Ultrasonic Pulse Velocity Test Research Articles

Utilization of Plastic Waste in Road Paver Blocks as a Construction Material

India is confronted with the substantial issue of plastic debris due to the absence of an efficient waste management infrastructure. Recycled plastic has the potential to enhance various construction materials, such as roofing tiles, paving blocks, and insulation. The aforementioned materials possess notable attributes such as high strength, low weight, and exceptional resistance to extreme temperatures and humidity. The objective of this study is to ascertain feasible alternatives for manufacturing road paver blocks utilizing plastic waste (Polyethene terephthalate (PET)), and M-sand (stone dust). Three variations of a discarded plastic cube measuring 150 mm × 150 mm × 150 mm were prepared for the experiment. The experimental findings indicated that a ratio of 1:4 was determined to be the most effective in achieving the desired level of compressive strength. I-section road and brick paver blocks were produced as an alternative to the traditional concrete ones. Compressive strength tests were performed on I-sections and brick paver blocks, revealing that the 1:4 mix ratio exhibited the highest average compressive strength for both materials. The findings indicated that including plastic waste positively impacted the compressive strength of the I-sections and brick paver blocks. Additionally, the quality grading of these materials was evaluated using an ultrasonic pulse velocity test. The ultrasonic pulse velocity test results demonstrated a high-quality grading for the I-sections and brick paver blocks. Scanning electron microscopy (SEM) tests assessed the microstructural behavior and performance. The results of this study demonstrate that incorporating plastic waste in combination with M-sand can effectively improve the mechanical characteristics of composite materials, rendering them viable for use in construction-related purposes.

Effects of High Temperature and Cooling Regimes on Properties of Marble Powder-Based Cementitious Composites

The demand for cement is increasing every day worldwide. To meet this demand, natural resources are rapidly being depleted. The excessive consumption of natural resources encourages researchers to conduct studies on the use of waste materials instead of cement. Marble waste is one of the major natural wastes abundantly generated worldwide. It has been evaluated that there is a gap in the literature regarding a study comparing the effects of different cooling regimes on cementitious composites with a marble powder (MP) replacement that has been exposed to high temperatures. In this study, waste marble powder (MP) was used as a replacement for cement at percentages of 5%, 10%, 15%, 20%, and 25% by mass. The water-to-binder ratio was kept constant at 0.5 for all mixture groups. Subsequently, the prepared cementitious composites were exposed to high temperatures (300 °C, 600 °C, and 800 °C) and subjected to air- and water-cooling regimes. Within the scope of this study, unit weight (Uw), ultrasonic pulse velocity (UPV), flexural strength (ffs), compressive strength (fcs), and mass loss tests were conducted. Additionally, a microstructure analysis was carried out using scanning electron microscopy (SEM) to examine the effect of MP replacement and the cooling regime. When examining the results of the samples tested in the laboratory, it was observed that the mortar with 5% MP replacement exhibited better mechanical properties compared with the others. In general, it can be said that the mechanical properties of samples cooled in air after exposure to high temperatures were better than those of samples cooled in water. As a result of this study, it was determined that MP replacement could positively contribute to the resistance of cementitious composites to high temperatures. Additionally, the use of a significant amount of waste MP can lead to savings in cement usage and significant reductions in CO2 emissions.

Rock‐like strength enhancement of Indian desert sand using commercially available polysaccharide biopolymers

AbstractBiopolymers are a nature‐friendly solution that can impart rock‐like strength in sand by developing bonds between grains. In this study, we assessed the behaviour of desert sand treated with commercially available pectin (P), acacia gum (AG) and sodium alginate (SA) polysaccharide biopolymers (1%, 2% and 3% concentrations) applied at 0.75 and 1 pore volume (PV). Non‐destructive ultrasonic pulse velocity (UPV) tests recorded maximum values of 1579 m/s for AG samples, 1490 m/s for SA samples and 1400 m/s for P samples, all showing rock‐like behaviour. Unconfined compressive strength (UCS) and split tensile strength (STS) tests showed that the strength level generally increased with biopolymer concentration. The minimum UCS value was 173 kPa for the P (1%) 0.75 PV composition, and the maximum was 1287 kPa for the AG (2%) 0.75 PV composition. The UCS value for the AG (1%) 0.75 PV was 1178 kPa, with optimal results compared with other compositions. Scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDX) and X‐ray diffraction (XRD) tests were performed for microstructural analysis. SEM revealed a strong bond between sand particles and biopolymers. EDX and XRD showed that the strength stemmed from gel formation in the pores, rather than mineralogical changes. The study results indicate the level of strength attained with varying biopolymer percentages and PVs and are useful for desert sand stabilization.

