Hydrophobic Admixture Research Articles

Estimation of corrosion resistance of modifying concrete in a solution of sulfuric acid

This study presents the test results of 8 concrete series in 5% sulfuric acid solution for 28, 56 and 180 days. Each series was made using two mixtures based on CEM II/A-S 32.5 and CEM III/A 32.5 cements. Modification of the properties of concrete was obtained by the introduction of superplasticizer, silica fume, complex of structure modifier and hydrophobic admixture. The water-binder ratio varied from 0.27 to 0.63, the compressive strength was 26 to 83 MPa, and water absorption from 3.4 to 8.4 %. Samples of test cubes (10x10x10 cm) and test beam (16x4x4 cm) were prepared to immersion in the acid solution. The assessment of corrosion resistance was carried out on the weight loss and strength of concrete in relation to the initial value of 28 days. The obtained results showed that the surface layer of concrete in all samples was destroyed after 28 days of exposure. The deterioration of the corrosion resistance of modified concrete in relation to ordinary concrete without additives was observed regardless of the type of cement. An exception was a series of concrete, which had a water-binder ratio of 0.27–0.28 and a compressive strength of 77–83 MPa.

A novel approach of introducing crystalline protection material and curing agent in fresh concrete for enhancing hydrophobicity

A new line of research to enhance the performance of concrete under adverse (harsh) and normal (air cured) curing conditions is presented. A crystallising hydrophobic admixture and curing agents were added to fresh concrete to improve its resistance against severe environmental conditions. A two-stage approach was pursued by adding the crystallising admixture to fresh concrete followed by curing agents, in a wax and liquid forms, in a separate application process, followed by exposing concrete to normal and adverse curing conditions. Results obtained suggests that protecting concrete with the crystallising admixture followed by applying wax based curing agent improves concrete strength and its resistance to water ingress than concrete cured with the liquid curing agent. When following the crystallising-wax treating system under adverse curing conditions, a more conserved strength was noticed compared to that produced by the crystallising-liquid system. Using the liquid curing agent in concrete with high water to cement ratio (w/c) has increased the cracks in the internal structure, while water permeability has decreased, either under normal curing conditions or adverse conditions. Following this protection-curing system in industry would resolve the problem of applying protection on wet surfaces and increase concrete’s resistance to deterioration. A microscopic study of the crystallising material was attained with a Scanning Electron Microscope (SEM) to check crystal growth with time.

Properties of Modified Lime-Based Plasters for Renewal of Historical Buildings Exposed to Accelerated Carbonation Test

This paper deals with determination of basic physical, mechanical, thermal and water transport properties of lime–based plasters whose composition was modified by the addition of diatomaceous earth. To eliminate possible deterioration of original lime plaster by natural weathering, the hydrophobic admixtures on the stearate and oleate basis were added into the plaster mixtures and boiled linseed oil as a painting was applied. All studied material parameters were tested after 28 days of wet curing and after exposition to accelerated carbonation. The results of examined properties of developed plasters gave promising outcomes for the use of hydrophobised materials in renewal of historical buildings. Based on the obtained data, plaster made of lime hydrate, diatomite, and combination of water repellent agents can be recommended for renovation purposes.

Stainless and Galvanized Steel, Hydrophobic Admixture and Flexible Polymer-Cement Coating Compared in Increasing Durability of Reinforced Concrete Structures

The use of stainless or galvanized steel reinforcements, a hydrophobic admixture or a flexible polymer-cement coating were compared as methods to improve the corrosion resistance of sound or cracked reinforced concrete specimens exposed to chloride rich solutions. The results show that in full immersion condition, negligible corrosion rates were detected in all cracked specimens, except those treated with the flexible polymer-cement mortar as preventive method against corrosion and the hydrophobic concrete specimens. High corrosion rates were measured in all cracked specimens exposed to wet-dry cycles, except for those reinforced with stainless steel, those treated with the flexible polymer-cement coating as restorative method against reinforcement corrosion and for hydrophobic concrete specimens reinforced with galvanized steel reinforcements.

