Sulfate Attack Research Articles

Study on Mechanical Properties and Erosion Resistance of Self-Compacting Concrete with Different Replacement Rates of Recycled Coarse Aggregates under Dry and Wet Cycles

Concrete that self-compacts is frequently utilized in engineering construction. Recycled coarse aggregate self-compacting concrete (RCASCC) is made by partially substituting recycled coarse aggregates (RCA) for natural coarse aggregates in order to conserve construction resources. This study examines the impact of linked sulfate erosion, dry and wet cycles, and RCA replacement rates of 0%, 25%, 50%, 75%, and 100% on the mechanical properties and durability of RCASCC. By using the mass loss rate, relative dynamic elastic modulus, corrosion resistance factor, X-ray diffraction (XRD), scanning electron microscope (SEM), and atomic force microscope (AFM) analyses, as well as other macroscopic and microscopic methods, it is possible to examine the deterioration patterns of RCASCC under dry and wet cycles. The results demonstrate that the addition of RCA has a notable impact on concrete’s resistance to sulfate attack during both dry and wet cycles. The erosion products steadily rise, the interfacial transition zone (ITZ) becomes rougher, and the sulfate resistance falls as the replacement rate of RCA rises. According to the findings of SiO2, AFt, and CaCO3, the examination of corrosion products from XRD and microstructure from SEM and EDS is carried out. The old mortar that has adhered to the surface of RCA, as shown by the AFM analysis of ITZ and the SEM analysis of RCA, can significantly affect the roughness of ITZ inside RCASCC.

Durability development of lightweight and high-strength engineered cementitious composites subject to combined sulfate–chloride attack under freeze–thaw cycles

A novel lightweight high-strength engineered cementitious composite (LECC) was developed, and its mechanical property changes and the resultant durability evolution under the triple coupling factors of chloride attack, sulfate attack, and freeze–thaw cycles were studied. The results indicate that the salt solutions can accelerate the failure of LECC under freeze–thaw cycles. Salt solutions accelerated the tensile properties degradation of LECCs, and the deterioration degree was LECC-S (sulfate) > LECC-CS (chloride-sulfate) > LECC-C (chloride). The influence degree of salt solutions on mass loss was LECC-CS > LECC-C > LECC-S, while their influence on relative dynamic elastic modulus was LECC-S > LECC-CS > LECC-C. The surface spalling and internal structure destruction of LECC after salt freezing provided a favorable channel for CO2 penetration in the environment and the external sulfate–chloride environment under low temperature offered highly suitable conditions for the formation of expansive thaumasite. The combined physical and chemical attacks of sulfate promoted chloride diffusion, but chloride ion delayed sulfate’s diffusion and expansion reaction. This study more comprehensively revealed the durability development of LECC in some abominable environments and provided data support for the engineering application of LECC.

Performance of Pozzolan-Based Reactive Magnesia Cement Mixes against Sulphate Attack

Reactive magnesia cement (RMC) has gained interest due to its lower production temperatures when compared to Portland cement. In this study, the performance of pozzolan-based RMC concrete samples against sulphate attack was examined. Cube samples, after being removed from their moulds, were stored in a CO2-rich environment to gain compressive strength. Information obtained from XRD showed the formation of Mg carbonates in different forms. The use of fly ash and slag in large volumes reduces the environmental impact of concrete, but the use of these components have been found to greatly affect the formation of Mg carbonates in RMC mixes. This is mainly due to their filler effects. The coexistence of Ca- and Mg-based products was found in the slag-RMC mixes. The concrete samples based on RMC underwent mass and strength losses when stored in a MgSO4 solution for up to 12 weeks. The removal of Mg from the microstructure of these samples was confirmed using SEM analysis. The use of the most widely used pozzolans at 50% by weight of the binder greatly affected the carbonation mechanism of the RMC mixes. This finding suggests that they should be limited in the design of Mg-based products that harden under CO2-rich conditions.

