Reference Concrete Research Articles

Effect of cenospheres on the proprieties of plain concrete exposed to elevated temperature

AbstractThe main objective of the study was to determine the effect of the use of cenospheres for C30/37 class concretes used in construction and road construction. As part of the research, four concrete mixtures were designed: three with the addition of cenospheres and one reference mixture, without the additive. In the three modified mixtures, 20, 40 and 60% of fine aggregate were replaced by cenospheres, respectively. Selected features of the mixtures were determined—consistency and density, as well as the strength properties of concrete. Strength tests were carried out after 28 and 56 days of maturation. Experimental tests of concrete after initial thermal treatment were also carried out at three selected temperatures: 300, 500 and 700 °C, with loading times ranging from 60 to 180 min. These times were selected in such a way that the samples could be heated in their entire volume. A separate group of experimental studies was microstructure studies, the aim of which was to assess the changes occurring in concrete under the influence of high temperatures and to try to justify why CS-I concrete containing cenospheres in the amount of 20% of concrete subjected to annealing at 300 °C has a higher compressive strength than the corresponding reference concrete. The negative influence of cenospheres on the strength of concrete after initial thermal treatment was unequivocally demonstrated. An increase in the amount of cenospheres causes a decrease in compressive strength. A similar negative relationship was also demonstrated in the case of non-heat-treated samples. Graphical Abstract

Comparison of fracture behavior of set concretes based on natural and crushed aggregates

Abstract The studies were carried out to diagnose the effects of coarse aggregate type on the mechanical behavior of plain concretes under incremental loading. During the studies mechanical parameters including compressive strength (fcm) and splitting tensile strength (fctm), as well as fracture parameters involving critical stress intensity factor (K_Ic^S) and critical crack tip opening displacement (CTODc) were evaluated. Crushed aggregates covered: basalt (BA), granite (GT) and limestone (LM) and natural peeble gravel aggregate (GL) were used in the concrete mixtures. The composite made on pebble aggregate acted as a reference concrete, as it were, in the analysis of the test results. For better understanding of the crack initiation and propagation in concretes with different coarse aggregates, a macroscopic failure surfaces examination of the tested beams is also presented. Both of the analyzed fracture mechanics parameters, i.e. 〖 K〗_Ic^S and CTODc increased significantly in the case of concretes which were manufactured based on crushed aggregates. They amounted in comparison to concrete based on gravel aggregate at levels ranging from 20% for concrete with limestone aggregate, to over 30% for concrete with a granite aggregate, and to as much as over 70% for concrete with basalt aggregate. Moreover, a clear correlation in the changes in the obtained results between the main strength parameters and fracture mechanics parameters was observed. The fracture process in each series of concrete was: quasi-plastic in the case of gravel concrete, semi-brittle in the case of limestone concrete, and clearly brittle in the case of the concretes based on granite and basalt aggregate. The results obtained help to explain how the coarse aggregate type affects the strength parameters and fracture toughness at bending.

Thermomechanical properties and microstructure of concrete made with recycled concrete aggregates after exposure to high temperatures

AbstractUsing recycled concrete aggregates (RCA) in concrete has emerged as a promising solution to produce concrete with reduced environmental impact and adequate performance. However, a deeper understanding of the thermal and mechanical behavior of concrete made with RCA is still needed for further application in real structures. The present paper addresses one of the crucial issues for structural concrete: its behavior after exposure to high temperature. Four concrete mixes are studied: a reference concrete made with natural aggregates (NA), two concretes including 40% and 100% of coarse RCA as a direct replacement (DR) for coarse NA, and a concrete made with 100% of coarse RCA relying on a strength‐based replacement (SBR). The SBR concrete mix was designed to achieve the same performance (28 days compressive strength and slump) as the reference concrete. All specimens were exposed to temperatures of 200, 400, and 600°C. After cooling, samples were evaluated for residual mass loss, thermal, and mechanical properties. Microstructural quantitative analyses were conducted over several square millimeters to show that interfaces between the old and new cement pastes, peculiar to concrete made with RCA, do not further promote fracture development. The results show that after exposure to high temperatures, the thermal and mechanical performances of concrete made with RCA are reduced in the same manner and extent as in concrete made with NA. When the RCA‐based concrete is designed to achieve similar performance as concrete with NA at room temperature (SBR), the residual thermomechanical behavior is similar between both concretes.