Application and verification of direct transesterification as a method to quantify fatty acids in cement and concrete

Fatty acids are increasingly being evaluated as phase change materials to enhance thermal regulation in buildings and as hydrophobic admixtures to reduce water ingress into concrete. This paper describes the development of a method for the rapid and accurate quantification of fatty acids in cement and concrete. The method is based on direct (in situ) transesterification of fatty acids into fatty acid methyl esters and their subsequent extraction in a single step, followed by quantification by gas chromatography. The method was validated using cement treated with olive oil and milk and showed a proportional relationship between dosing and fatty acids quantified. This method provides an accurate alternative to existing qualitative procedures.

Properties of Lime Plaster with Hydrophobic Admixture

The effect of metakaolin and hydrophobic agent admixture on properties of newly designed lime plasters is analysed in the paper. The overall majority of physical - chemical building deterioration is related to the penetration of moisture and soluble salts into the building structure. For that reason, the modified lime plasters were in the wide range of various properties tested. Comparative measurement declared the usage of metakaolin and zinc stearate does not significantly influenced basic physical parameters and water vapour transport, but reduced the liquid water transport which is very positive finding.

Durability of superhydrophobic engineered cementitious composites

Key elements of infrastructures throughout the United States are displaying poor durability, especially in northern regions where freeze–thaw damage is prevalent. One main factor leading to the early deterioration of concrete is related to the infiltration of water into the porous structure of the concrete matrix. To account for this, sealers or water repellant coatings are often applied on the surface of cementitious materials to reduce the ingress of water into the material. However, when the material develops micro-cracks, which is unavoidable, water can easily penetrate and saturate the bulk of the material. By incorporating a hydrophobic admixture within the concrete mix, water is restricted to enter the capillary voids and porous space, where, upon freezing, damage occurs. This type of modification is achieved in superhydrophobic engineered cementitious composites (SECC) designed with hydrophobic or superhydrophobic air voids evenly distributed throughout the cementitious matrix, providing effective protection against water infiltration. Moreover, SECC incorporates fiber reinforcement tuned to limit the crack opening. The reported research demonstrates the improved durability in fiber reinforced cementitious materials by creating a 3-dimensional hydrophobization to reduce the water absorption and permeability as well as to improve the freeze–thaw performance.

Characterization of silane-based hydrophobic admixtures in concrete using TOF-MS

Silane-based hydrophobic admixtures especially alkyltrialkoxysilanes are used as water repellent agents for the surface protection of concrete. To optimize the structure of alkyltrialkoxysilanes in terms of their performance and their long term durability it is important to understand the chemical reactions taking place between the silicon organic compounds and the materials on which they are applied. For this purpose the characterization of alkyltrialkoxysilanes and their reaction products in concrete is necessary. Therefore we adapted an analytical method based on time-of-flight mass spectrometry (TOF/MS) combined with electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI). Monomeric alkyltrialkoxysilanes could be analyzed by the former method, reaction products which could be identified as Silsesquioxanes (SSOs) by the latter one. The results indicate that ESI-TOF/MS and MALDI-TOF/MS serve as a reliable and convenient tool to characterize monomeric silane-based hydrophobic admixtures as well as their reaction products resulted from hydrolysis and condensation.

Moisture Transport Properties of Hydrophilic Mineral Wool

Mineral wool materials are widely used for thermal insulation of buildings due to their low thermal conductivity and high fire resistivity. On this account, they are popular materials for passive fire protection of buildings. Thermal insulation boards are usually provided with hydrophobic admixtures that ensure their functional properties even in the contact with moisture. In this paper we focused on investigation of hygric transport properties of hydrophilic mineral wool materials that could find application in interior thermal insulation systems as well as in desalination and drying of salt laden materials and building structures. The obtained results give evidence of the effect of fiber orientation on studied material properties and reveal that fiber orientation perpendicular to board surface is a perspective way of materials development.

A study of the properties of portland cement modified using peat-based hydrophobic admixtures

Industrial production of portland cement with the simultaneous introduction of hydrophobic components is simulated. Their effect on the properties of the modified portland cement is determined. The method developed provides insulation of the cement from drip and, partially, vaporous moisture. The interaction between the dispersed phase of the cement and molecules of the organic admixture takes place by forming hydrogen bonds between surface silanol groups of cement particles and oxygen-containing groups of the admixture. The industrial applicability of the hydrophobization method is shown.