Ultrasonic Pulse Velocity Testing for Monitoring the Degradation of Infill Masonry Walls and Access Their Impact on the Durability of the Envelope of Buildings with Reinforced Concrete Structure

Buildings with reinforced concrete structure (RCS buildings), including unreinforced masonry (URM) infill walls, can be negatively affected by anomalies in their envelope, such as cracking and water penetration, which worsen the aesthetic aspect and reduce the safety and level of comfort of those buildings. To access the relevance of these anomalies and their evolution along service life, a corresponding survey and monitoring during service life are essential. Non-destructive test methods (NDT), in particular ultrasonic pulse velocity (UPV) testing, are currently used in that survey and monitoring. In the context of monitoring the degradation of the URM infill walls and access their impact on the durability of the RCS building envelope, UPV testing can be a type of NDT method to be used, considering that it can contribute to the evaluation of the state of conservation of the construction elements, such as masonry and concrete. It is intended here to access the potential use of UPV testing in the monitoring of anomalies related to the degradation of building facades due, particularly, to cracking and to water penetration associated with WDR (wind driven-rain). The preliminary assessment of the use of UPV testing is made through the previous analysis of the results of the application of UPV testing for the detection of sub-surface and surface cracking in compression tests of masonry specimens. Following that analysis, an evaluation is made of the conditioning aspects of the use of UPV testing to access durability problems of the building envelope. Particularly, the main characteristics of cracking with interest for the assessment of the potential use of UPV testing are generally discussed. And, finally, an evaluation is made of the risk of water penetration through the cracks, for potential use of UPV testing in monitoring the presence of humidity in the cracks.

Influence of Blast Furnace Slag on Pore Structure and Transport Characteristics in Low-Calcium Fly-Ash-Based Geopolymer Concrete

Alkali-activated fly ash slag (AAFS) has emerged as a novel and environmentally sustainable construction material, garnering substantial attention due to its commendable mechanical attributes and minimal ecological footprint. This investigation delves into the influence of slag incorporation on the strength, pore structure, and transport characteristics of AAFS, encompassing various levels of fly ash replacement with slag. To assess the mechanical properties of AAFS concrete, unconfined compression and ultrasonic pulse velocity tests were conducted. Meanwhile, microstructural and mineralogical alterations were scrutinized through porosity, N2-adsorption/desorption, and SEM/EDX assessments. In addition, transport properties were gauged using electrical surface resistivity, water permeability, and water vapor permeability tests. According to the results, a remarkable refinement in the pore volume was found by increasing the slag content. The volume of the gel pores and surface area increased significantly associated with the increase in tortuosity. Accordingly, Ca inclusion in the cross-linked sodium aluminosilicate hydrate gel remarkably reduced the transport properties.

Durability Assessment of Alkali-Activated Concrete Exposed to a Marine Environment

This study investigated the performance of two alkali-activated concretes (AACs) subjected to marine exposure for 2 years. The AACs were synthesized from a low-calcium Class F fly ash (FA) and a blast-furnace slag. Concrete specimens were exposed in a marine environment in a port facility in southern Australia for 2 years. The specimens were subject to a range of nondestructive testing (NDT) techniques, including resistivity, Schmidt hammer, and ultrasonic pulse velocity (UPV) tests. In addition, chloride diffusion coefficients were calculated from concrete cores taken from specimens exposed in the marine environment. Microscopy analysis was undertaken using Fourier-transform infrared (FT-IR), nuclear magnetic resonance (NMR), and thermogravimetric analysis (TGA), and comparative data were taken on laboratory specimens at 28 days. Furthermore, the chloride diffusion coefficients were compared with the results of standard laboratory tests undertaken on the control samples at 28 days, including rapid chloride permeability testing (RCPT) using a 10-V driving voltage, an NT Build 492 test, and a bulk diffusion test, to determine the relationship between the 28-day laboratory tests results and the site performance. The data showed good correlation between the predicted performance based on the 28 day laboratory tests and the 2-year site data. The chloride diffusion of the ground granulated blast-furnace slag (GGBS) concrete agreed very accurately with the predicted value from the modified RCPT test, whereas the performance of FA concrete was superior to that predicted.

