Concrete Age Research Articles

Probabilistic analysis of crack widths associated with quality control procedures

AbstractExisting concrete specifications limit the crack width in order to fulfill the limits of serviceability and durability. The crack width calculation results differ depending on the influences of the variability of the used materials, the geometry, the actions and the uncertainty of the used calculation model itself. In this contribution, the influence of the variability of the input parameters on the calculated crack width is investigated using probabilistic methods in a real case study of a highly loaded tunnel lining cross‐section. The primary objective of this study is a sensitivity analysis to identify the geometric and material‐related input parameters with the most significant influence, which must be particularly controlled during execution for quality control purposes. The study in this article is based on the Eurocode deterministic model for calculating crack width for a stabilized cracking stage in late concrete age.

Early age bond-slip behavior of reinforcing steel bars in concrete subjected to uniaxial lateral pressure: An experimental study

The bond between reinforcing bars and concrete is a crucial factor concerning the serviceability of reinforced concrete structures, particularly for those during construction in some developing areas where plain bars were still used as reinforcements. Despite numerous studies on early age bond behavior between steel bars and concrete, little research has been conducted to quantify the effect of uniaxial lateral pressures on this bond. This study involved testing a total of 378 pullout specimens to evaluate the early age bond-slip behavior of plain bars in concrete under uniaxial lateral pressure. The main test parameters included the concrete ages (1, 3, 7, 14 and 28 days), lateral pressures (0, 0.1, 0.2, 0.4 and 0.6 times the compressive strengths of concrete), concrete strength grades (C20, C35 and C45), and bar diameters (12, 16 and 20 mm). Based on the experimental results, a series of analytical expressions were developed for bond strength, maximum bond slip and residual bond stress predictions considering the effects of early age and lateral pressure. The results demonstrate that degradation of bond strength at early ages can be effectively mitigated by uniaxial lateral pressures. As the age decreases from 28 to 1 days, the bond strength exhibits a significant decrease of up to 51.59 %, while this adverse effect can be reduced by around 10 % in the presence of lateral pressures. Increasing the pressure level from 0 to 0.4 results in a significant increased early age bond strength by 112.6 % to 199.0 % for different bar diameters. However, the residual-to-maximum bond stress ratio remains nearly constant at 0.49 regardless of age and lateral pressure, as the pressure primarily contributes to frictional forces at the bar-concrete interface. An age-dependent bond-slip constitutive model considering the effect of uniaxial lateral pressures was finally proposed and verified with the test results. The paper concludes that given the concrete compressive strength at 28 days, the proposed bond strength and bond stress-slip models can predict the early age bond responses of plain bars in concrete under uniaxial lateral pressures with reasonable accuracy.

Carbonization test and orthogonal polynomial regression analysis of steel fiber reclaimed concrete

To enhance the carbonation resistance of reclaimed concrete, several key factors affecting its performance were investigated. An orthogonal array L16(4³×2⁶) was employed to design the carbonation tests for steel fiber (SF) reinforced concrete. The study included varying SF volume ratios, along with considerations of different concrete ages (T) and water-cement ratios (W/R). The effect of SF volume ratio, regenerated crude aggregate (RCA) replacement rate, W/R, and T on the carbonation resistance of recycled concrete was analyzed. The test results indicated a trend of increasing carbonation depth over time. However, a lower W/R ratio resulted in a reduced carbonation depth. Notably, a 50% RCA replacement rate led to a shallower carbonation depth compared to other replacement rates. After 28 d, recycled concrete containing 1% SF exhibited a carbonation depth that was 6.9%, 1.5%, 1.5%, and 9.3% lower than concrete with 0%, 0.5%, 1.5%, and 2% SF, respectively. Therefore, the incorporation of 1% SF was found to be the most effective in improving carbonation resistance. Orthogonal polynomial regression analysis was employed to develop a regression equation relating carbonation depth to SF volume ratio, RCA replacement rate, W/R, and T. The regression coefficients were calculated and tested, leading to the identification of the optimal regression equation and its corresponding confidence interval.

