Nondestructive evaluation of concrete permeability: techniques, challenges, and research trends

Prediction of physical-mechanical properties of hollow interlocking compressed unstabilized and stabilized earth blocks at different moisture conditions using ultrasonic pulse velocity

ABSTRACTAlkali-silica reaction, sulfate attack, and reinforcing steel corrosion can compromise the long-term durability of concrete structures. The anticipated economic impact of an extensive infrastructure repair scheme has produced a renewed interest in the development of advanced characterization methods to assess the degree of deterioration in the concrete experiencing these deleterious reactions. The products of the alkali silica reaction, sulfate attack, and corrosion as well as the cement hydration products are extremely sensitive to humidity. Consequently, characterization techniques that require high vacuum or drying, as many existing techniques do, are not particularly appropriate for the study of these reactions in concrete as artifacts are introduced. A high resolution instrument which allows the examination of these reactions and their products without drying and at normal pressures will promote understanding of the reactions and provide further insight into means of mitigating the damage they cause. Only soft x-ray transmission microscopy provides the required high spatial resolution to observe the reaction process in situ. The alkali-silica reaction can be observed over time, in a wet condition, and at normal pressures, features unavailable with most other high resolution techniques. Soft x-rays also reveal information on the internal structure of the sample. This paper reviews published and ongoing applications of soft x-ray transmission microscopy for the study of expansive reactions that occur in concrete.

Cemented paste backfill (CPB) plays an important role in sustainable mining by providing structural support and reducing surface subsidence. While traditional destructive testing methods such as unconfined compressive strength (UCS) tests offer valuable understanding of material strength, they require a lot of resources, are time-consuming, and environmentally unfriendly. However, non-destructive testing (NDT) techniques such as ultrasonic pulse velocity (UPV), electrical resistivity (ER), and acoustic emission (AE) provide sustainable alternatives by preserving sample integrity, minimizing waste, and enabling real-time monitoring. This study systematically reviews and quantitatively compares the effectiveness of UPV, ER, and AE in predicting the strength of CPB. Meta-analysis of 30 peer-reviewed studies reveals that UPV and AE provide the most consistent and reliable correlations with UCS, with R2 values of 0.895 and 0.896, respectively, while ER shows more variability due to its sensitivity to environmental factors. Additionally, a synthetic model combining UPV, AE and ER demonstrates improved accuracy in predicting strength. This hybrid approach enhances predictions of material performance while supporting sustainability in mining and construction. Our research advocates for better testing practices and presents a promising direction for future infrastructure projects, where real-time, non-invasive monitoring can enhance material performance evaluation and optimize resource use.

Compressive strength evaluation of structural lightweight concrete by non-destructive ultrasonic pulse velocity method

This paper aims at evaluating the compressive strength of structural sand lightweight aggregate concrete (LWC) by the non-destructive ultrasonic pulse velocity method. To this end, a comprehensive experimental study was carried out involving more than 70 different compositions tested between 3 and 180 days with mean compressive strengths ranging from about 30 to 80 MPa and density classes from D1.6 to D2.0. The influence of several factors on the relation between the ultrasonic pulse velocity (UPV) and compressive strength was examined, including the type and binder content, type and volume of aggregates. It is found that lightweight and normal weight concretes (NWC) are affected differently by mix design parameters. NWC is more affected by the volume of aggregate and the dispersion effect caused by concrete heterogeneity tends to be lower in LWC. The prediction of the concrete's compressive strength by means of the non-destructive UPV test is analysed. Based on the dependence of the UPV on the density and elasticity of concrete, a simplified expression is proposed to estimate the compressive strength, regardless of the type of concrete and its composition. High correlation coefficients were obtained taking into account several results for different types of aggregates and concrete compositions.

