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Concrete structures face significant challenges in sulfate-rich environments, where sulfate attack can affect their durability and structural integrity. This study explores innovative approaches to enhancing concrete performance by integrating hydrophobic and densification technologies. It emphasizes the critical role of anti-sulfate erosion inhibitors in mitigating sulfate-induced damage, reducing water absorption, and inhibiting corrosive reactions. This research addresses prevalent issues in Chinese engineering projects where high sulfate concentrations are common, necessitating robust solutions for sulfate resistance. Through rigorous testing, including wet–dry cycling tests with 5% and 10% Na2SO4 solutions following the GB/T 50082-2009 standard, concrete formulations achieved exceptional long-term sulfate resistance, meeting or exceeding KS200-grade requirements. These findings provide valuable insights into optimizing concrete durability in sulfate-rich environments, offering practical strategies to enhance infrastructure resilience and reduce maintenance costs. [ABSTRACT FROM AUTHOR]

Immersion tests with 5 wt.% Na2SO4 solution were carried out to investigate the deterioration of calcium silicate hydrate (C-S-H) gel in a sulfate environment. C-S-H gels with different Ca/(Si + Al) molar ratios were used for comparison. Particular attention was paid to the changes in element composition and Si-O-Si chain structure of the C-S-H gel. The results show that the C-S-H gels with a low Ca/(Si + Al) ratio (0.8–1.0) and appropriate Si-O-Si chain length (14.8) presented better stability in a severe sulfate environment. The C-S-H gels with a higher Ca/(Si + Al) ratio (>2.0) were more sensitive to the attack of sulfate ions. Calcium ions dissolved rapidly during the immersion process, causing the loss of cohesive strength of the C-S-H gel, and then decomposed into fine particles. The C-S-H gel with a lower Ca/(Si + Al) ratio (about 1.1) rarely leached out calcium ions and maintained good micromorphology. The 29Si MAS-NMR results indicate that the Si-O-Si chains with too short or too long chain lengths will break and recombine under the attack of sulfate ions. The Si-O-Si chains with an appropriate chain length (14.8) maintained the stability of the structure of the C-S-H gel in a sulfate environment. These changes are closely related to the asymmetric layered structure of amorphous C-S-H gel. Partial calcium ions between the layers of the main chain structure of Si-O-Si are easily taken away by sulfate ions, leading to the structural instability of the C-S-H gel. [ABSTRACT FROM AUTHOR]

The expansion induced by sulfate attack on cement-treated aggregates (SACA) is a well-known problem that can be solved. It causes obvious heaves in road bases and railway subgrades. In this paper, the effects of the sodium sulfate content, cement content, degree of compaction, sulfate types, attack types, aluminum ion supply, concentration of curing sulfate solution, and temperature on the expansion behavior induced by SACA were investigated over 60 days in the laboratory. Based on the Sobol sensitivity analysis method, the influence of the sensitivity of each factor on the expansion was quantitatively analyzed, and the dominant factor of expansion was proposed. Results show that sulfate content is the domain factor of expansion that is induced by SACA, and it presents a logarithmic function relationship with strain. The 0.5% sodium sulfate content is the minimum sulfate content which causes the expansion that is induced by SACA. When the sulfate content is less than 1%, the expansion induced by SACA is minor. When the sulfate content is between 1% and 3%, the expansion behavior is expressed in four stages as follows: rapid strain increase, followed by a short stagnation period, then a significant strain increase and, finally, constant strain. When the sulfate content is greater than 5%, there are two stages comprising the expansion behavior as follows: the rapid strain increases and constant strain occurs. Greater sulfate content, greater degree of compaction, and lower temperature have positive effects on the expansion induced by SACA. The cement content does not have a consistent effect on expansion behavior. Compared with a sodium sulfate attack, both the reaction rate and expansion of cement-treated aggregates that are attacked by gypsum are smaller, and the attack period is also longer. When the sulfate content is greater than 1%, the addition of kaolin promotes the progression of the expansion induced by SACA. A small amount of water is sufficient for the demand for the sulfate attack. When the sulfate content is at a certain level, the expansion induced by SACA that is under external attack is much smaller than the expansion that is under internal attack. This study is expected to serve as a reference for future research on the mechanics of SACA, and it attempts to provide theoretical support for amending expansions that are induced by SACA. [ABSTRACT FROM AUTHOR]

The use of byproducts as supplementary cementitious materials (SCMs) and recycled coarse aggregates (RCAs) can contribute to the production of more sustainable self-compacting concrete (SCC) while modifying the durability properties of these mixtures. Thus, this study addresses the combined use of concrete waste (CW) as RCA and residue of masonry (RM) as SCM, the CW and RM obtained from construction and demolition waste, to generate SCC mixtures and to evaluate the performance of these mixtures under sulfate attack (5% Na2SO4 and 5% MgSO4 solutions). In detail, a reference SCC (M1) and three SCCs with 25% of RM and different level RCAs (0%, 50%, and 100% replacement by volume) were cast. The hardened properties of the SCC mixtures were assessed in terms of compressive strength and sulfate attack. The results showed that the SCC mixtures with RM and RCA, cured in water, exhibited lower compressive strength results in all the evaluated ages compared with M1 (reference mixture, without RM and RCA). However, the SCC mixture with RM presented the maximum compression strength result among the different mixtures at 180 and 360 days. When mixtures were exposed to sulfate solutions, the SCC mixture with RM showed the best performance, and even the SCC mixtures with RM and RCA exhibited lower linear expansion and loss of compressive strength when compared with M1. The presence and severity of the sulfate attack were assessed via X-ray diffraction and scanning electron micrograph, which confirmed the presence of ettringite and gypsum in all the exposed SCC mixtures in the Na2SO4 and MgSO4 solutions. [ABSTRACT FROM AUTHOR]

In this paper, firstly, the effects of graphene oxide on the mechanical properties of concrete were investigated. Secondly, the degradation and mechanism of the mechanical properties of graphene oxide concrete (GOC) under sulfate attack and a freeze–thaw environment were investigated. In addition, the dynamic modulus of elasticity (MOEdy) and uniaxial compressive strength (UCS) of the GOC were measured under different environmental conditions. According to the test results, the incorporation of graphene oxide in appropriate admixtures could improve the mechanical properties of concrete in these two working environments. It is worth noting that this effect is most pronounced when 0.05 wt% graphene oxide is incorporated. In the sulfate attack environment, the MOEdy and UTS of the GOC0.05% specimen at 120 cycles decreased by 22.28% and 24.23%, respectively, compared with the normal concrete specimens. In the freeze–thaw environment, the MOEdy and UTS of the GOC0.05% specimen at 90 cycles decreased by 13.96% and 7.58%, respectively, compared with the normal concrete specimens. The scanning electron microscope (SEM) analysis showed that graphene oxide could adjust the aggregation state of cement hydration products and its own reaction with some cement hydration crystals to form strong covalent bonds, thereby improving and enhancing the microstructure density. [ABSTRACT FROM AUTHOR]

External sulfate attack is an important factor causing a decrease in the mechanical properties of cement-based materials. In this paper, a computational prediction model of elastic modulus, considering the characteristics of sulfate corrosion from outside to inside and the influence of the interface transition zone (ITZ), was established to predict the elastic modulus of mortar under the external sulfate attack. Firstly, the backscattered electron (BSE) images of mortar and the algorithm of image threshold segmenting were used to determine a reasonable thickness of corroded ITZ. Secondly, the nanoindentation test was adopted to acquire the microscopic elastic parameters of phases (sand, cement, and ITZ) in corroded mortar. Moreover, the mortar mix proportion and Lu and Torquato's model were adopted to calculate the volume fractions of phases. Finally, a computational prediction model of elastic modulus of mortar under sulfate attack was proposed with homogenization methods. The results indicate that the thickness of corroded ITZ is 20 mm, and the error values of elastic modulus between the theoretical prediction results and the experimental results are within 8%, indicating that the macroscopic elastic modulus of corroded mortar can be precisely predicted by the computational prediction model of elastic modulus. [ABSTRACT FROM AUTHOR]

