30/04/2014 - Revision

Today I will be revising Concrete and Concrete structures.

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Lecture one

concrete is a mixture of cement, water, fine aggregate, coarse aggregate.
Cement and water makes up paste at 1:0.5 ratio. Add in fine aggregate to make mortar at two ratio and concrete coarse aggregate at three ratio.

Making Cement:Water:Fine Aggregate: Course Aggregate = 1:0.5:2:3
add in 2% steel Rebar

Cost: £28-£48 per tonne, £70-100 per metre cubed
Usual density: 25kNm^-3
Usual strength: 20 to 80 Nmm^-2


Aggregates:

• Fine
• Natural Sand
• Crushed Limestone
• Course
• Gravel
• Crushed Limestone
• Crusted Granite

All 300-400Nmm^-2

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Lecture two: Manufacture, Chemistry & Properties

Manufacture

1. Minging
1. Explosives are used to collect limestones
2. Higher up you get more impure wiht silica, iron and aluminium oxide
2. Transport
1. Transported in 50t trucks to the processing plant
3. Primary crushing
1. Softball size
2. Water is sprayed to stop dust leaving
4. Secondary crushing
1. Golfball size
5. Storage and mixing of high and low purity
1. Tripper makes piles of correct proportion
2. These piles are raw mix.
6. Raw mix grinding
1. Ground in a roller mill
7. Blending and storage
1. Minerals addrd
1. Silica
2. Iron
3. Aluminium oxide
2. Called raw meal.
8. Pre heater
1. Bonds minerals for hardening
2. uses heat from rotery kiln via heat exchanger
3. Removes carbon via flash calcinator
1. CaCO_3 --> CaO + CO_2
4. 800 degrees C
9. Rotary Kiln
1. 49 -80 meters long
2. 1500-1700 degrees C
3. Powder fuses into marble size
4. Clinker
5. Cooled quickly to 80 degrees C with large fans
10. Finish Grinding
1. Gypsum added here
1. Used so that the cement retains workability for up to 2 hours before hardening
2. Ball mills 
1. Uses little iron balls of different size to grind

Electrostatic Precipitator used to take dust away (fires charged electrons at the dust which contact then move to positvely charged plates which get banged to let the dust fall)

Packed into 25kg bags.

The kiln fuel is a mixture of coal and tyres

200kg of coal makes 1 tonne of cement
100kg of rubber tyres makes 1 tonne of cement

Chemsitry

C₃A    - 10.8
C₃S    - 54.1
C₂S    - 16.6
C₄AF  - 9.1

This makes up 93-95% and the rest are minor compounds like magnesium,, potassium and sodium.

C = CaO
S = SiO₂
A = Al₂O₃

F = Fe₂O₃

Properties

Can be changedto suit wants and needs

OPC - Ordinary portland cement                                  C₃S+C₂S>67%

RHPC - Rapid hardening portland cement                     C₃S is greated  but still <70% (C₂S is lower)

SRPC - Sulphate resistant portland cement                    C₃A+SO₄₊H₂O      and C₃A <3.5%

White - White portland cement                                      C₄AF<1%

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Lecture 3: Aggregates

Why?

• Paste has 
• Low modulus of elasticity
• High creep and shrinkage

This means that it has a high dimentional changes

The maximum aggregate size is preferablefor strength.

Source?

• Primary
• Made for concrete
• Secondary
• By-product from another process (e.g. metal mining)
• Recycled
• Recycled from demolition sites etc.

Extraction

• Crushed Rock
• Drilling/blasting
• Crushing
• Screening
• Blending
• Stockpiling
• Sea dredged
• 15% of uk sand and gravels
• Good quality
• Smooth
• Fine aggregates
• Size <4mm
• Lighweight aggregates
• obtained from air voids
• density < 200kgm^-3
• f_c>15MPa
• Pumis, Ligtag, Perlite

Grading

• Use a seive
• Find the % passing
• Draw grading curve
• compare to EN12620 table 2,

Particle Size

• Take account of shape unlike sieve & grading
• influences void size (smooth packs down better
• Tyoes
• Flaky, elongated, round, angular, irregular
• Angularity Index

A=67-(100G)/(V_wγ)=67-100(V_agg/V_w)

V_w = Volume of water to fill the voids in a control vessell
γ = Specific gravity of aggregate
67 = % volume occupied by perfect spheres
G= weight of aggregate in vessel

Strength

• Concrete strength < Crushed aggregate strength
• Stength of parent rock not necessarily the strength of the crushed aggregate

Graph of Parent rock strength vs. 10% fine crushed value

One tested in cube test, the other tested by crushing in a vessell and stop when 10% of the sample is <2mm in size.

