Neutral Depth Research Articles

Effect of barnacle oyster attachment on concrete properties

In view of the fact that the surface of marine concrete structures is quickly adhered to a large number of barnacles and oysters, and there is still no consensus on the positive and negative effects on concrete structures, this paper studies the evolution of the properties and microstructure of concrete specimens with or without barnacles and oysters adhesion on the surface at different ages in the tidal range area of the exposed sea area, to further clarify the influence of barnacles and oysters adhesion on concrete properties. The study results showed that barnacles and oysters began to adhere to the surface of the specimens after 56 d of exposure, and the maximum chassis diameters of barnacle and oyster increased by 210 % and 229 %. The concrete samples without barnacle and oyster attachment were set as NBO group, and those with barnacle and oyster attachment were set as BO group. The mass change rates of NBO and BO were 1.443 % and -0.493 % after 240 d of exposure. Compared with the initial stage, the compressive strength of NBO increased by about 25.9 %, and the BO increased by 30.1 %. The pH of the NBO sample decreased from 12.0 to 8.0 after 240 d of exposure, and about 143 % of the pH decreased in the BO sample. The neutralization depth of NBO is 7.0 mm, which is about 233 % of the neutralization depth of BO. The 0-50 mm electric flux of the NBO sample from the concrete surface reached 932.8 C, and the BO electric flux was only 556.5 C, while the mass change rate between NBO and BO after 100 freeze-thaw cycles was small. The amount of gypsum and ettringite and the loss of C-S-H gel were more significant than those of BO, making the resistance of NBO 24.3 % lower than that of BO. After 240 d of exposure, the maximum pore volume of NBO is 54.6 % larger than that of BO. Within 240 d of exposure, the attachment of barnacles and oysters positively affected concrete performance.

Acid rain resistance of geopolymer recycled pervious concrete featuring top-bottom interconnected pores under freeze-thaw cycles and fatigue loads

While pervious concrete with top-bottom interconnected pores enhances the performance of pervious concrete pavements, its resistance to acid rain under combined freeze-thaw cycles and fatigue loads remains unexplored. To fill this gap, this study investigated the influence of three different qualities of recycled coarse aggregates on the acid resistance, acid neutralization, and permeability of geopolymer recycled pervious concrete (GRPC) (Low-quality, middle-quality and high-quality geopolymer recycled pervious concrete (L-GRPC, M-GRPC and H-GRPC)) under the couple effects of simulated acid rain wet-dry cycle spraying, fatigue loads and freeze-thaw cycles. After experiencing the combined action of fatigue load and freeze-thaw cycle, only the compressive strength of L-GRPC increased slightly by 9.1 % after acid rain spraying, but it had a negative impact on the flexural strength. With the increase of coupling environmental factors, the neutralization depth of GRPC was less than 4 mm, and the permeability coefficient was higher than 0.5 mm/s. Furthermore, more gypsum crystals were observed in the SEM images, and new peaks corresponded to the gypsum phase (CaSO4) appeared at 2θ = 29.4° and 2θ = 21.6° in the XRD spectra. The research results provide a broader perspective for the application of GRPC in concrete pavement engineering in acid rain area.

Performance of the one-part geopolymer stabilized soft clay under acids attack

The evolution of globalization and rapid industrialization, coupled with intensive human activities, leads to a significant release of acidic gases and particles (e.g., NOX and SO2) is unavoidable. These emissions eventually result in dry and wet acid depositions due to atmospheric circulation. This infiltration of acidic elements alters the chemical properties of water systems, thereby deteriorating ground stability. The economically developed soft clay areas face considerable threats from these acid environmental attacks. This study focused on employing a ''one-part'' geopolymer (OPG) comprising ground granulated blast furnace slag (GGBFS), fly ash (FA), and solid sodium hydroxide (NH) to stabilize the soft clay. Simultaneously, the deterioration behavior of OPG stabilized soft clay under two different acids (HNO3 and H2SO4) with various pH values (pH of 2, 4, and 6) and varied immersion periods up to 240 days was evaluated including the mass loss, neutralization depth (ND), pH value, and unconfined compressive strength (UCS). Additionally, scanning electron microscopy (SEM) and X-ray energy spectrometry (EDS) characterized the evolution of microstructure and hydrate composition of OPG-stabilized soft clay post varied acid immersion. The results highlighted the superior acid resistance of the stabilized soft clay with an 80:20 GGBFS/FA ratio compared to other ratios. The presence of significant hydration products, such as calcium silicate hydrates (C–S–H), calcium aluminate (aluminosilicate) hydrates (C-A-(S)–H), and sodium aluminosilicate hydrates (N-A-S-H), was observed in the OPG stabilized soft clay. In addition, the contents of Si in the OPG played a significant role in enhancing the acid resistance of the OPG stabilized soft clay. Based on these experimental results, two proposed mechanisms detailed the deterioration and acid resistance of the OPG stabilized soft clay under HNO3 and H2SO4 attack. The findings of this study contribute to advancing scientific comprehension concerning the acid resistance of the OPG stabilized soft clay in ground improvement practices.

