The admixture industry in India is an evolved one. With usage history in mainstream projects of more than three decades, admixture usage has seen a tremendous upswing. The trend is quite clear, and it is certain that in future concreting operations, the admixtures shall become an integral part of the concrete mix. The earlier attitude of taking recourse to the use of admixtures only after facing problems is changing fast, and now, in most of the large projects, the admixtures are already included in the specifications.
As the infrastructure projects are more specific and need dependent, specific concretes will have to be designed to suit individual requirements. The durability would be the prime consideration as these structures cannot be easily replaced or repaired. Depending upon the appropriate selection of exposure classes, specialized specifications for concrete mix designs would need to evolve. In this regard, integral waterproofing additives are gaining momentum as a solution to help mitigate durability problems.
Concrete has an affinity to water and therefore is a wettable material. Water enters the concrete through continuous capillaries either under hydrostatic pressure or by capillary action. The porosity of concrete is one of the major factors contributing to ingress of water into the concrete. Good waterproofing needs a good base concrete. Thus, it is imperative that the concrete should be produced with a low water cement ratio and minimum permeability. That is where usage of Integral Waterproofing / damp proofing additives comes into the picture.
THE PROCESS OF WATER INGRESS IN CONCRETE AND CONSIDERATION IN THE DESIGN OF WATERPROOFING SYSTEMS
The ingress of water in concrete depends upon the degree of saturation of concrete and mechanisms of entry. The rate of water entry depends upon the micro-structure of the concrete paste. If unsaturated concrete is exposed to water, it will be absorbed into concrete even in absence of pressure due to capillary suction. Permeation properties of near surface concrete are very important while determining the entry of water into the concrete. Liquid, Gas or Ions can migrate in concrete by diffusivity because of a concentration gradient. In most of the circumstances capillary action rather than permeability controls the passage of water and this should be a major consideration in the design of waterproofing systems.
FUNCTIONING OF INTEGRAL WATERPROOFING ADDITIVES IN CONCRETE DENSIFICATION
The aim of integral waterproofing is to densify the concrete to prevent water ingress and/or convert wettable capillaries to non-wettable types that would eventually lower the penetration of water into the system. Figure 1 shows the concept of hydrophilic and hydrophobic capillary action. The theory of capillary and the concept of capillary rise and capillary depression provide a basis for working of hydrophobic waterproofing materials. Wettable surfaces have low contact angles and difficult to wet surfaces have higher contact angles. The high contact angles have a two-fold effect on concrete. Firstly, the pressure required to enter the concrete is positive whereby capillary action is nil and a high-water pressure (approximately 14 m head of water) would be required to penetrate the concrete surface. Hydrophobic surfaces exhibit high contact angles of water as shown in Figure 2. Integral Waterproofing Additives use this theory to affect permeability reduction in concrete/mortars.
In Short, waterproofing admixtures belong to a class of admixtures that improve concrete durability by controlling water and moisture movement and by reducing permeability and hence chloride ingress. This class of admixtures is referred to in IS: 2645. EN-934 refers them as water-resisting admixture and ACI 212.3R refers to the same as permeability reducing admixture. These admixtures are generally sub-divided into two categories (ACI Comm.212), viz., permeability reducing admixtures for concretes exposed to non-hydrostatic conditions (PRAN) and concrete exposed to hydrostatic conditions (PRAH).
TYPES / BASES OF INTEGRAL WATERPROOFING ADDITIVES BASED ON THE APPLICATION OF THE BASE CONCRETE MORTAR OR PLASTER
These admixtures can be based on different chemistry depending on the application of the base concrete, mortar or plaster. Damp-proofing admixtures or PRAN are water-repellent / hydrophobic. These are more suited for use in situations where the base concrete is not subjected to high hydrostatic heads. These for example can be used in external above ground walls in buildings, plasters, mortars, architectural concrete, concrete blocks, etc. Integral-waterproofing admixtures or PRAH may be hydrophobic (not necessarily). These are more suited for use in concrete/mortars subject to hydrostatic pressure heads. These for example can be used in water storage tanks, wet areas, basements, STPs, Tunnelling Concrete, Underground structures and other similar structures. Classification and materials used in Integral Waterproofing / Damp-proofing Admixtures is given in Table 1 below.