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Lecture 4: Properties of Fresh Concrete

Mixing

• 50-80 seconds - Drum Mixer
• 40-70 seconds - paddle/blade mixer
• 30-50 seconds - Superplasticiser

All running at 15-20rpm

Delivery

• 12m^3 (50% water added on site)
• or add all water on site
• Take consistency sample 15 mins after mixing

Placement

• Use a laser screed to level
• bleed water on the surface must be vacuumed off

Properties

• Fresh
• Workability - Enables mixing/transport/compacting without segregation of aggregate and paste and without bleed water on surface
• Hardened
• Strength
• Durability

Test

• Slump
• Pour cement into a container
• poker to make sure air is out
• Lift container
• Measure from top of container to top of concrete
• This is the slump
• High workability (100-175)
• Low workability (0-25)
• Compacting factor
• w_1 = Weight of uncompacted concrete
• w_2 = Weight of compacted concrete

C.F.=w_1/w_2

• RC mix is usually 0.8 - 0.9
• V-B time
• Vebe consistometer
• make slump test in a circular container
• time to get a level surface in larger container after slump container removed and vibrator switched on.

Compaction

• Poker vibrator
• Stop when water/cement slurry rises to surface
• Better than hand compaction
• Hand compactor
• Pour concrete in layers 
• Look at graph in notes showing concrete strength with compaction vs. water/cement ratio

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Lecture 5: Properties of Hardened Concrete

For sutrctures

• Compressive strength
• f_ck=20-50 Nmm^-2
• Tensile strength in flexure
• f_ctm=2.5-4.5 Nmm^-2
• Direct Tensile Strength
• f_ctd=1.5-3.0 Nmm^-2
• Young's modulus
• E_cm=30-38 kNmm^-2
• Poisson's ratio
• 0.15-0.25
• Zero when cracked

For building services

• Thermal movement
• α=11x10^-4 
• Shrinkage
• 300x10^-6 strain (0.3%)
• Curing can be used to stop this, continually supply water to the concrete for the first few days. 
• Vibration
• Acoustic
• Fire

Tests

• Compressive Strength
• Cylinder test
• L/d=2
• f_ck=P_max/area
• Cube test
• f_cu=P_max/area
• f_ck=f_cux1.2
• Tensile Strength due to Flexure
• Flexure Bending Test



f_ctm,fl=M/Z
M=Pa/2
Z=a^3/6
f_ctd=(0.7xf_ctm,fl)/1.5
• Splitting tensile Strength
  

f_ctm,sp=(2P)/(pi x LD)

f_ctd=(0.9xf_ctm,fl)/1.5

• Young's Modulus

E_cm=22[(f_ck+8)/10]^0.3 

(x by 0.9 for limestone)

• PUNDIT
• Time for ultrasonic pulse to pass through prism
• Velocity calculated from this
• long equation here (can't be bothered to type out!
• ERUDITE
• Finds the first natural frequency of the concrete prism

E_c(t)=4 x 10^-15 x n^2 x L^2 x density

n=frequency

E_cm=E_c(t)/1.05

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Going for a run now, then I will try and get to the end of at least Lecture 7 before bed.

Lecture 6: Concrete mix design

 A short lecture, it goes through the basic steps for mix design, this is not necessary for the moment, I will go over it before the exam.

Statistics are used - this is because of a lot of samples.

Aim to make 30Nmm^-2
Look for 95% characteristic strength.

This margin is = ks where k is a constant and s is the standard deviation.

f_m=f_k+ks
where f_m is the mean strength and f_k is the 95% characteristic strength

The rest of the lecture is the mix design.

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Lecture 7: RC Intro

Limit states design

• Limit state design makes sure the structure is safe under worst loads
• It also makes sure there are no extreme deformations whilst under working loads that can effect:
• appearance
• durability
• performance

Partial Safety Factors

• γ_f
• Partial Safety Factor for loads.
• Dead = 1.35
• Live = 1.5
• γ_m
• Partial Safety Factor for materials
• Concrete = 1.5
• Rebar = 1.15
• Design Strength f_cd = [Characteristic Strength (fck)] / [PSF γ_m]
• Design Load = [Characteristic Load] x [γ_f]

On your beam, find the largest possible bending moments: 

Load our beam with different cases combine choose greatest from each section (hogging & sagging) This generates the Bending Moment Envelope.