Effect of chitosan bio-polymer stabilization on the mechanical and dynamic characteristics of marl soils

The strength of marl soils decreases drastically in the variation of the water content. This has caused such soil to be introduced as problematic soil in geotechnical projects. In the present study, the effect of chitosan biopolymer on the static and dynamic properties of marl soil was investigated. To this end, different amounts of chitosan (up to 0.16%) were mixed with marl soil. Then samples were cured for 7, 28 and 90 days and finally subjected to 0, 1, 4 and 8Freeze-Thaw (F-T) cycles. Unconfined compressive strength (UCS), direct shear, Ultrasonic Pulse Velocity (UPV) and bender element tests were performed on the samples. The results showed that the UCS of the samples stabilized with 0.16% chitosan (as the optimal composition) increased by 227% after 7 days compared to that of unstabilized soil. Moreover, the values of cohesion and internal friction angle for the optimum mixture after 7 days of curing were equal to 38.76 kPa and 21.07°, which was much higher than 21 kPa and 18.26° related to the unstabilized marl soil. Chitosan was able to increase dynamic characteristics such as shear wave velocity and maximum shear modulus of samples by about 51 and 128% after 7 days of curing even after 8F-T cycles compared to those of unstabilized samples. Finally, chitosan exhibited that it can be a suitable alternative to traditional additives as an environmentally-friendly material, as confirmed by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) analyses.

Mechanical performance of fiber-reinforced concrete and functionally graded concrete with natural and recycled aggregates

This study aims to assess the mechanical performance of functionally graded concrete (FGC) in comparison to conventional plain cement concrete (PCC) and fibre-reinforced concrete (FRC). For this purpose, five concrete mixes were prepared, defined in eleven patterns, including PCC as a control mix, two FRC mixes, and eight combinations for FGC mixes. The hooked-end steel fibres and recycled thin polyethylene terephthalate (PET) strips from used bottles were utilized as fibres in 0.75 % of the volume of the mix in the FRC and FGC mixes. The natural aggregates were replaced by 15 % by weight with recycled plastic aggregates (RPA) and recycled concrete aggregates (RCA) in the FGC mixes. The mechanical performance of all specimens was assessed by compressive, split tensile and flexural strength tests, whereas the concrete quality was evaluated by the ultrasonic pulse velocity (UPV) test. The results revealed that the FRC mix containing steel fibres has 50.6 % higher compressive strength, while PET-FRC exhibited 42.4 % lower strength than the PCC. The best combination of the FGC mix is RCA + SFRC (H), which showed 27.6 % more compressive strength than PCC. The steel fibre-reinforced concrete (SFRC) mix has the highest split tensile strength, which is 47.5 % higher than the PCC. The best combination of FGC mixes is SFRC + PET-FRC (J), yielding 29.3 % higher tensile strength than PCC. On the other hand, both fibres contribute to the flexural strength enhancement of FRC. The FGC mix (K) yielded the highest flexural strength, with PET-FRC and SFRC in the upper and bottom layers, respectively, giving 40 % more flexural strength than the PCC specimen. The UPV values depicted that fibres and recycled aggregates in FGC specimens enhanced the quality of concrete. The highest value of UPV was recorded in the mix PCC + SFRC (G) containing PCC and steel fibres, which almost reached the upper limit of the recommended UPV values.

Effect of low-calcium fly ash inclusion on long-term mechanical properties and durability of ground granulated blast furnace slag-based cement-free mortars

The present study focused on fabricating cement-free mortar based on ground granulated blast furnace slag incorporating low-calcium fly ash as precursors in an alkaline solution of sodium hydroxide and sodium silicate. The main purposes of the study were not only to find the optimum mixture proportions to confirm the fly ash role in contributing to the long-term mechanical properties and durability but also to expand the use of fly ash in cement-free binders based on ground granulated blast furnace slag. The ground granulated blast furnace slag was replaced with fly ash in the cement-free mortar at various levels of 30, 40, 50, 60, and 70% by mass. The cement-based sample as a control sample was prepared for comparison purposes. Results showed that the cement-free mortar samples with fly ash had the more superior long-term mechanical properties (i.e. flexural and compressive strengths and volumetric compaction via ultrasonic pulse velocity test) and durability (i.e. total charge passed via rapid chloride penetration test and sulfate resistance via length change of samples exposed to sulfate solution), lower water absorption and porosity, and denser microstructure than the control sample up to 120 days. The 40% replacement of ground granulated blast furnace slag by fly ash as an auxiliary source of alumina and silica was the optimum ratio in enhancing the long-term mechanical properties and durability of the cement-free mortar samples, which is in agreement with reducing the porosity and water absorption. The results of the environmental analysis indicate that using cement-free mortar samples has much lower environmental impacts. The cement-free mortar sample using 60% ground granulated blast furnace slag and 40% fly ash is found as an optimal mixture in terms of technical and environmental features.

