Concrete

Basics

• The Combination of Aggregate and Cement
• It takes 5 94 lb bags of cement to make a yard of concrete [1]. In other words, a 50kW Solar Concrete plant will make a yard of concrete daily. Or, 10 days to make a slab foundation for Rosebud models of the Seed Eco-Home

Formula

• To make 1 yard - To make 1 cubic yard of concrete, you'd need seven 94-pound bags of cement, about 1/2 cubic yard of sand and just over 3/4 cubic yard of gravel. The amount of water you use depends on how wet the sand is.Oct 1, 2009 [2]
• 10% cement, 75% aggregate, 15% water [3]
• 150 kg/m3 of cement - with concrete at 4000 lb/cu yd [4] - was sufficient to get about 6000 psi concrete strength [5]. Does this mean abouut 8% of cement?
• 500 lb per yard of cement in concrete is recommended - read a thesis on it - [6]
• Lean or rich: 7-15% cement by volume -

• Lean concrete per california codes is 300 lb cement per yard of concrete, and is 700 PSI at 7 days. [7]
• Lean is used below foundations - and is 700 psi or 1100 psi [8]

Slab Requirements

• 2500 PSI concrete minimum for slab on grade in Oregon - [9] and Georgia [10]

Tools for DIY Mix

• Cement Mixer - [11]
• Industry standards - $175/yard delivered
• Water source -
• Forms - 2x4 + rebar stakes.
• Concrete Bags - [12]. Need 60 per yard. $270 per yard. Weight is ~4000 lb/yard. 1 Yard is about 100 square feet.
• Cement instead?
• Solar Concrete is the answer
• Cement Calculator - 3 yards for a 10' wide strip, 3", and 32" wide across hangar.

• Moisture barrier - 6 mil poly
• Steele Mixer

Challenges Introduced by the Curing Process

• Unlike Metal or Plastic or Dimensional Lumber , A Concrete Mixtures FINAL qualities will only be known once it cures
• The conditions in which the concrete cure also impact this

Potential Solutions

• ”Overbuild” such that even if a mix underperforms it still meets the required Concrete Specifications for that Concrete Mix
  • Main Downside of this is Cost
• Thorough Recordskeeping + Concrete Tests
• Pre-Cast Concrete
  • Rather than try and account for uncontrolled conditions…control the conditions
  • Main downside is this takes away the advantage of not having to transport the giant Concrete Slab and just being able to move smaller bags or boxes or a Concrete Mixer etc
  • If designed properly, such as in the widespread use of Precast Concrete in the USSR such as Plita Aerodromnaya Gladkaya or Brezhnevkas etc it CAN be done

Recordkeeping / Sample Collection

• For QC / QA / Inspections+Insurance

Concrete Slump Test

Measures inches of collapse, from 0-12", of a wad of concrete in a cone. 12" means it's complete water. 4" is very stiff.

Test Cores

• Cylinders of the same mix, cured then tested it estimate properties of the poured concrete

Lab Samples

• Done at the point of mixing/cured+tested in a lab
• Main downside is the controlled conditions of the lab may not match the conditions in the real world where the concrete cured

Field Samples

• Cured “in situ” at the same place the concrete is being poured
• Thus they account for any impacts of Temperature/Humidity
  • Also transport of the mix from the plant, if relevant.

Nondestructive Testing

• Concrete Visual Inspection / Concrete Nondestructive Testing

Internal Links

• Reinforced Concrete

External Links

• The Wikipedia Page on Concrete
• YouTube Channel of Professor Tyler Ley
• A Video by the YouTube Channel Practical Engineering” Titled “Concrete’s Greatest Weakness is Time” ( ‘’’~17 Minute Watch’’’ )