Research on Salt Corrosion Resistance of Lithium-Based Protective Coating on Mortar Substrate.

The present study concerns hydrophobic surface treatments with silane-based coating on concrete surfaces against external ionic transport. The nano-modification and organic-inorganic modification were carried out on it and applied to the mortar matrix and concrete matrix. Lithium-based protective coating (PC1, PC2), nano-modified coating (NC1, NC2) and organic-inorganic composite coating (OL1) were prepared. The salt erosion resistance of the mortar matrix and concrete matrix was tested, compared with the blank group and the market. The test results found that the organic-inorganic modified OL1 and LC1 coatings have the greatest influence on the chloride penetration resistance of the mortar matrix, in which the chloride penetration depth of 28 days is reduced by 73.03% and 63.83%, respectively, compared with the blank group. The rate of mass change of the blank group, PC1 and PC2 coatings, and NL1 and NL2 coatings were 0.17%, 0.08%, and 0.03%, respectively. The result demonstrated that the lithium-based coating could effectively delay the penetration rate of chloride ions and sulfates into the mortar, and the nano-modified properties could improve the salt resistance. The scanning electron microscopy (SEM) showed that coating treatment would promote the secondary hydration of cement-based materials, by reducing the content of Ca(OH)2 in hydration products of cement-based materials and producing C-S-H gel, which is conducive to strength enhancement and pore refinement. The nano-component would promote the reaction degree, while the organic-inorganic coating would have the respective advantages of the two components.

Prediction for elastic local buckling stress and ultimate strength of H-section beam.

The local stability of the H-section beam is essentially determined by the width-thickness ratios of flange and web. Current design codes provide width-thickness ratio limits to classify sectional ranks regarding local buckling. However, the local buckling stress and ultimate strength cannot be accurately predicted using the width-thickness ratio alone. This study aims to develop highly accurate calculation methods for both elastic local buckling stress and ultimate strength. We present a simplified theoretical method for elastic flange local buckling that considers rotational restraints and torsional restraints provided by the web. It is confirmed that the buckling stress of a single flange obtained by theoretical analysis corresponds closely with the results of the finite element analyses when local buckling is controlled by flange local buckling. Besides, based on the theoretical analysis, important parameters are determined. Through a parametric study, a model for calculating the local buckling stress of the H-section beam covering all cases of local buckling types is suggested. It is demonstrated that the local buckling slenderness ratio based on the improved calculation method has a strong correlation with the experimental normalized ultimate strength of the H-section beam. Finally, we propose a design formula that outperforms conventional methods in predicting the normalized ultimate strength.

Effects of an Amphiphilic Micelle of Diblock Copolymer on Water Adsorption of Cement Paste.

To reduce the inhibiting effects of polystyrene-based emulsion on the hydration process and strength development of cementitious materials, an amphiphilic diblock copolymer polystyrene-block-poly(acrylic acid) (PS-b-PAA) was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization and demonstrated in cement paste system for improving the resistance to water absorption without significantly reducing 28-day compressive strength. Firstly, the dissolved PS-b-PAA was added into water, and it quickly self-assembled into amphiphilic 80 nm-sized micelles with hydrophobic polystyrene-based core and hydrophilic poly(acrylic acid)-based shell. The improved dispersion compared to that of polystyrene emulsion may minimize the inhibiting effects on strength development, as the effects of PS-b-PAA micelle as hydrophobic admixtures on rheological properties, compressive strength, water absorption, hydration process, and pore structure of 28-day cement pastes were subsequently investigated. In comparison with the control sample, the saturated water absorption amount of cement pastes with 0.4% PS-b-PAA was reduced by 20%, and the 28-day compressive strength was merely reduced by 2.5%. Besides, the significantly increased hydrophobicity instead of slightly decreased porosity of cement paste with PS-b-PAA may contribute more to the reduced water adsorption characteristics. The study based on prepared PS-b-PAA micelle suggested a promising alternative strategy for fabricating polystyrene-modified concrete with reduced water absorption and unaffected compressive strength.

Resistance of blended alkali-activated fly ash-OPC mortar to mild-concentration sulfuric and acetic acid attack.