Study on corrosion characteristics of reinforcing bars in concrete under industrial SO2 environment

Sulfur dioxide (SO2) is the primary pollutant in industrial atmospheres, leading to significant damage to industrial buildings. The corrosion caused by SO2 in concrete, including neutralization and solid phase volume expansion, poses particular concerns. However, there is a lack of research on the electrochemical behaviour and corrosion mechanisms of reinforcing bars embedded in concrete. This study conducted indoor simulations of reinforced concrete specimens exposed to industrial SO2 corrosion utilizing an SO2 testing chamber. The corrosion behavior of the reinforcing bars was monitored through half-cell potential, weak polarization, and electrochemical impedance spectroscopy (EIS). Additionally, the corrosion mechanisms of the reinforcing bars under SO2 exposure were investigated using scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD), and Raman spectra. The results demonstrated a consistent correlation between variations in corrosion potential (Ecorr) and corrosion current density (icorr) of steel rebars in different types of concrete. The corrosion rates of the reinforcing steel in C1 (w/b=0.57), C2 (w/b=0.47), and C3 (w/b=0.37) concrete exceeds 0.1 μA/cm2 after 42, 72, and 90 days of SO2 corrosion, respectively. At this time, the ratio of the depth of neutralization to the thickness of the protective layer is 0.51–0.65. The rust exhibits a layered structure with a presence of S elements adsorbed and deposited on the surface of the rust layer. Moreover, the research has identified the accumulation of S elements within corrosion pits, which can be attributed to localized acidification reactions. The rust products identified include iron hydroxide (FeOOH), and iron oxide (Fe2O3), rozenite (FeSO4·4 H2O). The formation of FeSO4·4 H2O in corrosion pits suggests that significant localized corrosion on the surface of reinforcing bars in concrete under the impact of SO2.

Effect of Curing Mechanism on Sulfuric Acid Corrosion Resistance of Geopolymer Recycled Aggregate Concrete

To explore the effect of curing mechanism on the mechanical properties and sulfuric acid corrosion resistance of the geopolymer recycled aggregate concrete (GRAC), the specimens were cured at high temperature (60°C, 80°C) for 6 h, 24 h and 48 h respectively, and then lasted up to 7 d at room temperature. After the curing period was over, the laboratory accelerated simulation test of specimens was carried out by the periodic immersion method: the GRAC specimens (ϕ 50 × 100 mm) were immersed in the sulfuric acid solution with pH = 1 for 5 d and then dried at room temperature for 24 h, with a total circulation of 90 d. The results showed that after being eroded by sulfuric acid solution, the GRAC specimens cured at 60°C for 48 h had higher compressive strength with 19.9 MPa, lower mass loss rate (only 0.23%) and neutralization depth (5.71 mm) than those under other curing time. The GRAC specimens cured 80°C for 24 h also had a good performance: compressive strength achieved 16.9 MPa and had lower neutralization depth (5.99 mm), which was less affected by sulfuric acid corrosion. However, the GRAC specimens cured at 60°C for 48 h had the better mechanical properties than that cured at 80°C for 24 h. Excessive high temperature curing (80°C) would lead to more voids and microcracks inside GRAC, and destroy the dense structure, thereby reducing mechanical property of concrete. These voids and pores provided more erosion channels for sulfuric acid solution, which accelerated the corrosion rate. From the point of view of energy saving and concrete performance, no more than 60°C of curing temperature is recommended for industrial use.

