files.transtutors.com · web viewdesign for durability deepanshu patel 12838607 giorgio schievenin...

Design for Durability Deepanshu Patel 12838607 Giorgio Schievenin 12696074 Will Davis 12049262

1


DESIGNFOR

DURABILITY

FACULTY OF ENGINEERING & INFORMATION TECHNOLOGY

UNIVERSITY OF TECHNOLOGY SYDNEY

TABLE OF CONTENT

2


1. Introduction…………………………………………………………........

5

2. Structural Members…………………………………………………........

5

2.1Substructure and Foundations…………….…………………………..

5

2.1.1Pile…………………………………………………………........ 5

2.1.2Headstock…………………….........…………………………… 6

2.2 Superstructure...................................................................................... 6

2.2.1Abutment……………………………………………………….. 6

2.2.2Pier…………………………………………………………....... 7

2.2.3Concrete Planks………………………………………………… 7

2.2.4Concrete Deck………………………………………….......…... 8

2.2.5Barriers………………………………………………………..... 8

3. Construction Process…………………………………….….…..………. 9

4. Environmental loads…………………………………………..………...10

4.1Analytical Results………………………………............................... 11

4.2Carbonation …………………………………………........….……...

11

4.3Sulphate induces corrosion …………………………..…….………. 13

4.4Surface chloride …………………………………….……………… 13

4.5Airborne chloride…………………………………..………………..

15

4.6ASR (alkali silica reactivity) ………………………………………..

15

4.6.1 Structure Classification………...........………………..............

20

3


4.6.2 Level of Precaution Definition ………...........………………..

21

4.6.3 Aggregate Reactivity Classification ………...........…………..

21

4.6.4 Aggregate Suggestion ………...........………………...............

21

4.6.5 Risk Reduction ………...........………………...........………...

22

5. Cathodic Protection ………...........………………...........…………......

23

6. Specification ………...........………………...........……….……….........

24

6.1Performance Specification………...........………………...........

………................. 25

6.1.1 Diffusion coefficient................................................................

24

6.1.2 Volume of Permeability. .........................................................

24

6.1.3 Sorptivity. .................................................................................25

6.1.4 Rapid Ion Permeability.............................................................

26

6.2 Prescriptive base specification...........................................................

27

6.2.1 Cover quantity.......................................................................... 27

6.2.2 Quality of concrete .................................................................. 28

6.2.3 Type of cement ........................................................................ 28

6.2.4 Use of SCM. .............................................................................28

6.2.5 Type of aggregate .................................................................... 28

4


6.2.6 Moisture penetration.................................................................

29

6.2.7 Additional protective measure APM........................................ 29

6.2.8 Casting and Curing ...................................................................

29

6.2.9 Service life inspection...............................................................

29

7. Reference................................................................................................. 31

LIST OF FIGURES

Figure 1. Pile…………………………………………….....……………………

6

Figure 2. Headstock……………………………………..………………………

7

Figure3. Abutment………………………………………………………………

7

Figure 4. Pier…………………………………………...………………………. 8

Figure 5. Concrete Planks……………………….......…………………………..

8

Figure 6. Concrete Deck……………………………………..………………….

9

Figure 7. Barrier……………………………………………………………...... 9

Figure 8 Local Cell Corrosion........................................................................... 23

5


Figure 9 Principal of cathodic corrosion protection …………………………...

23

Figure10 Diffusion coefficient D365 .………………….................................. 24

Figure 11 Diffusion coefficient D28.................................................................. 24

Figure 11. Sorptivity……………………………………......................…….....

24

Figure 12. Properties of SCMs……………………………..............……….....

25

Figure 13. Aggregate Reactivity……………………………………................ 25

Figure 14. Potential reactivity of different aggregate........................................ 26

LIST OF TABLES

Table 1. Environmental Loads………………………..........……………….... 11

Table 2. Analytical Results …………………….…………………................. 12

Table 3. Correction Factors……………………………………….................. 13

Table 4. Carbonation Coefficients………………………………………........ 13

Table 5. Results……………………………………….................................... 13

Table 6: ACEC Classification ……………………......................................... 14

Table 7: DC classifications............................................................................... 15

Table 8: In situ concrete.................................................................................... 15

Table 9: Pre-cast concrete................................................................................. 16

Table 10: Diffusion coefficients of concrete in tidal areas..................................