Modification of the polymeric admixture based on polycarboxylate ether using silica-derived secondary materials obtained from fly ash and the efficiency of its application in concrete

The rising energy prices and the costs of CO2 emissions into the atmosphere are forcing the construction industry to search for ways to reduce cement consumption in concrete technology by optimizing concrete mixtures and making greater use of chemical admixtures. The scientific problem lies in understanding how polymers modified with silica-derived secondary materials, such as those obtained from fly ash (e.g., synthetic zeolites, mesoporous silica), interact with the concrete matrix and influence their durability and strength. The present study investigated the effect of a polymeric admixture based on polycarboxylic ether (PCE) modified with silica-derived secondary materials obtained from fly ash (synthetic zeolites, mesoporous silica) on the physical and mechanical properties of concrete. The study considered the effect of the modified polymer admixture dosed in 3 different amounts (0.4%, 0.8% and 1.2%) by weight of cement on the fresh properties of the concrete mixture, i.e. consistency and air content. The research scope also included determining the physico-mechanical properties of the concretes and investigating the effect of the modified admixture on the frost durability of the cement composite. In order to study the modification of the concrete microstructure, XRD phase analysis and air pore structure analysis by MIP were carried out. The study showed an increase in compressive strength after 28 days of curing in concretes containing the modified polymer of about 8-12% compared to the reference concrete. In addition, it was observed that strength increased with increasing admixture dosage. The resulting pore structure, contributed to improving the frost resistance of the concretes by reducing compressive strength loss from about 14% in reference concretes to about 2-9% in concretes with the modified polymer after 150 cycles of alternating freeze-thaw. At the same time, it was observed that the use of the modified polymer resulted in an increase in weight absorption from 2% do 4.5%, a more than twofold increase in depth of penetration of water under pressure and a more than 70% increased total porosity. In conclusion, the polymer-modified MCM-41 can positively affect the mechanical and durability properties of concrete, but it causes a change in the pore structure, which could have a negative effect on water absorption and total porosity.

Recycling of Brick and Road Demolition Waste in the Production of Concrete

Construction and public works sites generate a significant amount of waste that is often costly to dispose of. To reduce the environmental impact and promote sustainability, recycling and recovering this waste is increasingly being recognized as a viable solution. This paper presents the findings of an experimental program investigating the feasibility of using brick and road demolition waste as concrete components. By substituting a portion of sand and cement with recycled materials, this study compares the properties of the reference concrete with concrete containing varying amounts of brick waste and road demolition debris. The obtained results demonstrate that the produced concrete with up to 40 % recycled content achieved a compressive strength exceeding 20 MPa after 28 days. This study suggests that recycled brick and road demolition waste could be a sustainable and economical substitute for conventional aggregates. Incorporating these materials into concrete reduces the cement content while maintaining or even improving the fresh and hardened properties of the concrete. However, it is crucial to limit the use of road demolition sand to 10 %, crushed brick fines to 20%, and brick sand (CBS) to 30% to ensure optimal performance.

Challenges of a Circular Economy: The Example of Raw Recycled Tyre Steel Fibres Added to Concrete.

This research was conducted to analyse the possibility of using raw, untreated recycled tyre fibres as an effective concrete reinforcement according to circular economy principles. The aim of the article was also to develop a method for dispensing tire fibres on a real scale. Additional treatment and homogenisation of recycled steel fibres entail higher energy consumption, emissions of greenhouse gases, and increased costs. However, obtaining durable and safe concrete effectively reinforced with steel fibres is critical. Finding a balance between environmental friendliness and product durability is a circular economic challenge. Reference concrete with commercial steel fibres (15 kg/m3) and two concretes containing various quantities of non-treated, raw tyre recycled fibres (25 kg/m3 and 45 kg/m3) were industrially produced. Tests were carried out on the properties of the concrete mixture and hardened concrete, such as compressive strength, flexural strength, splitting strength, modulus of elasticity, residual flexural tensile strength, and fibre distribution in concrete. Tests revealed that increasing the amount of raw tyre fibres disturbs the structure and causes air entrainment and the formation of fibre clusters. Smaller quantities of raw tyre fibres turn out an effective concrete reinforcement. The use of non-treated tyre fibres as concrete reinforcement is possible but requires more stringent control of the concrete parameters. Implementation tests on an industrial scale are a novelty in this study, presenting an analysis of the possible dispensing of tyre fibres in a ready-mixed concrete production plant and testing the characteristics of manufactured concrete.

