Concrete Fundamentals - CIV 1202: An Overview

• Fundamentals of Concrete Part 1 - CIV 1202

Learning Outcomes

• The definition of concrete and its uses will be explained
• Concrete admixtures will be described, as well as what they are used for
• The role of concrete curing and associated methods will be briefly described
• Concrete types and their differences will be identified
• How water content impacts concrete quality will be described
• The differences between fresh and hardened concrete will be described

What is Concrete?

• According to Kosmatka, S,H, et. al. (2002), concrete constitutes of a mixture of aggregate and paste
• The functions of the paste, comprised of Portland cement, are to bind gravel and sand aggregates together, ultimately hardening into a rocklike mass during "hydration", which is a chemical process
• Concrete is made from coarse and fine aggregates
• The particle sizes of fine aggregates are up to 9.5 mm
• Course aggregates are up to 150 mm, and are retained in the No. 16 sieve
• Paste is made of cementitious material, water, and air
• Portland cement is the most used type of cement

Applications

• Concrete is used to make bridges
• Concrete is used to make buildings, whether high-rise or low-rise
• Concrete is used to construct pavements, parking lots, gas stations, and roadways

Concrete Admixtures

• Concrete admixtures reduce water content by 12 to 30%, as well as improve workability, compaction, and concrete strength
• Accelerators increase the speed at which concrete sets and increase early strength development
• Retarders slow the chemical process so that the concrete remains plastic and workable for a longer duration, and include air-entraining agents
• Concrete gains strength over time if kept in a moist setting
• Concrete theoretically gains 90% of its strength within the first 28 days

Role of Concrete Curing

• Curing is performed in a laboratory setting or construction site after concrete is placed
• Curing time length depends on mixture proportions, specified strength, weather conditions, and future exposure conditions

How Concrete Curing is Performed

• Maintaining mixing water in concrete during the hardening process is important, and uses the following methods:
  • Ponding and immersion- Used for smaller projects and mainly used in laboratory settings
  • Spraying and fogging- Used to raise humidity by spraying a water mist to keep moisture
  • Saturated wet coverings
  • Leaving concrete in the forms- Protects against moisture loss as the forms are made of wood and kept moist in dry and hot weather
• Minimizing the loss of mixing water from the concrete's surface is also important and includes covering the concrete with impervious paper or plastic sheets

Concrete Types

• There are two types of plain cement concrete known as (PCC) and reinforced cement concrete (RCC)
• PCC is a concrete mixture without reinforcement, has good compression strength but poor tension
• PCC is commonly used for paving and flooring
• RCC is made of cement, sand, aggregate and reinforcement, and has increased tensile strength

Quality of Concrete

• Concrete quality is influenced by the bond between the paste and aggregate
• Hardened concrete quality is influenced by the water to cement ratio
• Too much water dilutes the cement paste
• Not enough water produces a stiffer mixture that is placed more easily
• Freshly mixed concrete should be plastic or semifluid to allow being molded

Fresh vs. Hardened Concrete

• Fresh concrete is at a stage where it can be molded in its plastic stage, and is also known as "green concrete"
• Acceptable fresh concrete should:
  • Be easily mixed and transported
  • Have a consistency allowing it to completely fill the forms it is designed for
  • Have good finishing characteristics
  • Have the ability to compact without a significant loss of energy
  • Be uniform throughout batches
• Hardened concrete represents the stage where the concrete is fully cured