Effect of hydrophobic admixture and recycled aggregate on physical–mechanical properties and durability aspects of no-fines concrete

No-fines concrete with a compressive strength in the range 7–30MPa at 28days of curing were optimized by changing the water/cement ratio from 0.41 to 0.34 and the aggregate/cement ratio from 8 to 4. Some mixtures were also repeated with the addition of a hydrophobic admixture and prepared by fully replacing the ordinary aggregate with recycled aggregate to evaluate durability effects. High susceptibility to carbonation was observed for all the no-fines mixes studied. The use of recycled aggregate increases capillary water absorption (about 50%); however, the related decrease in durability could be easily counteracted with the use of a hydrophobic admixture.

Effect of low dosages of waste GRP dust on fresh and hardened properties of mortars: Part 2

Part 1 of the work reported that by replacing 5–10% of sand volume with GRP dust, workability, autogeneous shrinkage, deformability and total porosity, though with a smaller average radius, of mortars increased, thereby reducing significantly the mechanical performance, when wet curing conditions are adopted. However, the risk of cracking induced by restrained shrinkage and the capillary water absorption is lower in the presence of GRP dust, leading to enhanced durability of GRP mortars when used as supporting role. Therefore, in the present work, plaster mortars manufactured by replacing 0–2.5–5% of sand volume with GRP dust were characterized. For comparison, the addition of an hydrophobic admixture at different dosages was also considered. Permeability is not significantly reduced by the low addition of GRP dust, but it is slightly increased by silane addition. Thermal insulation properties, capillary water absorption and resistance to efflorescence are better with waste GRP dust addition, especially when combined with silane.

Use of no-fines concrete as a building material: Strength, durability properties and corrosion protection of embedded steel

Although no-fines concrete has been generally used for paving applications, it could be considered in other non-structural applications, such as reinforced panels, thanks to its acoustic, thermal and permeability properties. In this work, mechanical, durability-related properties and the protection provided by no-fines concrete to embedded steel against carbonation-induced corrosion have been investigated on mixtures with compressive strength in the range 7–30MPa. Additional protections, such as a mixed-in hydrophobic admixture, the coating of cement paste on the reinforcing bar or the use of galvanized or stainless steel bars, are also considered. Results show that, although no-fines concrete is susceptible to fast carbonation and it cannot provide long-term passivation to embedded steel, it may prevent corrosion in elements exposed to the atmosphere and sheltered by rain. In case of frequent contact with water, additional protections are required, preferably based on the use of corrosion resistant bars.

Combined effect of expansive, shrinkage reducing and hydrophobic admixtures for durable self compacting concrete

This paper presents the results of an investigation carried out to develop white self-compacting concretes (SCCs) especially devoted to durable architectural structures. In fact, shrinkage-free SCC mixtures were studied, obtained by combining CaO-based expansive agent and shrinkage reducing admixture. Also a hydrophobic admixture was added to SCC in order to preserve the white surface from the growth of micro-organisms as well as to increase concrete durability. Rheological tests were carried out on cement pastes, as well as on fresh SCCs, containing the three admixtures in order to study their influence (alone or in combination) on cement paste and concrete rheology. Also thermogravimetric analysis was carried out on cement pastes in order to evaluate the influence of various admixtures on portlandite solubility. Hardened SCCs were characterized by means of compression tests, free dying shrinkage, and restrained expansion measurements.

The effect of silane-based hydrophobic admixture on corrosion of galvanized reinforcing steel in concrete

Sound or deliberately pre-cracked concrete specimens, with 0.5 or 1 mm wide crack, were manufactured with water to cement ratios ( w/ c) of 0.45 and 0.75, both in the presence and in the absence of a silane admixture. The specimens were exposed to wet–dry cycles in a 10% NaCl aqueous solution. The results, in terms of electrochemical measurements, and visual and metallographic observations carried out on the galvanized steel reinforcement removed from the specimens, showed that the hydrophobic concrete is able to protect galvanized steel reinforcement from corrosion even in the presence of cracks in the concrete cover, especially when a high w/ c is used.