The traditional cementitious product is prone to suffer from a high degree of deterioration in the case of exposure to acid solutions because of the decomposition of the binder network. However, the degradation of concrete structures in service by mild concentrations of acid under conditions involving sewage, industrial waters, and acid rain is more common and results in a significant environmental problem. The utilization of alkali-activated materials has been seen to potentially offer an attractive option with regard to acceptable durability and a low carbon footprint. With the aid of visual observation, mass loss, compressive strength tests, X-ray diffraction, Fourier transform infrared spectroscopy, and field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy, the acid resistance of alkali-activated fly ash mortars in which the precursor was partially replaced (0-30% by mass proportion) with ordinary Portland cement (OPC) was evaluated after 180 days of exposure to mild-concentration sulfuric and acetic solutions (pH = 3). A conventional cement mortar (100% OPC) was used as a reference group. The results demonstrate that the addition of OPC into the alkali-activated system causes a significant increase in compressive strength (around 16.08-36.61%) while showing an opposite influence on durability after acid attack. Based on a linear mean value and nonlinear artificial neural network model simulation, the mass losses of the specimens were evaluated, and the alkali-activated pure-fly ash mortar demonstrated the lowest value (i.e., a maximum of 5.61%) together with the best behavior in the aspect of discreteness at 180 days. The results from microstructure analysis show that the coexistence of the N-A-S-H and C-S-H networks in the blend system occurred by both OPC hydration and FA. However, the formation of the gypsum deposition within the fly ash-OPC blend systems at sulfuric acid was found to impose internal disintegrating stresses, causing a significant area of delamination and cracks. In addition, alkali metal ion leaching, dealumination, as well as the disappearance of some crystalline phases occurred in specimens immersed in both types of acids.

Volume Deformation of Steam-Cured Concrete with Slag during and after Steam Curing.

In order to better predict the development of shrinkage deformation of steam-cured concrete mixed with slag, a deformation-temperature-humidity integrated model test, a hydration heat test, and an elastic modulus test were performed. The effects of the steam-curing process and the content of slag on shrinkage deformation, hydration degree and elastic modulus of concrete were studied. The results indicate that during the steam-curing process, the concrete has an "expansion-shrinkage" pattern. After the steam curing, the deformation of concrete is dominated by drying shrinkage. After the addition of slag, the shrinkage deformation of steam-cured concrete is increased. The autogenous shrinkage increases by 0.5-12%, and the total shrinkage increases by 1.5-8% at 60 days. At the same time, slag reduces the hydration degree of steam-cured concrete and modulus of elasticity. A prediction model for the hydration degree of steam-cured concrete is established, which can be used to calculate the degree of hydration at any curing age. Based on the capillary tension generated by the capillary pores in concrete, an integrated model of autogenous shrinkage and total shrinkage is established with the relative humidity directly related to the water loss in the concrete as the driving parameter. Whether the shrinkage deformation is caused by hydration reaction or the external environment, this model can better predict the shrinkage deformation of steam-cured concrete.

Design of CNS-Li2SiO3 Permeable Protective Coatings and Effects on Mortar Matrix.

In this paper, we prepared permeable protective coatings composed of lithium silicate (Li2SiO3), where the coating was modified by colloidal nano-silica (CNS). Three levels of lithium silicate (i.e., 30 wt. %; 40 wt. %; 50 wt. %), sodium silicate (i.e., 5 wt. %; 10 wt. %; 15 wt. %), and surfactant (i.e., 0.05 wt. %; 0.1 wt. %; 0.15 wt. %) were involved in this study. An orthogonal experiment design selected the optimal proportion basedon thestrength and water absorption requirements of mortar. The effects of CNS-Li2SiO3 coating on the resistance to permeability of chloride ions and carbonation of specimens were also studied. The outcomes were interpreted using scanning electron microscopy (SEM), X-ray diffraction (XRD), and mercury intrusion porosimetry (MIP) techniques. The results showed that the optimum mix formulation consisted of 40 wt. % of lithium silicate, 10 wt. % of sodium silicate and 0.1 wt. % of surfactant within the mixtures investigated. Meanwhile, compared tothe control group, after the specimens were coated at 21 days curing age of mortar, the strength development, 48-h water absorption, resistance to chloride ions penetration, and carbonation of CNS-Li2SiO3 coated specimenswere improved. This could be attributed to the second hydration, leading to a reduction of the content of Ca(OH)2 and an increase of the amount of C-S-H gel within specimens. Thus, the microstructure of mortar matrix was improved after coated with CNS-Li2SiO3 permeable protective coatings.

The Effect of a Corrosion Inhibitor on the Rehabilitation of Reinforced Concrete Containing Sea Sand and Seawater.

