Crack Free and Durable Concrete Repairs with the BaenzigerBlock, experiences since 1995

ICRI Convention, October 2010, Pittsburgh

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Crack Free and Durable Concrete Repairs with the BaenzigerBlock, experiences since 1995

Heinz Bänziger, Sika Services AGSenior Vice President BU ContractorsHead Technical Department ConstructionHead Market Field Refurbishment & Strengthening


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Crack Free Repairs with the BaenzigerBlockPresentation at ICRI Congress October 25, 2001


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Crack Free Repairs with the BaenzigerBlockThe basics of successful concrete repair

A concrete repair mortar has to fulfill the requirements which are necessaryto support the existing damaged concrete structure regarding-

- Strengths (compressive, flexural, tensile)- Bond to substrate (> 1.5 MPa)- Durability (a part of sustainability)- Protection- Elastic modulus (e.g mortars with polymeric binder)- Cracking

But the most important requirement is:

Workability, placement only mortars with excellent processing can reach the high expectations

Bad Workability, placement = Bad Quality


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3. Adhesion to substrateNo adhesion = not usable - return to R&D

2. Crack behaviorCracks = reduced protection - return to R&D

1. WorkabilityBad placement = bad quality – return to R&D

Crack Free Repairs with the BaenzigerBlockDevelopment: The philosophy Test facility with fastest possible respond of the most important properties! Killing factors visible after 1 day to max 28 days with one single test!


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2. Crack behaviorCracks = reduced protection

3. Adhesion to substrateNo adhesion = not usable

1. WorkabilityBad placement behavior = bad quality

Crack Free Repairs with the BaenzigerBlockDevelopment The philosophyTest facility with fastest possible respond of the most important properties!

Killing factors visible in shortest time span as possible!


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Restrained shrinkage

Tensilestress[N/mm]

100% RH90% RH80% RH70% RH60% RH50% RH40% RH30% RH

0%RH 20%RH 40%RH 60%RH 80%RH 100%RH

Free drying shrinkage

Shrinkagestrain [mm/m]

Baenziger Block

!Drying induced „free“ contraction of the samples!!Free contraction restrained due to mechanical property of substrate!

free

vs.

res

trai

ned

sh

rin

kag

e

Strength limit

!Cracking!


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Crack Free Repairs with the BaenzigerBlockCrack simulation of concrete repair mortars needs

• bond to a concrete substrate• specimen sizes which reflects reality• edges • free shrinkage parts• restrained shrinkage parts• connection joints repair to existing• corners• substrate roughness according practice• variable layer thickness• water absorption of substrate concrete• re-produce able climatic conditions

Job Site

BaenzigerBlock

300mm

1000mm


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Job Site


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Job Site


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Job Site


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• bond to a concrete substrate• specimen size which reflects reality• edges • free shrinkage parts• restrained shrinkage parts• connection joints repair to existing• corners• substrate roughness according practice• variable layer thickness• water absorption of substrate concrete• re-produce able climatic conditions

Job Site


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Job Site

3cm

6cm


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Job Site

Climate Chamber


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Crack Free Repairs with the BaenzigerBlockThe Size of the BaenzigerBlock


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Crack Free Repairs with the BaenzigerBlockThe Preparation of the Block

Due to reproducibility reasons we use only one concrete mixture


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Crack Free Repairs with the BaenzigerBlockTesting, alternative conditions


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Crack Free Repairs with the BaenzigerBlockResults and Interpretation


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Crack Free Repairs with the BaenzigerBlockResults and Interpretation


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Crack Free Repairs with the BaenzigerBlockBaenzigerBlock and practice 15 years ago!

Concrete Repair Mortar in practice 15 years ago


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Crack Free Repairs with the BaenzigerBlockToday Benchmark of so called “Non Cracking Cement Mortars”

Mortar 1“non cracking mortar”

Mortar 2“non cracking mortar”

Mortar 3“low cracking mortar”


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Crack Free Repairs with the BaenzigerBlock1. Sample Results “Crack evolution over time”

After 2 days

After 4 days


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After 9 days

After 28 days


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After 28 days

After 56 days


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After 90 days

The crack development of cement mortars is different!Some mortars are cracking within the first 24 hours others just start to crack after

a few days or a few weeks!

From our long term experience we know:The cracking behavior of cement concrete repair mortars should be tested

up to one year!


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Crack Free Repairs with the BaenzigerBlockToday Benchmark of “Non Cracking Cement Mortars”

It’s possible!No cracks after 1 year!


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Crack Free Repairs with the BaenzigerBlockAdditional Test Methods


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Crack Free Repairs with the BaenzigerBlockResults “Crack evolution over time”

The BaenzigerBlock enables a lot of additional information:• date when the cracks appears• wideness of the cracks and wideness progress• crack development in length• numbers of cracks and development of cracks over time• type of cracks, e.g. single crack, spider web cracks• sensitivity of crack behavior, at corners, at edges on full surface etc.• loss of bond (de lamination) of the substrate due internal strengths and restricted shrinkage

The BaenzigerBlock reflects the reality!But the final approval of the cracking performance

Is always the application on a real structure!


