Since 1824 the invention ofÂ Portland cement, concrete materialÂ hasÂ beenÂ 180Â years of history. Currently, the world'sÂ annual productionÂ of concreteÂ has reachedÂ more than 30 billionÂ cubic metres,Â and isÂ widely used inÂ civil engineering, water conservancy, construction engineering, marine, transportation, highwayÂ andÂ railway projects, and evenÂ aerospace engineeringÂ and so on.Â It can be said thatÂ concrete materialsÂ made â€‹â€‹a greatÂ huge contribution towards the developmentÂ of human civilization.
In recent years, many literatures reported due to the lack of durability of concrete structures causing hugeÂ economic loss. The United States had a loss of 700 billion U.S. dollars in 1975 due to corrosion of concrete structure, and in 1985 it reachedÂ
1680Â Billion; it cost the United States 91 billion Dollars only to repair damaged bridge due to lack of durability; the United Kingdom spent up to 200 million pounds each year for the cost of repairing reinforced concrete structure.Â
De Sitter's "law of five" stated that one dollar spent in getting the structure designed and built correctly is as effective as spending $5 when the structure has been constructed but corrosion has yet to start, $25 when corrosion has started at some points, $125 when corrosion has become widespread.
At present, the UK is experiencing more and more extreme weather during winter and there isÂ a wide range ofÂ chloride ionÂ corrosion to the road and bridge structures as a result of de-icing gritting, andÂ the existence ofÂ acid rainÂ in some industrial areas also cause concrete structures to suffer.Â Therefore, the corrosionÂ ofÂ these structuresÂ is particularly important,Â and the durability of concreteÂ has become one of the most focusedÂ issues in relation to the water conservancy, transportation and building construction.
1.2 durability of concrete
The AC1201Â Committee defines the durability of concreteÂ as the resistance of climate, chemical attack, abrasion and other damage process. Concrete structures are vulnerableÂ in the course ofÂ the natural environmentÂ or humanÂ activity;Â in fact aging is another factor which is liable for concrete materials to damageÂ over time, resulting inÂ decreasedÂ bearing capacity and durability.
There are a number of causes responsible for reducingÂ the durability ofÂ concrete structures, theÂ carbonation of concrete,Â reinforcement corrosion, chlorideÂ ion penetration,Â freezing and thawing, alkaliÂ attackÂ andÂ some times due toÂ micro-organisms. However there is a lot more issuesÂ related toÂ durability, the impactÂ factors andÂ failure mechanismÂ is veryÂ complex.Â The followingÂ brieflyÂ describesÂ several effect, respectively,Â the failure mechanismÂ and impact.Â
1.2.1 CarbonationÂ of concrete
Carbonation of concrete is one of the important factors that are influencing theÂ durability ofÂ concrete structures. CO2, SO2Â and other acidic gasesÂ or liquids penetrate into theÂ concrete, triggering the chemical reactionÂ with alkaline substances and lowering theÂ pHÂ value. This brings a neutralisation of concrete, where CO2 inducedÂ the neutralizationÂ process that is known asÂ concreteÂ carbonation.
TheÂ mechanism ofÂ carbonationÂ are:Â CO2 penetrate into theÂ concrete poreÂ andÂ start chemical reaction with Ca(OH)2 producing CaCO3 andÂ H2O.Â On the other hand cement hydrationÂ also takes place and 3CaO Â· 2SiO2 Â· 3H2O (C-S-H)Â is generatedÂ which gets involved inÂ carbonationÂ reaction.Â The main chemicalÂ reaction as follows:
CO2 + H2O â†’ H2CO3
Ca(OH)2 + H2CO3 â†’ CaCO3 + 2H2O
3CaO Â· 2SiO2 Â· 3H2O + 3H2CO3 â†’ 3CaCO3 + 2SiO2 + 6H2O
2CaO Â· SiO2 Â· 4H2O + 2H2CO3 â†’ 2CaCO3 + SiO2 + 6H2O
When theÂ carbonationÂ causesÂ the pHÂ value to fall down to about 8.5,Â it has beenÂ generally believed thatÂ concreteÂ is carbonised.Â Steel's passive filmÂ loses its steady state whenÂ theÂ pH value of concrete is less thanÂ 11.5. When theÂ carbonationÂ depth exceeds concrete's its protectiveÂ layer,Â givenÂ theÂ appropriate temperature, air and moisture conditions, and the steelÂ inside of the concrete rustÂ easily, thus affectingÂ the durability ofÂ concrete structures.Â Meanwhile, during theÂ carbonationÂ process, theÂ reduction of alkali gives a chance to allow cementÂ hydrationÂ products to decompose and release crystallised water,Â initiating irreversible shrinkage of concrete. If thisÂ process isÂ carried out under theÂ constraints,Â often lead toÂ the formation ofÂ micro-cracks on the concrete surface, whichÂ further accelerate the carbonationÂ reaction.Â Furthermore, carbonationÂ also makes concrete to be brittle and its ductilityÂ deteriorated.
