Hydrophobic Admixture Research Articles

Water-soluble fluorosilane supplemented with fumed silica as admixture for producing hydrophobic concrete: Effects on cement hydration, mechanical properties and water protection properties

Hydrophobic admixtures protect concrete from water-related degradation, although they may have negative effects over cement hydration, mechanical properties and have low miscibility with water. Aiming to overcome these drawbacks, this work studies the properties of concretes containing admixtures based on a water-soluble fluoroalkylsilane and fumed silica to densify the structure. The effects of the admixture were evaluated in terms of hydrophobic, mechanical and chemical properties.The admixture decreased capillary absorption by over 70% while also increasing the internal cohesion, despite an increased porosity. Raman and XRD analysis indicated it promoted the consumption of C3S and the formation of portlandite and C–S–H gels with higher silicon content, compensating the effect of porosity on the concrete resistance. Incorporation of fumed silica in the admixture delayed the early development of hydrated phases, but after full curing promoted a more compact structure of the cement matrix, decreasing water absorption rate and improving mechanical properties.

Magnesium oxychloride cement with hydrophobic pore network for utilizing as oil well cement

Magnesium oxychloride cement (MOC) possesses some excellent characteristics, which can be used as oil well cement, to deal with the complex environmental conditions in oil and gas wells. However, the water resistance property of MOC is poor. In this study, a new type of magnesium oxychloride cement (MOC) with improved water resistance was developed by modifying the pore structure of pure MOC using hydrophobic admixtures. To assess the performance of the new MOC, a range of tests were performed, including compressive strength, softening coefficient, capillary water absorption, pore size distribution, mineral composition and microstructure analysis. The results showed that the pore size distribution of the MOC was altered from a large pore-dominant structure to a small pore-dominant one. The hydrophobic admixture and the gel substance formed on the strength-providing phases prevented them from water erosion, resulting in enhanced strength and water resistance. This new type of MOC has the potential to be used in challenging environments, such as oil and gas wells and underwater structures.

Effects and mechanisms of capric acid/silica capsule on water absorption reduction of cement paste

Inspired by the structure design on biomaterials for drug delivery, the encapsulation of hydrophobic capric acid (CA) core with a hydrophilic silica shell was proposed and demonstrated in a cement paste system for improving the resistance to water absorption. Firstly the fabrication of CA/silica capsule by interfacial polymerization reaction was reported. Subsequently, the effects of CA/silica capsule and mono-doped CA-hollow silica as hydrophobic admixtures on the compressive strength, water absorption, hydration process and pore structure of 28-day cement pastes were studied. Compared with the mono-doped one, the cement paste incorporated with the capsule exhibited an increased compressive strength and hydrophobicity with reduced water absorption. The increment in the compressive strength and the resistance to water absorption of capsule/cement paste was further ascribed to the improved dispersion and possible sustained release of CA/silica capsule in water, resulting in the improved hydration degree with refined pore structures and the hydrophobicity of the cement paste matrix. The study based on prepared capsule materials suggested a simple but effective approach to the fabrication of hydrophobic cement-based materials with reduced water absorption and extended service life.

Dispersion of hydrophobic waste amorphous carbon powder in cementitious environment and its effect on the permeability of cement paste