Effect of Adding Polypropylene Plastic Waste on Compressive Strength and Flexural Strength Concrete

Indonesia is the second largest producer of plastic waste in the world after China with an annual contribution of 187.2 million tons of plastic waste. This study aims to analyze the effect of the addition of plastic seeds with polypropylene substitution on the compressive strength and flexural strength of concrete with the intention of reducing waste waste and utilizing it as a concrete mixing material and making concrete properties into green concrete. The method used is the experimental method by making several variations of concrete mixtures with plastic seeds of polypropylene type as a substitute for part of the sand. The mixing of plastic seeds is divided into several variations, namely, 3% polypropylene seeds and 6% polypropylene seeds. Analysis of the test results of the addition of polypropylene seeds compared to the concrete mixture without polypropylene seeds resulted in a compressive strength of 24.14 MPa for the addition of 3%, as well as a value of 23.25 MPa for the addition of 6% each at 28 days of concrete age. As for the flexural strength, an increase value of 0.16 MPa was obtained for the addition of 6% and the addition of 3% at the age of 28 days. This study shows that the results of the study have reached the planned quality target, namely the quality of fc'20 Mpa.

Long-term effects including shrinkage and interfacial creep on bond behavior of concrete-filled steel tubes (CFST): Experiment and design

Concrete-filled steel tubes (CFST) are widely used in significant projects due to their high performance stemming from full utilization of combined material advantages. The interfacial bond behavior is the foundation of their high performance, but will deteriorate during the long-term service. Due to the difficulties on carrying out long-term experiments and decoupling the multi-constitutive component bond strength including chemical adhesion, micro-interlocking and friction, there is still a lack of research on long-term interface constitutive models, restricting the safe design of CFST structures throughout their full-lifecycle. Here, push-out tests were carried out on CFST specimens considering long-term effects spanning 850 days including concrete age and duration of long-term interfacial load. The steel plate-concrete specimens, reversed push-out tests and interfacial normal pressure calculation were used to decouple the components of bond stress. the CFST interface database considering long-term effects was established and the mechanism of long-term effects have been revealed. As the duration increases, the bond stress decreases at the beginning, and thereafter stabilizes where the friction component dominates. Compared to that without interfacial load, long-term interfacial load accelerates the damage to chemical adhesion and micro-interlocking at initial stage, but the difference of their effects on bond stress is not significant in the later stage. On this basis, a long-term interfacial constitutive model for its full-lifecycle safe design and a simplified numerical method for long-term effects on bond behavior have been proposed.

Performance of self-compacting concrete with treated rice husk ash at different curing temperatures

Self-compacting concrete (SCC) is currently gaining traction as a replacement to conventional vibrated concrete. Its distinct microstructure leads to varied mechanical behaviour under different curing temperatures. In the past various supplementary cementitious materials (SCMs) were used in SCC to investigate their respective effects on the performance. However, there has been no systematic studies conducted to determine the effect of different curing temperature on the sensitivity reaction of rice husk ash (RHA) in SCC. This research focuses on high-strength SCC with SCMs such as RHA, silica fume (SF), fly ash (FA), and ground granulated blast-furnace slag (GGBS), exploring their applicability for concrete structures under varying curing temperatures. Heat of hydration, compressive strength and open porosity of SCC specimens were assessed at various temperature. Results indicate high curing temperatures expedite the hydration and pozzolanic reaction, refining the microstructure and increasing the early-age concrete strength, but compromising the long-term performance, potentially mitigated by the use of SCMs. Conversely, lower curing temperature, impedes hydration leading to gradual strength gain, particularly with SCMs, yet yielding significant strength increases at later concrete age. SCMs presence and curing temperature significantly influence maturity function-based strength predictions, impacting strength trends in the samples studied.