1.2.2 Steel corrosion
Carbonation andÂ reinforcement corrosionÂ are the main reasons lead to loss of durability ofÂ reinforced concrete structures. Discussed above is the mechanism ofÂ carbonationÂ of concrete, and steel corrosion mechanism is briefly described below.
Under normal circumstances, concreteÂ pore solution appears to be alkaline, and the pHÂ value isÂ betweenÂ 12Â andÂ 13. In thisÂ strongly alkalineÂ environment, a layer ofÂ dense oxideÂ (nFe2O3 Â· H2O)Â forms on theÂ steelÂ surface to protect theÂ steelÂ from corrosion.Â However, if theÂ protective layer isÂ wholly or partiallyÂ damaged, a large potential difference in different parts ofÂ the surface will be formed, and the formation ofÂ cathode andÂ anode.Â InÂ the presence of moistureÂ and oxygen, steelÂ electrode reactionÂ occursÂ and starts corrosion process.Â SteelÂ corrosionÂ is usually divided intoÂ natural electrochemical corrosionÂ and stray currentÂ corrosion.Â Corrosion of reinforcing steel bar in concreteÂ is generallyÂ the naturalÂ electrochemical corrosion, the electrochemicalÂ reactionÂ as follows:
AtÂ the anode, Fe2+Â along with OH-Â formÂ insolubleÂ Fe (OH) 2,Â and furtherÂ oxidisedÂ to produce Fe (OH) 3,Â the reaction is as follows:
The generatedÂ forcing its inner layerÂ of ironÂ intoÂ the cathode, there byÂ further development ofÂ corrosion.Â Some of theÂ may also be subjected toÂ water loss,Â formingÂ FeOOH (oxyÂ iron hydroxide),Â and some willÂ generate Fe3O4 Â· nH2OÂ dueÂ to insufficientÂ oxygenÂ for reaction, create a layer of looseÂ rust on the steel surface.Â As a result of corrosion, the volume of steel reinforcement could expand about 3 to 7 times of its original, which wouldÂ haveÂ exerted a large tensile stress to the surrounding. Since concrete is not good against tension, cracks may form andÂ will accelerate theÂ corrosion ofÂ steel even more, leading toÂ a vicious cycle.Â Therefore,Â the resultÂ is caused byÂ steel corrosion,Â crackingÂ of concreteÂ upÂ to the protective layer,Â reducingÂ the effective area ofÂ â€‹â€‹reinforcement, and ending up inÂ structural damage.
1.2.3 Chloride Corrosion
ChlorideÂ ionsÂ are the most important andÂ one ofÂ the common media that are liable for destroying the steel passivation layer.Â During the concrete manufacturing process, its mix materials or addedÂ admixturesÂ may containÂ chloride ions, whileÂ concreteÂ can be exposed toÂ waterÂ orÂ de-icingÂ saltÂ gritting environment. TheseÂ factors canÂ make the chloride ionÂ concentration on theÂ steel surfaceÂ to reach a critical point where corrosion of reinforcement takes place.
When chloride ion dissolves in water its penetrating ability increases dramatically, that can be easily adsorbed and kept on the steel surface, leading to greater corrosion. The reaction is as follows:
1.3 durability andÂ permeabilityÂ of concrete
1.3.1Â The relationship betweenÂ concrete'sÂ durability andÂ permeability
From theÂ above mechanism ofÂ various types ofÂ corrosion, it can be seen that H2O, CO2, O2 and chloride ionsÂ play a key role, and in particularÂ the role ofÂ water:
H2O and CO2 penetrate into theÂ concreteÂ leading to the formation of H2CO3,Â which isÂ a necessary condition forÂ carbonation of concrete. Carbonation of concrete would not continue without the presence of those two elements.