Impact of Rubber Content on Performance of Ultra-High-Performance Rubberised Concrete (UHPRuC)

This study investigated the effect of rubber content on the mechanical characteristics of ultra-high-performance rubberised concrete (UHPRuC). The results revealed a distinctive non-linear decrease in the dry density of UHPRuC as the rubber content increased. Notably, lower rubber content led to a columnar failure mode, while higher content (≥ 20%) exhibited a mixed failure mode with vertical cracking and diagonal fracture. Importantly, the compressive strength showed minimal reduction compared to conventional concrete, presenting a remarkable 50% mitigation of strength reduction compared to previous studies. Utilising reference concrete with robust bond strength proved highly effective in preserving strength in rubberized concrete. Despite its effectiveness in mitigating compressive strength reduction, UHPC could not effectively offset flexural strength loss, which ranged from 1.5 to 3 times that of compressive strength loss. The addition of rubber aggregate in UHPC reduced the peak flexural strength, residual strength, and flexural toughness at a similar rate, while significantly increasing the vibration decaying rate. Incorporating 40% rubber in UHPRuC reduced the eCO2 up to 37%. Our findings emphasise the importance of reference concrete with good bond strength and shows that the addition of rubber aggregate in UHPC leads to reductions in strength but increases the energy-dissipating capacity.

Geothermal Nano-SiO2 Waste as a Supplementary Cementitious Material for Concrete Exposed at High Critical Temperatures.

The partial replacement effect of Portland cement by geothermal nano-SiO2 waste (GNSW) for sustainable Portland-cement-based concrete was investigated to improve the properties of concrete exposed at high critical temperatures. Portland cement was partially replaced by 20 and 30 wt.% of GNSW. The partial replacement effect on Portland-cement-based concrete subjected to 350, 550, and 750 °C was evaluated by measuring the weight changes, ultrasonic pulse velocity, thermogravimetric and differential thermal analysis, X-ray diffraction, surface inspection, and scanning electron microscopy under residual conditions. The ultrasonic pulse velocity results showed that the GNSW specimens maintained suitable stability after being heated to 350 °C. The SEM analysis revealed a denser microstructure for the 20 wt.% of partial replacement of Portland cement by GNSW specimen compared to the reference concrete when exposed to temperatures up to 400 °C, maintaining stability in its microstructure. The weight losses were higher for the specimens with partial replacements of GNSW than the reference concrete at 550 °C, which can be attributed to the pozzolanic activity presented by the GNSW, which increases the amounts of CSH gel, leading to a much denser cementitious matrix, causing a higher weight loss compared to the reference concrete. GNSW is a viable supplementary cementitious material, enhancing thermal properties up to 400 °C due to its high pozzolanic activity and filler effect while offering environmental benefits by reducing industrial waste.

Toxicological Effects of Leachates Extracted from Photocatalytic Concrete Blocks with Nano-TiO2 on Daphnia magna.

The incorporation of titanium dioxide nanoparticles into concrete blocks for paving adds photocatalytic functionality to the cementitious matrix, providing self-cleaning and pollutant-degrading properties. However, wear and leaching from these pavements can release potentially toxic compounds into water bodies, affecting aquatic organisms. In this context, this study evaluated the toxicological effects of leachates from photocatalytic concrete containing nano-TiO2 with an average size of 10 nm and anatase crystallinity on Daphnia magna. Acute and chronic toxicity tests on neonates were conducted with two leachate extracts: one from reference concrete and one from photocatalytic concrete (with 9% nano-TiO2 added by mass of cement). In terms of acute toxicity, the reference concrete extract had an EC50 of 104.0 mL/L at 48 h, whereas the concrete with TiO2 had an EC50 of 64.6 mL/L at 48 h. For chronic toxicity, the leachate from reference concrete had a significant effect (p < 0.05) on the size parameter with an LOEC of 4 mL/L, whereas the leachate from concrete with 9% nano-TiO2 did not have significant toxicological effects on any of the analyzed parameters (longevity, size, reproduction, and age of first posture) (LOEC > 6.5 mL/L). Furthermore, FTIR analysis indicated that TiO2 nanoparticles were not detected in the leachates, suggesting efficient anchoring within the cementitious matrix. The results indicate that there was no increase in the chronic toxicity of the leachate from the cementitious matrix when nanoparticles were added at a 9% mass ratio of cement.