P445 HEART RATE VARIABILITY AND HYPNOTIC COMMUNICATION

Abstract Background Heart rate variability (HRV) can be influenced by the autonomic nervous system and several studies showed that hypnotic communication could modulate the autonomic nervous system. In particular, HRV is related to the activity of the vagus nerve and an increment of the vagal activation has been associated to an improvement in prognosis. It is, however, unclear whether hypnotic communication could influence HRV. Aim of the study The aim of the present study is to evaluate the impact of hypnotic communication on HRV. Methods Seven volunteer were included in the present study (5 M/2F) from June to August 2022. Each one of the volunteer underwent 1 hour of ECG registration in normal condition, 30 minutes during depth hypnotic communication and 1 hour after the hypnotic communication. The hypnotic communication was performed via 30 minutes of neutral depth hypnosis; the parameter considered for HRV evaluation were sNN50 (dec), SDNN(ms), SDNNi, RMS SD and the triangular index, analyzed throughout the dedicated software Pathfinder SL (V 1.9.3.13414, spacelabs healthcare Ltd 2021, WA, USA). The variation of each parameter was evaluated by Student T test. Results There was no statistically significant variation of sNN50 (dec), SDNN(ms), SDNNi, RMS SD among the normal condition, the hypnotic communication and the post hypnotic communication. There was a statistically significant variation of the triangular index (Fig.1) and of heart rate (Fig. 2). Conclusion Hypnotic communication could increase HRV, assessed as triangular index (the index suggested by European society of cardiology (ESC) and American college of cardiology (ACC) to measure HRV). The absence of a statistically significant variation between the normal condition and hypnotic communication could be explained by the deep modification in the respiratory pattern and heart rate induced by hypnotic communication; those parameter could mask the increment in the vagal activity due to hypnotic communication, that is unmasked in the post–hypnotic period in which the heart rate and the respiratory return to normal value. Further studies are needed to understand whether the increment in HRV due to hypnotic communication could show an improvement in prognosis in cardiopathic patients, as it has been demonstrated for the HRV increment due to muscular training.

Corrosion damage and life prediction of concrete structure in the coking ammonium sulfate workshop of iron and steel industry

Iron and steel plants emit a large amount of CO2 and SO2 in the production process, and the high concentrations of acid gases lead to serious corrosion damage of concrete structures. In this paper, the environmental characteristics and corrosion damage degree of concrete in a 7-year-old coking ammonium sulfate workshop were investigated, and the neutralization life prediction of the concrete structure was carried out. Besides, the corrosion products were analyzed through concrete neutralization simulation test. The average temperature and relative humidity in the workshop were 34.7 °C and 43.4%, and they were 1.40 times higher and 1.70 times less than those of the general atmospheric environment, respectively. Both the concentrations of CO2 and SO2 were significantly different in various sections of the workshop, and they were much higher than those of the general atmospheric environment. The appearance corrosion and compressive strength loss of concrete were more serious in the sections with high SO2 concentration, such as vulcanization bed section and crystallization tank section. The neutralization depth of concrete in the crystallization tank section was the largest, with an average value of 19.86 mm. The corrosion products gypsum and CaCO3 were obviously visible in the surface layer of concrete, while only CaCO3 could be observed at 5 mm. The prediction model of concrete neutralization depth was established, and the remaining neutralization service life in the warehouse, synthesis section (indoor), synthesis section (outdoor), vulcanization bed section, and crystallization tank section were 69.21 a, 52.01 a, 88.56 a, 29.62 a, and 7.84 a, respectively.

Influence of Alkali-Activators on Acid Rain Resistance of Geopolymer-Recycled Pervious Concrete with Optimal Pore Size.