17

6


1. Introduction

Durability of a structure describes qualitatively the ability of a structure and its component to

perform the functions for which they have been designed, over a specified period of time,

when exposed to their environment. Cracking in a structure leads to exposing of

reinforcement steel which undergoes corrosion. We prepared a durability report of imaginary

highway twin bridges for design life of 100 years. The bridge is located near Ballina which is

736 km by road from Sydney.

2. Structural Components

The structural components of bridge are placed under the two sections:

Substructure or Foundations

Superstructure

2.1 Substructure or Foundations

The structural part below the ground is called substructure. Foundation is important structural

part of the bridge. The main role of foundation is to bear the load of all the members above it.

This includes:

2.1.1 Pile:

The piles used at the construction site are precast piles which transfers the load from

headstock to the ground. The piles are octagonally shaped at the bridge site.

Fig.1 Pile

7


2.1.2 Headstock:

It is the structural component which is rests on the pile.

Fig.2 Headstock

2.2 Superstructure

The structural part above the ground is called superstructure. The structural components that

are classified under this section are:

2.2.1 Abutment:

Fig.3 Abutment

8


2.2.2 Pier

It is the structural component which rests above the headstock. The height of the pier

headstock is 1400 mm.

Fig.4 Pier

2.2.3 Concrete Planks:

Precast prestressed concrete planks are used at the construction site. 300 mm diameter void is

provided at the centre of it. Height of concrete plank is 600 mm. Bearing strips are provided

between the pier headstock and concrete plank layer.

Fig.5 Concrete Planks

9


2.2.4 Concrete Deck:

180 mm thick concrete deck slab is provided on the precast prestressed concrete planks. 75

mm thick bituminous surfacing is done on the concrete deck

Fig.6 Concrete Deck

2.2.5 Barriers:

Precast barriers are used at the construction site which is provided on the concrete deck.

Fig.7 Barrier

10


3. Construction process

The construction of the twin bridge system will include two way of construction:

Pre-cast-rigid formwork; used to achieve certain mechanical properties of the

concrete elements. This method allows to have better concrete elements with a higher

resistance to external attack and longer durability.

In-situ- general formwork; used to cast the element that cannot be pre-casted.

The following procedure will be adopted to construct the twin bridges:

1. The piles will be pre-cast off-site and transported to the site before being

mechanically driven into the ground;

2. The formwork for the abutments are to be placed on the piles, and the abutments are

to be cast in-situ;

3. Headstock/pier formwork have to be constructed above the piles, and members need

to be casted in-situ;

4. Pre-cast concrete planks are to be transported to site and placed across the spans

between the piers;

5. Install 18mm fibre cement sheeting between concrete planks;

6. The pre-casted deck sections are transported in the construction site, lifted and lay

down up to the planks;

7. Pre-cast barriers are installed;

8. The asphalt is applied on the surface.

Precautions must be taken to prevent any cracking or damage to the pre-cast members

during the transportation on site.

11


4. Environmental Loads

In the comparison of all the environmental loads present both above ground and below

ground, it has been concluded that carbonation and chloride-induced corrosion will cause

most damage to the structural members. Another corrosion mechanism that may affect the

structure is the Alkali Silica Reaction, which will be most critical in the concrete planks,

which do not experience any wetting or drying and are exposed to the atmosphere.

Structural member Exposure

Classification

(AS3600, AS5100)

Environmental Loads Construction

Technique

Piles C2 (Tidal/splash

zone)

Carbonation

Sulphate

Surface Chloride

Pre-cast, driven

Abutments B2 (Coastal) Carbonation

sulphate

airborne chloride

Cast in-situ

Piers C1 (spray zone) Carbonation

Airborne chloride

In-situ

Concrete Planks B2 (Coastal) Carbonation

Airborne Chloride

Pre-cast

Deck B2 (Coastal) Minimal

carbonation

Pre-cast

Barriers B2 (Coastal) Carbonation Pre-cast

Table 1: Environmental loads

4.1 Analytical Results

12


Table 2: Analytical Results

4.2 Carbonation

Carbonation has a major effect on most of the structural members of the twin bridge system

as most members are exposed to the atmosphere and CO2. The deck is protected by an 75mm

asphalt layer on top and concrete planks and 18mm fibre cement sheeting below, therefore it

will only experience a minimal amount of carbonation, if any at all.

