Plastic shrinkage cracking in recycled aggregates concrete

Presented by : Amrutha P MGuided by : Mr.Noushad Bin Jamal

Asst. Professor civil department

05/03/2023 2

1. Introduction

2. Properties recycled aggregate

3. Plastic shrinkage cracking

4. Causes of plastic shrinkage

5. Measurement of plastic shrinkage materials & methods.

6. Testing procedures

7. Study on experimental results

8. Recycled aggregate – advantages & disadvantages

9. How to minimize plastic shrinkage

CONTENTS

05/03/2023 3

Aggregates are most important part of a concrete.

Indian construction industry today is among the five largest in the world

Aggregates supply has emerged as a problem in some of the metropolis in India.

The use of construction and demolition waste obtained from building demolition as recycled aggregates for the production of new concrete has become more common for the last decade.

Recycled aggregate from concrete demolition waste provides good enough features for its use in structural concrete.

INTRODUCTION

05/03/2023 4

Urbanization growth rate in India is very high due to industrialization.

Growth rate of India is reaching 9% of GDP (Gross domestic product)

For achieving GDP rate, smaller structures are demolished & new towers are constructed.

For production of concrete, 70-75% aggregates are required. Out of this 60-67% is of coarse aggregate & 33-40% is of fine aggregate.

Influence of recycled aggregate

05/03/2023 5

Recent research of Freedonia group has found:Global demand of aggregates for construction• 46 billions tones by 2011• 49 billions tones by 2012• 52 billions tones by 2013• 57 billions tones by 2014• 65 billions tones by 2015

(World Construction Aggregates, www.freedoniagroup.com)

05/03/2023 6

Demand on construction aggregates worldwide

Demand on construction aggregates worldwide (The Freedonia Group 2012)

05/03/2023 7

If same rate of construction continues, What will happen in 2050 ?

• No any natural aggregates

• No one can construct any buildings, industries, bridges ,dams ,roads pavements……

MEANS

05/03/2023 8

The final product collected from crushing and separated from other

contamination obtained from construction and demolition wastes

such as concrete wastes, broken bricks, gravel, bridge supports, road

pavements, concrete roadbeds etc. that has been previously used in

construction are recycled aggregate.

Recycled concrete aggregate

05/03/2023 9

[http://www.braenstone.com/2015/04/recycled-concrete-aggregate-advantages/]

Recycled concrete aggregate

05/03/2023 10

The use of recycled aggregate obtained from the waste concrete, as a

component of the new concrete mixture, implies a thorough understanding of

its basic properties.

Considering that some of them may significantly differ from the properties of

aggregates obtained from natural resources.

The differences primarily depend on the quantity and quality of cement

mortar.

Which is attached to the grains of recycled aggregate .

Properties of recycled aggregate

05/03/2023 11

[Mirjana Malešev1, Vlastimir Radonjanin1, Gordana Broćeta2 ,2014]

05/03/2023 12

1. AGGREGATE GRADING

2. MORPHOLOGY AND SURFACE TEXTURE OF AGGREGATE PARTICLES

3. WATER ABSORPTION

4. BULK DENSITY OF AGGREGATE

PROPERTIES

05/03/2023 13

Grading of recycled coarse aggregate normally satisfies the standards for natural aggregate.

While in the case of recycled fine aggregate there was often a certain amount of grains larger than what is required by standards for natural aggregate.

Presence of recycled fine aggregate has a negative impact on the physical-mechanical properties of concrete.

Through a careful mix design and application of appropriate production technology these effects can be reduced to an acceptable level.

1. AGGREGATE GRADING

05/03/2023 14

In terms of morphological characteristics, recycled aggregate is less favourable than natural aggregate.

The grains are irregular, mostly with angular shape, rough and with cracked surface and porous .

These grain characteristics grains significantly affect:

1. The workability of fresh concrete

2. The permeability of liquids

2. MORPHOLOGY AND SURFACE TEXTURE OF AGGREGATE PARTICLES

05/03/2023 15

MORPHOLOGY AND SURFACE TEXTURE OF AGGREGATE PARTICLES

[Mirjana Malesev et al, 2014]

05/03/2023 16

Recycled concrete aggregate has a significantly higher absorption level

compared to natural aggregates.