Geopolymer-recycled pervious concrete (GRPC) is a novel concrete that can effectively inhibit the corrosion of acid rain and alleviate urban waterlog. The goal of this study is to ascertain the optimal pore size of GRPC and study its acid rain resistance activated by different alkali-activators. Three different sizes (0.8, 1.0, and 1.2 mm) were separately chosen as the pore diameters of GRPC. The alkali-activator solution adopted sodium hydroxide (NaOH), sodium silicate (Na2SiO3), and a mixture of the two. The mechanical properties and permeability coefficient were tested to determine the optimal pore size of GRPC. After that, specimens with the optimal pore size were immersed in a simulative acid rain solution (sulfuric acid solution with pH = 4.0) for 6 d and were dried 1 d until 56 d. The effects of different alkali activators on acid rain resistance of GRPC were analyzed by compressive strength, neutralization depth, and mass loss. The results manifested that the mechanical properties of GRPC were excellent, the compressive strength of GRPCH+N reached more than 60.1 MPa, and their splitting tensile strength attained more than 5.9 MPa, meeting the strength requirement of the road for heavy traffic load. Considering the mechanical properties and the acid rain purification effect of alkaline GRPC required a relatively small permeability coefficient; the optimal pore size was 1 mm. When specimens with optimal pore size were exposed to acid solution, the corrosion products (gypsums) would block the pores of GRPC to inhibit further corrosion, keeping the stability of the compressive strength. GRPC activated by the mixture of NaOH and Na2SiO3 generated a more stable amorphous three-dimensional network structure, endowing GRPCH+N with better mechanical properties and acid corrosion resistance.

Corrosion behavior of concrete fabricated with lithium slag as corrosion inhibitor under simulated acid rain corrosion action

Concrete has great potential for local applications as a building material. Utilization of lithium slag in concrete can effectively and quickly solve its stacking problem. In this study, we used lithium slag to fabricate concrete and used a self-designed indoor dry-wet cycle spraying equipment to explore its acid rain corrosion resistance properties to promote its resource utilization because acid rain corrosion is very serious in Jiangxi Province. First, we investigated the fresh properties and the hardened properties of the concrete with lithium slag, and the mechanisms of acid rain corrosion resistance of concrete with lithium slag were studied. The study showed that lithium slag can accelerate the hydration reaction and improve the acid rain resistance of concrete, with better appearance integrity, and the lower decrease rate of compressive strength and mass loss of concrete. Unfortunately, lithium slag enhanced the neutralization depth of concrete. The compressive strength and mass loss of concrete with lithium slag are sensitive to the concentration of SO42−, and the neutralization depth is sensitive to the concentration of H+. Adding lithium slag can decrease the tendency for formation of CH crystals in the matrix, increase the hydration degree of cement, improve the microstructural compactness of concrete and decrease the Ca/Si of C–S–H gel. Therefore, lithium slag is beneficial for resisting the acid rain corrosion of concrete, and can be used as an acid rain corrosion inhibitor.

Cratering Induced by Slow Highly Charged Ions on Ultrathin PMMA Films

Highly charged ions are a well-known tool for the nanostructuring of surfaces. We report on the thickness dependence of nanostructures produced by single 260 keV Xe38+ ions on ultrathin poly(methyl methacrylate) (PMMA) films (1 nm to 60 nm) deposited onto Si substrates. The nanostructures induced by slow highly charged ions are rimless craters with a diameter of around 15 nm, which are roughly independent of the thickness of the films down to layers of about 2 nm. The crater depth and thus the overall crater volume are, however, thickness-dependent, decreasing in size in films thinner than ~25 nm. Our findings indicate that although the potential energy of the highly charged ions is the predominant source of deposited energy, the depth of the excited material contributing to crater formation is much larger than the neutralization depth of the ions, which occurs in the first nanometer of the solid at the projectile velocity employed here. This suggests synergism between kinetic and potential-driven processes in nanostructure formation in PMMA.

Corrosion Damage and Life Prediction of Concrete Structure in a 41-Year-Old Steelworks.

Iron and steel industry emits a large amount of CO2 and SO2 in the process of steelmaking, and these acid gases lead to the serious corrosion damage of concrete structures. In this paper, the environmental characteristics and corrosion degree of concrete in a 41-year-old steelworks were investigated, and the neutralization life prediction of the concrete structure was carried out. The results showed that the temperature, relative humidity, CO2 concentration, and SO2 concentration in the steelworks were 1.32, 0.62, 1.28, and 13.93 times higher than those of the general atmospheric environment, respectively. These environmental characteristics in various sections were significantly different. The appearance change of concrete in the ingot casting bay was more serious than that of concrete in the billet bay. Both the compressive strength of concrete in the ingot casting bay and billet bay decreased, and the strength in the billet bay was relatively low. The neutralization depth of concrete in the ingot casting bay was 2.35 times larger than that of concrete in the billet bay. The prediction model of concrete neutralization depth was established, and the remaining neutralization service life in the ingot casting bay and billet bay were 194.68 a and 202.07 a, respectively.