The presence ofÂ O2 and H2O makeÂ it possible forÂ steel corrosion, and ifÂ neither is dispensableÂ toÂ the formation ofÂ the cathode, therefore notÂ to generate Fe(OH)3Â and rust layer.
ChlorideÂ ions could only penetrate concrete easily when dissolved inÂ waterÂ and it catalysesÂ the corrosion of passivation layer.Â If without the presence of water, the external chloride ions could not enter theÂ concrete system, orÂ accumulate withinÂ the concrete structure to reach aÂ critical concentration.
External H2O, CO2 and chlorideÂ ions have been able toÂ enter the concrete, mainlyÂ depends uponÂ permeable of concrete.Â Large number of studies show thatÂ the permeabilityÂ of concreteÂ and its durabilityÂ is closely related (Figure 1.1). Permeability is generally consideredÂ to be a crucial indicator to evaluate concrete's durability. AsÂ some expertsÂ commented, concrete with lower permeability generally has better durability.
The figure belowÂ conciselyÂ reflects theÂ relationship between the durability andÂ permeability.
Figure 1.1 relationships between the durability andÂ permeability of concrete.
1.3.2 Dynamics Affecting Permeability of ConcreteÂ
To reduce theÂ permeability of the concrete, we must firstÂ understand theÂ features affecting permeability of concrete.
Concrete isÂ solidifiedÂ byÂ cementÂ hydration withÂ sand and gravelÂ aggregate, and existing as heterogeneousÂ porousÂ material. TheÂ permeabilityÂ subjected the speed of proliferation orÂ migration of gas, liquid, and ionsÂ under pressure,Â chemical potentialÂ or theÂ electric fieldÂ in the Concrete.Â A point of viewÂ from the microstructure is that concreteÂ isÂ porous, and itsÂ permeability is closely related to porosity, porosityÂ distributionÂ and poreÂ continuity.
The sources of poresÂ in concrete can be divided intoÂ two major categories:Â constructiveÂ pores andÂ structural pore.Â Constructive pores are formed during the manufacturing process owing toÂ insufficient degree of vibration, resulting inÂ unsatisfactory density,Â therefore leaving pore spaces inside of concrete. Structural pores are formed during concrete's hydrationÂ process, due toÂ excessive moisture evaporation. The pores can also be classifiedÂ according to theirÂ size:
GelÂ pore- that is,Â the pores existing in the gridÂ structureÂ of cementÂ gel, cement hydrationÂ producesÂ porousÂ calcium silicateÂ gel, counting forÂ 28% ofÂ gel volume, and itsÂ sizeÂ is generallyÂ 1.5nm to 3.0 nm,Â slightly bigger than water molecules in terms of magnitude, and the permeability coefficientÂ is small,Â about 10-6cm/s to 10-9cm/s, is one ofÂ the smallestÂ structural pore and is generally consideredÂ impermeable.
Capillary poreÂ -Â that is, space left in the concrete after evaporation ofÂ excess waterÂ during the cementÂ hydration process.Â The sizeÂ of it variesÂ from 10nmÂ - 100nm. The waterÂ content needed for cement hydration is around 20%-25% of cement, but the actualÂ quality ofÂ waterÂ is muchÂ larger than thisÂ value.Â Some part of theÂ pore volumeÂ in cement hydrationÂ process will be occupiedÂ when theÂ cement gelÂ formedÂ (cementÂ hydrationÂ generatedÂ solid volumeÂ of cementÂ isÂ 2.1 timesÂ the original), butÂ the cementÂ hydrates are stillÂ unable to completelyÂ fillÂ the spaceÂ originallyÂ occupied by water. Therefore,Â the greater theÂ water-cement ratio,Â the more the poresÂ left behind afterÂ water evaporation, the larger the pore space and the worse the resistance to permeability.
Deposition poreÂ - aggregate particlesÂ in concrete are mostly surrounded by cement,Â so the greatest impactÂ on the permeability of concreteÂ isÂ permeableÂ cement, whereas aggregateÂ particles themselves have little impact on permeability.Â However,Â condensationÂ in the concreteÂ hydrationÂ process leads toÂ the formation ofÂ pores due to sandÂ and aggregateÂ settlement and inconsistent deformation ofÂ sandÂ andÂ aggregate materials and surfaceÂ waterÂ evaporationÂ also lead to the formation ofÂ connected poresÂ which are even largerÂ than theÂ capillary pores. Those are theÂ main reasons forÂ permeability of concrete.