Internal corrosion characteristics of endogenous sulfate introduced by recycled aggregates in recycled aggregates concrete: Insights into the macro-mechanical and meso-mechanical properties

The old cement paste adhering to recycled aggregates (RA) carries some sulfate corrosion media because of the external sulfate attack occurred in parent concrete. These sulfate corrosion media would be introduced into recycled aggregates concrete (RAC) that is prepared using RA. For studying the effects of the internal sulfate corrosion media on RAC, different Na2SO4 solutions (0%, 1%, 5% and 8%) were used to soak RA for 120 days. The effects of the soaked RA on macro-mechanical properties and meso-mechanical properties of RAC were explored. It was found that the endogenous sulfate ions diffused from RA into the new cement paste to react with cement hydration products (such as Ca(OH)2) to generate corrosion products, ettringite and gypsum. The moderate corrosion products could fill pores and cracks at interfacial transition zone (ITZ) to enhance the early compressive strength and flexural strength of RAC. However, as the erosion level of RA and curing time of concrete increased, much corrosion products caused the obvious deterioration in strength of RAC and microhardness of ITZ, as well as the increase of thickness of ITZ. For easing the comprehensive evaluation of microhardness and thickness of ITZ, a new parameter (Δζ) was proposed. The smaller the Δζ, the higher the quality of ITZ.

Role of delignified and lignin-containing cellulose nanofibers in enhancing durability performances of portland cement composites

This study investigates the effectiveness of cellulose nanofibers (CNF) in enhancing the long-term durability performance of ordinary portland cement (OPC) composites against sulfate attack and alkali-silica reaction (ASR). Two different types of cellulose nanofibers, namely lignin-containing cellulose nanofibers (LCNF) and delignified cellulose nanofibers (DCNF), were used in three different dosages (0.05%, 0.1%, and 0.3% by weight of the cement) to produce mortar samples. The heat of hydration and microstructural studies confirmed that none of the selected CNFs negatively affected the early-age cement hydration. Dynamic vapor sorption (DVS) isotherms revealed that the addition of CNF increased the amounts of C–S–H of the paste samples and therefore, resulted in the densification of the matrix. LCNF and DCNF-containing mortar samples were exposed to 5% MgSO4 and 5% Na2SO4 for 6 months. The results showed that incorporating CNF improved the resistance of mortar against sulfate attack. Specifically, after 6 months of sulfate exposure, the compressive strengths of the control samples were reduced by nearly 50%. In the case of 0.3% DCNF and 0.3% LCNF-containing batches, the strength reductions were less than 20% after the same sulfate exposure duration. Moreover, the expansion due to the ASR of CNF-containing mortar bars was nearly 97% lower than the samples without CNF after one year of exposure test. For all the tested parameters, LCNF-containing samples showed better performance compared to DCNF-containing samples.

Experimental study on damage anisotropy of 3D-printed concrete exposed to sulfate attack

3D concrete printing (3DCP) technology has grown substantially in recent years and expanded from use in the development of architectural landscapes to the manufacture of load-bearing structures. The durability performance of 3D-printed concrete materials is crucial for the application of 3DCP in engineering structures. In this study, polypropylene (PP) fibre-reinforced sulfoaluminate cement-based composites were prepared for 3D printing, and their mechanical and durability performances after exposed to a sulfate-attack environment were experimentally assessed. The surface damage, mass loss, dynamic modulus, and residual strength of the prepared 3D-printed concrete were quantified during 150 cycles of sulfate attacks. The damage anisotropy of 3DCP exposed to sulfate attacks was introduced and elucidated from both the meso- and microscales. The pore characteristics of the matrix and interfaces were investigated through computerised tomography (CT) scanning and scanning electron microscopy (SEM) to uncover the influence of interfaces on the sulfate resistant performances. The results indicate that the damage anisotropy of 3DCP after exposed to sulfate attack was reduced due to the self-healing properties of sulfoaluminate cementitious composites.

Experimental research on pervious concrete performance with partial replacement of foundry sand nano and GGBS

Roads serve a crucial role in linking geographical areas and people around the world. Road system construction requires additional engineering expertise in the areas of material selection, weight carrying capability, duration, etc. Fortunately the majority of new roads suffer from seepage of water from the top to the bottom, which deteriorates the road's surface. We are creating and putting in pervious concrete to enable water to drain fast. Pervious concrete is a special type of high-porosity concrete utilised for concrete flatwork applications. The fine aggregate in typical pervious concrete is minimal to non-existent, and there is just enough cement paste to cover the coarse aggregate while preserving the interconnectivity of the voids. Concrete is treated with nanosilica to reduce the amount of carbonization duringproduction process. The explanation is that the concrete's microscopic flaws and UV damage to the polymer molecules are lessened by the nano-SiO2 particles. Then, GGBS (Ground Granulated Blast Furnace) is used to protect against both sulphate attack and chloride attack and to acquire strength over a longer period of time in production settings. The major goal of this concrete is to produce high-porosity concrete. This concrete allows rainwater to pass through as well as investigating the behaviour of nanosilica, GGBS and foundry sand substituted from various sources. As a result, by minimising runoff, groundwater levels could be improved. To examine the effect of nanosilica, GGBS, and foundry sand on the quality and performance of pervious concrete, compressive strength of concrete was done in the laboratory. Finding the right combination and proportion for constructing concrete with the right amount of strength while maintaining engineering performance and quality is the innovative aspect of our work. The findings of this study recommends the use of low volume pavements, slope stabilisation and pavement in residential roads, alleys and driveways.

