressive strength and ultrasonic velocity are negatively impacted by increased pore volume, while freeze–thaw resistance improves due to a more favorable pore size distribution. The findings demonstrate that optimizing the admixture dosage can effectively balance durability and mechanical performance, and that quantitative stereological parameters provide a valuable basis for predicting the behavior of air-entrained concrete.

According to the World Bioenergy Association, electric production of 483 TWh means that around 10 million tons of ash are globally produced only from electricity production. Large quantities are landfilled or used in agriculture. However, landfilling becomes less and less allowed in European and North American countries. Classical coal fly ash can be used for the production of cement or concrete, but it is however not yet the case for biomass ash. An overview of recent research projects shows some perspectives in contributing to the stabilization of pollutants and heavy metals. Specific treatments are also proposed for the development of green cement and concrete through substituting cementitious constituents with biomass ash.

The construction sector should have much to offer in terms of helping to achieve circular economy goals, among others the use of waste materials. The example of such materials is biochar, a black porous and carbon-rich matter that could be converted from various waste biomass. A biochar could be utilized as microfiller in polymer concretes. This application of biochar is promising due to good interfacial bonding with polymer, no reactivity between surrounding polymer matrix and filler particles and fact that even fillers with irregular particles and large specific surface area could be utilized in polymer matrix. These create real opportunity to effectively dispose waste materials as a replacement of natural aggregates in polymer concrete technology. The presented paper is a second part of the research concerning the utilization of ecofriendly biochar in polymer composites conducted by authors. To better understand the impact of modification by biochar, already performed tests were supplemented by measurements of ultrasonic pulse velocity and quantitative analysis of microstructure.

Partial replacement of quartz flour microfiller in polymer composites with biocarbon is one of the potential ways to utilize this waste. The article discusses the possibility of using biocarbon as a component of vinyl ester mortars, in the context of their chemical resistance. The tests were carried out for mortars with different quantitative compositions, and therefore with different biocarbon contents. They were subjected to 12-month exposure to a chemically aggressive environment. Solutions of 0.5% sulfuric acid(VI) and 5% sodium hydroxide were used. Measures of resistance were changes in weight, compressive strength, longitudinal ultrasonic wave velocities and quantitative changes in microstructure compared to chemically unstressed samples. The results show that vinyl ester mortars with biocarbon are more resistant to chemical aggression with sulfuric(VI) acid solution. A significant decrease in compressive strength, ultrasonic wave velocity and an increase in the values of stereological parameters were observed after exposure of the composites in sodium base solution. This is in contrast to the chemical aggression in the acid solution, after which the changes in the properties and microstructural parameters of the mortars were not so clear

The article presents the results of the assessment of the durability of polyester concretes containing waste microfiller (obtained from the dedusting of road aggregate) made after many years of exposure of the elements to the sulfuric acid environment. Concretes with different quantitative compositions (waste dust partially or completely replaced the commercial quartz microfiller) were exposed to the H2SO4 environment with a concentration of 0.5 M for a period of 1 month and 8 years. The measure of concrete’s acid resistance were changes in compressive strength compared to reference concretes tested immediately after obtaining technical efficiency. Additionally, 8-year-old concretes were subjected to NDT tests – the velocity of the ultrasonic wave passing through the composite was determined. It was experimentally confirmed that dust from road aggregate dedusting is a good partial substitute for commercial microfillers in polyester concretes in the context of their durability. After 8 years of exposure to H2SO4, the differences in the strength of concrete compared to analogous compositions exposed for 1 month amounted to an average of 4.9%, and compared to compositions not exposed to chemicals – an average of 9.5%. It was also shown that there is a clear relation between the ultrasonic wave velocity and the compressive strength of concrete, and any changes after exposure to acid (matrix discoloration and deposits) were only on the surface.

Ground penetrating radar (GPR) is one of the most useful non-destructive techniques for locating underground objects. Advancements in this technology have facilitated the development of new sensors over the past decade. In this paper, an accuracy assessment of the location of underground objects using various GPR antennas is presented. To achieve the stated goals, measurements of 5 concrete slabs, reinforced with steel bars of various diameters and located at variable depths were taken. The experiment includes the usage of three GPR antennas to assess the format, characteristics, and differences of extracted data. This set of antennas from different manufacturers varied in terms of operating frequency. Additional lidar data from TLS (terrestrial laser scanning) was utilized in the methodology to provide precise surface measurements and therefore, external orientation of the surveyed data. The experiment allowed for the determination of vertical and horizontal accuracy for three tested antennas and the assessment of increasing errors value with greater depth of the measured items, which is important for surveying accuracy forecasting.

The circular economy includes, among other things, the use of waste materials. One such material is biochar, which should not be used as a fuel because its combustion generates large amounts of air pollution. This study evaluates the feasibility of using biochar as a partial filler in a polymer concrete. The components of the polymer concretes used in this study were vinyl-ester resin, traditional microfiller—quartz powder, waste microfiller—biochar and quartz aggregate with grain sizes up to 2 mm. The quartz aggregate was dosed at a constant rate of 1458 kg/m³ of concrete, whereas the dosage of resin and microfiller was formulated according to the experimental plan for mixtures and executed based on the volume of the remaining space: resin (65–85%), quartz powder (5–35%) and biochar (0–10%). The effects on the setting process, the consistency of the fresh composite mix and the flexural and compressive strengths were investigated. The study revealed significant deterioration of technological parameters (over 15% of biochar content makes a mixture unworkable) and slight deterioration of mechanical ones (flexural strength did not change significantly, and the compressive strength decreased by up to 15%). These results indicate that, despite some limitations, the use of biochar as an alternative pro-ecological filler is possible.

In this paper an analysis of the influence of polymer concrete sample shape and dimensions on ultrasonic wave propagation is carried out. Compositions of tested fly ash polymer concretes were determined using a material optimization approach. The tests were carried out on the samples of three shapes: cubes, beams, and plates. The ultrasonic testing was done by a direct method (transmission method) using a digital ultrasonic flow detector and piezoelectric transducers of 100 kHz central frequency. Propagation of the ultrasonic wave was characterized by pulse velocity. Frequency spectra and time-frequency spectrograms obtained using Fourier transform and Fourier-based synchrosqueezing transform were also presented. The correlation analysis showed that neither the path length nor the lateral dimension to the direction of wave propagation are not statistically significant for the UPV variability. However, a general trend of decrease in the UPV with increasing the path length was noticed. The analysis of the signal in time-frequency domain seemed to be useful in the analysis of particulate composites properties, especially when UPV changes are not clear enough, since it revealed greater differences in relation to changes in sample geometry than frequency spectra analysis.

The study of the effect of cement type on the action of an admixture increasing the volume of concrete (containing aluminum powder), used in amounts of 0.5–1.5% of cement mass, was presented. The tests were carried out on cement mortars with Portland (CEM I) and ground granulated blast-furnace slag cement (CEM III). The following tests were carried out for the tested mortars: the air content in fresh mortars, compressive strength, flexural strength, increase in mortar volume, bulk density, pore structure evaluation (by the computer image analysis method) and changes in the concentration of OH⁻ ions during the hydration of used cements. Differences in the action of the tested admixture depending on the cement used were found. To induce the expansion of CEM III mortars, a smaller amount of admixture is required than in the case of CEM I cement. Using the admixture in amounts above 1% of the cement mass causes cracks of mortars with CEM III cement due to slow hydrogen evolution, which occurs after mortar plasticity is lost. The use of an aluminum-containing admixture reduces the strength properties of the cement mortars, the effect being stronger in the case of CEM III cement. The influence of the sample molding time on the admixture action was also found.