Characteristics of non-steady-state chloride migration of self-compacting concrete containing recycled concrete aggregate made of fly ash and silica fume

• Quantified the effect of w/c ratio on multivariate NDT strength prediction accuracy. • Combined rebound hammer, UPV, and curing age in a mix-sensitive regression model. • Proposed model achieved low prediction errors (RMSE = 1.46 MPa; MAE = 1.26 MPa). • Demonstrated limitations of generic SonReb correlations for local materials. • Developed a locally calibrated correction factor for rebound-based strength estimates. Accurate estimation of concrete compressive strength using non-destructive testing (NDT) methods remains challenging because widely used empirical correlations often neglect key mix design parameters, particularly the water–cement (w/c) ratio. This study investigates the influence of the w/c ratio on concrete compressive strength and on the predictive performance of combined rebound hammer (RH) and ultrasonic pulse velocity (UPV) models through controlled laboratory experiments using locally sourced Nigerian materials. Six concrete mixes with w/c ratios ranging from 0.45 to 0.70 were prepared with a constant 1:1:2 mix proportion and tested at curing ages of 7, 14, and 28 days. RH and UPV measurements were conducted on laboratory-cured cube specimens and correlated with compressive strength obtained from standard destructive tests. Pearson correlation analysis revealed strong positive relationships between compressive strength and RH (r = 0.96) and UPV (r = 0.93), while increasing w/c ratio consistently reduced both strength and NDT responses. A multivariate regression model incorporating RH, UPV, and curing age was developed to predict compressive strength across the investigated mixes. The model achieved a coefficient of determination (R²) of 0.79 with low prediction errors (RMSE = 1.46 MPa; MAE = 1.26 MPa). Comparative analysis showed that the proposed model outperformed single-parameter approaches and highlighted the limitations of generic SonReb correlations when applied without local calibration. The results demonstrate that reliable NDT-based strength prediction is strongly mix-sensitive and requires locally calibrated models for accurate laboratory-based quality control.

Concrete strength assessment is pivotal in ensuring the structural integrity and longevity of various constructions. Non - destructive testing (NDT) methods have emerged as indispensable tools for predicting concrete strength in situ, facilitating timely interventions and quality assurance protocols. Among these methods, the Schmidt rebound hammer (RH) and ultrasonic pulse velocity (UPV) techniques have gained prominence due to their simplicity, cost - effectiveness, and on - site applicability. This study delves into the relevance and efficacy of RH and UPV techniques for predicting concrete strength, focusing on the development of mathematical correlation models between NDT parameters and compressive strength. The research involves conducting comprehensive experimental investigations on a diverse range of concrete specimens encompassing different mix designs, strength ranges, and ages. Compressive strength, the gold standard for concrete strength determination, was evaluated through destructive testing methods. Concurrently, non - destructive assessments employing RH and UPV were performed on the same specimens. The rebound values from Schmidt Rebound Hammer test and the velocity of ultrasonic pulses were correlated with compressive strengths to establish predictive models. Uni - parametric (RH - Strength and UPV - Strength) correlation models, as well as combined models, were developed to explore the relationship between NDT parameters and concrete compressive strength. In evaluating concrete strength using the Schmidt rebound hammer test, it was observed that this surface test exhibited less sensitivity to variations in concrete mix design within the same strength range. Instead, its sensitivity primarily stemmed from variations in concrete strength, attributed partly to the density of the cement paste at the surface. Conversely, the Ultrasonic Pulse Velocity test emerged as more relevant for assessing concrete strength, given its ability to investigate concrete depth. However, it displayed lower sensitivity to variations in concrete mix design when dealing with high - strength concretes. Despite these nuances, the proposed correlation models demonstrated reliability and accuracy, evident from the coefficients of correlation obtained. Furthermore, the utilization of combined models facilitated an improvement in prediction accuracy compared to uni - parametric models alone. Notably, it was observed that concrete mix design and the age of concrete exerted significant influence as factors diminishing the precision of concrete strength prediction using non - destructive testing (NDT) methods. These findings underscore the importance of considering such influencing factors and refining model calibration processes to further improve the reliability of NDT - based concrete strength assessments. RH and UPV techniques offer valuable insights into concrete strength prediction, aiding rapid on - site assessments and quality control during construction projects. While both methods present strengths and limitations, integrating them alongside conventional testing approaches enhances the reliability and efficiency of concrete strength evaluation. The development of correlation models facilitates quantitative predictions of concrete strength based on NDT parameters, advancing the state - of - the - art in non - destructive evaluation of concrete. Further research focusing on refining testing protocols and calibration techniques is warranted to optimize the accuracy and applicability of these techniques in concrete engineering practices.