A Proper dispersion of powder-based hydrophobic admixtures in cementitious composites is challenging due to the presence of water. Studies have shown that amorphous carbon powder (ACP), a hydrophobic by-product of refining waste materials of paraffin production can be used as a hydrophobic agent. However, mixing methods and dispersing agents for modifying cementitious materials with ACP can significantly impact their mechanical properties, workability, water-repellency (hence the durability), and dispersion quality of ACP. Lack of information about the extent of their impact on different aspects mentioned above can hinder the practical use of ACP as a hydrophobic agent. To fill this gap, the objective of this study is to comprehensively investigate factors in the dispersion of ACP in cementitious materials and the tradeoff between mechanical properties and water permeability of ACP-modified cementitious materials when more than one mixing method is adopted. The impacts of different dispersing agents and mixing methods, including ultrasonication, dry mixing, and after mixing, on dispersion quality of ACP in cementitious environment analogous with aqueous solutions and hardened cement paste were assessed. Polycarboxylate ether-based superplasticizer (PCE) proved to be the most effective dispersing agent. Compressive strength of ACP modified cement paste can be increased or decreased with or without the workability reduction effect of ACP along with PCE respectively. Based on volume fraction of ACP clusters in X-ray micro-CT 3D reconstruction of hardened cement paste, ultrasonication was identified as the most effective mixing method and dry mixing was the worst in terms of achieving a uniform distribution of ACP in cement paste. However, all mixing methods presented more than 85% volume fraction of uniformly dispersed ACP areas with no major difference in terms of hydrophobic modification capability. Modifying cement paste with a higher amounts of ACP (5 to 15% by weight of cement) substantially increased water contact angle (up to 171% for w/c ratio of 0.35) and decreased water absorption. The hydrophobic modification capability of ACP increases with a decrease in the quality of cement paste and is diminished by the presence of PCE. Consequently, without PCE, water absorption rate was reduced by up to 92% in similar ACP modified cement paste samples, which also led to a major reduction in compressive strength.

Chloride Ion Diffusion Resistance of Bulk Hydrophobic Concrete: Comparison of w/c and Dosages

Abstract Post-cast application of hydrophobic agents onto hardened concrete is successful at reducing external ion diffusion into cement paste, this work examines pre-cast application of hydrophobic admixtures in fresh concrete. Concretes, with water to cement ratios (w/c) 0.45 and 0.50 (CEM I; low C3A), were mixed. Adding alkyltrialkoxysilane or triacylglycerol admixtures ranging from 1 to 3 wt%cem in these concretes were evaluated. Increasing the dosage of hydrophobic admixtures decreased the compressive strength. The usage of these admixtures did not hinder the further development of the microstructure as all concretes gained strength after one year, but not in the same percentage increase as the reference concrete. Chloride ion diffusion, after exposure to 3 wt% NaCl solution at 20 °C for 91 days, in concretes with 1 wt%cem admixture showed slight reductions in diffusion rate (8-17%) compared to the reference. At 3 wt%cem, triacylglycerol admixtures showed better hindering effects of inward chloride diffusion, this was especially evident in w/c = 0.45. Equivalent addition of alkyltrialkoxysilane-based admixtures increased the diffusion of chloride ions transferred into the cement matrix.

Cement-fly ash-based anti-icing concrete coating material for application onto tunnel-lining surfaces in cold regions

Large icing areas on the tunnel-lining surface can affect safe operation of roads and railways in cold regions. However, traditional deicing technologies (i.e., thermal and manual deicing) have problems, such as high-energy consumption, high cost, and low-deicing efficiency. To effectively solve the problem of “easy freezing and slow deicing”, we prepared an anti-icing concrete coating material using cement and fly ash, which exhibits cost-effectiveness and high anti-icing efficiency. The high performance of the coating material mainly relied on the developed low-cost and high-efficiency emulsion-type hydrophobic admixture and the micro-/nanobinary rough structure resulting from the recycled nylon mesh and metakaolin nanoparticles. Based on the systematic surface properties and freeze–thaw (F-T) and ice adhesion tests, we found that this material exhibited satisfactory anti-icing ability, easy deicing performance, and remarkable F-T durability. In addition, the superhydrophobicity mechanism and easy deicing property were studied via X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. Finally, we established a novel contact angle (CA) model considering the micro-/nano binary structure of the concrete surface and a theoretical model of ice adhesion. Based on this, the influence of surface CA and ice adhesion was theoretically analyzed. This research provides important guidance for solving the anti-icing problem of the tunnel-lining surface in cold regions and can realize the transition from “passive deicing” to “active anti-icing”.

Internal hydrophobization of cement-based materials by means of silanes

The paper shows the opportunity of application of an organosilicon compound such as triethoxyoctylsilane (OTES) containing long, hydrophobic alkyl sidechains (octyl groups – C8H17) attached to the silicon atoms, as the admixtures for internal hydrophobization of cementitious building materials characterized by a porous internal structure. The study included the cement paste, mortar and concrete with three different hydrophobic admixtures based on triethoxyoctylsilane, but with miscellaneous concentration of the triethoxyoctylsilane in the admixture and different dosage in the fresh mix. The impact of organosilicon hydrophobic admixtures on the mechanical properties such as compressive strength, capillary water absorption of the cement mortar and concrete and the microstructure of cement paste was investigated. The hydrophobic, silicon-based admixtures decrease the capillary water absorption coefficient significantly. Even by 81.1% in case of cement mortar. The mechanical strength of cement mortar is also decreased, by 23.6%. The noticeable changes in the internal structure of pores of cement paste only for one admixture is observed.