In order to study the performance of a new cement-based grouting material under the coupling of freeze–thaw cycle and sulfate erosion, tests related to the performance of the new grouting material were designed and carried out to analyze the damage mechanism of the material under the coupling of freezing and thawing and Na2SO4 solution by testing the mass change, relative dynamic elastic modulus, compressive strength loss and mineralogical and microstructural properties of the new grouting material. The test results show that with the increase in the number of freeze–thaw cycles, the mass loss and compressive strength loss of the specimens in 15% Na2SO4 solution gradually increased, and the relative dynamic elastic modulus showed a decreasing trend. When the freeze–thaw cycle number was 30, the mass loss rate, compressive strength loss rate and relative dynamic elastic modulus of the specimens in Na2SO4 solution were 4.17%, 24.59% and 84.3%, respectively, which showed better erosion and frost durability. Mineralogical and microstructural analysis showed that SO42− in solution led to the decomposition of the C-S-H gel and the formation of CaSO4•2H2O inside the specimen, and the internal deterioration was exacerbated by the widening of the crack width being aggravated, suggesting that the rate of material deterioration under the coupling of the two factors increased. [ABSTRACT FROM AUTHOR]

Sulfate attack is one of the main factors affecting the durability of concrete structures. In recent years, multi-walled carbon nanotubes (MWCNTs) have attracted the attention of scholars for their excellent mechanical properties and durability performance. In this paper, the influence of sulfate attack and dry–wet cycles on the performance of multi-walled carbon nanotube–lithium slag concrete (MWCNT-LSC) with varied MWCNT content (0 wt.%, 0.05 wt.%, 0.10 wt.%, and 0.15 wt.%) and varied water–cement ratios (0.35, 0.40, and 0.45) were investigated. In addition, scanning electron microscopy (SEM) and X-ray computed tomography (CT) tests were conducted to analyze the microstructure and pore structure of the concrete. The results showed that concrete incorporated with MWCNTs could effectively mitigate sulfate attack. The resistance to sulfate attack of concrete was negatively related to the water–cement ratio when the dry–wet cycle was fixed. The MWCNT-LSC showed the best compressive strength at the water–cement ratio of 0.35 and 0.10 wt.% MWCNTs. The SEM test results showed that the MWCNTs filled the pores and cracks within the specimen and formed bridges between the cracks, enhancing the resistance to sulfate attack. The CT test results also showed that the addition of MWCNTs could reduce the porosity of concrete, refine the pore size and inhibit the generation and development of cracks, thus optimizing the internal structure of concrete and improving its resistance to sulfate attack. [ABSTRACT FROM AUTHOR]

Sulfate-induced deterioration can reduce the service life of recycled aggregate concrete (RAC). To demonstrate the transport behavior of sulfate ions in RAC, a two-dimensional, six-phase numerical model of RAC is proposed in this study. Sulfate ion diffusion coefficients were defined for different phases [attached mortar, new mortar, interfacial transition zone (ITZ) between attached mortar and original aggregate, ITZ between the new mortar and original aggregate, and ITZ between the new mortar and attached mortar] of RAC. The effects of ITZ width and porosity on ion transport behavior in RAC were analyzed. The results show that the numerical model agrees with the experimental data. Numerical results indicate that the six-phase model of RAC provides more-accurate simulation results because tortuosity is reflected in the model. The width and porosity of ITZs both affect the diffusion of sulfate ions in concrete. However, due to the low volume fraction of ITZ in concrete, just improving ITZ performance has no significant effect on ion attack resistance of concrete. The ITZ is a crucial zone where damage may originate and develop. [ABSTRACT FROM AUTHOR]

This study examined the influence of the crystallinity of added nano-alumina on the sulfate resistance of ordinary Portland cement (OPC) paste. Two crystalline types of nano-aluminas (α-and γ-phase) were incorporated in cement pastes, which were exposed to sulfate solution. In the results, both paste samples having α- and γ-phase aluminas had accelerated compressive strength loss and increased length expansion compared to the sample without alumina addition. In particular, the rapidly decreased dynamic elastic modulus of the nano-alumina added samples postulates the greatly increased internal stress likely by the increased formation of volume expansive reaction products, such as ettringite, which was supported by the XRD and TG results. The greater ettringite formation in the nano-alumina added samples was likely due to reactive AH3 (=Al(OH)3) gel formation as the higher consumption degree of portlandite in the alumina added samples indirectly indicates the active AH3 gel formation, resulting in additional ettringite formation from the reaction of AH3 with Na2SO4 solution. A further degree of sulfate attack was observed in the γ-alumina added sample for the long-term Na2SO4 exposure (180 days) mainly due to the greater degree of gypsum formation inducing more internal expansive stress compared to the α-alumina added sample. [ABSTRACT FROM AUTHOR]

Sulfate and chloride in the marine environment threaten the lifespan of concrete structures. Predicting the strength of concrete under different degrees of ion erosion is essential for marine structure design and maintenance. In this paper, a novel method was developed to predict the compressive strength evolution due to sulfate and chloride attack. The degradation and ion diffusion behavior of cement-based materials was investigated by analyzing the visual appearance, compressive strength, porosity, and ion distributions of mortar soaked in sulfate and chloride solutions with different concentrations. The damage degree was observed to increase with sulfate concentration and decrease with chloride concentration. Additionally, it was discovered that chloride and sulfate ions inhibited the diffusion of each other, and a higher concentration resulted in a more substantial inhibition effect. The total effective sulfate and chloride intrusions were proposed to describe the erosion degree of mortar based on the evaluation of the ion distributions with Fick's second law. A compressive strength assessment method was established based on the analysis of the correlation between the strength contribution of sulfate reaction and the total effective chloride and sulfate intrusions. This method exhibits the potential for estimating the concrete strength of actual marine structures damaged by sulfate and chloride with accelerated laboratory tests. [ABSTRACT FROM AUTHOR]

Recycling coal gangue as aggregate to produce concrete in situ is the most effective way to solve the problem of deposited coal gangue in mines. Nevertheless, the mine environment underground is rich in sulfate ions, posing a threat to the durability of coal gangue concrete (CGC). Hence, the degradation process of sulfate-attacked CGC is investigated. A series of tests is performed to evaluate its variation law of mass, dynamic elastic modulus, compressive strength and sulfate ion distribution. Meanwhile, the microstructure and phases of sulfate-attacked CGC are identified by scanning electron microscopy, X-ray diffraction and thermogravimetric analysis. The results indicate that the residual compressive strength ratio of CGC is higher than that of normal concrete after a 240 d sulfate attack, implying a superior sulfate resistance for CGC. Additionally, the higher the sulfate concentration, the more severe the degradation. Except for the secondary hydration of CGC itself, the diffused sulfate ions also react with Ca(OH)2, forming gypsum and ettringite; this plays a positive role in filling the pores at the early stage, whereas, at the later stage, the generated micro-cracks are detrimental to the performance of CGC. In particular, the proposed sulfate corrosion model elucidates the degradation mechanism of CGC exposed to a sulfate-rich environment. [ABSTRACT FROM AUTHOR]