Typical Cross Section

Usually h / b = 1.5 - 3.0

A_s is the area of steel, usually between 1-4% for main bars and 0.13-1% secondary bars

Generally the distance between rebar pieces is > the size of aggregate + 5mm or 20mm. whichever is bigger.

All rebar must have links turning 90^o around them at some point.

That's it for tonight, I will continue on Dissertation all tomorrow and probably geotechnics the day after.

29/04/2014 - Dissertation

Previous Word Count: 2698/8000
Current Word Count: 3216/8000
Word Count this session: 518

Today I have started writing out lab report. I think alot of the words I have written are rubbish so take that number with a pinch of salt.

Tonight is revision.

28/04/2014 - Dissertation

Today was just a day in the lab, I got my results and analysed them so everything is ready to go with regards to writing the rest of my report. Lets get on it.

26/04/2014 - Revision

Today I have started my Environmental Geotechnology revision.

I want to get through four topics, we'll see. Going home at 2am.
Poker tournament tomorrow at DTD so won't get much done. hopefully bust early. Can be at uni early then.
Getting really scared.

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There are three different types of transport movement, advection, diffusion and dispersion.

ADVECTION
Starting on Advection:

Darcys law dictates the flow through soil and strata horizontally.

Q=-Aki where i is teh rate of change of head = DeltaH/L

k is the permeability.
This can be used to get the velocity through the soil
v=-ki

This is not the actual velocity in the pores though so it must be devided by the porosity which is always less than 1.

v_s=-ki/n where n=V_voids/V_total

Therefore the transit time, the time for one particle of water to move from one area to another, is t=L/v_s

Advective Flux: this is teh rate of contaminanet movement
F_A=vC=v_s.n.C

Permneability of soil if not water passing through:
K=k.gamma.mu (gamme is the unit weight of the liquid and mu is the dynamic/absolute viscosity)
K=k.ro.g/mu = g.nu (nu is the kinematic viscosity)


DIFFUSION

Flcisk law is the  main thing used here:
F_D=-D_o(deltaC/deltaL)

Where deltaC/deltaL is the concentration gradient, this usually changes with time but in this is assumed to be constant. It also assumes concentration doesn't change as contaminant moves

When in static water a contaminent will diffuse to tryh and get equal conentration, this is due to the concentration gradient., in moving water it will both flow and diffuse.

Effective diffusion coems from the gfact that the pathway for a contaminent to diffuse is actually alot longer than a straight line due to the nature of uneven particle layers in the soil:

F_D=-D*.n.(deltaC/deltaL) where D*=omega.D_o

As the conentration gradient is not going to be constant unless more conentration is added constantly, the conc. gradient will change with time thus:

-n.(deltaC/deltat)=-D*.n.(delta^2C/deltaL^2)
Which is integrated to give:

C{L,t}=C_o.E_c(L/(2.SQRT(D*t)) Where E_c is the complementary error function and the brackets are related to the normal distribution=sigma^2/2t

C/C_o will always be less than 1, usually it will balance at around 0.5

DISPERSION

Dispersion is the mechanicle distribution of contaminent due to the tortuous nature of the particles inthe soil.

Again it uses Flick's law:

F_m=-D_m.n.(deltaC/deltaL)

Where D_m=alpha_L.v_s^beta

Where alpha is the londitudinal dispersivity (m) which can be found from the graph, This is usually 4-6 times larger when in-situ because the soil is more compacted obviously.

In this case C/C_o will eventually reach 1, at the point where it reaches 0.5 this is known as the breakthrough time.

There are three different ways in which a contaminent can disperse:

• Through fractured flow
• Through Longitudinal Dispersion
• Through transverse dispersion

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Most of the time these movement mechanisms work together:

Combing the fluxs gives:

F=F_A+F_D+F_m

But F_D is alot smaller than F_m and F_A and so F=F_m+F_A
where diffusion is taken in by F_m

GENERAL ADVECTION-DISPERSION EQUATION

Form the above:

F=n.v_s.C-D_h.n.(deltaC/deltaL)

Where D_h=D*+D_m this is thge hydromatic dispersion coefficient

Obviously like before this becomes time dependet as the contamination gradient changes:

F=n.(deltaC/delta t)=D_h.n.(delta^2 C/delta L^2)-n.v_s.(deltaC/deltaL)

PLUMES

The aboves equation applies to line sources, but point sources give a 3D movement and so the previous equation does not apply.