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.

Effects of a novel hydrophobic admixture on the sulfate attack resistance of the mortar in the wet-dry cycling environment

The sulfate attack tends to cause deterioration in the performance of cement-based materials. An innovative hydrophobic agent named Yellow River Engineering Consulting (YREC) was developed to improve the resistance of the mortar to sulfate attack in wet-dry cycling environment. In this study, an investigation was conducted to investigate the effects of the acid, alkali and salt solutions on the durability of the YREC. Meanwhile, a series of hydrophobic mortars with varying YREC mass fractions were prepared to explore the sulfate resistance in the wet-dry cycling environment. The water migration in wet and dry process was compared by conducting the water absorption and desorption tests. In addition, the XRD, FTIR, ESEM and MIP were applied to further analyze the properties of the YREC. According to the analytical results, the microstructure and hydrophobic functional group of the YREC remained unchanged under the erosion of the acid, alkali and salt solutions. The YREC could significantly reduce the surface cracking, strength loss and structural loosening of the mortar under the wet-dry cycling sulfate attack. In addition, the YREC played a role in reducing the rate of the water absorption and desorption, resulting in a decrease in the sulfate concentration and penetration depth. Finally, the mechanism analysis showed that the YREC could enhance the inhibitory effect on bi-directional water migration through hydrophobization and refining the pore structure of the mortar.

Pore Structure and Permeability of Cementitious Materials Containing a Carboxylic Acid Type Hydrophobic Agent

Integral hydrophobic treatment is the most effective method to prolong the service life of the concrete by resisting the transport of water containing aggressive ions. The hydrophobicity phenomenon of cementitious materials with carboxylic acid type admixture has been presented, and experimental studies, including water adsorption, amount of hydration products, and pore system, are conducted to reveal the hydrophobicity mechanism. It is reported that cementitious materials containing hydrophobic admixture present excellent water resistance ability, and the experimental results of nitrogen adsorption isotherm show that carboxylic acid type admixture addition increases pore volume and surface area of cement pastes. In addition, the fractal geometry theory is applied to reveal the relation between the pore structure and the permeability coefficient of cement pastes with a hydrophobic agent. In conclusion, the high tortuosity fractal dimension and the hydrophobicity of the pore surface result in water resistance when the cementitious system is mixed with a new type of hydrophobic admixture.

The effect of nano-scale calcium stearate emulsion on the integral waterproof performance and chloride resistance of cement mortar

Cement-based concrete materials are vulnerable to water and aggressive ions owing to hydrophilic and porous structure, which severely reduces their durability. Therefore, it is significant to improve the integral waterproof performance of cement-based concrete materials by using hydrophobic admixture. This paper studied the effect of nano-scale calcium stearate emulsion (NCSE) prepared by using non-ionic surfactant through a nascent saponification method on the integral waterproof performance and chloride resistance of cement mortar. The properties and morphology of calcium stearate emulsions prepared by using different non-ionic surfactants were also studied. The results showed that NCSE with particle size of 321.3 nm, viscosity of 180 mPa·s, good dispersibility, fluidity and storage stability was prepared by using fatty alcohol polyoxyethylene ether O-25 as non-ionic surfactant. The introduction of NCSE increased water contact angle on the internal and external surfaces of modified cement mortar. The water contact angle on external surface of modified cement mortar with calcium stearate (CS) content of 1.2 wt% reached 130°. The chloride resistance of cement mortar modified by NCSE was greatly improved. Compared to the blank group, the water absorption of modified cement mortar with CS content of 0.8 wt% at 48 h was reduced by 39.02%, the strength didn’t decrease significantly. The water absorption of modified cement mortar with CS content of 1.2 wt% at 48 h was reduced by 51.22%, the compressive strength and flexural strength decreased by 14.96% and 13.95%, respectively.