Self-healing capability of engineered cementitious composites with calcium aluminate cement

The reduced heating temperatures required for producing calcium aluminate cement (CAC) make it highly suitable for reducing CO2 emissions in engineered cementitious composites (ECCs) known with their significant amount of cement. However, it is not clear to what extent this can influence the advanced mechanical and self-healing ability of control ECC, especially with the risk of conversion in CAC reaction products. This study investigates the self-healing capability of ECCs produced using CAC instead of conventional ordinary Portland cement (OPC). It also assesses the impact of incorporating fly ash (FA) into CAC-ECC blends at different FA/CAC ratios. In addition to the mechanical characterisation of sound specimens, flexural properties, cracking behavior, ultra-sonic pulse velocity (UPV) and rapid chloride permeability test (RCPT) were performed on preloaded OPC- and CAC-ECCs. The study also analyzed the microstructural changes of self-healing products associated with the high alumina content of CAC. The results show that CAC can be used to produce high mechanical strengths ECCs, with more than 34% and 7% higher compressive and flexural strengths respectively than those of ECC-CTL at early age, though the addition of FA was important to reach improved patterns of mechanical properties at advanced ages. In addition, significant improvements were recorded for the recovery rates of CAC-ECCs, reaching more than 29% for flexural strengths, 11% for UPV and 75% for RCPT than the ECC-CTL. The self-healing products characterized with SEM-EDS confirmed the occurrence of conversion when FA was not included in CAC-ECCs, nevertheless with limited effect on the self-healing efficiency of these mixtures.

Strength and durability properties of recycled aggregate concrete blended with hydrated lime and brick powder

Concrete is an important material for the construction of buildings, and highways. However, natural resources are being depleted by using natural coarse or fine aggregates for the production of concrete. The substitution of natural coarse aggregate (NCA) with recycled coarse aggregate (RCA) efficiently manages construction waste and preserves natural resources. In the present study, 50 and 100% NCA have been replaced with RCA for the preparation of recycled aggregate concrete (RAC) with blended hydrated-brick powder (RAC-HBr). Additionally, cement was replaced by 10 and 20% of blended HBr in the preparation of RAC mixes. To investigate the strength and durability properties of RCA-HBr mixtures, compressive strength, water permeability, chloride penetration test, and ultrasonic pulse velocity (UPV) tests were conducted. The outcomes indicate that the optimum percentage of blended HBr enhances the compressive strength of RCA mixes. However, blended HBr positively influenced the RCPT, water permeability, and ultrasonic pulse velocity of the RCA concrete mixes. Further, the RCPT outcomes show that the chance of corrosion was reduced by 20%, while the UPV value confirms that the density of the RAC-HBr mixes was enhanced by 28.7% at the age of 56 days. Furthermore, based on the FESEM and EDS analysis, the pozzolanic materials have densified the concrete matrix by reducing the pores and voids of RAC-HBr mixes. Thus, practically, 100% RCA with blended hydrated lime and brick powder can be used to create M35-grade concrete.

Mechanical and durability properties of alkali-activated slag/waste basalt powder mixtures