This paper investigated the influence of dry–wet cycles and sulfate attack on the performance of magnesium potassium phosphate cement (MKPC) as well as the effect of waterglass on MKPC. X-ray diffraction (XRD), TG-DTG, and scanning electron microscopy (SEM-EDS) were used to examine the phase composition and microstructure of MKPC. The results showed that the flexural and compressive strength of an MKPC paste increased initially and subsequently decreased in different erosion environments. The final strength of the M0 paste exposed to the SK-II environment was the highest, while that of the M0 paste exposed to the DW-II environment was the lowest. The final volume expansion value of MKPC specimens under four corrosion conditions decreased in the following order: DW-II, M0 > SK-II, M0 > DW-II, M1 > SK-I, M0 > DW-I, M0. Compared to the full-soaking environment, the dry–wet cycles accelerated sulfate erosion and the appearance of damages in the macro and micro structure of the MKPC paste. With the increase in the number of the dry and wet cycles, more intrinsic micro-cracks were observed, and the dissolution of hydration products was accelerated. Under the same number of dry–wet cycles, the strength test and volume stability test showed that the durability in a Na2SO4 solution of the MKPC paste prepared with 2% waterglass (M1) was superior to that of the original M0 cement. The micro analysis indicated that waterglass can improve the compactness of the microstructure of MPC and prevent the dissolution of struvite-K. [ABSTRACT FROM AUTHOR]

The durability of C3S-C3A paste with varied C3A content (0%, 5%, 10%, and 20%) against sulfate attack at various attack ages (3 d, 7 d, 28 d, and 180 d) was investigated in this study through the examinations of corrosion product composition, Ca/Si and Al/Si of calcium-(aluminum)-silicate-hydrate (C-(A)-S-H) gel, formation and evolution of microstructure, migration and transformation of Al containing phase products, and pore structure. The results indicated that sulfate attack can promote the hydration reaction in C3S-C3A paste, thus accelerating the production of C-(A)-S-H gel in the paste. With the increase of C3A content, the acceleration effect becomes more significant. In addition, sulfate attack led to the dealumination and decalcification of C-(A)-S-H gel, resulting in the reduction of the gelling power of C-(A)-S-H gel. The degree of dealumination and decalcification of C-(A)-S-H gel increases with the increase of C3A content. At the same time, free Al and Ca promote the formation of expansive products such as ettringite and gypsum. Finally, under the action of sulfate, the pore characterization of C3S-C3A paste deteriorated, showing a decrease in specific surface area, cumulative pore volume and average pore diameter. [ABSTRACT FROM AUTHOR]

Sulfates when present in the formation water would attack and deteriorate the cementitious system. In the quest to investigate the possibility of using geopolymer systems in oil-well cementing, the durability of geopolymer in various corrosive environments has been simulated. Lightweight geopolymer systems exhibit different microstructural and macroscopic properties compared to the conventional geopolymer systems whose durability under sulfate attack has been widely investigated. It is therefore important to study the resistance of lightweight geopolymer to sulfate attack. A ternary geopolymer was formulated at 13 ppg (1.56 g/cm3) by admixing metakaolin, ground granulated blast furnace slag (GGBFS), and silica fume in an alkaline solution composed of sodium silicate and 10 M sodium hydroxide solution in a mass ratio 1:3. The geopolymer specimen was cured in a water bath at 163 °F for 72 h and subsequently submerged in a 50 g/L sodium sulfate solution for up to 2 days. The effect of the sulfate solution on the strength and the mechanism of the sulfate attack was analyzed using analytical techniques, pH, and ion exchange measurements. The compressive strength of the specimen at 72 h, having a value of 802 psi decreased by 19.8% and 26.2% after day 1 and day 2 in the sodium sulfate solution, respectively. Investigation of the mechanism indicated that the loss in strength was not a result of the formation of deleterious phases but rather the leaching of Na ions from the geopolymer indicated by the rise in the pH and amount of Na ions in the sodium sulfate solution after the geopolymer was submerged in a sulfate solution. Lightweight geopolymer has a relatively loose microstructure that reduces its tendency to inhibit the transport of alkalis during sulfate attack, making the effect of the sulfate environment more pronounced. [ABSTRACT FROM AUTHOR]

Destructive processes accompanying sulfate corrosion of concrete significantly affect the durability of products and structures based on Portland cement. In the presented study, the long-term effect of sulfate corrosion on the electrical properties of electrically conductive sand concrete was studied. In the course of the study, the following were tested: an electrically conductive composition and a control composition based on plain Portland cement. The analysis of changes in the mineral composition of the samples over the course of time in an aggressive solution was carried out. The results show that during the exposure period of the samples from 28 to 224 days, the absorption of sulfate ions slows down and averages 26% for the control composition and 29% for the electrically conductive composition, of the total volume of absorbed sulfates. At the same time, the course of sulfate corrosion was accompanied by a 6% increase in the density of samples of both compositions, as well as a cyclic change in mechanical strength within 15%. In its turn, the key indicator of the electrical characteristics of the compositions—electrical resistivity—tended to increase throughout the experiment. These results can be recommended for assessing the durability and the nature of the operating conditions of electrical concretes used in aggressive environments. [ABSTRACT FROM AUTHOR]

This study investigated the effect of layered double hydroxides (LDHs) on the deterioration process of cement paste in the sulfate environment. Cement pastes with the addition of original and calcined LDHs at 2.5 wt.% and 5.0 wt.% of cement were exposed to Na2SO4 solution for 360 days. The macroscopic performance of the cement paste was assessed based on mass variation, porosity, compressive strength, and content of sulfate ions. Furthermore, the microhardness, microstructures, and composition of the degraded pastes were examined using Vickers hardness (HV), mercury intrusion porosimetry (MIP), scanning electron microscope (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The results indicate that cement paste incorporated with LDHs can mitigate the corrosion caused by sulfate effectively, especially in the case of calcined LDHs (C-LDHs), which primarily increase the adsorption of sulfate. Compared with the control specimen, the 180 d compressive strength loss ratio of specimens with 2.5 wt.% and 5.0 wt.% of C-LDHs decreased by 63.66% and 80.51%, respectively. Moreover, LDHs can reduce the amount of ettringite crystals, densify the microstructure, and refine the pore structure to mitigate the cement paste's sulfate corrosion significantly. Compared with the control specimen, the 180 d harmful pore volume fraction of specimens laced with 2.5 wt.% and 5.0 wt.% C-LDHs decreased by 43.77% and 54.51%, respectively. In terms of the content of C-LDHs, an optimal content of C-LDHs could ensure the dominant effect of adsorption, while excessive C-LDHs could refine pores. In addition, Vickers hardness has an excellent correlation with compressive strength, which could precisely predict the compressive strength. Moreover, by combining the Vickers hardness distribution and content distribution of sulfate ions, the cross-section of the paste could be classified into four regions to evaluate the deterioration process accurately: the degraded zone, the strengthened zone, the invaded zone, and the intact zone. [ABSTRACT FROM AUTHOR]

The sulfate attack (SA) of cementitious materials widely exists, which severely reduces the mechanical properties and durability of cementitious materials. However, few numerical SA damage models of cementitious materials have been comprehensively developed. The understanding and simulation of the chemo-mechanical behavior of cementitious materials are beneficial to better modeling, predictions and designs of underground structures. In this research, a numerical chemo-micromechanical damage model under the SA and loading is proposed to explore the cracking process of the cementitious materials based on the discrete element method (DEM). Some inherent characteristics of the chemical attack can be well considered in the proposed numerical model. The local damage effect can be simulated, as well as the sulfate corrosion degree and the material component. The performance of this proposed model is confirmed and validated by available experimental results. We examine the dependence of the strength and the elastic moduli of the cementitious material on: (a) the content of ettringite, (b) the distribution of ettringite, (c) the mechanical properties of the cementitious matrix, (d) the void ratio of the cementitious materials, (e) the confining pressure, and (f) the expansion coefficient of sulfate corrosion products. The softening and fluctuating phenomena are witnessed in the stress-strain curves. The failure mode of cementitious materials with the SA is different from that of specimens without the SA. The damage parameters of cementitious materials under the SA are examined in depth. The numerical results reveal that the proposed damage model is feasible and valuable in the modeling, predictions, applications and durability of chemo-mechanical sulfate attack problems in cementitious materials. [ABSTRACT FROM AUTHOR]

