How do you calculate air content in concrete?
Air Content – Air content is calculated by subtracting the unit weight, ρ, from the theoretical unit weight, T, divided by the theoretical unit weight, T, multiplied by 100 as shown below. Example: Theoretical Unit Weight = 151.7 lbs./cu. ft.
What is concrete air mix?
Air entrainment is the intentional creation of tiny air bubbles in concrete. A concrete maker introduces the bubbles by adding to the mix an air entraining agent, a surfactant (surface-active substance, a type of chemical that includes detergents).
How is entrained air calculated?
When you measure air in concrete, the percentage reading represents the total amount of air—entrapped and entrained air. For example, if the reading on an air meter is 6% air, it means that approximately 1.5% of the total is entrapped air and 4.5% is entrained air.
How much air do I add to concrete?
Entrained air should fall between 4% and 7% of the concrete’s volume. For concrete that will be regularly exposed to freeze/thaw cycles, aim for 6%. Anything less than 4% would not have the durability needed to last through multiple winters. Be careful not to go overboard with air entrainment, however.
How do you calculate the yield of concrete?
Yield is determined as batch weight divided by density. This is converted to relative yield, which is the total volume of the concrete received divided by the volume the producer intended to provide. If relative yield is 1.00, then it’s exactly the same. But this is expressed as cubic feet per cubic yard.
What causes high air content in concrete?
Cement • An increase in the surface area (or fineness) of cement will decrease the air content. A high cement factor concrete will entrain less air than a lean mix. As the soluble alkali content of cement increases, the air content will increase.
Does air entrained concrete crack?
OTHER KNOWN BENEFICIAL QUALITIES OF HAVING AIR-ENTRAINED CONCRETE ARE; Increases the porosity of the concrete while at the same time, reducing its permeability to water and liquids in general. Increases the concrete’s resistance to cycles of wetting and drying which make it susceptible to cracking and fissures.
Should I use air entrained concrete?
The primary use of air-entraining concrete is for freeze-thaw resistance. Hard-troweled surfaces are not recommended for exterior concrete slabs, because the smooth finish becomes slippery when wet. Hard troweling is also not recommended for air-entrained concrete for several reasons.
What does too much air in concrete do?
A.: Strength loss is the major effect of too much air. Each percent increase in air content can reduce compressive strength by 2% to 6% for moderate-strength concrete. The degree of strength loss depends on the cement, admixtures, and other concrete ingredients used.
Is code for air content in concrete?
Air-content of freshly mixed concrete shall be determined by the pressure method given in IS 1199. Time of setting, initial and final, shall be determined as given in IS 8142. Bleeding shall be computed at a percentage of the net amount of mixing water in the concrete.
Why do you put air in concrete?
The primary use of air-entraining concrete is for freeze-thaw resistance. The air voids provide pressure relief sites during a freeze event, allowing the water inside the concrete to freeze without inducing large internal stresses. Another related use is for deicer-scaling resistance.
What is yield strength of concrete?
Properties of normal strength Portland cement concrete Density – ρ : 2240 – 2400 kg/m3 (140 – 150 lb/ft3) Compressive strength : 20 – 40 MPa (3000 – 6000 psi) Flexural strength : 3 – 5 MPa (400 – 700 psi) Tensile strength – σ : 2 – 5 MPa (300 – 700 psi) Modulus of elasticity – E : 14 – 41 GPa (2 – 6 x 106 psi)
How to calculate the air content of concrete?
1 Weigh the container with the concrete (2) – record value to nearest tenth of a pound 2 Subtract the empty container weight from the full container weight (2) – (1) = weight of concrete (3) 3 Divide the weight of concrete by the known volume (3) / (4) = density, or fresh unit weight
What kind of air entrainment do you need for lightweight concrete?
A: (Bruce) Normally lightweight concretes need air entrainment–and normally the air entrainment can be purchased in the concrete by ordering Type 1A portland instead of regular Type 1. Or, in a pinch, people have used non-sudsing detergent (e.g. the type used in washing machines or dish washing machines–not the type used in kitchen sinks.
How to calculate the volume of a concrete mix?
Basic Concrete Mix Design Materials Pounds of material S.G. Abs Volume 667 3.15 X 62.4 Cement 667 3.15 3.39 – Total Cementious667 Miller Stone 1590 2.6 9.80 Evert Sand 1242 2.65 7.51 Water 300 1 481 1590 2.60 X 62.4 1242 2.65 X 62.4 4.81 Air 5.5% 1.485 Total 3799 27.00 w / cm 0.45 Unit Wt. 140.72 Basic Concrete Mix Design
When was the air entrainment in concrete invented?
ACI Mix Design Air-Entrained Concrete One of the greatest advances in concrete technology was the development of air-entrained concrete in the late 1930s. Today, air entrainment is recommended for nearly all concretes, principally to improve resistance to freezing when exposed to water and deicing chemicals.