Midterm 1 Flashcards
What are important aspects of sustainable development?
Social, economic and environmental aspects have to be respected for the present and the future generations for development to be deemed sustainable
What are examples of inderect energy input
transport of raw materials, processing and manufacturing, extraction
what can engineers consider to improve sustainability?
design choices, material source, mode of construction, Durability, maintenance plan
three types of energy implicated in construction materials, what aere they
Inderect, direct and reccuring. Inderect is all the energy put in the creation the material and putting it on the market. Direct is when it is used for its purpose. Reccuring is for repairs and maintenance
What are the three scales of structure?
macro, micro, nano
Name all the categories of engineering materials, and describe them briefly.
Metals and alloys, ceramics and glasses, polymers, composites. Metals are good conductors for heat and electricity, usually used for ductility in structures, they have reccuring and homogeneous microstructure. Ceramics are brittle and have good compressive strength, Electrical resistance, homogeneous microstructure. Polymers are an infinite chain of repeating molecule (hydrocarbons), High degree of plasticity. Composites have a wide range of properties, they consist of two or more engineering materials used together.
What is the difference between force and stress
stress is a force applied over a certain area. Force is a certain amount of strenght exerted
What makes a material more brittle (list more than one cause)
Low temperature, Higher degree of triaxiality
describe fatigue
Fatigue is caused by the existing weaknesses in the material and a cyclic application of a high enough degree of stress that will cause cracks and make them propagate at every cycle, until it reaches capacity resistance and fails.
what is the fatigue limit
it is the threshold at which the stress levels are accounted for as a “high enough degree of stress”, therefore getting closer to failure. If the stress isn’t high enough to get past the threshold, failure will never occur
describe creep
Long term plastic deformation under sustained loads below yield point. Creep failure is time-dependant and deformation causes additionnal stress on the structure, which leads to deformation beyond the material resistance (gradual resistance)
Give the corresponding shortcuts to CaO, SiO2,H2O,Al2O3 and SO3
C, S, H, A, S (with bar on top)
What are C-H-S and C-H and how do they contribute to the concrete?
CHS is calcium silicate hydrate, and it contributes to the long term strenght of the concrete. It is dense and amorphous, which helps with impermeability, improving the concrete’s durability
What are the three main phases of hydration? (explain each steps)
Dormant period, initial set, curing. Dormant period is when concrete is still workable, adding water will increase w/c ratio. initial set is when crystals grow enough to connect and form a matrix, water is being used for the reaction. Curing is solidifying the matrix, adding water will not affect w/c ratio, it will simply improve the strenght of the crystal matrix.
why is concrete weaker at interfacial transition zones?
Wall effect
name the three levels of concrete and name what they consist of
paste: cement + water; mortar: paste + fine aggregates; mortar + coarse aggregates
What is the advantage of taking into consideration mass and volume for the design and making of concrete?
volume is good for determining the air content of the mixture, mass is more practical as aggregates have variable masses.
Why can’t slacking be done under water?
The reaction depends on the evaporation of water
What are the main compounds needed to make concrete?
Calcium, iron, silica, alumina, sulfate
what is the difference in terms of impact on concrete between tricalcium silicate and dicalcium silicate (Ca3SiO5 vs Ca2SiO5)
tricalcium impacts early strength, while dicalcium impacts ultimate strenght
around what temperature are belite crystals formed?
1200C
What are the major steps of the production of cement?
acquiring raw materials, processing (crushing, mixing, quarrying), Firring (calcined and burned @ about 1200C, makes clinker), Grinding
What does Calicum Silicate and Water give as products? Why is it a generality in concrete making?
It gives CSH (calcium silicate hydrate) and CH (Calcium Hydroxyde). These two elements are determinants in concrete’s strenght.
Describe CH’s impact on on concrete throughout hydration
CH is made at higher proportions from C3S, which reacts faster than C2S, hence providing the early strenght of concrete. Once the hydrated cement paste is not reacting anymore, the CH’s microstructure forms capillary pores, which increases permability, which decreases durability. It also reacts with sulfates and can be dissolved, which is a process called leaching, both of which are detrimental to durability.
Is porosity directly connected to weakness in the concrete?
It has a close relationship, but the real cause for weekness is the probability of connections between voids, which enables transport of outside elements inside the concrete. The higher the porosity, the higher the chances of the voids to be connected.
decribe the size effect.
The chances of having a weakness in the microstucture of an element is proportionnal to its size. Therefore having multiple smaller elements to fill the same volume can be beneficial to decrease the risk of having a weakness in the microstructure.
name the effect of tricalcium aluminate(C3A), tetracalcium aluminoferrite (C4AF) and gypsum (CSH2) on concrete’s hydration process
Flux, fast set and sulfate attacks; gives clour to concrete, Flux; prevents fast set by forming ettringite, which is insoluble and slows down the hydration process.
what are the the types of concrete and their properties and uses?
type 10: GU - general use
type 20: MH - moderate heat of hydration (moderately less C3S), MS - moderate sulphate resistance, used in arrid environments (moderately less C3A)
type 30: More early strenght (high in C3S-> more CH; or grinded smaller, which makes greater surface area)
type 40: LH - low heat of hydration, used for water (low in C3S and C3A)
type 50: LS - resistant to sulphates ( lowest concentration of C3A - >5%)
Sea water has a high concentration of sulfate but is treated like a moderate exposure. Why?
sulfate is soluble to chloride which is also in seawater, therefore the sulphate that will stay in concrete is going to be lesser than the actual concentration of the water
describe pozzolans
They are either natural (volcanic remains) or industrial waste (fly ash, silica fume). They cannot react with water alone, therefore cement is still recquired. Once the cement reacts with water, the pozzolans react with the CH and form more CSH, making the concrete more durable! They also lower the heat of hydration and improve workability
what are the main steps of concrete production
1: batching
2: Mixing
3: Transport
4: finishing
5: curing
define cimentitious SCMs
Cement addition that reacts with water to make aluminum-substituted CSH. The most common is blast furnace slag
list three benefits of using SCMs and explain why
economical, because you can cut the amount of cement used, which is the most expensive part of concrete making. environmental, because cement produces CO2, so replacing it is better (also reusing the waste). strenghtens the concrete (more CSH produced!)
why would it be advantageous to use a water reducing admixture, and how does it work?
It prevents flocculation of cement grains, which entraps water. This enables the concrete to be designed with a lower w/c ratio.
how does plastic shrinkage crackage occur and what are its consequences (and what do the cracks look like)?
When not enough water is added to the curing process, layer dries out and middle doesn’t. Restrained shrinkage leads to cracking due to tensile stress, which are pathways for bad things to get in. Discontinuous shorter cracks
How does temperature affect curing?
Higher temperatures can weaken the microstructure, as reactions happen too quickly. Lower temperatures take longer, but the microstructure will be stronger
what are the three most influencial factors that affect the mode of failure
degree of triaxility, temperature and strain rate
what are the main differences between the 3 point and 4 point flexural tests?
The three point experiences more shear than the 4 point, while the four point experiences a more constant moment that the three point.
what are the two types of machines to test fatigue
constant displacement and constant load.
What are SN curves?
stress versus number of cycles
what are the main transport properties of concrete? Explain the concept.
permeation, absorbtion, diffusion.
Permeation - movement of fluid through pressure gradient
absorbtion - transport of liquids to unsaturated pores due to surface tension.
diffusion - transfer of mass trough ions thanks to concentration gradients
why is gypsum important to concrete
It has a retarding effect, it prevents a flash set