The effect of silanes as integral hydrophobic admixture on the physical properties of cement based materials

The paper explores the possibility of using organosilicon compounds (e.g., poly(dimethylsiloxane) and triethoxyoctylsilane) in commercial admixtures as internal hydrophobization agents for porous cement-based materials. The study involved the cement mortar with five different hydrophobic admixtures. Four of them is based on triethoxyoctylsilane, but with various concentration of the main ingredient, and one of them on poly(dimethylsiloxane). Mechanical properties, capillary water absorption, as well as microstructure were investigated. The organosilicon admixtures efficiently decrease the capillary water absorption even by 81% decreasing mechanical strength of cement mortar at the same time even by 55%. Only one admixture, based on poly(dimethylsiloxane) caused significant changes in microstructure of cement mortar.

An experimental investigation on the impermeability and durability of concrete with a novel and multifunctional hydrophobic admixture addition

AbstractIn order to improve the durability of concrete, hydrophobic technology is used to isolate the contact between concrete and external water. The addition of hydrophobic admixture is a popular method, but most of the hydrophobic agents mixed with cement sacrifice the partial strength of concrete to improve the hydrophobicity. In this paper, a novel and multifunctional hydrophobic admixture named YREC was prepared, which has a positive effect on strength, impermeability, and durability under freeze–thaw attack. The chloride resistance permeability of concrete mixed with YREC increases by 5.3 times. Water contact angles up to 108 ± 2° were achieved on the concrete. The action mechanism of YREC was investigated using multiscale pore size distribution by means of nitrogen adsorption and mercury intrusion porosimetry, scanning electron microscope, X‐ray diffraction testing, and thermogravimetric analysis (TG). The results indicate that YREC particles can accelerate cement hydration based on TG‐DTG analysis. YREC can be more effectively applied in practical engineering due to the simpler preparation process and cheaper raw material.

The effect of replacing sand with aggregate from sanitary ceramic waste on the durability of stucco mortars

During processing and transport, the ceramic industry generates big amounts of waste. In order to limit the number of landfills and to minimise consequences of such waste that is clearly noxious for the environment, this industry remains under great pressure to find effective recycling methods for its waste and by-products. What is more, given the limited resources of traditional aggregate, energy savings and protection of the environment, the construction industry is seeking for new sources of aggregate. For this reason, ceramic waste is increasingly frequently used as coarse and fine aggregate, both in mortars and in concrete mixtures. The goal of studies presented in the paper was to analyse the impact of recycled ceramic aggregate on the frost and salt spray resistance of stucco mortar used in the construction industry. Mortar recipes also contained admixtures that modify properties of the mixture and of the hardened product, such as copolymer of vinyl acetate and methylcellulose with a hydrophobic admixture. Elementary testing was performed related to mechanical and physical parameters of mortars. Among others tests were carried out of compressive strength and flexural strength, a determination was made of density, open and total porosity, absorbability, resistance to salt spray corrosion and frost resistance after 25 freeze–thaw cycles of samples. Replacement of sand by recycled ceramic aggregate causes a change in physical parameters of mortars. It has a positive impact on strength parameters of mortars with concurrent reduction in absorbability and capillary action. Testing of mortar with the addition of ceramic aggregate has proved better frost resistance and resistance to salt crystallisation as compared to mortar to which sand had been added.Graphic abstract

Preparation and properties of foundry dust/Portland cement based composites and superhydrophobic coatings

In this study, Found dust (FD) and Portland cement (PC) based bulk composites and superhydrophobic coatings were prepared to utilize the solid waste FD and improve the water permeability. First, the compositions, structures, pore parameters, and mechanical properties of the FD/PC composites were tested and analyzed, indicating that the mechanical strength of the FD/PC composites decreased with increasing FD content. The flexural compressive strength and compressive strength of the FD/PC composites with an FD content of 10% reduced by only 8.5% and 9.8%, respectively, compared to that of the neat hardened cement paste (HCP). At greater than 10% FD content, the mechanical strength of the FD/PC composite material drastically reduced. Second, the FD and PC based superhydrophobic coatings were prepared using a simple brush-coating method by introducing polydimethylsiloxane as a hydrophobic admixture. The composite coating exhibits superhydrophobicity after stored at room temperature for 24 h. In addition, the mechanical robustness of the FD and PC composite based coating is excellent in the abrasion and peeling test and was further improved by double-layer coating method. Particularly, the superhydrophobic coating can be easily repaired after getting damaged. Furthermore, the water absorption of the superhydrophobic coating modified FD/PC composites reduced by more than 76% in comparison with that of the uncoated FD/PC composites.