Pengaruh Air Laut terhadap Kuat Tekan, Permeabilitas, dan Mikrostruktur Beton Geopolimer dengan Flyash dan Tanah Putih sebagai Pengganti Semen

The increasing infrastructure development of an area is sometimes located in an aggressive environment, one of which is in coastal areas so that direct contact with sea air cannot be avoided. This research aims to determine the effect of sea water on geopolymer concrete using fly ash and white soil as cement substitutes with testing parameters for compressive strength, permeability and microstructure. The test objects used were cylindrical in shape measuring 150x300 mm and 100x200 mm. The ratio of fly ash and white soil used was 85%:15% and the activator used was NaOH 8M and Na2SiO3 with a ratio of 1:2,5. The mixture proportion using a ratio of 1 fly ash: 1,497 sand: 2 split: 0,451 alkali activator with a mutual plan is 35 MPa. Tests were carried out after the concrete had gone through a curing process for 56 days, then the concrete was conditioned without soaking and with soaking for 28 days. Tests were carried out at concrete ages of 56 and 87 days. The test results show that geopolymer concrete with the influence of sea water has a higher compressive strength value and a smaller permeability coefficient compared to concrete without the influence of sea water. Microstructural testing of geopolymer concrete under the influence of sea air produces a matrix-shaped structure morphology that is denser with fewer pores compared to concrete without the influence of sea air.

Development of mechanical properties of concrete in vacuum tunnel of vacuum-based maglev train

The vacuum-based maglev train is an emerging transportation system currently under development worldwide. While concrete is a technically viable material for constructing vacuum tunnels, its mechanical performance in this unique environment remains unclear. This paper investigates the behavior of concrete in vacuum using a large customized vacuum tube. The results show that concrete undergoes significant water loss in vacuum, resulting in impeded cement hydration and porous hydration products with a foam structure. Vacuum exposure during the early ages of concrete has negative effects on mechanical properties. However, once the cement hydration reaches a high level of maturity, further vacuum exposure has little influence. Compared with atmospheric conditions, the shrinkage of concrete in vacuum is significantly increased. These findings provide a valuable experimental database and new insights for the use of concrete in vacuum-based maglev trains.

Comparative study on the behavior of ordinary and lightweight concrete using natural pozzolan aggregates

This study is part of a comprehensive research project focused on exploring the integration of natural pozzolans into concrete production. It investigates how these materials enhance the physical properties and mechanical behavior of concrete, with a specific emphasis on improving economy, strength, and overall performance. Key objectives include evaluating workability and compressive strength through comparative tests across various concrete formulations. Special attention is given to analyzing the influence of the water-to-cement ratio and concrete age on compressive strength, particularly in comparing ordinary and lightweight concrete mixes. The findings indicate significant enhancements in concrete characteristics with the inclusion of natural pozzolans, particularly beneficial for applications prioritizing thermal insulation over high mechanical strength. This study provides valuable insights into optimizing concrete mix designs tailored to specific construction needs. Furthermore, the research underscores the potential environmental and economic benefits of incorporating natural pozzolans, promoting sustainable construction practices. By demonstrating the feasibility and advantages of these materials in concrete applications, this study contributes to advancing materials science and engineering solutions for resilient and efficient built environments.

Analisis Kuat Tekan Beton dengan Variasi Agregat Kasar Dicuci dan Tidak Dicuci

This research aims to determine the effect of washed coarse aggregate and unwashed coarse aggregate on the compressive strength of concrete. In this research, the method used was making concrete test objects in the laboratory of the Indonesian Technocrat University. This research was carried out on 8 cylindrical test objects measuring 15 x 30 cm. Of the 8 test objects made, 4 test objects used washed coarse aggregate and 4 test objects used unwashed coarse aggregate. The tests carried out were concrete compressive strength tests at concrete ages of 7, 14, 21 days. The results of the compressive strength of concrete with washed coarse aggregate, the results of conversion calculations for 28 consecutive days were 244.76 Kg/cm2, 212.19 Kg/cm2, 249.88 Kg/cm2, and 226.99 Kg/cm2. The results of the compressive strength of concrete with aggregate rough unwashed, the results of conversion calculations for 28 consecutive days were 229.64 Kg/cm2, 176.27 Kg/cm2, 179.05 Kg/cm2, and 185.86 Kg/cm2. Based on data from research that has been carried out, it can be seen that concrete that uses washed coarse aggregate material has a stronger compressive strength than concrete that uses unwashed coarse aggregate.