Nearshore bathymetric changes along the Alaska Beaufort Sea coast and possible physical drivers

Erosion rates along Alaska's Beaufort Sea coast, among the highest in the world, are negatively impacting communities, industrial and military infrastructure, and wildlife habitat. Decreasing maximal winter ice extent and increasing summer open water duration and extent in the Beaufort Sea may be making the coast more vulnerable to destructive storm waves than during recent, colder, icier decades. Previous studies of Beaufort Sea coastal change have been limited to subaerial analyses of the shoreline. Here we describe nearshore seafloor change by comparing post-World War II (WWII) (1945-53) bathymetry data to recently acquired (1985–2018) bathymetry data and relate the observed seafloor change to adjacent shoreline change near Utqiagvik, within Stefansson Sound, and immediately west of Barter Island and Kaktovik. Within the Utqiagvik region, seabed erosion was generally highest (>1.0 m of loss) offshore of Point Barrow and along the eastern end of the Tapkaluk Islands, while there were lesser amounts of deposition (<0.5 m of gain) within the protected waters of Elson Lagoon. Sedimentation was generally highest offshore of Point Barrow, in a region of converging currents, and on the landward side of the barrier islands and spits fronting Elson Lagoon, which is likely related to a regional trend of westerly sediment transport and landward migration of the barrier islands. Within Stefansson Sound, perhaps the most notable changes from post-WWII bathymetry data compared to recent data are a switch from mixed, low erosion and deposition in 1997 to low deposition (<0.5 m) in 2018 east of the Boulder Patch, a switch from low erosion in 1997 to neutral depth change in 2018 in the channel between the north and south Boulder Patch areas, and higher deposition from 1997 to 2018 landward of the rapidly retreating barrier islands along the Sound's northern border. At Barter Island, high erosion near north-facing shorelines and high deposition near west-facing shorelines generally matched shoreline changes. One of our goals is to identify possible processes responsible for the depth changes we quantified. Using simple metrics that relate sediment characteristics with modeled waves and non-wave induced currents, we show that sediment resuspension and transport by both wave and non-wave driven currents likely contribute to the overall patterns of change within the ∼13 m isobath along the open coast, and that the influence of wave action affecting sediment transport is expanding seaward.

Characterization and Comparison of Corrosion Layer Microstructure between Cement Mortar and Alkali-Activated Fly Ash/Slag Mortar Exposed to Sulfuric Acid and Acetic Acid.

In this study, we investigated the formation and evolution of the corrosion layers in alkali-activated mortar and ordinary Portland cement mortar exposed to sulfuric acid and acetic acid environments with different pH values, and explored the differences in the deterioration mechanisms. The experimental results indicated that ordinary Portland cement (OPC) mortars experienced more severe deterioration in terms of appearance, mass loss, and strength loss as compared with alkali-activated mortars exposed to an acetic acid environment, but their neutralization depths were smaller. Alkali-activated fly ash (AAF) mortar had a the relatively intact appearance but the greatest neutralization depth, which was due to its stable three-dimensional network but highly porous structure. To sum up, alkali-activated fly ash/slag (AFS) mortar had the best resistance to acid attack. In addition, the mortars exposed to acetic acid suffered greater deterioration than those exposed to sulfuric acid with the same pH values, which was mainly due to the highly porous corrosion layer formed in acetic acid, whereas crystallization of gypsum in sulfuric acid had a pore filling effect. However, for alkali-activated slag (AAS) and OPC mortars exposed to a sulfuric acid environment, extensive gypsum resulted in the formation of micro-cracks, and the corrosion layer of OPC mortar was more prone to fall off. OPC mortar also had the greatest resistance difference values of the continuously connected micro-pores before and after acid corrosion, followed by AAS, AAF, and AFS mortars, and these values for all the specimens were smaller in sulfuric acid. Furthermore, the gaps between acetic and sulfuric acid attacks increased with increased calcium content in binders, which were 7%, 13%, 21%, and 29% for AAF, AFS, AAS, and OPC mortars, respectively. Thus, it can be inferred that an appropriate amount of gypsum existed in the corrosion layer which could act as a barrier to some extent ina sulfuric acid environment.