The study on the influence of early age damage of concrete on its long-term strength development is of great importance. In this work, 102 concrete cubes with and without supplementary cementitious materials (SCMs) were prepared. The pre-loading with loading degrees of 20%, 50%, and 80% of the corresponding compressive strength at 3-, 7-, 14-, and 28 d age was applied to the concrete samples. Then, concrete samples were further cured to 270 d, and the compressive strength was tested by the uniaxial compression test. The acoustic emission signals during the compressive strength test were collected. It is found that the pozzolanic reaction healed the damage caused by the early age damage, and the compressive strength of concrete with the incorporation of SCMs at 270 d age after pre-loading was higher than that of ordinary concrete without SCMs. The peak frequency of the uniaxial compression acoustic emission of concrete can be divided into four frequency intervals to correspond to different damage mechanisms of concrete, namely: interval I (12 ± 5 kHz), interval II (38 ± 5 kHz), interval III (171 ± 5 kHz), interval IV (259 ± 5 kHz).

Acoustic emission and ultrasonic pulse velocity of concrete

Damage characterization of concrete under multi-step loading by integrated ultrasonic and acoustic emission techniques

This article aims to improve the knowledge on ‘crack classification’ in reinforced concrete (RC) beams using acoustic emission (AE) testing and ultrasonic pulse velocity (UPV) test. The present study reports on usage of AE and UPV testing methods on fracture mode in RC structures. Gaussian mixture modelling (GMM) method was used for crack classification. Support vector machine (SVM) method was used for separating AE data related to tensile cracking and shear cracking. It was observed that the UPV along the span of the RC beam reduced at places where cracks were formed. The locations in the RC beam where the cracks developed, an increase in the travel time between receiver and transmitter was observed. More AE hits were observed at locations where UPV value was less. It was observed that at 60–100% of the load, the RC beam with shear reinforcement exhibit higher shear hits (e.g. approximately 20–30%) while the beam without shear reinforcement exhibit much less, showing the effect of the shear stirrups. The RC beam without shear reinforcement failed more like a plain concrete beam due to tension. The observations made in this study provide a reference for conducting non-destructive testing of large RC structures.

The rapid expansion of civil engineering projects and the growing need to utilize problematic soils have highlighted the importance of developing innovative approaches for soil improvement and performance evaluation. In this study, the combined effects of lime and nano-aluminum oxide (nano-Al₂O₃) as supplementary additives were investigated for stabilizing highly plastic clay (CH). To evaluate the mechanical and microstructural properties of the treated soils, a series of tests was conducted, including standard Proctor compaction, unconfined compressive strength (UCS), indirect tensile strength (ITS), ultrasonic pulse velocity (UPV) as a non-destructive test, and scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results revealed that the addition of nano-Al₂O₃ caused a decrease in the maximum dry density (MDD) and an increase in the optimum moisture content (OMC), which is attributed to changes in the soil structure and the occurrence of pozzolanic reactions between the lime and nanoparticles. The optimal mixture of 9% lime and 1.2% nano-Al₂O₃, after seven days of curing, resulted in 42% and 26% increases in UCS and ITS, respectively. Furthermore, the UPV value for this mixture increased by approximately 72% compared with lime-stabilized soil, indicating higher density and improvement in the fine-grained structure of the soil. Increasing the curing time to 90 days also resulted in a continuous growth in UCS and UPV by 97% and 113%, respectively, demonstrating the continuation of pozzolanic reactions and a gradual improvement of the soil structure. Moreover, microstructural results confirmed enhanced formation of hydration products and a denser cementitious matrix in the optimized mixture. Based on data analysis, exponential correlations were established between UPV and mechanical parameters (UCS and ITS), with coefficients of determination of R2 = 0.84 and R2 = 0.79, respectively. These results indicate that the non-destructive UPV test can be used as an efficient tool for in-situ monitoring and prediction the strength of soils stabilized with lime and nanoparticles.

Aggregate gradation effects on dilatancy behavior and acoustic characteristic of cemented rockfill

Frost damage evaluation of concrete irrigation structure by X-ray CT and AE energy release trend at the initial loading stage