Nano-silica (NS) is an effective material to improve the strength and durability of high-performance concrete (HPC), but little information is available regarding its role in HPC response to long-term sulfate attack. In this study, six different dosages of NS (0%, 1%, 2%, 3%, 4%, and 5%) as cement partial replacement were mixed into HPC and the casted specimens were soaked in sulfate solution for different periods (0, 100, 200, and 300 days). The mass change, dynamic elastic modulus, compressive and splitting strength, microstructure morphology, and porosity characteristics of HPC specimens were measured by mass tests, mechanical properties tests, scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) tests. The results showed that the incorporation of NS decreased the mass loss, elevated the compressive and splitting strength, and reduced the porosity formation of HPC in front of sulfate attack. The percentage of 1% NS was among the most effective dosages as, after soaking for 300 days, it decreased the mass loss by 13.5%, elevated the elastic modulus as well as compressive and splitting strength by 50.4%, 31.7%, and 69.8% in comparison of unmodified HPC, respectively. The sulfate attack resistance was delayed in a higher (2–5%) mixed dosage, mainly due to the agglomeration of nano particles, especially after long-term reactions. This study can provide experimental references regarding the performance of HPC mixed with NS in front of sulfate attack. [ABSTRACT FROM AUTHOR]

Sulfate attack is the most common form of the durability damage of hydraulic concrete, and the performance degradation of cracked structural components is more significant at the position of water level change. Fly ash, a widely utilized supplementary cementitious material, can effectively improve the durability of concrete. In this paper, fly ash was used to partially replace Portland cement at 0 w%, 40 w%, 50 w%, 60 w%, and 70 w%, respectively. Through the three-point bending beam test with notch and the dry–wet cycle of sulfate attack, the change law of the fly ash content on the fracture mechanical properties of steel fiber reinforced self-compacting concrete (SFSCC) and its degradation mechanism under sulfate attack was studied. The results show that the load–crack mouth opening displacement curve of SFSCC changed from a steamed bread peak to a sharp peak under 30 dry–wet cycles of sulfate attack. The fracture toughness, peak load, and fracture energy of SFSCC with a high-volume fly ash increased with the increase in the fly ash content, while they reversed after sulfate attack. When the percentage of fly ash was 70 w%, the retention ratio of the fracture parameters was lower than that of SFSCC without incorporating fly ash, and when the percentage of fly ash was 50 w%, SFSCC had good bearing capacity, fracture mechanical properties, and corrosion resistance. The corrosion product of the reference SFSCC with 30 dry–wet cycles of sulfate attack was ettringite, whereas the SFSCC with a high-volume fly ash had no obvious corrosion products and the microstructure became looser. [ABSTRACT FROM AUTHOR]

Sulfate attack is one of the drawbacks of cementitious materials for stabilized soils. In the current study, a durability comparison of stabilized soil with cement (Type IV) and waste paper fly ash (WPFA) was conducted. First, the treated soil's unconfined compressive strength (UCS) was tested. Next, the treated soil was subjected to various wetting/drying cycles with various sulfate concentrations and temperatures for a year. In the meantime, samples were taken for DRX, FTIR, and TGA microstructural analyses. Additionally, samples were manufactured to track swelling over an 800 day period. The outcomes show that WPFA's UCS remained constant. Furthermore, ettringite development can be seen in the microstructural studies, however testing on linear displacement over 800 days revealed no significant changes in swelling. Finally, SEM was used to verify the ettringite formation at 360 days in order to confirm the previous findings. All the results indicated that stabilizing soil with 5% of WPFA and 3% of cement IV is possible even in presence of high sulfate concentrations, while maintaining the durability of the structure. [ABSTRACT FROM AUTHOR]

The stability of the grouting material under the coupling effect of sulfate attack and dry–wet cycles is essential to engineering safety. As a novel grouting material, the stability research of high‐water quick‐setting material (HWQSM) under different corrosive environments is in the initial stage. Moreover, the stratified damage characteristics (SDC) of HWQSM under sulfate attack were not fully explored. To this end, the strength degradation and SDC of HWQSM exposed to three kinds of sulfate solutions (i.e., 10% MgSO4 solution, 10% Na2SO4 solution, and hybrid solution of 5% Na2SO4 and 5% MgSO4) and dry–wet cycles were analyzed by using ETM‐C mechanical testing machine, scanning electron microscopy (SEM), XRD, and AFM. The results show that the strength reduction rate, the thickness of the corrosion layer, and roughness between the corrosion layer and the transition layer of HWQSM are all positively correlated with the concentration of Mg2+ in the erosion solution for the increase in dry–wet cycles. Under the combined action of ion erosion and carbonization, the pores and cracks of the corrosion layer expand, which would reduce the permeability resistance but increase the erosion damage rate. This research furnishes new views into the SDC of HWQSM under sulfate attack and dry–wet cycles, which would deeper our understanding to this special material undoubtedly; the research results are expected to furnish theoretical guidance of HWQSM resistance to different sulfate solutions. [ABSTRACT FROM AUTHOR]

In order to analysis the sulfate diffusion process in polypropylene fiber concrete, the influence of the introduction of polypropylene fiber on the porosity was calculated at first based on the spatial distribution features of polypropylene fiber in concrete, which was classified into three types, penetration type, half through type and embedded type. On the basis of Fick's second law and reaction kinetics equation, the diffusion model of sulfate ions in polypropylene concrete was established. The numerical solution was achieved with the adoption of finite difference method and the concentration of sulfate ions at any position can be calculated. At last, the numerical solution was verified using the results of polypropylene fiber reinforced concrete sulfate attack test. The results show that the relative error between numerical calculation and the actual test results is less than 17.65 %, the accuracy of the model is relatively high. [ABSTRACT FROM AUTHOR]

Concrete structures without sufficient durability can be damaged by sulfates in groundwater and from surrounding rock layers. To evaluate the performance of a concrete mixture, precise and performance-oriented test methods are a must. Therefore, a new a performance oriented concrete test procedure based on tensile strength measurements was developed considering experiences reported in international literature and recommendations of state-of-the-art reports. A vast parameter study with approx. 3850 tensile tests on ASTM briquets, 1900 flexural tensile tests on standard prisms and 2100 expansion tests on mortar flat prisms of different ages and with different storage conditions was statistically assessed. Based on the results a performance-oriented test method could be defined which considers not only the chemical, but also the physical resistance of a concrete against sulfate attack. The method was verified by 23 concretes with different cements or cement fly ash combinations and additional field tests. It could clearly be demonstrated that the results represent the performance of a practical concrete in case of sulfate attack. Furthermore, it leads much faster to an evaluation of the sulfate resistance compared to the most other practical oriented methods. [ABSTRACT FROM AUTHOR]