Evaluating the use of harvested fly ash as a sustainable alternative in cementitious mixtures

This study investigated the feasibility of utilizing harvested fly ash from landfills and ponds as a sustainable alternative to traditional fly ash in cementitious mixtures. The research examined the fresh properties, compressive strength, dimensional stability, transport properties, alkali-silica reaction, and sulfate resistance of pastes, mortars, and concretes made with traditional class F fly ash (TFA) and two sources of class F harvested fly ash (HFA1 & HFA2). The results showed that the cementitious mixtures containing both traditional and harvested fly ash consistently exhibited superior performance across all properties compared to the reference mixture. Amongst the fly ash samples, the mixtures containing traditional fly ash (TFA) demonstrated the best performance, followed by HFA1 and HFA2.At 28 days, reference mortar showed 8–39 % higher compressive strength than fly ash mortars, while TFA-15, HFA1–15, and HFA2–15 mortars surpassed the reference strength by over 10 % at 90 days. TFA-15 mortar showed drying shrinkage of 259 microstrains, which was 10 % and 13.7 % lower than HFA1 and HFA2, respectively. At 30 % replacement, TFA’s shrinkage was 19 % and 26.4 % lower than HFA1 and HFA2. Water absorption in TFA, HFA1, and HFA2 mortars at 15 % replacement was 52 %, 41 %, and 21 % lower than the reference (C100) at 28 days. At 90 days, TFA-15 exhibited 44–49 % and TFA-30 showed 35–27 % reductions in water absorption before and after boiling, respectively, compared to 28 days. For resistance to chloride ingress, TFA, HFA1, and HFA2 concretes at 15 % replacement showed 228 %, 133 %, and 119 % higher resistance compared to C100, respectively. At 30 % replacement, TFA showed 142 % higher resistance, while HFA1 and HFA2 showed 39 % and 30 % higher resistance, respectively. In terms of sulfate resistance (SR) at 28 days, fly ash-containing concrete at 15 % cement substitution showed over 100 % higher SR than the reference concrete (C100). TFA-15 exhibited 26 % and 48 % higher SR than HFA1–15 and HFA2–15, while TFA-30 showed 35 % and 74 % higher SR than HFA1–30 and HFA2–30, respectively. In alkali-silica reaction tests, TFA-20 and HFA1–20 mortars reduced 14-day expansion by 86 % and 83 % below the 0.1 % threshold, and by 84 % and 76 % at 28 days, respectively, staying below the 0.28 % failure limit. TFA-15 reduced expansion by over 34 % and 40 % compared to HFA1–15 and HFA2–15 at 28 days, and by 55 % and 49 % at 30 % replacement.

Mechanical and physical characteristics of concrete mixed with sugarcane bagasse ash and recycled polyethylene terephthalate

The goal of this study was to produce sustainable concrete by reducing reliance on cement, which contributes to high carbon footprints, and natural sand, which is being depleted. Sugarcane bagasse ash (SCBA) was used to partially replace cement at 5 %, 10 %, and 15 %, while recycled polyethylene terephthalate (RPET) was used to partially replace sand at 5 %, 10 %, 15 %, and 20 %. The effects of these substitutions on concrete's mechanical and physical properties were examined after 28 days of water curing. The study observed a decrease in fresh density by 0.36 %–2.67 % with SCBA and RPET inclusion. The slump values ranged between 93 mm and 140 mm, indicating good workability. The reference concrete's compressive strength was 39.65 MPa, while the mix with 5 % SCBA and 10 % RPET achieved 38.23 MPa. This mix also showed a 1.2 % higher split tensile strength than the reference concrete. Although the reference concrete's flexural strength was the highest at 4.56 MPa, all SCBA-RPET mixes remained within 86 % of this value. All modified mixes weighed less than the reference concrete, with the compressive strength-to-weight ratio of the mix with 5 % SCBA and 10 % RPET being closest to the reference mix with only a 2.44 % reduction. These findings suggest that SCBA and RPET can be effectively used to produce sustainable concrete with comparable mechanical properties to conventional concrete.