There are several studies investigating the feasibility of basalt powder as a precursor in alkali-activated cement production. The originality of this research lies in investigating the mechanical and durability features of alkali-activated mortars manufactured by partially substituting granulated blast furnace slag (GBFS) with waste basalt powder (WBP). In this study, 20% of GBFS was replaced with WBP, and high temperature (300 °C, 600 °C, and 900 °C) and magnesium sulfate (5% concentration) resistance of the manufactured mortars were investigated. The deteriorations of the mortars subjected to high temperature and magnesium sulfate were examined by compressive strength test, ultrasonic pulse velocity test, scanning electron microscopy analysis, and Fourier transform infrared spectroscopy analysis. The compressive strength of the mortar produced with 20% WBP substitution was 9.9% lower compared to the mortar containing 100% GBFS as the precursor. However, the performance of alkali-activated slag (AAS), known for its good resistance to high temperatures, did not decrease with the WBP substitution. The reduction in strength of both mortars after 900 °C was approximately 86%. No excessive changes were observed in the visual appearance and the compressive strength of the mortars after 3 months of exposure to magnesium sulfate. Microstructure analyses also revealed that WBP substitution had a limited effect on the high temperature and sulfate resistance of AAS.

Macro-mesoscopic mechanical properties and damage progression of cemented tailings backfill under cyclic static load disturbance

Frequent mining stress disturbances in deep-earth resource extraction lead to different degrees of initial damage within cemented tailings backfill (CTB), which in turn changes the structural characteristics of the matrix and significantly affects the stability of CTB. To simulate the stress disturbance process of CTB during mining activities more realistically, cyclic loading and unloading disturbances were performed on the CTB. The stress disturbance levels (SDL) were 20, 40, 60, and 80% uniaxial compressive strength (UCS), and the stress disturbance counts (SDC) were 5, 10, 15, and 20 times, respectively. Subsequently, a series of experimental studies were conducted on CTB and disturbed damage CTB (DCTB) using UCS, nuclear magnetic resonance, ultrasonic pulse velocity (UPV) testing, and acoustic emission (AE) monitoring. The results show that the UCS of the backfill decreased with increasing SDL and SDC, except for 20% SDL and 5th SDC. The elastic modulus exhibited a rise at 20%–40% SDL and a fall at 60%–80% SDL. Compared with CTB, the stress–strain curve of DCTB showed a left shift - overlap - right shift - accelerated right shift change in the compacting stage with increasing SDL. Moreover, the porosity and UPV reflected by the mesoscopic structure correspond to the trend of UCS. The correlation mechanism between mesoscopic structure and macroscopic strength was determined, and the initial damage degree of DCTB was defined in terms of the average variation characteristics of macro-mesoscopic parameters. According to the AE monitoring results, it was observed that increasing SDL and SDC led to a significant increase in the AE energy active stage during loading. The damage curve established from the AE energy considering the initial damage degree rose exponentially. As the initial damage degree intensified, a noticeable and wide-range drop in the b-value before the peak was observed, indicating the occurrence of frequent large-scale fracture activities within the DCTB. Also, the damage degree of DCTB intensified, the collapse zone increased, and the failure mode of the backfill transformed from tensile to mixed tensile-shear damage. The research results can provide theoretical support and a reference basis for the stability analysis and strength design of the backfill under the action of mining stress.

An experimental study on the usage of silica fume in bacterial concrete

This paper shows the bacteria’s (Bacillus Megaterium) effect on the high-strength silica fume concrete made with M−sand. Various tests like split tensile strength, compressive strength test, RCPT, and ultrasonic pulse velocity test have been carried out. The concentration of bacteria was optimized and eight concrete mixes were designed. While making different concrete mixes the cement has been substituted with 10%, 15%, and 20% of silica fume by weight, with and without bacillus megaterium solution of 105 cfu/ml optimum concentration also used. Results indicated that the incorporation of bacillus megaterium in high-strength concrete enhances the split tensile strength, compressive strength, and ultrasonic pulse velocity and reduces the rapid chloride permeability and water absorption. The strength improvement and depletion in chloride permeability may have been due to the deposition of CaCO3 produced by bacteria in concrete pores. XRD confirms the engagement of bacillus megaterium in CaCO3 precipitation. The durability tests of specimens using H2SO4 and NaCl solutions will show the effectiveness of bacterial concrete using silica fume and M−Sand in Marine environments. The modelling of strength properties of different mixes is quantitatively correlated with Regression analysis.