Measures to mitigate carbonation that can be controlled include:

Cement type;

Water/cement ratio;

Curing (Degree of Hydration);

Compaction;

Cracking.

These factors are controlled effectively through the pre-cast process where the concrete

members are cast and cured in a controlled environment, increasing the mechanical properties

of the concrete. For the in-situ members, formwork is to remain for a minimum of 7 days

after casting to control crack development.

To determine the depth of carbonation, the following equation is used:

13

Location Depth(m) pH

Moisture Content

(%)

Sulphate

(SO42)

(mg/kg)

Chloride(CL)

(mg/kg)BH - Abut A SB 8.50 8.1 24.8 670 2,360BH - Pier 2 SB 7.00 7.8 23.8 1,000 1,670BH - Abut A NB 1.00 8.2 16.5 50 200BH - Pier 1 NB 8.50 7.4 21.2 15,600 2,280BH - Pier 2 NB 1.00 8.1 23.4 1,000 1,560BH - Abut B SB 2.50 7.5 18.0 90 700


Dc = K x t0.5

Dc- Depth of carbonation

K- carbonation coefficient

t- time (i.e. 100 years)

the following tables are used to determine the carbonation coefficient and correction factors

for each structural member. All members will consist of a compressive strength >35 MPa and

have fly ash content between 30-40%.

Table 3: Carbonation Coefficients

Member(s) Carbonation

Coefficient

Correction Factor Depth of

Carbonation

Piles, piers,

abutments, barriers

1 1.10 11.0mm

Planks 2.5 1.10 27.5mm

Table 5: Results

The engineering drawings provided allow for a minimum concrete cover:

50mm piles

45mm for abutment areas in atmospheric exposure,

60mm for abutments areas in contact with the ground

70mm for the piers

30mm for the barriers, therefore all structural members have adequate cover in terms

of carbonation.

14

Table 4: Correction Factor


4.3 Sulphate-induce Corrosion

The highest sulphate value has been found at the BH-PIER 1 NB, 8.50m.

SULPHATE=15600 mg/Kg

The Sulphate classification and analysis has been done through the BRE method.

Based on the Aggressive Chemical Environment for Concrete Table (ACEC), considering the

sulphate value converted in mg/l and the pH value equal to 7.4 is possible to define the

Design Sulphate Class for location as:

DS-5 AC-4s

After that the class for location has been determined, and based on 100 years working life is

possible define the specification of concrete and additional protective measure (APM)

through the following table.

15

Table 6:ACEC Classification


4.3.1 Cast in situ

The table 8 are for concrete cast-in-situ, while the figure 9 if for precast concrete products.

For table 7 for elements cast in situ, the DC class and the APMs are suggested as:

DC-4+APM3f

For this classification the BRE suggest two type of APM that are coatings and water resisting

barrier. We will adopt:

COATINGS

The BRE gives also the indication for the W/C ratio, aggregate size and type of cement.

16

Table 7: DC classifications

Table 8: In situ concrete


Where the the cement suggested for a water/ ratio= 0.35 is:

CEMII/B-V+SR; Portland cement with addition of fly ash (FA) content should be not less

than 25% of the total cement content.

4.3.2 Precast

Form the precast table the come out with the same result.

CEMII/B-V+SR; Portland cement with addition of fly ash (FA) content should be not less

than 25% of the total cement content.

In addition, in the highly chloride rich environment, the sulphate ions are mitigated and any

sulphate attack will be delayed by the chloride ions.

4.4 Surface Chlorides

To determine the effect surface chlorides, have on the steel reinforced concrete, we must

determine the chloride concentration at the depth of the steel reinforcement. This

concentration is then to be compared to the critical chloride threshold level, which is

determined by the type of cement, use of SCM’s, compressive strength and weight/binder

ratio of the mix. This calculation is to be conducted at the most critical area of the structural

17

Table 9: Precast concrete


members, which has been determined to be the area on the piles that is exposed to the tidal

zone where there is a constant change in relative humidity and the adverse effect of wetting

and drying.