Using crushed stone dust as a substitute for fine aggregates in concrete

Generation of waste from mining and high consumption of natural aggregates resulting from civil construction works have significant economic and environmental impacts. Aiming to use the stone dust residue from the rock crushing process, this study experimentally evaluates the use of crushed stone dust as a partial substitute for fine aggregates in concrete with a compressive strength of 30 MPa, thus providing an alternative in civil construction activities. Crushed stone dust was evaluated through physical, chemical, mineralogical, petrographic, and micromorphological characterization tests. The characterization results indicated that the material is classified as medium and fine sand, with 68.2% silicon dioxide and quartz peaks, i.e., similar to natural sand. Axial compression tests were performed on twenty cylindrical specimens with diameters of 100 mm and heights of 200 mm, broken at 28 days. Five of such specimens were made of reference concrete, without stone dust, while fifteen contained concretes with stone dust. In this approach, the percentage of stone dust in the concrete specimens ranged between 20%, 50%, and 100%, and compressive strength was kept constant at 30 MPa, with five cylinders with stone dust for each percentage of sand replacement. The results show the contribution of stone dust to the mechanical behavior of the concrete specimens, which corroborate the possibility of applying it as a substitute for fine aggregates, as compressive strength was higher in the concrete specimens with 20% and 50% stone dust compared to the reference concrete.

Determination of Fracture Mechanic Parameters of Concretes Based on Cement Matrix Enhanced by Fly Ash and Nano-Silica.

This study presents test results and deep discussion regarding measurements of the fracture toughness of new concrete composites based on ternary blended cements (TCs). A composition of the most commonly used mineral additive (i.e., fly ash (FA)) in combination with nano-silica (NS) has been proposed as a partial replacement of the ordinary Portland cement (OPC) binder. The novelty of this article is related to the fact that ordinary concretes with FA + NS additives are most often used in construction practice, and there is a decided lack of fracture toughness test results concerning these materials. Therefore, in order to fill this gap in the literature, an extensive evaluation of the fracture mechanic parameters of TC was carried out. Four series of concretes were created, one of which was the reference concrete (REF), and the remaining three were TCs. The effect of a constant content of 5% NS and various FA contents, such as 0, 15%, and 25% wt., as a partial replacement of cement was studied. The parameters of the linear and nonlinear fracture mechanics were analyzed in this study (i.e., the critical stress intensity factor (KIcS), critical crack tip opening displacement (CTODc), and critical unit work of failure (JIc)). In addition, the main mechanical parameters (i.e., the compressive strength (fcm) and splitting tensile strength (fctm)) were evaluated. Based on the studies, it was found that the addition of 5% NS without FA increased the strength and fracture parameters of the concrete by approximately 20%. On the other hand, supplementing the composition of the binder with 5% NS in combination with the 15% FA additive caused an increase in all mechanical parameters by approximately another 20%. However, an increase in the FA content in the concrete mix of another 10% caused a smaller increase in all analyzed factors (i.e., by approximately 10%) compared with a composite with the addition of the NS modifier only. In addition, from an ecological point of view, by utilizing fine waste FA particles combined with extremely fine particles of NS to produce ordinary concretes, the demand for OPC can be reduced, thereby lowering CO2 emissions. Hence, the findings of this research hold practical importance for the future application of such materials in the development of green concretes.

Sustainability-driven application of waste steel and tyre rubber fibres as reinforcement in concrete: An optimization study using response surface methodology