Petrographic and Geotechnical Features of Dir Volcanics as Dimension Stone, Upper Dir, North Pakistan

The utilization of dimension stone in construction has been prevalent since ancient times; however, its application in modern construction has gained significant attention over the last few decades. This research aimed to assess the physical and strength properties of volcanic rocks from the Kohistan Island Arc for their potential use as dimension stone. Five types of andesites (MMA, PMA-1, PMA-2, CMA, and FMA) and two types of agglomerates (AG-1 and AG-2) were identified based on their composition, color, and texture. The samples were characterized in terms of their petrography (compositional and textural), physical properties (specific gravity, water absorption, and porosity), and strength properties (unconfined compressive strength and unconfined tensile strength). Two non-destructive tests (ultrasonic pulse velocity test and Schmidt hammer) were conducted, and the degree of polishing was evaluated. Correlation analyses were carried out to establish possible relationships among these parameters. The presence of chlorite, epidote, sericite, and recrystallized quartz indicated signs of low-grade metamorphism in andesites. The study revealed that feldspar, amphibole, and quartz imparted good physical and strength properties to samples MMA, CMA, FMA, AG1, and AG2. On the other hand, PMA-1 and PMA-2 exhibited reduced physical and strength properties due to the abundance of alteration products like chlorite, sericite, and epidote. The unconfined compressive strength exhibited a strong correlation with ultrasonic pulse velocity, skeletal density, porosity, and water absorption. Weathering grade considerably affected the values of ultrasonic pulse velocity and Schmidt hammer. Consequently, samples PMA-1 and PMA-2 are not recommended for load-bearing masonry units and outdoor applications due to their high water absorption and low strength values. On the other hand, samples FMA and MMA exhibited excellent properties like high strength and good polishing, indicating their potential use as decorative and facing stones, external pavement, ashlar, rubbles, and load-bearing masonry units.

Mechanical characterisation of adobe samples from the state of Morelos, Mexico

Properties of adobe are highly dependent on the local soil composition and can vary significantly depending on fabrication techniques, configurations and state of conservation. The effect of the earthquakes that occurred in 2017 in Mexico relaunched discussion regarding the adequacy and safety of adobe-based constructions – a debate that involves many economic, cultural and social facets related to vernacular expressions and ways of life, long-term sustainability and risk management. In an effort to contribute to this, this paper includes and discusses a series of experiments carried out in typologically representative adobe constructions in the municipality of Tepoztlán (state of Morelos, Mexico). A campaign of ultrasonic pulse velocity tests was conducted on 13 historical buildings with the objective of assessing the variability of the adobe material present in those buildings. Some adobe units were then collected and tested in a laboratory to assess their compressive strength and stress/strain behaviour. From these two sets of experiments, it was possible to obtain valuable insights into the mechanical properties of the adobe that constitutes the characteristic housing typology in the region.

Assessing the performance of concrete made with recycled latex gloves and silicone catheter using ultrasonic pulse velocity

Significant advances in concrete technology in modern times have prompted the search for environmentally friendly materials that could improve the properties of concrete. The inclusion of recyclable materials to conventional concrete can help in conserving key resources and produce environmentally friendly concrete. The incorporation of latex gloves and silicone catheter waste in concrete is one of the most important approaches to minimize the environmental problems associated with their disposal. In this study, an experiment was conducted to evaluate the effects of using latex gloves and silicone catheter waste as a substitute for coarse aggregates in concrete mixes. Concrete which was made with latex gloves and silicone catheter waste were subjected to UPV evaluations, i.e., ultrasonic pulse velocity tests at 28 curing days. Compressive strength and workability tests were also performed for reference and compared to the replacement sample. The inclusion of latex gloves and silicone catheter waste in proportions of 2.5%, 5%, 7.5 and 10% decreased the UPV values of the concrete. The results showed that the UPV values of the concrete decreased significantly from excellent to very good to poor for all specimens as the proportion of silicone catheters and latex gloves increased. The results showed that the addition of different proportions of latex gloves and silicone catheters decreased the compressive strength of the concrete by 86% and 59%, respectively, when the proportion of latex gloves and silicone catheters in the concrete mix was replaced by 10%. In addition, the fresh concrete property of concrete containing latex gloves and silicone catheters was decreased by 22% and 53%, respectively, when the proportion of latex gloves and silicone catheters was replaced by 10%. This study helps to raise environmental awareness by improving understanding of the waste generated and the importance of reusing waste as a substitute in concrete mixes.