Effect of Nano-SiO2 on the Mechanical Properties, Microstructure, and Hydration Process of Cementitious Materials Incorporating Hydrophobic Admixture

AbstractIn this study, the effect of nano-SiO2 on the mechanical properties, microstructure, and hydration process of cementitious materials incorporating hydrophobic admixture (CM-HA) was studied ...

Internal hydrophobization of cement mortar by addition of siloxanes

Hydrophobic substances contain in its structure non-polar groups by which have the capability to "repel" water molecules. Because of them the material become hydrophobic, i.e. it is not water-wettable. Hydrophobic additives are used in various areas, including buildings, bridges, ceramic materials, underground constructions and marine constructions. The use of hydrophobic admixtures is one of the ways to protect building elements from adverse water effects, thereby increasing their durability by reducing the water absorption. In our study we investigated the influence of siloxanes on compressive strength and absorbability of cement mortar. The modification of cement mortar microstructure due to addition of organosilicon compounds was analyzed by mercury intrusion porosimetry. Finally we assessed the effectiveness of poly(dimethylsiloxane) and water solution of methyl silicon resin as hydrophobic admixture by measuring the water absorption coefficient.

Recycled Glass as Aggregate for Architectural Mortars

The possibility of recycling mixed colour waste glass as it is for manufacturing decorative architectural mortars, has been investigated. In mortars, the 0–33–66–100% of calcareous gravel volume has been replaced with recycled glass cullets, with no other inorganic addition. To mitigate the possible alkali–silica reaction, mixes with a hydrophobic admixture were also compared. The obtained results show that the replacement of calcareous gravel with glass cullets of similar grain size distribution permits to reduce the dosage of the superplasticizer admixture to obtain the same workability of fresh mortar; it does not affect significantly the mechanical performances, the water vapour permeability and the capillary water absorption but it reduces significantly the drying shrinkage deformation. The used recycled glass is classified as no reactive in terms of alkali–silica reaction neither in water nor in NaOH solution following the parameters of the current normative, even in the absence of the hydrophobic admixture. The hydrophobic admixture further delays the expansion trigger but not the speed of its propagation.

Influence of Hydrophobic Agent on Rheological Behavior of Historical Plaster. Part 1: Initial Hardening Time

The influence of time on rheological properties of modified lime plaster is analyzed in this paper. Effect of composition of mixture is examined as well. Especially changes of paste due to hydrophobic and pozzolanic admixture. Main aim of rheological test is determination of flow curves, obtained by applying a succession of constant strain rates for short times. Base on performed experiments, it can be concluded that hydrophobic admixture eliminated influence of pozzolana. Also both time and temperature caused significant changes in rheological properties. Increasing values decreases the flow characteristic of the plaster. A comparative measurement with pure lime plaster was done as well.

Development of hydrophobic concrete by adding dual‐crystalline admixture at mixing stage

A novel approach has been presented to add a dual‐crystalline hydrophobic admixture in fresh concrete for improving hydrophobicity against chloride and harmful chemicals. Dual‐crystalline material can utilize water of the fresh concrete to form crystals, but the challenge is to maintain adequate hydration and strength while improving hydrophobicity. This study presents the results from a comprehensive laboratory investigation on the application of 1, 2 and 8% of crystallizing aqueous and cementitious hydrophobic mineral in fresh concrete. Despite the high slump in the fresh mixture, no segregation was observed in the matured concrete. There was a marginal reduction of strength when a high percentage of admixture was used. Despite this, significant reduction of water absorption was observed indicating greater hydrophobicity. The optimum performance was found in mixtures with 2% admixture. Mixture with 2% aqueous hydrophobic admixture revealed marginal strength gain compared to 2% crystalline cementitious hydrophobic admixture, although water protection appears to be better in cementitious mixture.