Table of Contents
Reasons Why Concrete Needs Waterproofing
Reasons Why Concrete Needs Waterproofing: Concrete waterproofing is critical in below-grade locations to avoid water infiltration and structural damage.
We have depleted the supply of construction sites with the desirable drainage pattern inherent in formerly plentiful high-ground terrain in many parts of the globe. As a result of this attrition, we’ve discovered that the only convenient and accessible locations are low-lying regions inside or near marshes, flood plains, along rivers and lakes, and so on.
These regions, with their elevated water tables and associated water pressures, also confront us with the possibility of even greater water heads as adjacent development progresses. Additionally, we have increasing water levels in a number of lakes and rivers. Numerous these locations also include pollutants known to be detrimental to a variety of kinds of concrete and concrete masonry units.
Waterproofing is necessary on concrete surfaces below grade for a variety of reasons. The main purpose for this is to keep moisture out of the facility. However, it is necessary to protect the structural contents from penetration of water, which may result in structural damage to the concrete or corrosion of the embedded steel.
By design, concrete is a porous substance that allows water to flow through through hydrostatic pressure, a water vapor gradient, or capillary action. Additionally, water may enter via cracks, structural flaws, or poorly built or fitted joints. Waterproofing is also needed to prevent concrete degradation caused by external and interior pollutants present on the construction site.
Chemical Resistance of Concrete
Concrete is chemically reactive owing to three main properties of its composition: permeability, alkalinity, and reactivity. The permeability of concrete to liquids and gases varies significantly across kinds. Even the most impervious concrete has some degree of permeability. Permeability rises quickly as the water-cement ratio rises and the moisture-curing time decreases. Fluid penetration into concrete is sometimes followed by chemical interactions with the cement, aggregates, and/or embedded steel, if any. Leaching of cement hydration chemicals or deposition of foreign crystals or crystalline reaction products may also contribute to the system’s degradation.
Acidic compounds react with the alkaline hydrated Portland cement binder. This reaction is often followed by the production and removal of soluble reaction products, ultimately leading in concrete disintegration. Due to the insoluble nature of the reaction products, deposits develop on the concrete surface or inside the concrete, resulting in a significantly decreased reaction rate. Typically, a rise in the concentration of aggressive chemicals in the solution increases the rate of assault.
The solutions may be alkaline, neutral, or acidic depending on their pH value. The pH value of neutral solutions is 7. Acid solutions have a pH less than 7, whereas alkaline solutions have a pH greater than 7. As the pH factor falls from 7, the solution gets more acidic, and its attacks on concrete becomes more violent.
The physical condition of the chemical agent is also critical. Dry solids have no effect on dry concrete. They may, however, attack wet concrete. A wet, reactive solid may behave similarly to an aggressive liquid or solution in attacking concrete. If the dry gases are aggressive, they may come into touch with enough moisture inside the concrete to enable the attacks. Gases that are moist and aggressive tend to be more damaging.
Alternate soaking and drying may be detrimental to the concrete structure, resulting in its disintegration as a consequence of an alkali–aggressive interaction. This happens when dissolved chemicals move through the concrete and accumulate at or near a surface susceptible to evaporation. The deposit that forms may be the original material or a product of a reaction in the concrete. As a consequence, efflorescence appears on concrete, brick, or stone walls.
Through freeze-thaw cycles, salt solutions may be more damaging to concrete than water alone. Water or salt solution damage may be avoided by including an appropriate quantity of deliberately entrained air in the concrete. This enables concrete of superior quality to generate air bubbles of the proper size, spacing, and distribution.
Numerous substances are corrosive to concrete. These substances are often found in the soil or adjacent regions of a below-grade construction. Prior to designing the waterproofing system, the designer is responsible for conducting a thorough chemical study of the soil. Additionally, the chemicals present may be detrimental to the waterproofing barrier. Acid waters, aluminum chloride, aluminum sulfate, ammonia vapors, ammonium sulfate, ammonium chloride, ferric sulfide, and ferrous sulfate are just a few of the chemicals that may dissolve concrete and attack the steel.
Along with chemical assaults from organic and mineral acids, some acidic industrial wastes, silage, fruit juices, sour milk, weak based salts, and certain untreated waters may deteriorate concrete. Additionally, ammonium salts and animal feces may oxidize and damage the concrete, causing it to deteriorate. Numerous chemicals attack concrete and cause irreversible chemical changes via reaction processes that are either partly or incompletely understood. Seawater, perhaps owing to its sulfate concentration, may be detrimental to permeable concretes or those constructed with a high tricalcium aluminate concentration in the cement. Typically, degradation develops as a result of calcium leaching from the concrete.
Not every chemical is corrosive to concrete. The majority of carbonates and nitrates, as well as certain chlorides, fluorides, and silicates, are common neutral salts that do not damage concrete. Limewater is generally helpful to concrete because it facilitates hydration without removing any lime from the mix. Generally, other mild alkaline solutions are not hazardous. When devoid of fatty oil additives or other potentially acidic elements, petroleum-derived products are generally safe to mature concrete. Certain of these materials may induce discoloration.
Concrete may fracture either during or after it has hardened.
Cracks, Openings, and Infiltration Points
Waterproofing is needed on concrete buildings to keep moisture out of the building and to preserve the concrete’s structural components and embedded reinforcing steel. Concrete may stay waterproof if its integrity is maintained. However, concrete may fracture both before and after it has hardened, and all of these fractures create opportunities for moisture penetration.