Development of sulfuric-acid resistant concrete with reduced carbon emissions

A recent social problem in Japan is the corrosion of concrete structures at sewerage facilities caused by sulfuric acid in the sewage, causing the structures to deteriorate before their expected life span. At the same time, low-carbon concretes using reduced amounts of cement are being developed as a response to concerns about global warming.The production of cement emits large amounts of carbon dioxide, so it is being replaced by blast furnace slag and fly ash, which are industrial by-products. In this study, low-carbon concretes with good sulfuric acid resistance are developed by replacing cement with various proportions of blast furnace slag fine powder, and fly ash. In particular, the concrete with 20% cement, 20% water-binder ratio has a high compressive strength of 60 N/mm2 or more and shows good resistance to sulfuric acid as demonstrated by a reduced mass change rate and neutralization depth in sulfuric acid immersion tests.

Resistance to Sulfuric Acid Corrosion of Geopolymer Concrete Based on Different Binding Materials and Alkali Concentrations.

Geopolymer binder is expected to be an optimum alternative to Portland cement due to its excellent engineering properties of high strength, acid corrosion resistance, low permeability, good chemical resistance, and excellent fire resistance. To study the sulfuric acid corrosion resistance of geopolymer concrete (GPC) with different binding materials and concentrations of sodium hydroxide solution (NaOH), metakaolin, high-calcium fly ash, and low-calcium fly ash were chosen as binding materials of GPC for the geopolymerization process. A mixture of sodium silicate solution (Na2SiO3) and NaOH solution with different concentrations (8 M and 12 M) was selected as the alkaline activator with a ratio (Na2SiO3/NaOH) of 1.5. GPC specimens were immersed in the sulfuric acid solution with the pH value of 1 for 6 days and then naturally dried for 1 day until 98 days. The macroscopic properties of GPC were characterized by visual appearance, compressive strength, mass loss, and neutralization depth. The materials were characterized by SEM, XRD, and FTIR. The results indicated that at the immersion time of 28 d, the compressive strength of two types of fly ash-based GPC increased to some extent due to the presence of gypsum, but this phenomenon was not observed in metakaolin-based GPC. After 98 d of immersion, the residual strength of fly ash based GPC was still higher, which reached more than 25 MPa, while the metakaolin-based GPC failed. Furthermore, due to the rigid 3D networks of aluminosilicate in fly ash-based GPC, the mass of all GPC decreased slightly during the immersion period, and then tended to be stable in the later period. On the contrary, in metakaolin-based GPC, the incomplete geopolymerization led to the compressive strength being too low to meet the application of practical engineering. In addition, the compressive strength of GPC activated by 12 M NaOH was higher than the GPC activated by 8 M NaOH, which is owing to the formation of gel depended on the concentration of alkali OH ion, low NaOH concentration weakened chemical reaction, and reduced compressive strength. Additionally, according to the testing results of neutralization depth, the neutralization depth of high-calcium fly ash-based GPC activated by 12 M NaOH suffered acid attack for 98 d was only 6.9 mm, which is the minimum value. Therefore, the best performance was observed in GPC prepared with high-calcium fly ash and 12 M NaOH solution, which is attributed to gypsum crystals that block the pores of the specimen and improve the microstructure of GPC, inhibiting further corrosion of sulfuric acid.

Diagnostic Reliability in the Assessment of Degradation in Precast Concrete Elements

In the past century, precast reinforced concrete has become the most widely used construction material in infrastructure engineering, especially for long-span structures. Nowadays, a growing research area concerns the assessment of concrete strength degradation due to environmental exposure and reinforcement corrosion. This paper reports an experimental campaign on some prefabricated concrete elements that were exposed to atmospheric agents for approximately 20 years. The campaign took the uncommon opportunity to access the full inspection and sampling of rebar. The included activities had different invasiveness and encompassed inspections, core sampling, corrosion potential mapping, compressive strength tests, as well as neutralization depth assays on cored surfaces, on chisel-split surfaces, and on drilling powders. The results bring together a global diagnostic picture of very limited degradation and of elements that are fully able to attend their design service life; the latter is estimated to be considerably higher than 20 years and to exceed 75 years if the concrete mix does not show quality issues. Results also permit drawing considerations on a hierarchy of diagnostic reliability in the evaluation of RC degradation, in which concrete core sampling plays the role of golden standard.