Other thanÂ the existence of pores, the impact ofÂ crack must not be ignored. Cracks inÂ concrete can be caused mainly from twoÂ aspects, plastic cracking andÂ shrinkage cracking. when the concreteÂ at theÂ plastic stage,Â a large amountÂ of waterÂ evaporate from its surface,Â theÂ surface tension acts to force concrete surface shrinking and this results in formation of plastic shrinkage crack. The other type of cracking happens during the cementÂ hydration process, chemical reaction generate heat and this makes aÂ temperature gradientÂ inside and outside theÂ concrete, causingÂ unevenÂ expansionÂ of concreteÂ volume, thus causing cracks forming. When theÂ crackÂ size reachesÂ 0.1mm, it willÂ beÂ vulnerable to water penetration.
In addition, exposingÂ concreteÂ to the weathering and erosion in the natural environment also reduces itsÂ impermeability. It is worth mentioning a chemical reaction takes place in concrete between tricalcium silicate,Â dicalcium silicateÂ and waterÂ to produceÂ calcium silicate hydrateÂ andÂ calcium hydroxide, which calcium hydroxide has greater solubility in water. When water goes inside the concrete, calcium hydroxide seeps through it leaving the concentration out of balance, and calcium silicate, calcium aluminateÂ and calcium oxideÂ that have already reacted with water willÂ be decomposedÂ into the water andÂ washedÂ away, leading toÂ structural pores to increase in size and quantity, and loosening the concrete structure, increasing its permeability and eventually reducing its performance.Â
From the aboveÂ review we can see there are three mainÂ reasons accountable for concrete permeability: (l)Â concreteÂ pore spaces;Â (2)Â internalÂ cracks;Â (3)Â concrete erosion by weathering forming water channel.
Due to variety ofÂ componentsÂ of concrete,Â complex hydration reaction, theÂ environment the concrete is surrounded by andÂ poorÂ weather conditions, the solutionÂ to theÂ impermeabilityÂ of concreteÂ is very difficult.
1.3.3 Methods to improve the impermeability of concrete structures
There are four conventional methods that are used to improve the impermeability of concrete:
Through theÂ different gradationsÂ ofÂ gravel,Â concrete can be made with improvedÂ density, but the procedure is veryÂ demandingÂ to the gravelÂ gradation, strictly conformed to the sieveÂ size distributionÂ curve. This methodÂ not only increaseÂ costs, but difficult for implementation, thus not commonly used in the UK.
Such as fly ashÂ added toÂ concrete,Â silica fume,Â granulated blast furnace slagÂ and otherÂ admixtures,Â not only can improve theÂ structural interface of concreteÂ andÂ cement pasteÂ pore structure, but also help improveÂ the flow, reduceÂ water consumptionÂ and increase theÂ impermeability andÂ DurabilityÂ . HoweverÂ this technology is heavily dependent on theÂ source raw material.
Incorporation ofÂ additives
ConcreteÂ mixed withÂ additives, such asÂ water-reducing agent, air entraining agent, expanding agentÂ andÂ water repellent and so on, to appropriately reduce water consumption as well as water-cement ratio, in order to improveÂ the workability of concrete andÂ to change the pore structure in the hardened concrete. Thus obtaining significant decrease in pore sizeÂ and porosity,Â the poresÂ are more subtle,Â more uniform which makesÂ the impermeabilityÂ and densityÂ of concreteÂ to be improved. Incorporation ofÂ additivesÂ to improve theÂ impermeability of the concreteÂ has obvious and effective results, but there are alsoÂ a number of downsides, whileÂ only suitable forÂ new construction.
Use of WaterproofÂ membrane andÂ waterproof coatingÂ outer cover
WaterproofÂ membrane andÂ waterproofÂ coatingsÂ can be used forÂ new orÂ existing projects.Â WaterproofÂ membrane in terms of classes and categories include asphaltÂ waterproofing membrane, flexibleÂ polymer bitumenÂ waterproofing membrane,Â plastic bitumenÂ waterproofing membrane, and ternaryÂ PVCÂ waterproofing membrane.Â Waterproof coatings areÂ usually acrylic,Â polyurethaneÂ coolÂ class, cementitious capillary crystalline and silicone based waterproof coating.