To study the damage evolution behavior of polypropylene fiber reinforced concrete (PFRC) subjected to sulfate attack, a uniaxial compression test was carried out based on acoustic emission (AE). The effect of sulfate attack relative to time and fiber hybridization were analyzed and the compression damage factor was calculated using a mathematical model. The changes to AE ringing counts during the compression could be divided into compaction, elastic, and AE signal hyperactivity stages. In the initial stage of sulfate attack, the concrete micropores and microcracks were compacted gradually under external load and a corrosion products filling effect, and this corresponded with detection of few AE signals and with concrete compression strength enhancement. With increasing sulfate attack time, AE activity decreased. The cumulative AE ringing counts of PFRC at all corrosion ages were much higher than those for plain concrete. PFRC could still produce AE signals after peak load due to drawing effect of polypropylene fiber. After 150 d of sulfate attack, the cumulative AE ringing counts of plain concrete went down by about an order of magnitude, while that for PFRC remained at a high level. The initial damage factor of hybrid PFRC was −0.042 and −0.056 respectively after 150 d of corrosion, indicating that the advantage of hybrid polypropylene fiber was more obvious than plain concrete and single-doped PFRC. Based on a deterioration equation, the corrosion resistance coefficient of hybrid PFRC would be less than 0.75 after 42 drying-wetting sulfate attack cycles, which was 40% longer than that of plain concrete. [ABSTRACT FROM AUTHOR]

In coastal areas, concrete of subway infrastructure can be jeopardized by coupled degradation conditions of stray current and sulfate solution. This paper focuses on the effect of stray current on the durability of cement-based materials exposed to sulfate-rich environments. In addition to chemical analysis, mechanical, transport, and microstructural properties of specimens exposed to five conditions were analyzed: (1) control environment with no degradation conditions, (2) stray current, (3) internal mixing sulfate, (4) stray current and internal mixing sulfate, and (5) stray current and external sulfate solution. Experimental results of this study reveal that (1) stray current can exacerbate leaching of cement-based materials, and 40-V stray current results in greater leaching compared to specimens subjected to 20-V stray current; (2) compared to specimens subjected to internal mixing sulfate alone, the combined effect of stray current on the production of gypsum and ettringite is slight due to the increase in particle collision induced by stray current; and (3) stray current has a migration effect on the rate of SO42− ions ingress, which significantly aggravates the external sulfate attack on cement-based materials. The primary degradation products were ettringite and gypsum, which results in the cracking and the maximum decrease in strength of 47.1% after exposure to coupled conditions of 40-V stray current and external sulfate solution for 150 days. [ABSTRACT FROM AUTHOR]

Construction and demolition wastes (C&DWs) have raised a large number of ecological and environmental problems. Recycling C&DWs into arecycled concrete aggregate (RCA) will help save natural resources effectively and reduce the negative impact of C&DW on the environment. Innovative pervious concrete (IPC) can mitigate extreme weather disasters, such as rainstorms, and overcome the low strength and poor durability of traditional pervious concrete. In this study, innovative recycled pervious concrete (IRPC) is prepared by combining RCA with IPC, which has broad application prospects and ecological friendliness. This study investigates the effect of RCA quality grades and replacement rates on the mechanical property, permeability, sulfate resistance and abrasion resistance of IRPC. IRPC mixtures were prepared with three different quality grades (high, medium and low qualities) of aggregates named as NA, RCA1 and RCA2. Moreover, the replacement rate of RCA for NA varied as 0%, 25%, 50%, 75% and 100%. The IRPC specimens were tested for compressive strength, mass loss and abrasion resistance after different sulfate wetting-drying cycles of 0, 30 and 60. The results exhibited that the initial compressive strength of all types of IRPC was more than 40 MPa. The compressive strength and mass of most IRPC increased first and then decreased slightly with the passage of a number of sulfate wetting-drying cycles, indicating IRPC has good resistance to sulfate attack. Sulfate attack and the addition of RCA will reduce the abrasion resistance of IRPC. However, when the replacement rate is lower than 50%, and the RCA quality is better (attached mortar content < 25%), the abrasion resistance of IRPC will be improved under sulfate attack. The experimental results might be useful as a reference and design methodology for employing IRPC in pavement applications in the future. [ABSTRACT FROM AUTHOR]

High-Density Polyethylene (HDPE) when used as partial substitute of fine aggregates in concrete is investigated to determine if it addresses sulfate attack in concrete. Since HDPE is known to be resistant against chemical compounds including sodium sulfate, it is hypothesized in this study that sulfate attack problems in concrete will be lessened by incorporating HDPE in concrete mix. Mechanical properties of concrete were determined to ensure that HDPE is limited to an amount where there will be no serious compromise to strength, hence, compressive, and split tensile test are included in the study. To determine the influence of HDPE in addressing sulfate attacks, length change of mortar specimen is investigated using ASTM C1012 (length change of mortar exposed to sulfate solution). Scanning Electron Microscopy (SEM) is also employed to qualitatively assess the microstructure of concrete with HDPE exposed to sulfate attacks. Mechanical test results showed that increasing HDPE did not adversely affect the compressive strength. However, there was a decrease observed in tensile strength. To achieve balance between mechanical properties, HDPE replacement of fine aggregates was set at 10% by weight of fine aggregates. The mortar bar test demonstrated that increasing HDPE resulted to an increased resistivity against sulfate attacks. SEM have also shown reduction in voids and ettringite with increasing HDPE content. [ABSTRACT FROM AUTHOR]

Sulfate attack–induced expansion of cement-treated aggregates is a well-known problem to be addressed causing remarkable heave in road and railway subgrades. The specific surface area (SSA) of the materials influences chemical reactions significantly. In this study, cement, sodium sulfate, and basalt powder were ground in a ball mill for 0 (without grinding), 5, 10, 30, and 60 min respectively to achieve different SSA gradients. Under the curing condition of a constant temperature of 10 °C and humidity of 70%, with 5% cement, the effects of sodium sulfate contents and SSA gradients on the expansion of sulfate attack in cement-treated aggregate (SACA) were investigated during 60 days in laboratory. Based on nitrogen absorption methods, microscopic tests, and swelling tests, the results show that, grinding within 60 min, the respective peak value of SSAs of cement, mixture of 3% (or 8%) sodium sulfate and basalt powder, and mixture of 3% (or 8%) sodium sulfate, cement, and basalt powder was 1.867 m2/g, 1.109 m2/g (or 1.393 m2/g), and 1.128 m2/g (or 1.404 m2/g), respectively. The SSAs increase as the aggregates refined, then decrease as the aggregates gathered. The strain variation can be generally divided into four stages with 3% sodium sulfate attack in cement-treated aggregate (3% SACA): rapid strain increase, short stagnation, continuous heave, and constant strain. Two stages of strain variation have been observed with 8% sodium sulfate attack in cement-treated aggregate (8% SACA): rapid strain increase, and a constant strain. Finer needle-like ettringite crystals (average length: 0.5–1 μm) filling in the smaller holes produce the greater expansion induced by SACA. Based on grey incidence analysis, the SSAs of cement, mixture of sodium sulfate and basalt powder (S+B), and the whole mixture of cement, sodium sulfate, and basalt powder (C+S+B) have a significant effect on strain. This work provides theoretical support for amending SACA at the SSA level. [ABSTRACT FROM AUTHOR]

This study investigates the acoustic emission (AE) and physicomechanical properties of concrete under three sulfate attack conditions: continuous immersion, wetting–drying cycles, and cyclic loading coupled with wetting–drying cycles. The characteristics of AE absolute energy during the concrete compression process were statistically analyzed by the histogram method and maximum likelihood (ML) method. The results from this study showed that the concrete specimens experienced two stages: an enhancement stage and a subsequent deterioration stage. Both wetting–drying cycles and cyclic loading accelerated the sulfate attack process. The probability density distribution of AE absolute energy satisfied a power law, and the distribution exponent was related to the degree of sulfate attack. The filling of expansion products during the enhancement stage led to the ML curves displaying a good plateau with lower exponents. Conversely, the cracking occurring during the deterioration stage created upturned ML curves with higher exponents. The results indicate that the exponent can accurately characterize the degree of concrete degradation under sulfate attack. [ABSTRACT FROM AUTHOR]

