Concrete is the number one building material in the world because it is strong, durable, and can provide a safe and comfortable environment in which to live and work. Many structures, such as our homes and offices, have concrete as the foundation, floor and wall elements. Over their lifetime, these elements have the potential to be exposed to rain or ground water. Because concrete is absorptive, porous, and susceptible to cracking, any water that penetrates through concrete acts as a carrier for deleterious materials that can lead to premature deterioration, thus shortening a structure’s service life. In addition, the living environment can be compromised from water penetration which can cause damage to its contents, and lead to high humidity levels, mold, and mildew, affecting well-being and comfort of the inhabitants.
How can we protect concrete structures from water damage? Fortunately, there are options to manage the infiltration of water to help keep structures dry and safe.
Managing Water Infiltration in Concrete
After concrete is placed, the first line of defense against water infiltration above grade is to divert rainwater away from structures by sloping the finished-grade or abutting pavement away from the structure.
Additionally, the use of externally-applied coatings or membranes below grade, and using drain boards against the outer side of poured concrete or block walls, can be utilized in combination with appropriate drain tile, and vapor barriers beneath concrete floors to effectively repel and divert unwanted water off into swales, ravines, or storm sewers.
Preventing Water Infiltration with a Good Concrete Mixture
Typically, good quality, uncracked concrete will not permit the passage of water. Therefore, it is important to start with a good quality concrete mixture that has a low water content. For concrete that is only in contact with water where low permeability is required, the American Concrete Institute Building Code (ACI 318) stipulates a minimum compressive strength of 4,000 psi (28 MPa) and a maximum water-cementitious materials ratio (w/cm) of 0.5, with no limit on the amount of supplementary cementitious materials (SCMs) that can be used. The permeability of concrete can be reduced further to enhance its watertightness, that is, its "waterproofing" performance, as discussed below.
Concrete with "Watertight" Performance
"Watertight" concrete can be obtained by:
- i) reducing the total amount of water used in the mixture;
- ii) using SCMs such as fly ash, slag cement, natural pozzolans (calcined clay), high-reactive metakaolin, and silica fume; and
- iii) adding integral waterproofing admixtures.
Working with Low Water Content Cement
To facilitate concrete placement, consolidation and finishing in concretes with relatively low water content, water-reducing admixtures, categorized as normal, mid-range, high-range, may be required. The BASF Master Builders Solutions brand offers a wide range of water-reducing admixtures, including mid-range water-reducing admixtures (MasterPolyheed® admixture) and high-range water-reducing admixtures (MasterGlenium® admixture). Fly ash, slag cement and natural pozzolans are cost-effective SCMs that can be used to reduce concrete permeability. However, their availability may be limited in some areas. High-reactive metakaolin and silica fume (MasterLife® SF 100 product) also provide significant reductions in permeability, thus are routinely chosen for enhancing the overall durability of concrete.
Crystalline Capillary Technology to Prevent Water Infiltration
To further address water infiltration, integral waterproofing admixtures, typically crystalline capillary-based (such as MasterLife® 300D admixture), are available. Crystalline capillary admixtures react in concrete in the presence of moisture to form insoluble crystalline products that fill fine pores and help to seal hairline cracks. Their ability to seal hairline cracks has led to increased acceptance and their widespread use in various concrete applications.
Preventing Drying Shrinkage that Can Cause Concrete to Crack
An often-overlooked factor is that even high-quality concrete, can crack and have widths beyond the narrow hairline cracks that crystalline capillary admixtures can help seal, and thus allow water penetration and leakage if exposed to water. A major cause of concrete cracking is drying shrinkage. To minimize cracking due to drying shrinkage, BASF recommends the use of either a shrinkage-reducing admixture (MasterLife® SRA 035 admixture) or a crack-reducing admixture (MasterLife® CRA 007 admixture), depending on the application.
Addressing Corrosion Cracking Potential
Cracking can also occur if other potential durability issues, including corrosion of steel reinforcement, are not addressed. In steel-reinforced structures exposed to chlorides in service, the use of a corrosion-inhibiting admixture (MasterLife® CI series of admixtures) is recommended to minimize corrosion cracking potential.
There are multiple options to consider for waterproofing concrete structures, each option has performance limitations. When designing and building a watertight concrete structure, the most effective waterproofing strategy is to use a combination of external water-repelling barriers, integral waterproofing of the concrete with an appropriate admixture solution, and proper drainage for water. This systems approach will help ensure a dry, comfortable structure and avoid inevitable, time-consuming, and costly options to remedy leakages after the fact.
Watch: Video showing sealing of a hairline crack with an integral crystalline capillary waterproofing admixture (MasterLife 300D)