Concrete made with sea sand and seawater is rich in chlorine ions which are the main factors that induce corrosion of the reinforcement. In this study, an innovative method to rehabilitate reinforcement is presented; the concentrations of chloride ions and the corrosion inhibitor in concrete were measured. Electrochemical chloride extraction (ECE) was applied as a control experiment via using saturated Ca(OH)2 solution as an external electrolyte. Bidirectional electromigration (BIEM)technology combined with the corrosion inhibitor could not only remove the chloride ions but also protect the steel bar in concrete, and animidazoline inhibitor mixed in concrete is more effective than thetriethylenetetramine inhibitor due to the specific molecular structure. It was found that the optimum ratio of N/Cl reached the maximum value 3.3, when the concentration of inhibitor was 1. Meanwhile, the experimental results also revealed that the corrosion inhibitor and chloride ion concentrations reached necessary levels on the surface of the steel, and the corrosion inhibitor migrated effectively. Overall, the contents of imidazoline and triethylenetetramine inhibitor in seawater concrete are0.75% and 1%, respectively. The results demonstrate that the addition of the corrosion inhibitor and the application of bidirectional electromigration would effectively improve the durability of reinforced concrete containing sea sand and seawater.

Effect of Organics on Heavy Metal-Contaminated River Sediment Treated with Electro-Osmosis and Solidification/Stabilization Methods.

This study focuses on the treatment of heavy metal ions and achieving enhancement of river sediment, which is rich in organics. Fulvic acid was used as the main representative of organics in which to study the transfer of Cu2+, Zn2+ ions in the electroosmotic system, in both the absence and presence of organics. In addition, the effects of the experiment parameters (i.e., voltages, displacement, and water content), heavy metal ion content (0.19% and 0.38%, respectively), and the concentration of organics (1.5%, 3%, and 4.5%) acting on migration of ions and physiochemical properties of sediment, before and after electro-osmosis treatment were investigated. Mineral composition of the soil and its microscopic characteristics were analyzed by scanning electron microscopy. The results show that the 4.5% fulvic acid added in the sediment can enhance the migration ability of Cu2+ and Zn2+ ions through complexation, and simultaneously effectively reduce the formation of colloids with the average reductions of Cu2+ ions and Zn2+ ions being 28 and 11 mg/kg, respectively. While the dewatering capacity of the sediment with higher fulvic acid content is weaker, fulvic acid can effectively reduce the corrosion of the electrode during the electro-osmosis process, due to the film formed on the metal surface. Moreover, the fulvic acid in the organics can be combined with the aluminum and calcium produced by the hydration of the cement, delaying the hydration of the cement, while simultaneously decomposing the hydration product and hindering the hardening of the cement, thereby affecting and destroying the formation of the sediment's structure and its strength.

Effect of Imidazoline Inhibitor on the Rehabilitation of Reinforced Concrete with Electromigration Method.

Steel bars embedded in reinforced concrete are vulnerable to corrosion in high chloride environments. Bidirectional electromigration rehabilitation (BIEM) is a novel method to enhance the durability of reinforced concrete by extracting chloride out of concrete and introducing an inhibitor to the surface of the steel bar under the action of an electric field. During the migration process, a higher ionization capacity of the inhibitor with a symmetrical molecular structure was introduced. A new imidazoline inhibitor was, therefore, employed in this study due to its great ionization capacity. The effect of imidazoline and triethylenetetramine inhibitor on chloride migration, corrosion potential, and strength of concrete were explored. The research results showed that the effect of chloride extraction and electrochemical chloride extraction made no significant difference on the surface of the concrete, where chloride extraction efficiency was more than 70%, and the chloride extraction efficiency was more than 90% around the location of the steel. while a dry-wet cycle test, the potential of concrete increased by about 200 mV by mixing imidazoline inhibitor. The imidazoline inhibitor was found to be effective at facilitating chloride migration and ameliorating corrosion, meanwhile, it had a negligible impact on the concrete's strength.

Stabilization/solidification characteristics of organic clay contaminated by lead when using cement.

Research about cement treated soil has examined various characteristics of strengthened and stabilized soil, but has mainly focused on either the unconfined compressive strength or potentially toxic element (PTE) stabilizing results respectively in response to cement dosing. This study investigates how factors including cement concentration, lead concentration, humic/fulvic acid content and curing age affect these two geotechnical and environmental characteristics. A laboratory study was conducted to measure unconfined compressive strength, and lead leaching under several test conditions. Knowing that humic acid and fulvic acid can weaken cementation in cement treated soil but can stabilize PTEs such as lead by different chemical reactions, it was found that the acids generally reduce lead stabilization in cement treated soil. In addition, the stabilized strength reaches a peak at a specific lead content in soil. Finally, scanning electron microscopy was used to observe more detailed changes and mechanisms.