Which constituents may be visible in a concrete microstructure image?
Unhydrated cement
Hydration products
Voids
Aggregates (coarse and fine)
Pore Solution
What is C-S-H and what is it characterized by?
Calcium-silica-hydrate gel, characterized by high surface area and being a poor crystalline material with a layered nanostructure.
Which concrete characteristic is C-S-H responsible for?
Concrete/paste strength, setting, hardening, and durability
What is the C/S ratio in C-S-H?
1.5 to 2 depending on water content
Compare the solubility of C-S-H and CH
C-S-H has a lower solubility, CH is leachable
What are the constituents of the hydrated solid paste volume by percent?
C-S-H = 50-60%
CH = 25%
C6AŜ3H32, ettringite/ C4AŜH12,monosulfoaluminate = 15-20%
What is CH and what are its characteristics?
Calcium hydroxide, stoichiometric with a well defined crystal structure
Which concrete characteristic is CH responsible for and why?
Adversely affects durability by participating in sulfate attack and contributing to a more acidic solution
What is the common name for C6AŜ3H32, ettringite/ C4AŜH12,monosulfoaluminate and what are their characteristics?
Calcium sulfoaluminates, primarily crystalline phases
Which concrete characteristic are C6AŜ3H32, ettringite/ C4AŜH12,monosulfoaluminate responsible for and why?
Contributes little to strength, affect sulfate durability depending on the order in which they form,
What is the size of capillary porosity and what can it affect?
10-1000nm, can affect permeability, strength, and shrinkage at high RH
Minimize to increase strength and durability
What is the size of gel porosity and what can it affect?
<10nm, can affect creep and shrinkage
What are the size of air voids and what can they affect? How can their effect be mitigated?
Entrained are 50-200 micrometers and entrapped are 3 mm
Significant effect on strength, mitigate by decreasing the w/c ratio
What are the 3 classifications of pores/voids?
Interlayer space in C-S-H
Capillary Voids
Air Voids
What size differentiates micropores and macropores? What do each of these types of pores affect?
50 nm
Micropores affect creep and shrinkage, macropores affect strength and permeability
What aspect of pores in concrete is the best indicator of the paste quality?
Pore size distribution (as opposed to total capillary porosity)
Which two factors affect pore size/ porosity refinement? Explain
w/c ratio: lower w/c ratio decreases pore size range and allows for less penetration. Larger CH and ettringite crystals form leading to high porosity, especially in the interfacial transition zone.
Age: as hydration proceeds, hydration products continue to fill pore spaces and pore diameter range and penetration volume decreases with age
List the 4 classifications of water in paste, how are they classified?
a. Capillary water
b. Adsorbed water
c. Interlayer water
d. Chemically bound water
They are all classified by how difficult the water is to remove
Which type of water in paste is the easiest to remove and why?
Capillary water, it acts like free water that is not influenced by attraction forces exerted by hydration products and is held by entrapped air voids and macropores.
Which types of water in paste will result in shrinkage when removed?
Adsorbed and interlayer water
What are the conditions for adsorbed water to be removed and what keeps it in the paste?
It is held in paste by hydrogen bonding by the charged surfaces of hydration products, it can be removed below 30% relative humidity
What is the typical pH of pore solution and how is it determined?
Around 13, it is determined by alkali content and presence of mineral admixtures
Describe characteristics of interlayer water and how it may be removed from the cement paste
It is water between layers of C-S-H that act like lubricant and reduce compressive strength
It may be removed at less than 11% relative humidity
Removal of which type of in-paste water will destroy the structure and can only be removed during product decomposition and heating? What are its other characteristics?
Chemically bound water, it is water incorporated into the crystal structure of hydration products such as C-S-H. May be removed by exposure to fire