From technicalÂ point of view of the four different methods described above:Â the most direct, simple, and effective way to improve theÂ impermeabilityÂ of concreteÂ is use of waterproof materials.Â In addition, theÂ waterproof coatingÂ andÂ waterproofing membraneÂ not only appropriate forÂ newly constructed buildings, but alsoÂ particularly suitable forÂ protective measures of the existing construction.
1.4 Silicone Silane
SiliconeÂ based silane is one category of the broad term waterproof coating, and it differs from other waterproof coatingÂ by:Â the formerÂ makes a good use ofÂ the permeability of concrete,Â with a certain depth ofÂ penetrationÂ into theÂ concrete surface, providing an immersionÂ protection, whereas the later completely blocksÂ the poresÂ on the surface. We can clearly tell from the comparison above that siliconeÂ based silane delivers impregnated protection,Â not onlyÂ greatly reduceÂ concrete'sÂ capillaryÂ water absorptionÂ but also preventÂ freeze-thaw damage, steelÂ corrosion due to carbonation and chloride ions attack,Â ensure its long-term durabilityÂ (alkali resistance,Â UV resistance).Â SinceÂ silane maintainsÂ the permeability ofÂ concreteÂ andÂ external appearance,Â so it will notÂ happenÂ the sameÂ way as otherÂ film-forming agent which causes cracking. Its features are especially useful forÂ roadsÂ and bridge structures that need resistance toÂ constant abrasionÂ and corrosion.Â
Figure 1.2 Ways of sealing pores on concrete surface
FillingÂ the pores b) FilmÂ coating c) Silicone Silane
By applying siliconeÂ silane throughÂ brush or spray, siloxaneÂ hydrophobicÂ membrane is formed on the silicate substrate surface, so thatÂ it changesÂ the nature ofÂ the substrate surface. When the angle, at point of contact between substrate surfaceÂ and water becomes greater than , the entryÂ of waterÂ into pore space is prevented, thus achieving theÂ waterproof effect.
Figure 1.3 the effect of contacting angle (angle of contact,)
Figure 1.4 the effect of contacting angle (angle of contact,)
1.4.1 Category of Silane
SiliconeÂ based waterproofing products usuallyÂ containÂ silaneÂ alkyl, siloxane,Â alkylÂ siliconÂ alkoxideÂ andÂ hydrogen silicone oilÂ as the main active ingredient.Â They areÂ composedÂ differently for various purposes, someÂ productsÂ contain 100% of theÂ active material, and some have their active ingredients dissolved in a solvent by a certain percentage. TheyÂ can be divided intoÂ the following categories:
Water-solubleÂ silicone based penetrant
The main componentÂ of water-solubleÂ siliconeÂ penetrant is methyl-silicate solution and is generallyÂ in the form of yellow or transparentÂ liquid.Â The methylÂ silicateÂ is susceptible to weak acidÂ and is easilyÂ decomposed when in contact withÂ water and carbon dioxideÂ in the air, forming a waterproofÂ poly-methyl-etherÂ siliconÂ membrane and soon making a good bonding with the concrete surface and through the internal layer to improve the penetrationÂ resistanceÂ of mortar.
Relatively cheap and easy to use
Slow reaction with carbon dioxide with 24h of curing required
Can only be used under correct circumstances since it is still vulnerable to rain and frost few hours after application, causing unreacted alkali metalÂ methylÂ silicateÂ to leave concrete surface and losing its functionality
Solvent based silicone based penetrant
The main componentÂ of solvent-based silicone penetrant is siloxane isobutyl silane, and organic solvents are added as a carrier. Active siloxane, especially the alkylation poly-siloxane, its polymer molecular chain contains a certain number of active groups such as hydroxyl, carboxyl, amino and so on.Â As such agent is sprayed on to the concrete surface, with catalyst or its self-introduced amino it solidifies, forming a hydrophobic layer. During the formation of hydrophobic membrane, it does not require the introduction of carbon dioxide from the air, or the production of alkaline carbonate substances which are harmful to the concrete.
Product is stable and therefore easy for storage
Durability of the hydrophobic membrane is higher than the methyl silicone alkoxideÂ , alkyl hydrogen silicone oil.Â
When applied to a surface of concrete, solvent evaporates very quickly, depositing a thin layer of film covering pores on the concrete surface.