To solve the problem of high carbon emission in RPC production, fly ash (FA) and ground granulated blast furnace slag (GGBS) were used to replace part of cement for the preparation of RPC in this study. The sulfate corrosion resistance of RPC containing mineral admixture was investigated through dry and wet cycle test using a 5% Na 2 SO 4 solution. The influence of different amounts of FA and GGBS replacing cement on the deterioration of the performance of RPC was studied, and the formulas for the mass and compressive strength loss of RPC under dry-wet cycling were developed. The results show that: after the Na 2 SO 4 solution penetrates RPC, it reacts with the cement hydration products to produce erosion products such as gypsum and ettringite (AFt), and due to the expansion effect of erosion products, the gel pores decrease, and the harmful pores gradually increase, causing changes in the strength and quality; the introduction of FA and GGBS serves to fill the pores and diminish the presence of hydrated calcium hydroxide, thus augmenting matrix densification. Strategic substitution optimally harnesses the "superposition effect" of FA and GGBS, resulting in a substantial enhancement of RPC's resistance to sulfate attack. In addition, there is a significant correlation between changes in the microscopic characteristics of RPC and its macroscopic performance. [ABSTRACT FROM AUTHOR]

This study analyzed changes in the durability characteristics of cement mortar incorporating carbon nanotube (CNT) and the electrical properties subjected to deterioration induced by sulfate attack. Powder types of multi-walled or single-walled CNTs were used and added to the composites with 1.0% and 2.0% mass fraction, and the specimens were immersed in 5% and 10% sulfuric acid solutions to investigate the durability of CNT cementitious composites. Although mechanical performance decreased due to relatively large pores (370–80 μm) caused by CNTs, specimens incorporating CNTs exhibited enhanced resistance to sulfuric acid as CNTs, which offered strong resistance to acid corrosion, and prevented contact between the cement hydrate and the sulfuric acid solution. Therefore, it is expected that self-sensing performance was exhibited because there were no significant differences in the electrical properties of cement mortar subjected to the deterioration by sulfate attack. [ABSTRACT FROM AUTHOR]

Dry–wet cycle conditions have significant effects on the corrosion of concrete under sulfate attack. However, previous studies have only applied them as a method for accelerating sulfate attack and not systematically studied them as an object. In order to explore the impact of sulfate attack with different dry–wet cycle periods on concrete, in this study, four dry–wet cycle periods (3, 7, 14, and 21 days) were selected. The flexure strength, relative dynamic modulus, and mass were tested, and the microstructures of the eroded specimens were also analyzed. The intensity and depth of sulfate erosion were influenced by the wet–dry cycle period. The results show that the deterioration of concrete first increased and then decreased with an extension of the dry–wet cycle period. Microstructural analysis indicated that, with an increase in the dry–wet cycle period, the corrosion depth of sulfate attack increased. Moreover, the erosion products such as ettringite and gypsum were greatly increased, in agreement with the macroscopic variations. However, excessively prolonging the dry–wet periods does not significantly further the deterioration of concrete's performance. Therefore, considering the strength and depth of corrosion caused by sulfate attack, it would be appropriate to employ dry–wet cycle periods of 7–14 days under natural dry conditions in studies on concrete. [ABSTRACT FROM AUTHOR]

Presented is a direct-comparison sulfate resistance study of mortars containing 3% or 6% cement replacement with either colloidal nanosilica (nS) or microsilica (mS), exposed to 6 months of full submersion in a 5% sodium sulfate (Na2SO4) solution. Mortar bar samples measured for linear expansion per current standards indicated that at 6% cement replacement, colloidal nS exhibited on average 75% of the expansion of the microsilica-containing counterpart. At 3% replacement, either form of silica reduced the sulfate attack–related expansion to a similar degree (by 35%±2%) in comparison with the control mixture. Supplemental rapid sulfate permeability (RSPT) and absorption testing current standards supported the expansion results. The 6% nS mortar mixture exhibited the least charge passed and smallest permeable pore volume, which indicated that the nS-containing mortars were physically more impermeable and more resistant to ion transport. Increasing nS replacement (i.e., from 3% to 6%) decreased a mixture's permeable pore volume, whereas increasing mS had an inverse effect. This countered the benefits of increasing the pozzolanic content in the sulfate attack test. Mercury intrusion porosimetry (MIP) testing also revealed evidence of paste and paste-to-aggregate interfacial zone densification, as well as pore-size refinement, which was further supported by higher increases in compressive strength in mixtures with nS over those with mS. [ABSTRACT FROM AUTHOR]

Sulfate attack and accelerated carbonation tests were conducted on five concrete mixes made with 50% recycled concrete aggregate (RCA) and 30% fly ash (FA) blended with 70% ordinary portland cement (OPC). The graphene oxide (GO) and graphene oxide ball-milled (GObm) added in the concrete mixes varied by 0.05% and 0.1% by weight of binders. The 28-day cured specimens of the mixes were exposed to sodium sulfate solution and accelerated carbonation chamber under a controlled environment. The change in mass increased but the residual compressive strength reduced with progressing exposure to sulfate solution. The carbonation depth decreased with an increase in graphene oxide inclusion in the mixes but with increasing exposure to CO2 , the carbonation depth increased. The X-ray diffraction analysis (XRD) was conducted on samples after 28-day exposure to sulfate solution to confirm the delayed ettringite formation and gypsums. The thermogravimetric analysis (TGA) was performed on 28-day exposure to accelerated carbonation in order to understand the variation in the degradation process. The porosity and pore size distribution for the mixes with GO and GObm addition showed lesser porous compared to the mix without graphene oxide, which was confirmed from the mercury intrusion porosimeter (MIP) analysis conducted on 28-day cured specimens. [ABSTRACT FROM AUTHOR]

The previous researches on the degradation process of concrete under sulfate attack mainly focus on non-damaged concrete. It may lead to an excessive evaluation of the durability of the structure, which is detrimental to the safety of the structure. In this paper, three different damage degrees of concrete specimens with non-damaged (D0) and initial damage of 10% (D1) and 20% (D2) were prefabricated and subjected to sulfate attack and wetting–drying cycles. With the increase of sulfate attack cycles (0, 30, 60, 90, 120, 150 cycles), the changes in mass loss, relative dynamic modulus of elasticity, and the stress–strain curve were studied. The results show that the mass of the D0 specimen had been increasing continuously before 150 sulfate attack cycles. The mass of D1 and D2 had been increasing before 60 cycles, and decreasing after 60 cycles. At 150 cycles, the mass loss of D0, D1, D2 were − 1.054%, 0.29% and 3.20%, respectively. The relative dynamic modulus of elasticity (RDME) of D0 specimen increases continuously before 90 sulfate attack cycles. After 90 cycles, the RDME gradually decreases. However, for D1 and D2 specimens, the RDME began to decrease after 30 cycles. The damage degree has an obvious influence on the compressive strength and elastic modulus. For the D0 specimen, the compressive strength and elastic modulus increased continuously before 90 cycles and decreased after 90 cycles. The compressive strength and elastic modulus of D1 and D2 specimens began to decrease after 30 cycles. The stress–strain curves of concrete with different initial damage degrees were established, and the fitting results were good. Finally, based on the analysis of experimental data, the degradation mechanism of concrete with initial damage under the sulfate wetting–drying cycle was discussed. [ABSTRACT FROM AUTHOR]