Biogenic sulfur attack in a reinforced concrete sewage treatment plant. Re-visited mechanism and rehabilitation proposal

Sewage treatment plants are examples of structures subjected to highly aggressive industrial environments. Given this, the objective of the present work is to evaluate the degree of degradation of the concrete structure of a sewage treatment plant located in Curitiba, Brazil. This plant was exposed to an environment within the process of wastewater treatment for nearly 20 years. Samples were collected from four slabs and four walls of the drainage channels of the sewage treatment plant reactor. Tests of the corrosion potential of the reinforcement, depth of neutralization, SEM/EDS, XRD, optical microscopy and uniaxial compressive strength were performed. Several exposed and heavily corroded reinforcement extensions were identified. The pH inside the slabs was found to be alkaline (over 10). With the analysis of SEM/EDS and XRD, it was possible to identify the predominance of gypsum in samples of the external part of the core and surface of the channel walls. The mechanical properties were preserved, with compressive strength even greater than that observed in the last inspection, which was 6 years ago. Finally, the results indicate that the attack on concrete initially occurred on the surface, advancing in depth over time. This attack was caused by the decalcification of C-S-H and resulted in the formation of gypsum as the final product of the degradation mechanism.

Physical and Chemical Relationships in Accelerated Carbonation Conditions of Alkali-Activated Cement Based on Type of Binder and Alkali Activator.

Alkali-activated cements prepared from aluminosilicate powders, such as blast furnace slag and fly ash, are rapidly attracting attention as alternatives to cement because they can significantly reduce CO2 emissions compared to conventional cement concrete. In this study, we investigated the relationship between the physical and chemical changes by accelerated carbonation conditions of alkali-activated cements. Alkali-activated cements were prepared from binders composed of blast furnace slag and fly ash as well as alkali activators sodium silicate and sodium hydroxide. Physical changes were analyzed from compressive strength, pH, and neutralization depth, and chemical changes were analyzed from XRD, TG-DTG, and 29Si MAS NMR. The C–(N)–A–S–H structure is noted to change via carbonation, and the compressive strength is observed to decrease. However, in the case of Na-rich specimens, the compressive strength does not decrease by accelerated carbonation. This work is expected to contribute to the field of alkali-activated cements in the future.

Prediction of Neutralization Depth of R.C. Bridges Using Machine Learning Methods

Machine learning techniques have become a popular solution to prediction problems. These approaches show excellent performance without being explicitly programmed. In this paper, 448 sets of data were collected to predict the neutralization depth of concrete bridges in China. Random forest was used for parameter selection. Besides this, four machine learning methods, such as support vector machine (SVM), k-nearest neighbor (KNN) and XGBoost, were adopted to develop models. The results show that machine learning models obtain a high accuracy (&gt;80%) and an acceptable macro recall rate (&gt;80%) even with only four parameters. For SVM models, the radial basis function has a better performance than other kernel functions. The radial basis kernel SVM method has the highest verification accuracy (91%) and the highest macro recall rate (86%). Besides this, the preference of different methods is revealed in this study.

Corrosion investigation of fly ash based geopolymer mortar in natural sewer environment and sulphuric acid solution

The objective of this research is to estimate the durability of low-calcium fly ash based geopolymer mortar (FA-GPm) in comparison with sulphate resistant Portland cement mortars (SRPCm) exposed to natural sewer environment. Their performance is also investigated in the sulphuric acid (H2SO4) solution to highlight the difference in the corrosion mechanisms between these two exposure conditions. Mortar samples were removed from natural sewer and 1.5 % sulphuric acid solution after 12, 24 months and 6 months of exposure, respectively. Visual and physical analyses showed greater neutralization and loss in alkalinity in FA-GPm compared to SRPCm. However, mass loss and strength reduction observed for SRPCm was greater compared to FA-GPm. Microstructural analysis showed widespread gypsum crystallization within SRPCm matrix compared to FA-GPm, leading to more severe matrix deterioration. Differences in corrosion mechanism were identified between natural and sulphuric acid exposure conditions which led to the variation in estimated corrosion depth. Data collected from these microstructural and physical investigations were utilized to develop simplified linear models to express the depth of corrosion, surface pH, mass loss and neutralization depth of FA-GPm and SRPCm as a dependent of exposure time, temperature and H2S concentration in natural sewer environments.