The analysis of age dynamics of causes of mortality of population of elderly age groups as reserve of maintaining population of older able-bodied age

The article analyzes age dynamics of initial causes of death according to records in medical death certificates of population of older age groups. Materials and methods. The records of causes of death of 34.914 persons aged 60 years and older were used as primary source of information. The initial cause of death was determined according to the ICD-10 rules. The rate of registration by reason of death was calculated as intensive value per 100 deaths in concrete age and sex group. Each cause was coded according to the ICD-10 rules (revision 2014-2016). The belonging to group was determined by first character (letter) in four-digit code that corresponded to the Class. On the basis of analysis of structure of causes of death, the group A of causes that included five Classes of ICD-10, determined 81.4% of all deaths in population aged 60 years and older. Two Classes: "Diseases of the circulatory system" (Class IX) and "Neoplasms" (Class II) determine in all studied age groups more than a half of all deaths (from 55% to 71% of males and from 59% to 67% in females) and namely they determine mortality rate in older age groups. There are no gender differences in age characteristics of registration rate in these groups (p > 0.05), however age dynamics differ. In case of diseases of circulatory system initial cause of death is increase rate of registration at increasing of age. In case of neoplasms at increasing of age decrease of registration rate as initial cause of death is established. At that, rate of decline is higher than rate of increase that determines certain decrease of structural significance of combined contribution of these two groups of causes at increasing of age. The Group B of causes, including three Classes of ICD-10 "Respiratory diseases" (Class X), "Diseases of the digestive system" (Class XI) and "Diseases of the nervous system" (Class VI), determined in overall 11.9% of all deaths in population aged 60 years and older. The age dynamics of causes of death of population of older age groups exists for certain groups of causes and it should be considered in organizing medical care of population of older age groups.

The Influence of Concrete Age on the Accuracy of Pile Integrity Testing on Bored Piles Foundation

Abstract Bored pile foundations are defined as deep foundations in the form of an elongated tube with a specific diameter made of reinforced concrete installed using the drilling method and in-situ casting concrete. The cast in-situ process in bored holes with a deep elevation below the ground surface can potentially cause integrity problems, such as voids, segregation, fracture, necking, bulging, and other concrete defects. Currently, many non-destructive test methods are available to ensure the quality of the bored pile; one is the Low Strain Integrity Testing method, also known as Pile Integrity Testing (PIT). ASTM recommends that PIT should be carried out no sooner than 7 days after casting or the strength of the concrete has reached a minimum of 75,0% of its design strength. In fact, the PIT test is carried out before the concrete’s age and/or its strength is achieved, considering the limited construction time. This could lead to misinterpretation of the PIT test results and inaccurate identification of the bored pile defect locations. The study aims to determine the effect of concrete age on the accuracy of bored pile defect locations on a laboratory scale. The test model consisted of four bored piles with a diameter of 0,3 meters and a depth of 2,0 meters, which were cast using reinforced concrete with a design strength of fc’ 30 MPa. The PIT was performed at <7, 14, and 28 days of concrete age, and then the confusion matrix method was used to create a binary classification model to determine the accuracy of the defect location. The defect locations were visually observed and validated by dismantling the test model after 28 days of casting. The results showed that the accuracy of identifying the location of concrete defects was not affected by the age of the concrete but was determined by the compressive strength of the concrete during testing. Referring to the F-score, bored piles with concrete strength >75,0% of the design accurately identify defect locations above 84,21%. On the other hand, bored piles with concrete strength <75,0% design resulted in accuracy below 66,67%.