The deterioration of cement composites containing nanosilica partially exposed to sulfate attack was studied, and the microstructure change of the composites was analysed by a scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results showed that nanosilica–cement composites had better sulfate resistance compared to plain cement composite under partial exposure to sulfate attack, and their sulfate resistance increased as the nanosilica content increased (in the range of 0 to 5 wt% replacing cement by weight). The main sulfate products were gypsum and ettringite within the surface and inner parts, respectively in both the immersed and evaporation portions of the nanosilica–cement composites, which was consistent with the plain cement composite. Thus, the incorporation of nanosilica did not change the distribution characteristics of the sulfate products within the composites partially exposed to sulfate attack. However, the addition of nanosilica reduced the amount of sulfate products in both the immersed and evaporation portions, and their amount decreased with the increase of nanosilica content. The evaporation portions of the composites suffered chemical sulfate attack rather than sulfate salt crystallization. Nanosilica–cement composites could be applied in real partial exposure environments containing sulfate ions. [ABSTRACT FROM AUTHOR]

Highlights • Continuous propagation of corrosion crack in concrete under sulfate attack is detected. • Temporal and spatial distribution of expansion stress and delayed ettringite are analyzed. • Propagation rate of cracks is directly proportional to the growth rate of delayed ettringite. Abstract The corrosive damages of plain concretes in marine environments are mainly attributed to delayed ettringite generated by liquid and solid phase reactions caused by sulfate ions entering concrete pores. This study investigated the correlation of corrosive crack propagation rate and growth rate of delayed ettringite. Cement mortar with water/cement ratio of 0.45 was employed as test sample and was immersed in 8% sodium sulfate solution. First, the correlation of corrosive crack length and corrosion time was obtained. Then, a temporal and spatial model considering the diffusion of sulfate ions and chemical reactions involved was established for the growth of delayed ettringite. The obtained results indicate that the growth of delayed ettringite is directly proportional to crack propagation. Based on that, we proposed a crack propagation model under sulfate corrosion. Also, sensitivity analysis of the diffusion model of sulfate ions was conducted and the obtained results indicated that damage played a key role in sulfate ions transmission. [ABSTRACT FROM AUTHOR]

Cement-stabilized pavement layers are subject to sulfate attack (SA) in sulfate-abundant regions due to internal expansion–induced damage throughout its expected service life. SA is a coupled physical-chemical-mechanical damage process for cementitious materials involving complicated chemical reactions between sulfate and components of cement composite. SA contains intricate interactions among porous media, moisture transport, and heat transfer. Engineering mechanics has been used to explain the failure process of the internal expansion caused by this coupled physical-chemical ingress phenomenon. Existing studies have considered only heat transfer or moisture content–dependent modeling. The literature lacks a comprehensive model that considers coupled interaction of temperature and humidity upon sulfate ingression. Thus, a chemomechanical (CM) model has been developed for capturing the true failure process of cement-stabilized pavement subgrades under SA. In this paper, a set of governing equations are developed, and a unique expression for a moisture-dependent and heat-dependent sulfate diffusion coefficient is proposed. Consequently, the equations are solved using the finite-element method. The results conform well with experimental results. The model has been validated to be accurate enough compared with previously implemented models. It is capable of evaluating and predicting SA-induced expansive failure in unsaturated cement-stabilized pavements. Two different models were combined to estimate the mechanical behavior of cement-stabilized subgrades subject to SA. Finally, the Drucker-Prager (DP) failure criterion was used for determining the damage zone. [ABSTRACT FROM AUTHOR]

Fly ash, a supplementary cementitious material, is normally used in conjunction with portland cement to improve the durability properties of concrete in the field, such as sea-crossing bridges, high-speed railways, and mass concrete in dams. Currently, these concrete structures are frequently exposed to sulfate environments. The object of this paper is to investigate the relationship among content of calcium hydroxide (CH), formation of gypsum, and compressive strength, as well as the relationship among the formation of ettringite, pore structure, and expansion properties in blend cement paste at long-term sulfate attack, up to 1,110 days. Mercury intrusion porosimetry (MIP) and thermo gravimetric (TG) analysis were used to evaluate the pore structure and content of CH, respectively. The results show that there is a significant negative relationship between CH content and the coefficient of compressive strength during sulfate attack as more gypsum formation is contributed for the loss of strength. Compared to the reference sample, the addition of 20% and 40% fly ash decreased the CH content by 16.7% and 25.1% through the pozzolanic reaction, which reduced the formation of gypsum and prevented the decalcification of calcium silicate hydrate (C-S-H). Crystallization pressure, due to the formation of ettringite in a limited space, is discussed to explain the cracking of cement-based materials. Several harmful pores (>0.1 µm) were formed in the reference sample due to crystal pressure with the formation of ettringite, which caused the expansion and exacerbated the diffusion of sulfate ions. The pozzolanic reaction of fly ash also improved the pore structures and reduced the degree of supersaturation of ettringite by preventing the ingress of external sulfate ions. [ABSTRACT FROM AUTHOR]

In this study, the effects of titanium dioxide (TiO2) nanoparticles on the sulfate attack resistance of ordinary Portland cement (OPC) and slag-blended mortars were investigated. OPC and slag-blended mortars (OPC:Slag = 50:50) were made with water to binder ratio of 0.4 and a binder to sand ratio of 1:3. TiO2 was added as an admixture as 0%, 3%, 6%, 9% and 12% of the binder weight. Mortar specimens were exposed to an accelerated sulfate attack environment. Expansion, changes in mass and surface microhardness were measured. Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), Thermogravimetry Analysis (TGA) and Differential Scanning Calorimetry (DSC) tests were conducted. The formation of ettringite and gypsum crystals after the sulfate attack were detected. Both these products had caused crystallization pressure in the microstructure of mortars and deteriorated the mortars. Our results show that the addition of nano-TiO2 accelerated expansion, variation in mass, loss of surface microhardness and widened cracks in OPC and slag-blended mortars. Nano-TiO2 containing slag-blended mortars were more resistant to sulfate attack than nano-TiO2 containing OPC mortars. Because nano-TiO2 reduced the size of coarse pores, so it increased crystallization pressure due to the formation of ettringite and gypsum thus led to more damage under sulfate attack. [ABSTRACT FROM AUTHOR]

Clayey soils are usually stiff when they are dry and give up their stiffness as they become saturated. Soft clays are associated with low compressive strength and excessive settlement. This reduction in strength due to moisture leads to severe damages to buildings and foundations. The soil behavior can be a challenge to the designer build infrastructure plans to on clay deposits. The damage due to the expansive soils every year is expected to be $1 billion in the USA, £150 million in the UK, and many billions of pounds worldwide. The damages associated with expansive soils are not because of the lack of inadequate engineering solutions but to the failure to identify the existence and magnitude of expansion of these soils in the early stage of project planning. One of the methods for soil improvement is that the problematic soil is replaced by suitable soil. The high cost involved in this method has led researchers to identify alternative methods, and soil stabilization with different additives is one of those methods. Recently, modern scientific techniques of soil stabilization are on offer for this purpose. Stabilized soil is a composite material that is obtained from the combination and optimization of properties of constituent materials. Adding cementing agents such as lime, cement and industrial byproducts like fly ash and slag, with soil results in improved geotechnical properties. However, during the past few decades, a number of cases have been reported where sulfate-rich soils stabilized by cement or lime underwent a significant amount of heave leading to pavement failure. This research paper addressed the some fundamental and success soil improvement that used in civil engineering field. [ABSTRACT FROM AUTHOR]

An ordinary portland cement and two portland limestone cements [15 and 35% weight-to-weight ratio (w/w) limestone content] were used for concrete and reinforced mortar specimens preparation. The specimens were exposed to two corrosive solutions (chloride sulfate and chloride) at 5°C. Total (acid-soluble) and free (water-soluble) chloride contents, and apparent chloride diffusion coefficients, were determined in concrete specimens. Reinforcement corrosion half-potential and current density, mass loss of steel rebars, and carbonation depth were measured in mortar specimens. Limestone cements showed very good behavior, although the environments were very corrosive. Total and free chloride ions concentration increased with exposure time and limestone content. Limestone cements showed less capability of binding chlorides than pure portland cement. The cement with low limestone content was the most effective in preventing reinforcement corrosion during mortar exposure to the combined chloride-sulfate solution, although it allowed the most intensive corrosion in the case of the chloride-bearing solution. The presence of sulfates led to higher chloride ion concentrations, less chloride binding and, generally, higher values of chloride diffusion coefficient, and also promoted reinforcement corrosion to a greater extent. Low temperature conditions retained a relatively low corrosion rate. [ABSTRACT FROM AUTHOR]