Mechanical and durability studies on fly ash based fibre reinforced concrete

The purpose of this study is to determine the fresh and hardened properties of fibre reinforced concrete along with durability properties with steel fibres (SF) and jute fibres (JF). This study presents properties of concrete prepared with Fly ash (FA) as a partial replacement to Ordinary Portland Cement along with the fibres. Concrete mix of M30 grade was prepared as per IS code guidelines. The specimens were prepared with 5, 10, 15 and 20 % Fly ash replacements along with 0.5, 1.0, 1.5 and 2.0 % Steel and Jute fibre replacements with respect to the binder. For comparison, control concrete mix corresponding to M30 grade was prepared with 0% FA and 0% fibres. Variation in workability with the addition of fibres was determined with the help of slump cone test. Various mechanical strength tests were conducted on the specimens to observe that the strength was enhanced due to addition of fibres. Ultra-sonic pulse velocity test was conducted to determine the strength of prepared specimens in non-destructive way and compared with destructive compression strength values. Durability tests - Carbonation, Acid attack, Sorptivity and Rapid chloride ion penetration tests were conducted to determine the optimum percentage of fibre replacement along with fly ash replacement for long term durability. According to the experimental results, adding 15% fly ash and 1.5% fibres enhanced the mechanical properties, whereas adding 10 and 15% fly ash, 1.5 and 2.0% fibres enhanced the durability properties in comparison with the properties of conventional concrete. This paves the way for developing sustainable alternatives in the construction industry by utilization of marginal materials such as fly ash and jute fibres.

Corrosion inhibitors for enhanced strength, durability, and microstructure of coastal concrete structures

The prevalence of catastrophic structural member failure caused by steel corrosion in civil infrastructure underscores the importance of reducing reinforcement corrosion to enhance overall infrastructure costs, reliability, and sustainable development. The present research investigates the potential of corrosion inhibitors to enhance the durability and strength of concrete structures, with a focus on their long-term effectiveness in resisting corrosion in reinforced concrete structures. Multiple approaches such as inhibitors, repairing processes, and coatings have been explored to prevent concrete corrosion damage, with an emphasis on concrete corrosion performance in coastal and corrosive situations. This study investigates the effect of six different corrosion inhibitors (zinc oxide, magnesium oxide, urea, sodium nitrate, sodium molybdate, and diethyl ether) on the compressive strength and durability of concrete samples. The compressive strength is assessed using both destructive (28 days cube compressive strength) and non-destructive (Ultrasonic Pulse Velocity) test methods, while concrete durability is evaluated using the rapid chloride permeability test (RCPT). The compressive strength of the admixture incorporated samples are found to be higher than the control sample by almost 50% and above with excellent concrete quality. The RCPT values of inhibitor-incorporated samples are moderate and low with control samples having high permeability even in adverse conditions of freezing, thawing, and deicing. The samples incorporated with inhibitors also show less negative half-cell potential which is 1.43 times less than that of the control sample indicating the lesser probability of occurrence of corrosion. SEM imaging is also conducted to analyze the microstructure of each mix. The findings of this study highlight the importance of inhibitors in enhancing the durability of reinforced concrete structures.

Effect of Activator Concentrations on the Postfire Impact Behavior of Alkali-Activated Slag Concrete

Changing concrete ingredients significantly affects its performance due to changing the type of hydration products formed. The stability of these hydration products will dominate concrete impact behavior before and after exposure to fire. Limited research had explored the role of activators, as the main ingredient of alkali-activated slag concrete (AASC), on impact performance. Hence, this study highlights the effects of activator characteristics on the impact behavior of AASC at an ambient condition (23°C) and after exposure to elevated temperatures (200°C, 400°C, and 600°C). Conventional ordinary portland cement (OPC) concrete was also tested for general performance comparison. Besides the drop weight impact test, compressive and indirect splitting tensile strength, shrinkage, ultrasonic pulse velocity and water absorption tests were conducted to evaluate AASC performance. In addition, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to confirm and analyze findings. Results confirmed the better impact performance of AASC compared to OPC concrete. Activator concentrations showed contrary effects on AASC performance at ambient and elevated temperatures. High activation levels improved strength and impact capacity at ambient temperature, showing lower internal defects and higher hydration product formation. Conversely, lowering the activation level at elevated temperatures was preferable and resulted in a higher residual strength and impact absorption capacity. This was ascribed to the high unreacted slag particle crystallization to akermanite at higher temperatures, leading to strength gain, fewer hydration products to decompose, and high microstructure ductility that accommodated the thermal incompatibility. Hence, designing AASC while focusing only on maximizing strength can be misleading based on the targeted performance and exposure conditions.