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Crack Free Repairs with the BaenzigerBlockConcrete Repair Mortar development within the last 15 years

High quality Concrete Repair under hardest conditions


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Crack Free Repairs with the BaenzigerBlockConcrete Repair Mortar development within the last 15 years

Today it is possible:Architectural Concrete without any Cracks


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Crack Free Repairs with the BaenzigerBlockInvestigations of independent Institutes

THE EFFECT OF CONCRETE SUBSTRATE STRENGTH ON THE ADHESION PROPERTIES OF POLYMER MODIFIED REPAIR

MATERIALSA.J.C. Jooste

Rand Afrikaans University

ABSTRACT.It is a known fact that the preparation of the concrete substrate plays an important role on the adhesion properties of

polymer modified repair materials. Some uncertainty exist as to the influence of the concrete substrate strength on the adhesion properties of concrete repair materials.

This paper reports on research done at the Rand Afrikaans University (South Africa), to investigate the influence of concrete substrate strength on the bonding properties of various repair materials. Different concrete substrate strengths were simulated by using the “Banziger test block” (20, 30 and 40 MPa). On these blocks seven different repair materials, from three different manufacturers, were placed. The placing specifications of the manufacturers were strictly followed. The samples were fully cured for 28 days, during which the crack behaviour was observed at 1, 7 ,14 and 28 days. The

influence of concrete substrate strength on crack behaviour was experimentally investigated. By determining the bonding strength between repair material and concrete after 28 days, the influence of concrete strength on bonding strength was

investigated. To compare practise with laboratory work a trial repair was done on a part of the R.A.U. complex. This repair was evaluated in the same manner as the “Banziger test blocks”. An important conclusion drawn from the

observations, is that the actual method of substrate preparation plays an important role in determining bond strength. In substrates of low strengths, micro-cracks are easily formed. These cracks lead to reduced bonding strengths.

1999


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2004


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Ring tests do not simulate reality!


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App. 2002


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App 2006


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Shrinkage does not correlate with cracking!

0

200

400

600

800

1000

1200

1400

0 1 2 3 4 5 6 7Ranking of cracking on Bänziger Block

Sh

rin

ka

ge

(µm

/m)

(EN

126

17

-4

fre

e -

21

°C -

60%

R.H

.)

No cracks Full of cracks

Mortar 2

Mortar 5Mortar 4

Mortar 6

Mortar 3Mortar 1

Crack Free Repairs with the BaenzigerBlockOur investigations: Correlation Cracking - Shrinkage

Bench mark at same age of specimens


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relative humidity [-]

t = 28 d

t = 56 d

t = 55.5 d

t = 59 d

Crack Free Repairs with the BaenzigerBlockOur investigations: Moisture conditions in concrete and mortar before and during the repair process

Development of internal moisture content during hardening and mortar application

Of course a block of steel would not show similar behavior and the results would be different!


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Target: smaller, less weight, reliable, reproducible

Correlation Measuring cracking time on different devices

Steel Ring Test does not simulate the site conditions:

Steel has no surface roughness, does not breath and does not absorb water of the repair mortar = 100 % moist in contact zone mortar/steel

Crack Free Repairs with the BaenzigerBlockOur investigations: Alternative Crack Testing Method based on our experiences

Cracking time of mortars Mortar 1 Mortar 2

Steel Ring Test 32 days 5-6 days

BaenzigerBlock 10-17 days 9-11 days

Alternative Laboratory

Test Method of Sika

14 days 9-11 days


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Based on fundamental research of Technology Center

Improved lab test equipment

Possibility to identify directly which formulation parameters impact cracking

Final laboratory testing will still involve BaenzigerBlock

The final market release of a concrete repair mortar is still pending on the performance of selective applications on job site!

Crack Free Repairs with the BaenzigerBlockConclusion of laboratory investigations, Alternative Crack Testing Method based on our experiences


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During the past 20 years we made big improvements and gained more knowledge regarding cracking behavior of cement mortars!

Cracking of mortars is influenced by different parameters Shrinkage of mortar Environmental conditions Concrete Substrate Application and placement quality Relaxation properties of the mortar

We have learned to formulate low (no) cracking mortars We introduced the BaenzigerBlock in all development centers around

the globe It is our best tool for benchmarking different formulations; or

comparisons with competitor’s products The BaenzigerBlock is one of the best tool to test the mortar due to

the close simulation of a real of concrete repair!

Crack Free Repairs with the BaenzigerBlockSummary of over 15 years experience


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Due to high investments in infrastructures over the past decades, costs for maintenance and refurbishment of all (concrete) structures will increase dramatically!

The costs have already exceeded the budgets of many states! Lack of maintenance is reality

Examples of collapses we see every day in the news

Functioning infrastructures are the backbone of every economy New structures must have high sustainability and durability The repair and protection of existing structures requires long lasting and

sustainable methods Sustainability is like a plant, it starts very small and is more important

and more powerful with the age! only if all components of a system meet the requirements of sustainability and

durability, the overall system can meet this requirement also!

It is one of our main tasks to invest in products which align with Sustainability!

Crack Free Repairs with the BaenzigerBlockOutlook 2020


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Thanks for Attention!

Crack Free and Durable Concrete Repairs with the BaenzigerBlock, experiences since 1995

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