For 1 D movement:

C=C_o/2(E_c((L-V_s.t)/(2SQRT(D_h.t)))-...)

The ... tends to zero with distacne/time.

RETARDATION

This works against the spread of the contaminant as the contaminant in lower concentration flows has ana ffinity to the soil solids and so is lost and will no,longer move, lowering the future contamination in front.

R=1+(ro.k_d)/n

Where k_d=C_soil/C_water

Thus :
(deltaC/deltaL) =(D_h/R)(delta^2 C/delta L^2)-(v_s/R)(deltaC/deltaL)

THIS APPLIES AT EQUILIBRIUM ONLY!

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So at this point it is 11.53pm after having to do a load of stuff to get my head around the next sextion so I am going to write it up then go home to go to sleep probably.

Soil Physics & Chemistry

Properties

Soil is:

• Continuous - It has ill defined boundaries
• Variable
• Anisotropic (directionally dependent)
• Stress dependent (current stress and historical stress)
• Environmentally dependent
• Temp
• Moisture
• Pore Fluid Chemistry
• 3 phases 
• Solid
• Clay -> Boulders
• Liquid
• Water, oils etc.
• Gas
• Air, methane, etc.
• Small particles mean a larger surface area
• Contaminants react on solid surfaces and so the larger the surface area the more reactions ( this is due to Adsorption. Therefore clay is very important (Small particles = big SA)

Clay Minerology

Clay is a silicate layer, it is a sheet of silicate, metal cations as part of a mineral structure, inonic inbalances occur.

The silicate layer = Si(4+) + 2O_2(2-) ->SiO_4

It is in a tetrahedra shape (trianle based piramid with the O at the points and Si in the center.

These join together in sheets of ionic bonds, with O in lop layer, Si middle layer and O bottom layer.

These sheets are balances but AL(2+) can sometimes take the place of Si (4+) as it has the same fit but can only go in the edge and givesa net -ive charge.

REAL TETRAHEDRAL SHEETS

They consist of groups of 5O(2-) + 2Si(4+) giving a -2 charge, these can be balances by joining in a mirror image to create 8O(2-) + 4Si(4+) or can be balanced by supplying external cations.

These sheets are known as Smectite

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Octrahedral sheets can also be created using both Aluminium and Magnesium:

Al(3+)

This has no ionic imbalance but it has holes in the structure which can take atoms.

This is called Gibbsite

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Mg(2+)
This also has no ionic imbalance and has no holes in the structure so is very stable.
This is called Brucite

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In practice these sheets can change properties atthe edges due to broken bonds and exchanging of cations that can change the ionic balance. Therefore sheets can join together.

These joined sheets at the boundaries can either have strong bonds from shared atoms or weak bonds from charge differences.

This is it for tonight, There will be more tomorrow after poker, I will continue on the bottom of this until the topic is finished then start a new one for the next two topics tomorrow.

Au revioir
Bon chance pour tomorrow.

25/04/2014 - Dissertation

Word Count:2698/8000
Word Count this session:(0)

Today I have done a lot of formatting, making sure i am using the correct font (Verdana for some stupid reason) and correct line spacing and size, 1.5 and 11pt respectively.

I have also added and acknowledgments section and moved the nomenclature to the top, I will probably change the name to list of symbols or something similar and might include a list of abbreviations depending on how I feel when I finish.

I have started the abstract but only a few words.

I am about to start on the measurement of stage and cross sectional area.

REMEMBER:

Mention that most of these methods apply to UK only.
What happens if it is a tidal flow.
What happens in large flows and flooding.

24/04/2014 - Dissertation

I have started writing my Dissertation on Latex, never used this software before.
Current Word Count:2742/8000
Word Count this session:0

So far I have only done research on the measurements of flow. I have still to do measurements of cross sectional area and stage. An Abstract and the analysis of the independent research I have conducted. I have an abstract and conclusion.

Introduction

This blog is a log of all my revision and Dissertation review. This is not made to be read by the public, but by all means have a look in.