Water Used in Concrete Mix

Course and Program Outcomes

This section outlines the intended outcomes for students studying the properties and implications of water in concrete design, specifically under civil engineering applications.

Course Outcomes:
- CO1: Predict basic engineering material problems based on their performance in civil engineering applications (C5).
- CO2: Demonstrate appropriate techniques and modern engineering tools to address civil engineering material problems (P5).
- CO3: Understand and effectively use well-established materials (A5).
Program Outcomes:
- PO2: Identify and analyze well-defined engineering problems, drawing substantiated conclusions using codified methods specific to their field.
- PO5: Apply appropriate techniques, resources, and modern engineering tools to defined engineering problems, understanding limitations.
- PO11: Demonstrate knowledge of engineering management principles and apply them in team settings to manage multidisciplinary projects.

Learning Outcomes

Upon completion of the module, students should:

Understand and explain the properties of water.
Identify impurities in water and their impact on concrete.
Assess the suitability of water for use in concrete mixes.

Importance of Water in Concrete

Water is a critical ingredient in concrete mixes primarily for initiating hydration—the chemical reaction that enables cement to set and harden. It serves several functions:

Dampens aggregates to prevent them from absorbing excess water.
Lubricates the mixture of gravel, sand, and cement for easier placement.
Facilitates the chemical reactions essential for setting and hardening the concrete.
Improves the workability of the mix, making it easier to manipulate.

Impact of Water Quantity

The proportion of water used in concrete mix is vital:

Insufficient Water:
- Leads to inadequate hydration, resulting in dry cement that is difficult to place.
- Weakens the cement, compromising the concrete's strength and durability, leading to increased voids and lower density.
- Can cause surface issues such as a chalk powder layer, hindering the bonding of subsequent layers.
- Results in 'honeycombed' concrete, where cement grout loss leaves only sand and aggregates.
Excess Water:
- Weakens the cement, reducing the overall strength and durability of the concrete.
- Can create voids as excess water evaporates, diminishing density.
- Concerns regarding structural integrity, with potential surface efflorescence and moisture issues.

Properties of Water

For effective use in concrete, water characteristics are crucial:

MUST be free from oil, acids, and alkalis.
Should have a pH value generally not lower than 6.
Must be devoid of harmful impurities such as iron or organic substances.
Saltwater is not advisable due to harmful salts that can corrode reinforcement.

Impurities in Water

Understanding the effects of various impurities in water is critical for ensuring concrete integrity:

Types of Impurities and Their Effects

Salt Water:
- Sea water may contain up to 3.5% dissolved salts, posing a risk of corrosion in reinforced concrete.
- Early strength can be higher, but later performance may drop, leading to structural failures.
Industrial Wastewater:
- Containing acids, alkalines, and organic matter, must be treated prior to use to avoid detrimental effects on concrete.
- Typical treatment reduces organic content significantly from 400 ppm to 20 ppm or less.
Silt or Suspended Particles:
- High levels contribute to decreased concrete strength and adverse bonding issues.
- Algal growth can trap air, reducing concrete strength and disrupting the aggregate-cement bond.

Acceptable Limits

To ensure quality, the following limits on impurities must be enforced:

Type of Impurity	Permissible % by weight
Organic	0.02%
Inorganic	0.30%
Sulphates	0.05%
Alkali Chlorides (Plain concrete)	0.20%
Alkali Chlorides (Reinforced concrete)	0.10%

Suitability of Water for Concrete

The suitability of water can be categorized based on its source:

Treated Water: Water that has undergone necessary treatment to remove harmful contaminants.
Natural Water: Water collected from natural sources, requiring testing for impurities.

Common Testing Methods

Determining water quality typically involves:

Initial Setting Time Test.
Compressive Strength Test.

Standards for Cement Classes

According to British Standards, the minimum initial setting times vary by type of cement:

Cement Type	Min. Initial Setting Time (min)	Required Initial Setting Time (min)
Ordinary Portland Cement (OPC)	45	75
Low Heat Portland Cement (LHPC)	60	90
Blast Furnace Slag Portland Cement (BFPC)	45	75
High Alumina Cement (HAPC)	120	150

Understanding the properties, implications, and treatment necessary for water used in concrete is essential for ensuring the quality and longevity of concrete structures.

Understanding Water in Concrete Mixes

Understanding Water in Concrete Mixes