Water impurities have a significant negative impact on the structural properties of concrete, notably its strength and durability. This is primarily evident in two aspects. Firstly, the setting times of Portland cement mixes using impure water differ from those using distilled water. Secondly, when comparing the strength of concrete specimens prepared with impure water to control specimens prepared with distilled water, there is a noticeable decrease in strength.
Effect of Water Impurities on Concrete Strength and Durability
The compressive strength of concrete is typically measured on the 28th day of curing. For assessing the quality of mixing water, a difference of up to 10% compared to the controlled test is considered acceptable. According to IS:456-2000, a deviation of +/-30 minutes in the initial setting time is allowed, provided that the initial setting time is not less than 30 minutes.
Concrete can be adversely affected by effluents from various sources such as sewerage works, sugar and fertilizer industries, paint, gas works, and textile industries. Tests have demonstrated that when water with a high concentration of dissolved salts is used or when structures are built near water bodies with excessive salt content, the compressive strength of concrete can decrease by 10 to 30% compared to concrete mixed with distilled water.
Elevated chloride levels in water can lead to surface efflorescence, persistent dampness, and increased susceptibility of reinforcement steel to corrosion. This problem is particularly severe in tropical regions, especially in lean concrete mixes. Table-1 provides information on the reduction of compressive strength in concrete structures caused by different salt concentrations in water.
Table-1: Effect of Different Salts in Water on Compressive Strength of Concrete
| Salt Content in Water (%) | Reduction in Compressive Strength (%) |
| 0.5S04 | 4 |
| 1.0 S04 | 10 |
| 5 NaCl | 30 |
| CO2 | 20 |
Water Impurities Effect on Concrete Properties
Various properties have an impact on the properties of concrete.
1. Suspended Particles in Water Effect on Concrete Properties
Suspended particles in the mixing water, up to 0.02 percent by weight of the total water used in concrete, do not have a significant impact on the properties of the concrete. While a higher concentration of suspended particles does not affect the strength of the concrete, it can affect other properties. The Indian code IS: 456-2000 sets a permissible limit of suspended particles in water, which should be below 2000mg/liter. Prior to using water in concrete, muddy water should be allowed to settle in a basin.
2. Miscellaneous Inorganic Salts in Water Effect on Properties of Concrete
The presence of salt in water can negatively impact the strength of concrete. Among the salts that can be found in water, manganese, tin, lead, copper, and zinc salts are the most common. Zinc chloride in water can delay the development of concrete strength, leading to a lack of strength gain on the second or third day of concrete testing. Another salt, lead nitrate, is also detrimental to concrete, significantly reducing its initial strength.
Sodium phosphate, sodium arsenate, sodium iodate, and sodium borate have a lesser but still noticeable effect on reducing concrete strength. Sodium and potassium carbonates, especially in high concentrations, cause rapid setting, resulting in weakened concrete. On the other hand, calcium chlorides enhance the setting and hardening process of concrete. However, the presence of calcium chloride should not exceed 1.5 percent of the total weight of the cement used in the mixture.
3. Salts in Seawater Effect on Properties of Concrete
Seawater consists of approximately 3.5% dissolved salts and its chemical composition remains consistent worldwide. The majority of chlorides are associated with sodium, some with potassium, while sulfates are associated with magnesium. Approximately 51.3% of the salt content in seawater is composed of chlorides, 3.6% of magnesium, 7.2% of sulfates, 28.5% of sodium, 1.3% of calcium, and 1% of potassium. However, the total salt content can vary significantly.
The penetration of ions from seawater into concrete is directly proportional to the salinity of the seawater, considering a specific mass of seawater. Among the chemical effects, sulfate is considered the most problematic, leading to the development of sulfate-resistant cement. Concrete with a very low water-to-cement ratio is favorable for achieving sulfate resistance. The salt content in seawater can reduce concrete strength by 10 to 20%. However, the corrosion of reinforcement is of greater concern than the strength reduction. Chlorides are the primary cause of corrosion, and the risk of reinforcement corrosion is higher when exposed to air rather than being submerged in water.
Chlorides also contribute to efflorescence. To mitigate this, it is recommended to use cement with a high content of C3A, as the chloride ions will be intercepted by the present aluminate. This leads to the precipitation of calcium chloroaluminate, which does not have any detrimental effects. This approach enhances the lifespan of steel and improves the durability of the structure.
The two main reasons for the presence of chloride ions in the concrete are
Calcium chloride is commonly used as an accelerating admixture in concrete. However, its use can negatively impact the sulfate resistance of non-sulfate resistant cements. This is not a concern if the cement already contains sulfate-resisting properties. In cold weather, calcium chloride can be used as an accelerator in combination with a certain amount of sulfate-resisting cement, equal to the amount used in regular cement. It’s important to note that codes generally discourage the use of calcium chloride when sulfate-resisting cement is employed. Nevertheless, in unavoidable situations, it can be utilized in plain concrete that will be submerged underwater.
4. Acids and Alkalis in Water Effect on Properties of Concrete
Industrial wastewater is unsuitable for use in concrete construction due to its harmful composition, which includes acids or alkalies depending on the specific waste produced by each industry. While a pH value above 6 indicates suitability for concrete construction, relying solely on pH does not provide an accurate measure of the acid content in the water. To assess the acid content accurately, the total acidity of the water can be determined by measuring the amount of 0.02 normal NaOH required to neutralize a 100ml water sample, using phenolphthalein as an indicator. For the water to meet the requirement, the volume of NaOH needed should not exceed 5ml. This acidity level corresponds to 49 ppm of H2SO4 or 36 ppm of HCl.