Use of machine learning models to predict the water penetration depth in concrete

Machine learning (ML) is a robust tool within the artificial intelligence domain that offers unique solutions for predictive modeling. Prediction of water penetration depth (Wpen) is crucial for assessing the durability and service life of concrete while reducing reliance on complex and time-consuming laboratory tests. This study investigates the impact of concrete composition, age, and compressive strength on Wpen using a dataset of 311 concrete specimens. Multiple supervised ML models were employed in predicting Wpen, including linear regression (LR), Gaussian process regression (GPR), support vector machine (SVM), random forest (RF), regression tree (RT), and hybrid RF-SVM models. Results revealed that hybrid RF-SVM model and regression tree accurately predicted Wpen. The models’ performance improved by including concrete age and compressive strength. The models were validated using data from relevant literature. This research provides valuable insights into predicting water penetration depth in concrete, offers practical tools for assessing concrete durability, and offers a more sustainable approach than laboratory testing.

The Influence of Peat Water on the Physical Properties of Underwater Concrete

Casting concrete underwater is concrete used for structural work underwater. The main problem in underwater casting is the separation of concrete constituent materials. Casting underwater also does not involve compaction. This study will examine the effect of peat water on the physical properties of underwater cast concrete. The additive used in this study is in liquid form, with a mixture of anti-washout material 1.8% and self-compacting concrete 5% to the weight of cement. The obtained slump flow value is 470 mm. The results of volume weight testing on variations of clean water mixtures immersed in clean water for seven days are 2248,14 kg/m3 and 2258,96 kg/m3 for 28 days, variations of clean water mixtures immersed in peat water for seven days are 2224,49 kg/m3 and 2219,39 kg/m3 for 28 days, and variations of peat water mixtures immersed in peat water for seven days are 2202,50 kg/m3 and 2191,08 kg/m3 for 28 days. The decrease in volume weight occurs in variations immersed in peat water. The results of porosity testing on 7-day and 28-day concrete age variations of peat water mixtures immersed in peat water are 9,94% and 10,78%, variations of clean water mixtures immersed in peat water are 9,84% and 10,28%, and variations of clean water mixtures immersed in clean water are 9,73% and 8,70%. The SEM test results show the surface shape of concrete using a magnification of 1000x, more pores on variations of peat water mixtures immersed in peat water, and variations of clean water mixtures immersed in peat water have uneven surfaces and pores. In contrast, variations of clean water mixtures immersed in clean water have better surfaces. The additive used can work well with peat water and clean water.

Concrete aging factor prediction using machine learning

Accurate prediction of concrete aging factor is pivotal for performance-based durability reinforced concrete design. This study introduces an innovative method leveraging machine learning techniques, employing seven algorithms: Bagging, Random Forest, AdaBoost, Gradient Boosting, XGBoost, CatBoost, and LightGBM. The dataset comprises 130 instances with seven input features describing cement type, cement content, pozzolan type, pozzolan content, w/b ratio, exposure condition, and age of concrete. Seventy models were trained across five scenarios, categorized into two groups: Group I using all features of the raw dataset, and Group II incorporating engineered features. Model performance, assessed by mean-absolute error (MAE), mean-square error (MSE), root-mean-square error (RMSE), and coefficient of determination (R²), reveals superior performance in Group II compared to Group I. Notably, the LightGBM algorithm in Scenario III outperforms all models with a remarkable MAE of 0.110, MSE of 0.018, RMSE of 0.133, and R² of 0.818. Subsequently, models from Scenarios V and IV exhibit strong performance. The implemented machine learning models demonstrate notable generalizability, effectively capturing feature interrelations without the need for resource-intensive experimental testing.