Concrete may fracture before to hardening as a result of construction movement, plastic or drying shrinkage, or early frost damage. After hardening, concrete may fracture due to settlement, seismic pressures, vibration, creep, excessive weight, or deflection caused by soil movement. Additionally, since concrete is a porous substance, it is vulnerable to moisture penetration in a variety of places.
All concrete joints, control joints, and expansion joints are potential moisture penetration points. Additionally, holes may form in tie rod holes, penetrations, and structural connections. Internal drains are additional sources of entrance for moisture. There is perpetual discussion about good vs negative side effects.
When making this choice, keep in mind that waterproofing is responsible for protecting the building. This is impossible with negative-side waterproofing. Waterproofing should always be put on the structure’s positive hydrostatic pressure side for maximum effectiveness.
By installing any system on the negative hydrostatic pressure side, the waterproofing system is exposed to the danger of being pushed off or disintegrated by moisture entering the concrete in vapor or liquid form. Waterproofing the structure’s negative side also tends to draw pollutants from the ground moisture into the concrete mass.
Treatment of Defects in the Concrete Surface
The condition of the concrete surface is a critical element influencing the effectiveness of waterproofing systems. A smooth, almost defect-free surface devoid of honeycombs, depressions, fins, holes, humps, dust, dirt, oils, and other surface contaminants is required to provide continuous support for the waterproofing material and enough adhesion between the membrane and the substrate. When unsupported material is subjected to water pressure, it may extrude, distort, and ultimately burst.
Adhesion between the concrete surface and the waterproofing membrane is also critical to preventing water migration and leakage if the membrane or concrete surface has any holes or flaws. Form coatings or release agents, as well as concrete curing membranes, may obstruct the formation of adequate adhesion and should be removed before to applying the waterproofing. In the concrete section of the requirements, the designer should define appropriate substrate preparation.
Typically, separate trades perform the concrete installation and waterproofing treatment, which may cause misunderstanding and difficulties. Disagreements often revolve on what constitutes adequate concrete preparation and who is responsible for doing the necessary repairs prior to waterproofing application. The designer may avoid these problems by including wording requiring concrete installation and repair to adhere to ASTM D 5925.
This is a great reference book that includes a list of remediation methods for detecting and fixing fins, insect holes, form kick-outs, and other inappropriate surfaces for waterproofing application. By referencing this standard in the Concrete Section and Waterproofing Section, possible issues throughout the project will be eliminated.
Additionally, the designer should obtain written approval from the waterproofing contractor prior to installation. The design requirements must address particular problems such as concrete repair after form removal and the removal and repair of any surface flaws that arise during construction. Precast concrete is often manufactured in a shop setting. Sharp offsets between precast sections should be rectified in the same way as new cast-in-place concrete is rectified. Surface imperfections, especially tie holes, should be rectified promptly after the removal of the forms.
All honeycombed and faulty concrete portions should be excavated to the sound concrete surface. If chipping is required, the edges should be perpendicular to or slightly undercut from the surface. There should be no feathery edges allowed.
The patched area and a 6-inch-wide zone around it should be moistened to minimize water absorption by the patching mortar. A bonding grout or bond coat should be produced by mixing roughly one part cement to one part fine sand to the consistency of thick cream.
Brush the mixture evenly into the surface. Fins, protrusions, and similar abnormalities protruding from the concrete surface should be chipped, hammered, or wire brushed back to the surface. Precautions should be taken to ensure that the waterproofing membrane system is applied on a fairly flat surface. Sharp surface offsets, such as those produced by misaligned formwork, should be mechanically abraded to provide progressive and smooth transitions between the offset surfaces.
Certain waterproofing methods may not need that all concrete surfaces be parallel to one another as long as transitions are gradual and smooth. In these instances, the waterproofing manufacturer should be contacted for particular needs. Prior to completely filling tie rod holes with a suitable patching substance, they should be properly cleaned and moistened.
Prior to waterproofing installation, the surface must be properly prepared.
Preparation of the Concrete Surface
A critical step in obtaining sufficient bond strength is paying close attention to the preparation of the surfaces to be waterproofed. Appropriate waterproofing performance is contingent upon proper surface preparation. The concrete surface must be free of contaminants that may impair the waterproofing membrane’s adherence to the concrete.
The exposed concrete surfaces must be devoid of loose, weak, or unsound components. Although concrete surfaces should be dry in general, certain waterproofing membrane manufacturers allow their products to be installed over wet concrete surfaces. In these instances, the waterproofing manufacturer should be contacted for particular needs.
During curing, care must be taken to avoid moisture accumulation at the contact between the concrete and the waterproofing membrane. Prior to applying the waterproofing membrane, testing should be conducted to verify the surface preparation’s sufficiency.
The strength of the prepared concrete, as well as the membrane’s capacity to cling to the concrete, are two critical factors that must be verified prior to the start of the project. In these instances, the waterproofing manufacturer’s specifications, as well as those of the American Concrete Institute and ASTM, should be examined for suggested procedures.
Assuring the Success of the System
Waterproofing is needed in sensitive and inhabited areas due to the porous nature of concrete. Numerous concrete roadways and driveways demonstrate the hazards that moisture penetration may bring. The waterproofing system’s effectiveness is contingent upon appropriate concrete surface preparation. Prior to waterproofing, all concrete surface problems must be corrected.
As an engineer, it is preferable to include appropriate concrete surface standards into the original design. This eliminates potential disagreement amongst the many trades engaged in waterproofing projects. This will result in success in one of the most challenging components of the building to design and one of the most disputed.