Table 1: Classification of Materials, Mechanisms and Applications for Integral Waterproofing Additives
|Classification||Raw Materials||PRAN/ PRAH||Mechanism||Applications|
|Water Repelling Materials||Soaps, Bitumen, Veg. Oils & Fats, Mineral Oils (Old Technology) Fatty Acids, Fine Wax Emulsions, Silicones, Silanes-Siloxanes (Latest Technology)||PRAN||Hydrophobicity and Pore Blocking||Above-Ground Concrete, Architectural Concrete, Concrete Blocks, Mortars, Plasters, Protective Screeds, etc.|
|Finely Divided Inert Pore Filling Material||Talc, Bentonite, Fullers Earth, Colloidal Silica, etc.||PRAH||Physical Pore Blocking||Universal|
|Finely Divided Reactive Pore Filling Material / Densifiers||Flyash, GGBFS, Slica Fume, Reactive Silicates, Calcined Clays, Colloidal Silica, etc.||PRAH||Pore Blocking, Capillary Reduction, Crystallization||Underground Structures, Wet Areas, Water Storage, Tunnels, Etc.|
|Conventional Admixtures – Water Reducers||Lignosulphonates, SNF, SMF, PCE Admixtures||PRAH||Capillary Reduction, Densification||Concrete|
|Conventional Admixtures – Air Entraining||Soaps, Rosinates, AOS, Etc.||PRAN||Making Capillaries Discontinuous||Mortars and Plasters, protective screeds|
|Conventional Admixtures – Acrylic / SBR Additives||Styrene Acrylic or SBR Emulsions||PRAN / PRAH||Hydrophobicity and Pore Blocking||Mortars, Plasters, Protective Screeds|
|Combinations of the Above||Multiple||PRAN / PRAH||Combinations||Multiple|
MODE OF ACTION FOR INTEGRAL WATERPROOFING ADDITIVES
Integral Waterproofing Additives generally function on the basis of one or a combination of the three mechanisms listed below.
- Reduction of Capillarity by w/c ratio reduction
- Hydrophobising Capillaries
- Physical or Chemical Pore Blocking
1. Reduction of Capillarity: This is achieved using Conventional water-reducers or Air Entraining Agents or by using reactive pozzolans and silicates. These additives may improve workability (increases slump) at the same w/c ratio or provide a reduction in w/c at the same workability levels. This property helps concrete achieve excellent compaction and denser hydration (C-S-H Gel Formation) thereby reducing capillary pores. Less capillary pores mean less transport of water through the cement matrix.
2. Hydrophobising Capillaries: This is achieved using hydrophobic additives such as Soaps, Bitumen, Veg. Oils & Fats, Mineral Oils (Old Technology) OR Long Chain Fatty Acids, Fine Wax Emulsions, Silicones, Silanes-Siloxanes, etc. (New Technology). These materials react with the cement constituents and form insoluble hydrophobic by-products that line the pores. This lining converts the water-absorbing capillary forces into water repellent capillary forces due to the hydrophobic effect of the constituent. The water is pushed out of the capillary pores and the concrete is kept dry. Fox e.g.: the stearates react with the calcium hydroxide in concrete to form insoluble calcium stearates that forms a hydrophobic layer on the walls of the pores in concrete. These admixtures are effective at reducing the capillary absorption under non-hydrostatic conditions only.
3. Pore Blocking (Physically or Chemically): Physical Pore Blocking can be achieved using inert powder fillers such as talc, bentonite, etc. or by using finely divided waxes, bitumens, or acrylic / SBR emulsions. When Hydrostatic Pressure is applied, these finely divided materials or emulsion globules are pushed into the capillaries, until they jam together, forming a physical plug, preventing further penetration of water.
Chemical Pore Blocking is achieved using advanced micro-fine latent hydraulic/reactive silicates or pozzolanic nano-particles to enable secondary hydration to achieve densest packing of C-S-H gel in the cement matrix on a nano-scale. The materials above use available free-lime [Ca(OH)2], in presence of water, to recrystallize and form new more stable, foil-like C-S-H and C-A-S-H phases. These materials when used as admixtures are also referred to as crystalline admixtures.
This crystalline mineralization process continues over time in presence of water, to reduce overall porosity, to heal micro-cracks and minimize the concrete pore volume. This process thus makes concrete watertight. Figure 3: shows the Working Mechanisms of IWP Admixtures
EFFECTS ON PROPERTIES OF CONCRETE THROUGH INTEGRAL WATERPROOFING ADMIXTURES
1.On Plastic Concrete
Integral waterproofing admixtures are formulated to affect the properties of the hardened concrete, and not those of concrete in its plastic state. Water repelling admixtures, conventional admixtures and air entrainers, may increase the workability of the plastic mixes slightly. On the other hand, inert pore fillers or reactive pore fillers, due to their finely divided particle sizes may decrease workability slightly. These materials mostly do not affect setting time or stability of the mixes. However, in all cases, it is advisable to test the material for required properties prior to use.