Age-dependent deflection analysis of high-volume fly ash RC beams: experimental and artificial neural network modelling

This research examines the influence of high-volume fly ash (HVFA) on reinforced concrete (RC) beam deflections over 180 days of continuous loading. The study comprises eight fly ash-based concrete mixes with varying fly ash ratios (0–60%). Experimental assessments were conducted on two load levels, corresponding to 25% and 50% of the initial cracking load. Thirty-two full-scale RC beams, each measuring 100 × 150 × 1800 mm, were fabricated for both load levels. Long-term deflections were monitored for all concrete mixes through sustained four-point bending tests at ages ranging from 1 to 180 days. A comparative analysis of the overall mid-span deflection between conventional and fly ash concrete RC beams was carried out against established design codes. It was determined that high-volume fly ash RC beams exhibited less creep and shrinkage deflection compared with conventional RC beams. Moreover, artificial neural network (ANN) modelling was also carried out to propose a significant model helpful in predicting the total deflection of RC beams containing any fly ash content and at any age of concrete. The present study offers valuable insights for engineers and designers, facilitating the evaluation of age-dependent deflection patterns in RC beams constructed with reinforced high-volume fly ash concrete.

Penggunaan Limbah Abu Batu Sebagai Campuran Pada Agregat Halus Terhadap Kuat Tekan Beton

Stone ash is a fine aggregate that passes through sieve no. 4 (diameter 4.75mm) but is retained on sieve no. 200 (0.075mm), thus making stone ash a waste that is useful as a mixture of construction building materials because stone ash can function as a fine aggregate as a substitute for sand in concrete mixtures. The purpose of this research is to find out whether stone ash can be a suitable and good material as a substitute for some of the fine aggregate (sand) in a normal concrete mixture or not, to find out the results of the compressive strength test of concrete by stone ash in a normal concrete mixture, and what percentage composition stone ash which produces optimal concrete compressive strength tests or according to plan. The test object used was a 150 × 300mm cylinder with a total of 36 samples. Stone ash waste with composition ratios of 15%, 25% and 35% has a fairly good bond as an added material to normal concrete mixtures as a substitute for fine aggregate and can even increase the compressive strength of concrete significantly. The composition of stone ash used as a mixture for fine aggregate is 15%, 25% and 35% with a planned concrete quality of 20 MPa and a concrete age of 7, 14 and 28 days. The compressive strength produced by normal concrete without a mixture of stone ash aged 7, 14, and 28 days produces concrete compressive strengths of 13.63 MPa, 19.57 MPa, and 20.53 MPa. Next, for concrete with a rock ash composition of 15% of fine aggregate with an age of 7, 14 and 28 days, the concrete compressive strength is 15.75 MPa, 18.02 MPa, 22.03 MPa. Concrete with a stone ash composition of 25% of fine aggregate with an age of 7.14 and 28 days produces a concrete compressive strength of 15.96 MPa, 19.02 MPa, 21.16 MPa. Concrete with a stone ash composition of 35% of fine aggregate with an age of 7, 14 and 28 days produces a concrete compressive strength of 23.49 MPa, 24.31 MPa, 24.95 MPa. From the research conducted, the 35% composition has the highest compressive strength value of concrete among the other compositions

Performance based concrete quality assessment with gas permeability testing on site

In terms of sustainability and durability, performance-based design is becoming increasingly important for the quality assessment of concrete structures. Up to now, prescriptive approaches for concrete composition and processing and the determination of concrete strength on cast samples have primarily been used as quality assurance. As this does not take into account the quality and pore structure of the as-built concrete cover, which has a significant influence on durability as a protective zone against penetrating media, the conventional approach to quality control is not representative for this zone. In particular, the permeability of the concrete cover, which is largely dependent on the pore structure, is responsible for the ability of aggressive substances from the environment to ingress into the concrete and, depending on its quality, determines damage processes in the reinforced concrete, such as carbonation. For this reason, investigations to gas permeability on real structures are presented here, which include the possibilities and limitations of measuring and evaluating gas permeability as a durability indicator. Long-term observation was carried out on concrete walls of a motorway construction site, from a young concrete age of 14 days to a higher age of max. 800 days, in order to determine changes in the material structure of the surface area and to analyse their influence on the gas permeability. The concrete walls were treated in advance during hydration up to an age of 7 days with different curing times and types in order to simulate good, medium and poor concrete surfaces. Clear differences in the quality of the concrete cover could already be determined by means of gas permeability. The influence of the surface structure, the effect of the environment and the long-term development of the concrete structure on the permeability are also addressed in this work.