Oxygen diffusion through hydrophobic cement-based materials

The oxygen diffusion coefficient through hydrophobic cement-based materials fully immersed in water was determined by potentiostatic measurements on concrete and by the use of a diffusion cell on cement pastes and mortars. The obtained results show that very high oxygen diffusion occurs through cement paste, mortar and concrete made with hydrophobic admixture as opposed to negligible diffusion through the reference cement matrix without admixture. Moreover, the oxygen diffusion coefficients measured through hydrophobic cement matrices immersed in water were comparable with those reported in literature for unsaturated cement materials in air. These experimental results appear to confirm that oxygen dissolved in water directly diffuses as a gaseous phase through the empty pores of a hydrophobic cement matrix. This could explain the severe corrosion of steel reinforcement embedded in cracked hydrophobic concrete immersed in an aqueous chloride solution observed in a previous work.

High Performance Stucco to Optimize Moisture Management in Wood-Frame Stucco Walls

Abstract Stucco or portland cement plaster is widely used in North America as an exterior cladding material for the wood-frame walls. Recent computer-based numerical simulation studies at the National Research Council (NRC) Canada, Institute for Research in Construction (IRC) have indicated that low liquid diffusivity and high water vapor permeability of the stucco material can positively influence the overall moisture management capacity of wood-frame stucco walls. This paper presents the results from experimental and numerical modeling studies carried out at the NRC-IRC on the development of high performance stucco materials and its effect on the overall moisture management capability of wood-frame stucco walls. Liquid water and water vapor transmission properties of several commercial/conventional stucco materials and some newly formulated compositions were measured and compared under laboratory conditions. The experimental results suggest that by appropriate choice of the mix composition, addition of a proper hydrophobic admixture, and using aggregates with a hydrophobic coating, stucco material with lower liquid water diffusivity can be produced without reducing the water vapor permeability. The results from the numerical modeling study show newly developed high performance stucco materials can significantly improve the moisture management capability of wood-frame stucco walls.

The effect of silane-based hydrophobic admixture on corrosion of reinforcing steel in concrete

The influence of a hydrophobic admixture based on silane on the corrosion resistance of steel reinforcement in concrete was studied. Sound or deliberately pre-cracked concrete specimens were manufactured with w/c of 0.45 and 0.80, both in the presence and in the absence of silane. The specimens were fully immersed in a 3.5% NaCl aqueous solution. The results, in terms of electrochemical measurements, visual observations, and weight loss measurements of steel reinforcement, show that silane blocked corrosion process in uncracked concrete specimens. On the other hand, in cracked concrete specimens, corrosion of steel reinforcements was unexpectedly more severe in hydrophobic specimens rather than in the corresponding not hydrophobic ones. It is believed that oxygen, which is needed to feed the corrosion process, diffuses faster in a gaseous phase through the open concrete porosity in the hydrophobic concrete, whereas in concrete without silane, oxygen diffuses much more slowly through the water filling the pores of the saturated concrete.

Thermal Conductivity of Mineral Wool Materials Partially Saturated by Water

The thermal conductivity of several types of mineral wool-based materials, namely, materials with hydrophobic admixtures, hydrophilic admixtures, and without any admixtures are measured as a function of moisture content from the dry state to the partially water saturated state. An impulse technique is employed for the measurements using both surface and needle probes. The data are analyzed using the Bruggeman effective media concept for different shapes of inclusions and Wiener’s basic formulas. It is found that for most materials, the experimental data for thermal conductivity in the range of low moisture content are close to the lower Wiener’s bound but in the range of higher moisture content the data are close to the upper Wiener’s bound.

The effect of initial moisture content on water transport in concrete containing a hydrophobic admixture

Tests on initially saturated and dried concrete containing a hydrophobic admixture showed that initial moisture content had a significant effect on measured water transport properties. Concrete specimens containing the hydrophobic additive significantly reduced water penetration when the concrete had been initially dried, and had limited or no positive effect on water penetration into initially saturated specimens. The reduction in water transport compared with the control was generally more pronounced in hydrophobic concrete of higher w/c ratio, as well as under conditions of limited curing and greater drying. The hydrophobic admixture had no significant effect on water vapour diffusivity. These results suggest that the ingredients in the admixture only become effective where a clear wet–dry interface is present and tend to influence water transport through larger pores.