In this study, the effects of the initial sulfate content on the properties of cemented paste backfill (CPB) made from coarse tailings has been investigated via mercury intrusion porosimetry. The combined effects of the sulfate content and curing time on the total porosity, pore size distribution, and unconfined compressive strength of the produced material were discussed. It was found that the specimens with an initial sulfate content of 5000 and 35,000 ppm exhibited higher unconfined compressive strength, while the resulting fine porous structures characterized by pore radii of 10-400 and 1-10 μm significantly improved the mechanical properties of the CPB. In addition, an increase in the curing time decreased the overall pore volume in the radius range of 1-400 μm but increased the pore volume at pore radii less than 1 μm. [ABSTRACT FROM AUTHOR]

Applied electric fields, the reason behind stray currents, accelerate the ingress of sulfate into cementitious materials. To identify mitigation approaches, this study investigates the effects of slag and fly ash on sodium sulfate attacks of cement pastes under a constant electric current. The mineralogical alterations induced by the attacks were analyzed using X-ray diffractometry, thermogravimetric analysis, scanning electron microscopy, and thermodynamic modeling. The dissolution of aluminates in the slag and fly ash induced a monosulfate-rich area (>∼20 mm from the cathode surface) to form next to the ettringite-rich area on the sample surface (<∼20 mm). This effect reduced the availability of SO 4 2− in the pore solution, thereby hindering the penetration of sulfate. Meanwhile, the consumption of portlandite by the pozzolanic reaction lowered the decalcification resistance of the materials. This produced a wide area that endured the decomposition of portlandite and carbonate-AFm. Overall, blending 30% fly ash did not improve the resistance of the material to either sulfate attacks or decalcification; blending 50% slag can effectively mitigate sulfate ingress, though decalcification may become a governing mechanism in the degradation process. [ABSTRACT FROM AUTHOR]

Aggressive environments significantly influence the durability and serviceability of hardened cement and concrete. This paper presents an evaluation of the resistance of ground-granulated blast-furnace slag (GGBS) activated with calcined dolomite, as a novel alkali activator, to 5% sodium sulfate attack and 5% magnesium sulfate attack. Two calcined dolomites, D800 and D1000, were prepared in the laboratory at 800°C and 1,000°C, respectively. The results demonstrated the good potential of using calcined dolomite activated slag in resisting sulfate attack. Immersion in Na2SO4 (aqueous) led to an increase in strength in both the D800 (D800S) and the portland cement CEM I 52.5 N (PCS) activated slag with a more pronounced effect in the former and a decrease in the D1000 (D1000S) activated slag. Conversely, calcined dolomite activated slag had less strength loss than PCS after MgSO4 attack. The products of sulfate attack and the deterioration processes are also analyzed by a range of tests, including pH, weight change, corroded depth, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). After Na2SO4 attack, the main product on D800S and D1000S was gypsum with a larger amount in the latter. Gypsum, thaumasite, and M-S-H were the main products of D800S and D1000S after MgSO4 attack. The better resistance of D800S to sulfate attack was attributed to the absence of portlandite in the hydrated paste. Conversely, the presence of portlandite in D1000S led to the inhomogeneous sulfate ions inward progression; hence, the severe deterioration of the sample was observed. [ABSTRACT FROM AUTHOR]

29Si and 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy techniques were employed towards evaluation of hydrated cement paste and concrete subjected to accelerated sulfate attack. Quantitative analyses of the 29Si NMR spectra of specimens subjected to different periods of sulfate attack indicated that the chain length CL of SiO4=AlO4 tetrahedra was lowered by sulfate attack. 27Al NMR spectra indicated that sulfate attack produced a significant rise in the intensity of ettringite and a sharp drop in the concentration of monosulfate hydrate, which are some primary indications of sulfate attack on concrete. Fourier-transform infrared (FTIR) spectroscopy method was employed in order to verify the result of NMR spectroscopy. [ABSTRACT FROM AUTHOR]

The paper presents and discusses the results of resistance to sulfate aggression cement mortars containing calcalerous gaize. Were tested cements containing 15-35% gaize (CEM II A, B) and the reference cement CEM I (no additive). Using DTA/TG, XRD investigated the effect of gaize on the hydration of cement. Linear change mortars were tested according to the procedure in PN-B-19707, complement the research was to determine the strength of the mortar as a result of following long-term storage of samples in corrosive environments. Mortar microstructure studies were performed using mercury porosimetry and SEM/EDS. The results of the study allow us to conclude that already 15% of the content of Gaize making cement resistant to corrosive environments rich in sulfate ions. [ABSTRACT FROM AUTHOR]

Properties of concrete (with additional 20% fly ash) subjected to freeze–thaw cycles in water and in sulfate solutions were investigated in this paper. The corrosion solutions include two types, namely, 5% sodium sulfate solution and 5% magnesium sulfate solution. Through the experiment, visual examination was conducted to evaluate the surface damage. The deterioration considering the weight loss, relative dynamic modulus of elastically (RDME) loss and compressive strength loss of concrete under the coupling effect were also investigated. To identify the products formed by sulfate attack, analytical techniques, including X-ray diffraction, scanning electron microscopy and thermal analysis were performed on the selected samples after freeze–thaw circulations. Test results show that freeze–thaw cycles and sulfate attack affected each other. On the one hand, a lower temperature during freeze–thaw cycles slows down the diffusion of sulfate ions in concrete. On the other hand, sulfate attack accelerates the formation of microcracks in concrete, which leads to more severe damage under freeze–thaw cycles. The rate of damage in concrete is significantly dependent on the types of sulfate solutions, and the concrete deterioration by magnesium sulfate covers the most aggressive corrosion subjected to freeze–thaw cycles. Furthermore, the compressive strength loss and RDME loss of concrete in sodium sulfate solution is less than that in water during the initial freeze–thaw cycles, but the damage is more severe in further test period. [ABSTRACT FROM AUTHOR]

• The fracture properties of concrete subjected to drying-wetting cycles in different types of sulfate solutions were investigated. • With the proposed method, the fracture toughness and the evolution of FPZ were studied. • The horizontal strain and displacement fields in the FPZ obtained by the DIC technique were analyzed. The fracture properties of concrete subjected to drying-wetting cycles in different types of sulfate solutions were investigated. Five exposure conditions, i.e. 5% and 10% sodium sulfate solutions, 5% and 10% magnesium sulfate solutions (by mass) and water were prepared. Three-point bending tests were carried out at the corrosion periods of 1, 2, 3, 5, 9 and 15 months with the digital image correlation (DIC) technique. The initial and unstable fracture toughness were calculated by the proposed method, and the evolution of the fracture process zone (FPZ) was studied. Results indicate that (1) with the increase of corrosion time, an initial increase stage and a followed decrease stage for the fracture toughness were noticed. The values of unstable fracture toughness obtained by the analysis method agreed well with those obtained by the experimental method. (2) The FPZ length increased linearly with the crack propagation until a full FPZ development, and then decreased gradually. The maximum FPZ length decreased slightly with the corrosion time. (3) Using DIC technique, the fracture path can be easily identified from the horizontal strain field, and the evolution of the FPZ can be determined by the horizontal displacement with high accuracy. [ABSTRACT FROM AUTHOR]