5. Algae Effect on Properties of Concrete
Algae can be found either on the surface of the mixing water or on the surface of the aggregates. When algae combine with cement, they weaken the bond between the cement paste and aggregates. Additionally, if algae enter the mix through water, it leads to significant air entrainment, which ultimately reduces the strength of the concrete.
6. Sugar Effect on Properties of Concrete
When the sugar content in water is below 0.05 percent by weight of water, no negative impact is observed on the concrete structure. However, if the sugar content reaches 0.15 percent, it retards the setting time and early strength of the concrete. Interestingly, it has been noticed that the strength of the concrete improves on the 28th day. Increasing the sugar content to 0.20 percent actually accelerates the setting time. However, excessive sugar beyond this point leads to rapid setting but adversely affects the strength of the concrete on the 28th day.
7. Oil Contamination Effect on Properties of Concrete
Mineral oil, devoid of any animal or vegetable oil, does not harm the properties of concrete. In fact, when the mineral oil content reaches 2%, it is reported to enhance the strength of the concrete. However, exceeding 8% mineral oil content has the opposite effect, leading to a decrease in strength. On the other hand, the inclusion of vegetable oil in water during concrete production demonstrates negative consequences on concrete strength during its later stages.
What are Maximum Limits of Water Impurities for Concrete Construction?
Table-2 provides the permissible limits for solid impurities in water utilized for concrete production. The recommended pH range for constructing concrete is typically 6 to 8. Ideally, water equivalent to drinking water is considered the most suitable for construction purposes. The determination of solid content in water follows the procedures outlined in IS: 3025.
Table-2: Limits of Permissible Impurities in Water for Concrete Construction
| Types of Impurities in Water | Limit of Permissible Salt (Percentage weight of water) |
| Organic Solids | 0.02 |
| Inorganic Solids | 0.03 |
| Sulfates (SO3) | 0.04 |
| Alkali Chlorides (as Cl2) | |
| 1. Plain Concrete | 0.2 |
| 2. Reinforced Concrete | 0.05 |
Impurities in Curing Water Effect on Concrete Construction
The primary purpose of curing concrete is to facilitate water absorption into the material. However, if proper measures are taken to prevent water loss, curing can be carried out without the need for additional water. While some water inevitably evaporates from the surface of concrete structures, the hydration process occurs within the interior.
Nevertheless, the lack of moisture at the surface due to evaporation necessitates curing. Using seawater for curing can introduce chloride ions into the surface zone, which may subsequently migrate inward through diffusion. It is important to note that most durability issues originate from the surface or progress inward from surface attacks. Marine structures designed for submersion in seawater face a significant risk due to dissolved salts.
However, these problems can be mitigated through proper curing with fresh water. The presence of iron or organic matter in curing water can lead to staining or deposits on the concrete surface. According to the guidelines outlined in IS: 456-2000, the use of water containing iron or tannic acid compounds is restricted for curing purposes.
FAQs about Water Impurities Effects on Concrete
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What is u003cstrongu003eeffect ofu003c/strongu003e water u003cstrongu003eonu003c/strongu003e concrete strength?
Water can have both positive and negative effects on concrete strength. Proper curing with adequate moisture helps achieve optimal strength. The water-to-cement ratio is critical, as excessive water can weaken the concrete. Excess water during mixing or placing leads to increased porosity and reduced strength. Cyclic wetting and drying, as well as chemical attack from certain substances in water, can cause cracking and degradation of strength. Controlling water presence, managing the water-cement ratio, and ensuring proper curing are essential for achieving desired concrete strength and durability.
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what is effect of hard water on concrete?
Hard water can have a negative effect on concrete. It contains minerals such as calcium and magnesium, which can react with the cement paste in concrete and form insoluble compounds. This reaction can lead to the formation of efflorescence, a white powdery deposit on the surface of concrete, which can affect its appearance. Additionally, the presence of minerals in hard water can increase the risk of scaling and corrosion of embedded reinforcement in concrete, leading to structural issues over time. It is important to consider the water quality when mixing and curing concrete to minimize the potential negative effects of hard water.
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What is quality of water used in concrete?
Water quality is important in concrete as it should be clean, free from impurities, and have an appropriate pH level. Excessive mineral content, chlorides, and sulfates can negatively impact the concrete’s strength and durability. The temperature of the water should also be suitable for the conditions. Using high-quality water helps ensure the integrity and long-term performance of the concrete.
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Can sea water be used in concrete?
Yes, sea water can be used in concrete, but it requires careful consideration and proper measures. Sea water contains a high concentration of chloride ions, which can be detrimental to the durability of concrete structures. However, in certain coastal or marine construction projects, where the use of fresh water is limited or not feasible, sea water can be used with additional precautions. These precautions typically involve the use of corrosion-resistant reinforcement, increased concrete cover, and special admixtures to mitigate the harmful effects of chlorides. Proper testing and monitoring are necessary to ensure the performance and longevity of concrete made with sea water.
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How we can perform water test for concrete?
To perform a water test for concrete, collect a sample of the water and measure its temperature, pH level, chloride ion concentration, total dissolved solids (TDS), and alkalinity. These tests help assess the water’s suitability for concrete mixing and its potential impact on the concrete’s performance. Follow testing standards and consult with professionals for accurate results.