Using the table below we can determine the weight/binder ratio, chloride concentration at the

surface (Cs), alpha (α), diffusion coefficient after 1 year (D1) and the critical chloride content

for the type of cement mix used. As described above in ‘Carbonation’, a compressive strength

of >35mPa and fly ash content of 30-40% will be used. The nominated concrete cover value

at the piles is 50mm and this will be used as the piles are the most susceptible structural

member to surface chloride attack.

Table 10: Diffusion coefficients of concrete in tidal areas

The highlighted line shows the required figures, which can be used in the following

equations:

18


Convert 100 years into seconds for the equation:

Then use the chloride concentration equation with the calculated values:

The critical chloride content, or the chloride threshold, as taken from the table above, is 0.05.

the calculated chloride concentration is below this, hence the concrete cover is adequate for

protecting the structure against surface chloride attack for the 100-year design life.

4.5 Airborne Chlorides

The twin bridges are to be designed to be within 1km of the coast, which will allow for

airborne chlorides to affect the bridge. Unfortunately, there is no procedure to determine the

exact concentration of airborne chlorides at any location. It is however known that surface

chlorides have a greater effect on reinforced concrete structures than airborne chlorides, and

as the concrete cover is adequate for the former, we can assume the structural members will

also be adequately protected from airborne chlorides

4.6 ASR-Alkali silica reactivity

The alkali silica reactivity has been considered has the most dangerous cause that can affect and reduce the service life of the bridge structure.

Based on the HB 79:2015 will be discuss and provide a guidance to contrast and minimising the alkali silica reactivity in order to guarantee the service life of the structure.

19


4.6.1 Structure Classification

For the table 1.1 in figure 11, the structure classification based on ASR damage

acceptance is;

S2

‘‘Minor ASR damage is acceptable of manageable’’

For table 1.2 in figure 9, the classification of the structure by the impact of the

environment on the likelihood of ASR is;

E3

20

Figure 11: Classification of structure by the consequence and acceptability of ASR damage.


4.6.2 Level of Precaution Definition

Based on the information acquired above, using the table in figure12 it is possible to define

the level of precaution needed to the minimise the damage due to ASR reaction.

Figure 12: Level of precaution required.

The level of precaution necessary for the structure to perform for the whole design life is

STANDARD. This means that the risk of damage due to the ASR attack is very low, despite

the aggravating condition.

4.6.3 Aggregate reactivity classification

As the AS1141.60.1 suggest, the aggregates to be slowly reactive must have E (mortar bar

expansion) equal to 0.10a after 21 days. Therefore, the aggregates used in this mix design

have:

E=0.10a

21

Figure 9: Impact of the environment.

Figure 13: Aggregate reactivity .


With a prism expansion less than 0.03% after 52 weeks.

4.6.4 Aggregates suggestion

The aggregates play a fundamental role in the ASR. For this reason, the choice of the

adequate aggregate is the main action that should be taken to mitigate the ASR and reduce he

risk of concrete damage. According to the HB 79, the classification for the level of

Precaution is STANDARD. Thus, for the figure 14 select the type of aggregate as:

SLOWLY REACTIVE.

From the the lecture give by Mr Peter Clark, it is possible to select a non or slowly reactive aggregate. Figure 15

22

Figure 14. Risk of concrete damage due to ASR.

Figure 15. Potential reactivity of different aggregate.


The road authority of New South Wales in order to have a further control on the aggregates,

has adopted an extra specification.

All aggregate need to be assessed for AAR using AMBT method. Annually test.

Aggregate classified as non-reactive ma be used without mitigative measures.

Aggregate assessed as slow reactive may be used with the addition of 25% fly ash.

Where aggregates are assessed as reactive the specification recommendation is to used an

alternative aggregate, or an alternative mitigate proposal.