2.On Hardened Concrete
Integral waterproofing admixtures are designed not to have any significant impact on the mechanical properties of concrete. With most materials there is no significant changes in compressive/flexural strengths or on elastic modulus of the mixes. The only properties they impact are related to permeability of the concrete. This can be measured by means of initial surface absorption (BS: 1881 or Equivalent) or water penetration under pressure (DIN 1048 or equivalent).
- When used as a preventive means to waterproof structures, IWPs can be a cost-effective measure, as it prevents future deterioration and repair cycles.
- Provides a reliable secondary barrier against rainwater, moisture and ground water ingress into the concrete
- Easy to use, just mix into the concrete at batching plant or at site or in the transit mixer
- Speeds up construction, when used with high performance joint treatment systems, it can enable not using an external membrane application
- Permanent protection from water penetration and absorption, improves concrete durability
- Makes the mix more workable (improves the slump) at lower w/c
- Does not change setting time nor adversely effect the reinforcement.
- Free from chlorides
- Not a substitute to bad mix design and manufacture, placing and curing practices.
- These may not be capable of preventing water ingress through deep cracks or structural cracks in the concrete.
- Requires a high degree of quality control during concrete manufacture, placing and curing.
- In case of integral waterproofing or any other waterproofing treatment for underground structures, joints become the weakest link in entry of water and should be adequately treated.
- Application of Integral Waterproofing Compounds should be considered after characterizing its performance and requirements as per site conditions that the concrete would be subject to.
PRACTICAL USAGE GUIDELINES FOR INTEGRAL WATERPROOFING ADDITIVES
Integral waterproofing additives are easy to use, either in the concrete batching plant or in a transit mixer at site. These materialsshould be added to the concrete after all other components of the mix have been added. Concrete should be mixed for at least a minute after addition of Integral Waterproofing Additives. Dosage is generally at 0.5 to 2.0% by weight of cement or as per manufacturer’s recommendations. Complete dispersion of the material should be ensured prior to placing. Concrete placement should be followed by proper finishing, compaction and curing practices to get the best benefits.
Modern Plaster Additives
Modern plaster additives are available in both powder or liquid form and can be used for site production or for large scale industrial production of dry-mix plaster. These additives are multi-functional and capable of imparting workability, stability, water retention, sag resistance and enhanced adhesive properties to cement plaster. A closeup of the plaster is shown in Figure 3a and 3b below:
Dampness entering the living space (especially through walls and ceilings) is an indication that the structure has failed its durability and that structural elements have already begun deteriorating. With high demands on durability, the thought process should turn to preventing water ingress through the living space, by providing the correct plaster as an envelope to the building. This method ensures that the structure is protected against water ingress and the structure is protected from failure through its design life.
External building plasters are the first line of defense in providing the external envelope to the building walls. Plastering the external walls in the building, today involves multiple problems on its own. These Include:
- Good Quality Cement
- Availability of good quality Natural Sand
- Wastage on account of Plastering Practices
- Skilled Labour for Application
Modern plaster additives such as SS – PlastProof IL combines multiple benefits into one well designed product, which improves the following properties in any wall/ceiling plaster:
- Water Reduction
- Ability to be used even with crushed sand
- Excellent Bonding, even to concrete blocks
- Smooth Finish
- Minimal to Zero Wastage
- Lesser Rebound
- Improved Sprayability
- Minimal labour requirement for Finishing
Modern plaster integral waterproofing additives provide the robustness to convert any mortar, to a sprayable, easily finishable, durable wall plaster. The robustness of this formulation allows it to be used with multiple raw material sources including crushed sand, manufactured sand, GGBSF, Flyash, Natural sand, PPC and other base raw materials for plaster.
Water-resisting admixtures have a positive effect on the durability of concrete by mitigating water ingress and hence chlorides, etc. Surface absorption is also reduced and when concrete is exposed to harsh environs this admixture has a beneficial effect on increasing the lifespan of a concrete structure. However, it is to be remembered proper mixing is essential for the performance of the waterproofing admixture. Excess dosage of the admixture has to be avoided and when used with other admixtures compatibility check has to be done.
About the author
Sunny Surlaker is Heading the Technical Services Division at Assess Build Chem Private Limited. He is a noted concrete, admixtures and materials technologist with over 13 years of experience in the construction chemical industry in India, Europe, Middle East and Brazil. Sunny specializes in concrete technology, admixtures and formulating cement-based systems such as grouts, screeds, waterproofing, repairs and protective systems. His core functional areas are Concrete, Waterproofing, Repair and Rehabilitation, Training, Public Relations, Marketing Strategies, Technical Selling, Lab Set-up and operation, Raw Material Sourcing and Construction Chemicals Development. Besides this, Mr. Sunny has worked in developing material testing protocols, non-destructive testing and product development.