A time-space porosity computational model for concrete under sulfate attack

A time-space porosity computational model for concrete under sulfate attack

Strength Degradation of Foamed Lightweight Soil Due to Chemical Erosion and Wet-Dry Cycle and Its Empirical Model.

Foamed lightweight soils (FLS) have been extensively used as backfill material in the construction of transportation infrastructures. However, in the regions consisting of salt-rich soft soil, the earth structure made by FLS experiences both fluctuation of groundwater and chemical environment erosion, which would accelerate the deterioration of its long-term performance. This study conducted laboratory tests to explore the deterioration of FLS in strength after being eroded by sulfate attack and/or wet-dry cycling, where the influencing factors of FLS density, concentration of sulfate solution, and cation type (i.e., Na+ and Mg2+) were considered. An unconfined compressive test (UCT) was conducted, and the corrosion-resistant coefficient (CRC) was adopted to evaluate the erosion degree after the specimens experienced sulfate attack and/or dry-wet cycling for a certain period. The research results show that the erosion of the FLS specimen under the coupling effect of sulfate attack and dry-wet cycling was more remarkable than that only under chemical soaking, and Na2SO4 solution had a severe erosion effect as compared with MgSO4 solution when other conditions were kept constant. An empirical model is proposed based on the test results, and its reliability has been verified with other test results from the literature. The proposed model provides an alternative for engineers to estimate the strength deterioration of FLS on real structures in a preliminary design.

Durability of mortar and concrete containing pozzolans as a partial cement replacement in the marine environment: a review

This paper reviews the durability of concrete containing pozzolans in marine environments, which mainly focuses on resistance to chloride ion penetration and sulfate attack. The results of previous literature showed that the main ions of seawater are almost similar but the salinity varies with location. The mechanism of chemical reaction between seawater and concrete was carefully reviewed and explained. Besides, the main attacks that caused the degradation of concrete structures in marine conditions were summarized. The results of previous research indicated that using pozzolans (fly ash, slag, metakaolin, rice husk ash, etc.) as a partial cement replacement in concrete improved the durability of concrete such as resistance to chloride ion penetration and resistance to sulfate. The use of pozzolans not only improves the durability of concrete in the marine environment but also solves environmental impacts such as reducing CO2 emissions and landfilling areas. It can be concluded that the utilization of pozzolans in concrete, particularly in marine concrete structures is a promising approach for sustainable development.

Durability of mortar and concrete containing pozzolans as a partial cement replacement in the marine environment: a review

This paper reviews the durability of concrete containing pozzolans in marine environments, which mainly focuses on resistance to chloride ion penetration and sulfate attack. The results of previous literature showed that the main ions of seawater are almost similar but the salinity varies with location. The mechanism of chemical reaction between seawater and concrete was carefully reviewed and explained. Besides, the main attacks that caused the degradation of concrete structures in marine conditions were summarized. The results of previous research indicated that using pozzolans (fly ash, slag, metakaolin, rice husk ash, etc.) as a partial cement replacement in concrete improved the durability of concrete such as resistance to chloride ion penetration and resistance to sulfate. The use of pozzolans not only improves the durability of concrete in the marine environment but also solves environmental impacts such as reducing CO2 emissions and landfilling areas. It can be concluded that the utilization of pozzolans in concrete, particularly in marine concrete structures is a promising approach for sustainable development.

Chemical Attack on Concrete in Wastewater Treatment Plant: A Review

Wastewater treatment plant (WWTP) has become one of the most important structures nowadays and concrete is considered to be the most suitable material for the construction of this kind of structure for its several useful properties like durability, compressive strength, impermeability, abrasion resistance, etc. However in an aggressive environment, with the effects of constituents of wastewater and different chemicals applied in the treatment process of wastewater, concrete’s performance is greatly challenged. Chemicals like acid, sulfides, sulfates, salt, and gases generated from different reactions, micro-organisms, etc. can cause chloride ingress, carbonation, corrosion, sulfate attack, bio-deterioration, and erosion of concrete in wastewater treatment plants. As a consequence, a large amount of money is spent on the maintenance and repair works for wastewater treatment plants every year. Therefore, the quality of the concrete used in structures like WWTP must be very high. This study aims to explore the detrimental effects of various harmful chemicals on concrete in wastewater treatment plants, degradation mechanisms, and different methods of enhancing the resistance of concrete. The study also represents the current scenario of Bangladesh regarding this issue with the help of some excellent references, codes, and guidelines of important organizations and practical surveys.