4.6.5 Risk Reduction

To reduce the risk of damage, the total Alkali content must be less than 2.8kg/m3. It is

determinate by the sum of content in:

A = Ac +B+H+W+D

Where;

A= Total alkali content of the concrete mix

Ac=Total alkali content of Portland cement

B = Total alkali content of SCM admixture

H = Reactive alkali contribution for NaCl in aggregate

W = Total alkali contribution from mixing water

D = Total alkali contribution from chemical admixtures and pigments

The high quantity of alkali is present in cement. The Type GP cement produced in Australia

has an alkali content between 0.5 to 0.6%. Therefore, to reduce the risk of the ASR is

necessary to reduce the amount of cement content into the concrete mix. HB79 suggests to

replace the cement content with SCMs as Fly Ash and Slag.

Fly Ash: 25% of it is sufficient to mitigate ASR. It can also be increase up to 40%

(low calcium ash) for highly critical structures with a long design life.

Slag: between 50 to 65% is sufficient to mitigate the ASR risk.

23


5. Cathodic Protection

It is a technique which is used to control the corrosion of metal surface by making it cathode of an electrochemical cell. The corrosion current is driven away be the cathodic protection current. The anode site transformed in cathodic, with a new anode system. The steel potential moves negative and the chlorides migrate away from steel (to anode).

Figure 8 Local Cell Corrosion Figure 9 Principle 0f cathodic corrosion protection

To ensure the service life of the reinforced and prestressed components, taking into account that:

Exposure classification is B2 Characteristic strength: 50 MPa Use minimum cover of 40 mm

Cathodic Protection is adopted for Pier Headstock and Abutment.

24

Figure 16 Properties of SCMs


For these elements, we decide to use the Cathodic Prevention (CPrev). Therefore, the cathodic protection is applied to the structures during the construction process, in order to reduce the costs and have a less laborious process in the future.

There are number of ways to do cathodic protection which are as follows. For this project we adopt the:

Sacrificial Anode

The reinforcement is connected to the negative terminal of power that supply and then apply current.

6. Specifications

6.1 Performance-based specifications

The following performance-based specifications will be used to ensure the durability

requirements of the twin bridge system are met.

6.1.1 Diffusion Coefficient

The diffusion coefficient De.365 is equal to 1x10-12m2/sec as determined from the

following graph for GB1 and 0.4% water/cement ratio:

Chloride diffusion

25

Figure 10 Diffusion coefficient D365


The diffusion coefficient D28 is equal to 3x10-12m2/sec for GB cement as determined from the

following table:

6.1.2 Volume of

Permeability

6.1.2 Volume of permeable voids (VPV) is 13.1%, determined from the following table

using the value for D365 = 2x10-12m2/sec:

6.1.3 Sorptivity

Sorptivity value of 14mm from the following graph:

26

Figure 11 Diffusion coefficient D28

Figure 12, Sorptivity.


6.1.4 Rapid Ion Permeability

Rapid Ion penetrability (RCIP) is 1000 Coulomb:

27


Specification Value

Compressive strength 50 Mpa

De.365 1x10-12m2/sec

D28 3x10-12m2/sec

VPV 13.1%

RCIP 1000 Coulomb

Sorptivity 14mm

To ensure the concrete delivered is to the standard and specification outlined, standard slump

tests will be performed as soon as it is delivered. A conservative value of 5% defective

concrete will be adopted.

Figure 1: Comparative Performance Table

6.2 Prescriptive base specification

28


6.2.1 Cover quantity:

Cover plays a fundamental role in the long-term structure performance. It guaranties a

protection against corrosion, protection against the aggressive external factors as: chloride,

sulfate and carbonation.

The time to corrosion initiation t, is strongly dependent to the cover quantity. It is a function

of square of cover x. Therefore, if 10% of cover thickness is lost there is a 19 % of service

life reduction.

According to RMS B80 clause 8.4 a control of cover is required before and after the

placement of concrete.

Pre-pour control: Is required a control to check is the distance between the steel

reinforcement and the formwork are respected as designed.

Post-pour control: A control of cover thickness by a cover meter is required after that

the concrete has been placed, to verify if the value specified is respected as designed.

6.2.2 Quality of concrete

The control of concrete quality is important to ensure the performance life of

the structure. If 10% reduction in quality correspond to 10% reduction is service

life. Therefore, in order to ensure the quality of it, 5% of defective level is

adopted.

6.2.3 Type of cement:

Type GBII, Low-alkali cement. GP with Na2O equiv non more than 0.6% and the addition of

SCMs.