Innovative use of waste materials has proven to be effective for improving concrete’s technical properties while eliminating the threat of environmental pollution. There is paucity of research regarding the combined use of Waste Steel Fibres (WSFs) and Waste Tire Rubber Fibres (WTRFs) in concrete. Thus, this study aimed to investigate the influence of WSFs and WTRFs as reinforcement in concrete and determine their optimal fractions for enhancing the concrete strength properties using Response Surface Methodology (RSM). WSFs of 0.3-1.5% with a 0.6% increment and WTRFs of 0.3-1.5% with a 0.6% increment by concrete volume as reinforcement in concrete with water-to-cement ratio (W/C) of 0.25–0.65 with 0.2 increment were designed using the Box-Behnken Design of RSM. A total of fourteen (14) concrete mixes with a design strength of 25 N/mm2 were prepared. The fresh and hardened properties (slump, density, water absorption, 7- and 28-day compressive and split tensile strengths) of concrete were determined using standard procedures. The RSM was used to evaluate the interaction between the concrete variables and identify their optimum combination which gave the peak values of responses. Furthermore, the characteristics and sustainability of the concrete under optimum variables were compared with that of the conventional concrete. The outcomes revealed that the inclusion of WSFs and WTRFs yielded concretes with maximum slump, density, water absorption and 28-day compressive and split tensile strengths of 25 mm, 2633 kg/m3, 5%, 41 N/mm2 and 4.54 N/mm2, respectively. The optimization technique showed the optimal variables combination which yielded the peak response values of WSFs (1.40%), WTRFs (0.66%) and W/C (0.54). The nominal variance with the absolute percent error of less than (9%) between the actual experimental verified results and predicted results for all the responses validates the predictability of the model. The split tensile strength and compressive strength increased by 28.33% and 48.85%, respectively at the optimum setpoint of variable with respect to the reference concrete. In addition, the WSFs and WTRFs-reinforced concrete exhibited lower embodied CO2 emission but the embodied energy and cost are slightly higher relative to conventional concrete. Nevertheless, the embodied energy of the concrete was significantly lesser than that of concrete that used individual fibers for reinforcement. Thus, the enhancement of concrete strength properties with the prospect for sustainable fibre-reinforced concrete production through the use of waste steel and tyre rubber fibres is feasible.

Enhancing concrete’s ballistic impact resistance using Alfa fiber

Natural fibers are gaining interest in recent years due to the increasing calls for eco-friendly materials production. Concrete reinforcement with Alfa fiber is attracting attention to take benefit of natural fiber advantages in the construction sector. The mechanical and physical characteristics of concrete reinforced with Alfa fibers have been primarily investigated. The current study seeks to analyse the ballistic protection performance of Alfa-reinforced concrete in response to the emerging need to withstand bullet impacts and protect occupants in light of the increasing armed hostilities. Eight formulations were selected for the concrete preparation by varying the Alfa fiber content from 0 to 100 kg/m³. After determining the mechanical characteristics of the concrete such as compressive, flexural and tensile strength, ballistic resistance to bullet impacts is determined by measuring the penetration depth, the crater area and the lost mass after impact in concrete slab 10 and 15 cm thick. The formulations of Alfa-reinforced concrete exhibited lower penetration depth, crater area, and lost mass compared to the reference concrete. Optimal values were achieved with 15 kg/m³ of fibers. A dependency between the ballistic response on the fibrous concrete and flexural strength of concrete is also remarked. In conclusion, the study demonstrates that incorporating Alfa fibers into concrete significantly enhances its ballistic resistance, with optimum performance observed at 15 kg/m³ of fiber inclusion. These findings underscore the potential of Alfa-reinforced concrete for use in military constructions and structures vulnerable to impact risks, paving the way for further research and practical applications in enhancing structural and occupant safety.

Mechanical and microstructural characterization of sustainable concrete containing recycled concrete and waste rubber tire fiber

The production of cement, which is the key ingredient of concrete, leads to environmental pollution by releasing massive amounts of CO2 and using significant natural resources. Therefore, shifting towards sustainable and greener materials is essential for mitigating these challenges. In this study, recycled concrete powder (RCP) was used as a cement replacement (0%, 5.0%, 10%, and 15%), solving the waste dumps issue and promoting sustainability. Furthermore, the concrete is also reinforced with steel fibers which were obtained from waste rubber tires to improve concrete tensile strength. The concrete properties were evaluated through slump cone test, compressive strength, failure patterns, tensile strength, scanning electronic microscopy, and FTIR analysis. The results indicate that the concrete strength properties improved with the substitution of RCP. The compressive and tensile strength of the optimum mix (10% RCP and 2.0% addition of steel fibers) are 15.8% and 23% more than those of reference concrete. However, the concrete flow is adversely impacted due to RCP angular particle shapes. Failure patterns indicate that RCP and steel fibers improved concrete ductility. SEM and FTIR analysis indicate microstructural improvement with RCP and steel fibers. Finally, the analysis concluded that the developed concrete showed better performance, solved waste dumps issues, and promoted sustainability.