Development of cementitious capillary crystalline waterproofing agents and durability study of concrete in the presence of chloride with sulfate in aqueous environment

In this study, the chemical composition of cementitious capillary crystalline waterproofing agents (CCCW) was developed by using the water penetration resistance test method. Response to impermeability by first permeability and self-healing properties by second permeability, five effective single components were obtained: Ethylene diamine tetraacetic acid (EDTA), l-aspartic acid, sodium sulfate, sodium silicate and nano-silica. With the help of chloride ion diffusion coefficient measurement and sulfate attack resistance test, it investigates the effect of five components on the durability of the concrete matrix. According to the differential thermogravimetric analysis (TG), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis methods, the waterproof mechanism of each component acting in the matrix was proposed. Finally, also combined with the results of macroscopic performance and microscopic analysis designed orthogonal experiments, the results show that the optimal blending of five waterproofing agent components up to 300% increase in substrate impermeability. The optimal amount of each component is 0.5% EDTA, 2% l-aspartic acid, 3% sodium sulfate, 2% sodium silicate, and 2% nano-silica.

Research on coupled erosion damage model of FRP bonded concrete beams subjected to Lemaitre assumption

AbstractIn cold regions, the coupling of freeze–thaw cycles and sulfate frequently impairs the performance of FRP‐bonded concrete, resulting in a shortened service life. Carbon fiber polymer (CFRP) and glass fiber polymer (GFRP) are used to paste pre‐cracked concrete beams in the experiment, and three unfavorable environments are created: freeze–thaw cycle, 10% sulfate solution erosion, and coupling erosion. This paper investigates the durability performance of FRP bonded beams using microscopic, mechanical and dynamic modulus of elasticity tests, as well as post‐erosion damage values and finite element modeling. After 400 h of coupled erosion, sulphate erosion and freeze–thaw cyclic erosion environments, the strength of the CFRP bonded beams was reduced by 66.3%, 14.6% and 42.0% and the GFRP bonded beams by 67%, 21.9% and 52.3% respectively. The results show that single sulphate attack does not cause significant damage to the beams, but it can exacerbate the damage caused by freeze–thaw cycles. A coupled damage model based on the Lemaitre strain equivalence assumption predicted the actual coupled damage of the specimens. The finite element model can accurately predict the damage and strength of the bond surface under loading.Highlights The durability performance of CFRP and GFRP adhered pre‐cracked concrete beams Microscopic, mechanical, and dynamic elastic modulus tests are used Freeze–thaw erosion environment in 10% mass fraction sulphate solution Coupled damage models for coupled salt and freeze–thaw cycles are developed FRP‐reinforced pre‐cracked beams subjected to erosion are simulated with ABAQUS

Investigating the effects of MWCNTs on sustainable alkali-activated mortar: physical, rheological, and mechanical analysis

Alkali-activated material (AAM) is a potential sustainable substitute for normal Portland cement-based concrete, but the composition of the material and the design of the mixture has a significant impact on fresh and hardened properties. This research describes the formulation and mechanical behavior of a multi-walled carbon nanotube (MWCNT)-reinforced-based alkali-activated nanocomposite. MWCNTs were incorporated into the fly ash/hydrated lime-based alkali-activated material at concentrations of 0.1%, 0.2%, 0.3%, and 0.35% by weight of the binder. The significant dispersion of MWCNTs within the matrix was achieved in an aqueous solution of surfactant and superplasticizer by employing both magnetic stirring and sonication procedures. The fresh-state characteristics of the MWCNT-based AAM were evaluated in terms of setting time and rheology parameters. Notably, samples containing 0.3% and 0.35% MWCNTs exhibited setting times of 26 and 25 min, respectively. The rheological behavior of the nanocomposite adhered to Modified Bingham's model, displaying shear-thinning properties. Moreover, an increase in MWCNT content led to an augmentation in yield stress, with the highest enhancement of 11.1% and 13.1% in yield stress and plastic viscosity, respectively, observed for mortar samples with 0.3% MWCNTs. Mechanical assessments were performed at 7, 14, and 28 days to investigate the compressive and flexural strengths of the specimens. The addition of approximately 0.3% MWCNTs resulted in an impressive boost of up to 14% in compressive strength and an even more remarkable increase of 28% in flexural strength. Furthermore, after exposure to acid and sulfate attacks, the ACN3 samples (0.3% wt. of MWCNTs) exhibited minimal strength loss, with only 5.1% and 3.9% decrease in compressive strength after acid and sulfate attacks, respectively. According to these results, the MWCNTs can function as effective bridges to reduce and limit the progression of microcracks through the AAM-based nanocomposite under the circumstances of homogeneous distribution and good adhesion between both the MWCNTs and the adjacent AAM paste.