6.2.4 Use of SCMs:

29


Elements Exposure

classification

Types

of

SCMs

% cement

material

content

rang

(kg/m3)

Maximum

water/cement

ratio

Piles C2 Fly Ash 25% 420-550 0.35

Headstock B2 Fly Ash 25% 370-600 0.40

Abutments B2 Fly Ash 25% 370-600 0.40

Piers C1 Blende

d

Minimum

65% BFS

420-600 0.40

Concrete

plank

B2 Blende

d

25% FA,

50% GP,

25% Slag

370-600 0.40

Concrete

deck

B2 Blende

d

25% FA,

50% GP,

25% Slag

370-600 0.40

Barriers B2 Blende

d

25% FA,

50% GP,

25% Slag

370-600 0.40

Figure 16 Use of SCMs

6.2.5 Type of aggregate:

They must be SLOWLY REACTIVE aggregate.

6.2.6 Moisture prevention:

The structure should be designed to avoid as much as possible any ponding. A maintenance

program should be stablished to keep the structure joint sealed and the cracks grouted to try

to avoid the moisture ingress.

6.2.7 Additional protective measure APM

30


Coating: The coating must be applied on the pier section in order to protect it against the

sulphate.

Cathodic protection: Cathodic protection must be applied to Pier Headstocks and

Abutments during the construction phase.

6.2.8 Casting and Curing

In order to reduce and control the cracks the casting and curing must be controlled.

Casting:

For the member casted in situ the formwork need to be kept for a minimum of

7 days after casting. While, for the pre-cast members, they must be casted in

rigid formwork and with high vibration.

Curing:

For the Headstock, Abutments and Piers, a wet curing to trowel finished

surfaces is required in accord to the AS3799

For Barriers, Planks and Piles, a low pressure and accelerate steam curing is

adopted according to the AS1597.2

6.2.9 Service life inspections

In order to check and ensure the service and the performance life of the bridge, a

periodical inspection between 6 and 10 years is required.

31


7. References:

Sirivivatnanon, V. and Cao, H.T., "The need for and a method to control concrete cover", Proceedings of the Second International RILEM/CEB Symposium on Quality Control of Concrete Structures, Belgium, June 1991.

Standards Australia 2004, Australian Standard AS 5100.5: Bridge design – Part 5: Concrete, Standards Australia, Sydney.Standards Australia 2008, Australian Standard AS 5100.5 Supplement 1: Bridge design – Concrete – Commentary (Supplement to AS 5100.5 – 2004), Standards Australia, Sydney

HB 79:2015 Handbook, “Alkali Aggregate Reaction- Guidelines on Minimising the Risk of

damage to Concrete Structures in Australia.

BRE brepress Construction division, Concrete in Agressive Ground. SD1: 2005

Standards Australia 2009, Concrete Structure, AS 3600-2009, Standards Australia, Sydney.

Sirivivatnanon, V. 2016, '11 Cathodic protection & other electrochemical methods’, UTS

Online Subject 42907, lecture notes, UTS, Sydney, 13 August 2016.

32


Sirivivatnanon, V. 2016, '10 QC of Concrete Cover & Abrasion Resistance', UTS Online

Subject 42907, lecture notes, UTS, Sydney, viewed 10 August 2016.

Sirivivatnanon, V. 2016, '7 Alkali Silica Reaction (ASR)', UTS Online Subject 42907, lecture

notes, UTS, Sydney, viewed 7 August 2016. Sirivivatnanon, V. 2016, '6 Corrosion of

Concrete', UTS Online Subject 42907, lecture notes, UTS, Sydney, viewed 5 August 2016.

Sirivivatnanon, V. 2016, '5 Chloride-induced Corrosion', UTS Online Subject 42907, lecture

notes, UTS, Sydney, viewed 1 August 2016.

Sirivivatnanon, V. 2016, '4 Carbonation-induced Corrosion', UTS Online Subject 42907,

lecture notes, UTS, Sydney, viewed 1 August 2016.

Sirivivatnanon, V. 2016, '2 Environmental loads', UTS Online Subject 42907, lecture notes,

UTS, Sydney, viewed 1 August 2016.

33

files.transtutors.com · web viewdesign for durability deepanshu patel 12838607 giorgio schievenin...

Documents