Utilizing Optimized Machine Learning Techniques to Predict the Compressive Strength of Concrete through Non-Destructive Testing Methodologies

Background:: Examining the concrete quality in its original location and optimizing machine learning models for precise forecasting of concrete compressive strength(fc) is crucial. Current research advocates the fine tuning of hyperparameters within machine learning methodologies in tandem with non-destructive testing techniques to forecast the compressive strength of concrete. Objective:: This study aimsto incorporate age as a crucial factor by utilizing data spanning from 3 days to 365 days. This approach enhances the study’s applicability for real-time forecasting purposes. Methods:: In the methodology of this current research, three machine learning (ML) models— specifically, Multi-Linear Regression (MLR), Decision Tree Regressor (DTR), and Random Forest Regressor (RFR)—are introduced within the context of age as a significant factor influencing measurements obtained from the Rebound Hammer (RN) and Ultra Sonic Pulse Velocity (UPV). These ML models were sequentially applied, followed by a meticulous process of hyperparameter finetuning conducted through grid search Cross-Validation (CV). To gain insights into the predictive results, the study also employed SHapley Additive exPlanations (SHAP) for interpretation purposes. Results:: The results of this study reveal the development of an empirical relationship using Multi- Linear Regression, which yielded an R2 value of 0.88. Furthermore, the evaluation showed that Random Forest Regression outperformed other models with an R2 value of 0.95 in the training and 0.92 in the testing datasets. These models hold promise for facilitating decisions about qualitative analyses based on UPV and Rebound Hammer measurements relative to the age of the concrete. Rigorous validation of the models was conducted through standard cross-validation techniques. Conclusion:: The research has created and validated hyper tunned machine learning models with the help of grid search cross-validation function, with Random Forest Regression being the most effective. These models can potentially guide decisions regarding qualitative analyses using UPV and Rebound Hammer measurements concerning concrete age. They provide a valuable tool for on-site assessments in construction and structural evaluations. The primary objective of the research is to introduce age as a significant feature. To achieve this, data ranging from 3 days to 365 days was integrated. This inclusion aims to enhance real-time decision-making in construction processes, facilitating actions like the prompt removal of formwork in high-speed construction projects.

Characteristics of fibres based on secondary raw materials and their use in concrete technology

Different types of fibres in cementitious composites, particularly in concrete, are currently used for a number of reasons. Fibres are being added to improve mechanical properties (especially steel and glass fibres), to increase the durability – to reduce occurrence of microcracks during the concrete aging (mainly synthetic and cellulose fibres), or to increase the fire resistance (polypropylene fibres). Within the study, characterization of different types of alternative fibres (fibres generated during waste recycling that would otherwise end in incinerators or landfills) with possible use in cementitious composites. These were fibres from recycled PET bottles, paper, and mineral wool, whose properties were compared to the traditionally used cellulose and polypropylene fibres. In the experimental part, the thickness, length, shape, and surface of individual fibres were monitored by an optical microscope. Furthermore, the amount of heat of combustion was determined by the calorimetric method, and the differential thermal analysis (DTA) was carried out for determination of the impact of high temperature on monitored fibres. The microstructure of fibres was monitored using a scanning electron microscope. The focus of the experimental study was on fibres usable in concrete and capable of enduring high temperature stress.