Experimental investigation on the fracture properties of concrete under different exposure conditions

The fracture properties of concrete subjected to sulphate attack are investigated. First, concrete beams were subjected to different exposure conditions, i.e., full immersion, partial immersion and dry-wet cycling, for 90, 180 and 270 days, and a subsequent three-point bending test was conducted. A softening constitutive relationship of concrete was then derived and a simplified bilinear model was proposed for different exposure conditions. Finally, a chemical titration test was conducted to obtain the profiles of sulphate ion contents along the depth of concrete. The results indicate that, when concrete is subjected to different exposure conditions, the initial fracture toughness increases but the unstable fracture toughness decreases with the exposure duration. The stress-free crack opening displacement in the simplified bilinear model decreases significantly, indicating that concrete attacked by sulphate becomes more brittle. In addition, the sulphate ion content decreases rapidly along the depth and the sulphate ion content in concrete under dry-wet cycling is obviously higher than those under the other exposure conditions, demonstrating that dry-wet cycling results in the most serious sulphate attack on concrete.

Experimental study on spatial evolution of mode-I and mode-II fracture toughness of cemented paste backfill under external sulphate attack

ABSTRACT External sulphate attack (ESA) interferes with spatial changes in fracture toughness of cemented paste backfill (CPB) and affects its mechanical stability. Large-scale curing column models are developed to investigate the spatial evolution of mode-I and mode-II fracture toughness (i.e. KIC and KIIC) under seepage- and diffusion-induced ESA. It has been found that the seepage-induced ESA leads to spatial changes in KIC and KIIC of CPB at advanced ages and higher extent of degradation of fracture toughness is measured at a deeper position in CPB. Comparatively, KIc can be used as a reliable quantity to estimate KIIc under the diffusion-induced ESA.

Six-Year-Old Ecological Concrete in a Marine Environment: A Case Study

The durability of ecological concrete in a marine environment is of concern for the coastal and offshore construction industry. The properties of such concrete taken from a marine structure were studied. Specimens of six-year-old submerged ecological concrete were taken from a breakwater located in the East Mediterranean Sea. The specimens were analyzed for their biological carbonate deposition cover, chloride effective diffusion, carbonation, compressive strength, and mineralogy. About 57% of the surface was found to be covered by biogenic-deposited carbonates. The effective chloride diffusion coefficient and the carbonation rate were found to be reduced proportionally to the biogenic-carbonate cover, relative to the prediction by a standard model. No significant change in compressive strength was detected. Most of the aluminates were found in non-crystalline minerals. No evidence of a sulfate attack was found. In conclusion, the effect of the biological growth on the concrete surface is mainly a reduction of effective diffusion, and no negative effects were detected.

Application of electro-injection method in improving cement mortar durability

An electrochemical method for improving the durability of cement mortar by injection of nanoparticles (alumina (Al2O3)-coated silica (SiO2)) is presented. In this method, nanoparticles are injected into cement mortar pores under an external electrical field, refining the pore structure of cement mortar. The efficiency of electro-injection nanoparticle treatment with different applied electric fields was evaluated by monitoring the evolution of cement mortar resistivity. The improvement of cement mortar durability after electro-injection of nanoparticles was assessed by examining the resistance to water absorption, carbonation, sulfate attack and chloride diffusion. The microstructure of cement mortar after the electro-injection treatment was analysed using scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), X-ray diffraction (XRD) and differential thermo-gravimetric analysis (DTG). The results show that cement mortar durability can be improved by the injection of nanoparticles under external electric field. The efficiency of electro-injection nanoparticle treatment increased with the increase of applied electric field. The resistance to water absorption, carbonation, sulfate attack and chloride diffusion were significantly improved by using the electro-injection method. The improvement in cement mortar durability can be attributed to the filling effect of nanoparticles.

Experimental-Computational Investigation of the Elastic Modulus of Mortar under Sulfate Attack.

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.