Since the layer is so thin that it almost does not change the natural appearance of concrete.Â
Silicone solvent is also less influenced by the outside environment than the methyl sodium silicate, therefore providing better resistance to water penetration.
It is suitable for reinforced concrete, marble and other low porosity substrate thanks to its decent durability, good penetrating ability.
The treatment surface must be dry when application.
Due to demand of organic solvents as a carrier, there may be some threads toward the environment, and the problem has raised a growing social concern, so it needs further research to resolve.
Silicone cream penetrant
In recent years,Â solvent-basedÂ siliconeÂ acrylic resinÂ is under more stringent environmentalÂ regulatory restrictions, the high performance, low-pollutionÂ water-basedÂ acrylicÂ siliconeÂ coatingÂ gradually becomesÂ a new focusÂ of attention.
SiliconeÂ creamÂ is aÂ water repellentÂ organic polymerÂ latexÂ (such as acrylic acid, acrylicÂ polymer cream, etc.) and activeÂ silicone creamÂ copolymerizationÂ of a structure coating. It can form aÂ transparentÂ organic polymerÂ creamÂ membraneÂ that has goodÂ adhesionÂ to theÂ concrete surface, butÂ it is relatively poorÂ in heat andÂ weather resistance.Â TheÂ activeÂ silicone creamÂ contains aÂ crosslinking agentÂ andÂ catalystÂ compositions,Â and water loss can be carried out at room temperature, forming aÂ poly siloxane network structureÂ of theÂ elastic membrane.Â This membrane has excellentÂ resistance against high andÂ low temperature and water repellence. But to an extend, not performing well in adhesion for someÂ filler.
Furthermore, in order toÂ overcome the serious loss ofÂ materialÂ whenÂ applying the siliconeÂ water repellentÂ products, to lengthenÂ the contact timeÂ with theÂ concrete surface, andÂ to increase theÂ penetrationÂ depth, scientists have further developed paste, gel, silicaÂ powder and so on to help achieve the competent performance.
1.4.2 Study and application of Silane
OrganicÂ silicon compoundsÂ born in the 19thÂ century, butÂ until theÂ mid-20th century, the United StatesÂ and European countriesÂ firstÂ began to use it forÂ waterproofingÂ of building structures.Â In the past two decades, organicÂ silicon has beenÂ a widespread concern inÂ the field of concrete structure waterproofingÂ research and application.
On going research in the world
In 1990, WACKER CHIEMIE GMBH (DE)Â patentedÂ the EP0442098. Huhn, Dr.Karl and many others whoÂ introduced theÂ organicÂ poly-siloxane silane with an averageÂ size less thanÂ 0.3. It can be madeÂ using a mixingÂ device at the rightÂ turbulent andÂ pressure of 0.01 - 1MPa (HBS)Â under the pressure to form a concentrated solution of organicÂ poly-siloxane, and then diluted with waterÂ underÂ similar conditionsÂ to achieve desired concentration,Â which can also be adjustedÂ by addingÂ acidÂ to attain a pH ofÂ around 3 - 7.
In 1991, Robert L. Cuthbert and Edwin P. Plueddemann from the Dow Corning Corporation patented US 5073195.
In 1993, Dr. Goebel Thomas Michel Rudolf and Alff Harald from DEGUSSA patented EP 0538555 and in which they presented that they have achieved less than 1 droplet of the silane cream.
In 1994, Dr. Montigny Armand and Kober Hermann patented EP0616989.
In japan, Hamasaka Mitsuo from the TOYO ink MFG co Ltd patented JP 09-202875. He introduced the composition which had better performance with long term storage, and stability, which could penetrate into capillary pores on the concrete surface, through bonding reaction to form a hydrophobic layer to improve water resistance.
In 1998, WACKER CHEMIE GMBH (DE) patented the EP0819665, enabling it to be publically used for buildings' waterproof treatment.
In 1999, Dow Corning Corporation introduced its new patents US 6103001 and WO 00/3406.
In 2000, Hwang In Dong from Korea improved the stability and penetrating ability of silicone based silane, achieving a penetrating depth greater than 4mm, and water absorption less than 0.1.
1.4.3 Products of silaneÂ protectiveÂ Coatings