Combined effect of supplementary cementitious materials and hot-dipped galvanized steel on performance of reinforced concretes subjected to chloride-induced corrosion

Concrete specimens with three types of cement (sulfate resistant high early strength – reference, pozzolanic, and with ground granulated blast furnace slag) reinforced with two types of steel (galvanized and carbon steel) were subjected to cycles of immersion in 1.0 M NaCl solution and drying at 40ºC. For each different steel-concrete condition, 6 rebars were tested. Experimental results show that galvanized steel presents longer corrosion initiation periods in concretes with supplementary cementitious materials. Particularly for pozzolanic concrete, this increased initiation period was 4.6 times longer on average, which reflects, in a similar way, on service-life simulations. In general, the average chloride thresholds of galvanized steel increased with a decrease in pore solution alkalinity. Compared to carbon steel, higher chloride thresholds were found for galvanized steel embedded in the lower alkalinity concrete matrix (calculated pore pH = 12.6). On the other hand, galvanized steel presented lower chloride thresholds for more alkaline pore pHs (pozzolanic and reference concretes).

Concrete with Accelerated Naturally Carbonated Recycled Concrete Aggregates

Recycled concrete tends to be increasingly investigated with respect to the environmental needs, such as resource depletion, circularity and lack of landfill disposal spaces. A naturally accelerated carbonation procedure by using atmospheric CO2 concentration level and a cyclic wetting and drying of the recycled concrete aggregates was applied. A two stages carbonation process was applied. The recycled concretes exhibited similar mechanical properties of the reference concrete or even better durability as compared to the reference concrete prepared with natural rock aggregates. The carbonation of the outer layer of the recycled concrete aggregates was achieved with a simple method that can be widely applied and is sufficient to significantly increase the properties of the recycled concrete aggregates.

Impacts of corrosion inhibiting admixture and supplementary cementitious material on early strength concrete

This research aimed to evaluate the influence of alccofine 1203 on a mineral admixture and sodium nitrite as a corrosion inhibitor on the properties of concrete. To achieve these aims, an experimental investigation was carried out on a set of composite samples comprising five distinct concrete formulations. Five different mixes for the concrete were used as the overlay materials such as NC as a reference concrete, alccofine concrete (i.e. 25% cement replaced with alccofine), and alccofine concrete with varying dosages of sodium nitrite (i.e. 1%, 1.25%, and 1.5%). Alccofine reduced the workability and water absorption and increased the compressive strength of the concrete (5%) at curing age of 28 days. Adding sodium nitrite further reduced water absorption of the concrete and workability but compressive strength of 29.15% and 26.93% for the curing period of 3 and 7 days, respectively. The pH of the concrete powdered solution became more alkaline with the replacement of alccofine and addition of sodium nitrite. Free chloride content dropped by 48 and 66%, respectively, with the introduction of GGBS and sodium nitrite. Corrosion properties of the concrete samples were examined using open circuit potentials and linear polarization resistance of various concrete mixes after being immersed in 1 M H2SO4 and 3% NaCl environment. The findings indicated a notable improvement in the corrosion resistance, water absorption test, thermal conductivity, strength properties, and microstructural properties of concrete with the incorporation of SN in combination with alccofine. The application of the response surface method allowed for the prediction, validation, and optimization of experimental data using a regression equation.

Discourse Implementation of “New Sincerity” in Communicative Space of Media

The article represents the peculiarities of “new sincerity” discursive representation in a media text. The research into this phenomenon from sociocultural angle presupposes conducting a multifaceted analysis, in particular, in communicative-and-cognitive and communicative-and-discursive perspectives. It is shown that the willingness of a linguistic personality to share their own thoughts and feelings in the public space is manifested in the generation of media discourse of “new sincerity”. The referential aspects of the “new sincerity” are revealed. The author establishes a repertoire of denotative-identifying reference (concrete, abstract referents, referent event), and a set of subject-marked text reference (emotive, evaluative referents). The explication of “new sincerity” is proved to become a tool of linguistic creative activity, as a result of which discourse scenarios are generated. They are focused on influencing the addressee (explication of personal significance, hypersensitivity). The macrostructural positions of the radio discourse of the “new sincerity” are revealed: lead, detailing, evaluative, emotionally oriented parts. Thematic dominants that form the discursive field of “new sincerity” are identified: “everyday life”, “life’s troubles”, “demonstration of weaknesses, inability”, “personal achievements and failures”, “personal preferences, secrets, qualities, interests, habits”, “fears and phobias”, “desires and dreams”, “details of personal life”. The television and radio discourses are rich in emotionally and personally oriented topics and concepts of sincerity, which leads to a change in the status of sincerity and sensitivity from peripheral phenomena to discourse-forming ones. It determines significant functional, qualitative changes in television and radio discourse.