The original cement mortar, which is an integral part of the recycled

aggregate, has a significantly more porous structure in comparison to natural

aggregate.

Through the influence on the water cement ratio porosity and consistency, an

increased water absorption of recycled aggregate also influences a range of

physical-mechanical properties of fresh, as well as hardened new concrete.

3. WATER ABSORPTION

05/03/2023 17

The bulk density of the recycled aggregate has a lower value than the

bulk density of natural aggregates.

Due to a higher porosity of mortar layer.

Bulk density of recycled aggregate 10% lower than the bulk density of

natural aggregates.

4. BULK DENSITY OF AGGREGATE

05/03/2023 18

Plastic shrinkage cracks are so-called because they form while the concrete is still

plastic, i.e. has not set.

Rapid drying of the surface of the plastic concrete causes it to shrink and crack

But the cracks are not always evident during finishing operations and may not be

discovered until the next day.

Plastic shrinkage cracks may form in a random manner or be roughly parallel to each

other.

The cracks are often almost straight, ranging in length from 25 mm to 2 m

PLASTIC SHRINKAGE CRACKING

05/03/2023 19http://jordangc.com/plastic-shrinkage-cracking/

PLASTIC SHRINKAGE CRACKING

05/03/2023 20

The risk of plastic shrinkage cracking based on the following values:

- Plastic Period [hours]

- Evaporation Rate [kg/m2/h]

- Bleeding Volume [kg/m2]

CAUSES OF PLASTIC SHRINKAGE CRACKS

05/03/2023 21

The Plastic Period of concrete is defined as the period after the

compaction of the concrete to the initial setting time (point of

stiffening) of the concrete.

For the case of self-compacting concrete it is the period from the

placing of the concrete to the initial setting time.

PLASTIC PERIOD

05/03/2023 22

 Plastic Period [hours]

Fast Setting Concrete 1 to 2

Medium Setting Concrete 2 to 3

Slow Setting Concrete 3 +

Typical values of the Plastic Period

1. Prof WP Boshoff(2012) Plastic Shrinkage Cracking of Recycled Concrete

Part 1: Guideline

05/03/2023 23

The Evaporation Rate is defined as the rate at which surface water

would evaporate from the concrete during the Plastic Period.

The Evaporation Rate is influenced by the ambient temperature,

concrete surface temperature, wind speed and relative humidity.

EVAPORATION RATE

05/03/2023 24

  Evaporation Rate [kg/m2/h]

Low Evaporation 0 to 0.5

Medium Evaporation 0.5 to 1.0

High Evaporation 1.0 +

Typical values of the Evaporation Rate

1. Prof WP Boshoff(2012) Plastic Shrinkage Cracking of Recycled Concrete

Part 1: Guideline

05/03/2023 25

Nomo graph to determine the evaporation rate of concrete surface water

(Ref): Prof WP Boshoff(2012) Plastic Shrinkage

Cracking of Concrete Part 1: Guideline

05/03/2023 26

Bleeding is the upward movement of water due to the settlement of

the concrete particles.

The Bleeding Volume is the total amount of water that migrates to

the surface and is measured in kg/m2.

Equation for bleeding volume isBleeding volume =

BLEEDING VOLUME

05/03/2023 27

  Bleeding Volume [kg/m2]

Low Bleeding 0 to 0.75

Medium Bleeding 0.75 to 1.5

High Bleeding 1.5 to 3.0

Typical Bleeding Volumes

1. Prof WP Boshoff(2012) Plastic Shrinkage Cracking of Recycled

Concrete Part 1: Guideline

05/03/2023 28

The experimental program focuses on two parameters.

The first parameter of the study is the initial water saturation of coarse aggregates.

The concrete mixture was made with 0% of RS at SSD and 100% of RG at different initial water saturations:

30%, 70%, 100% and 120% of SSD state.

The second parameter is the substitution of natural aggregates with recycled aggregates, all (gravel and sand) being at the SSD state.

MEASUREMENT OF PLASTIC SHRINKAGE MATERIALS AND METHODS

05/03/2023 29

Details of the investigated concrete mixtures

Ahmed Z. Bendimerad et al (2016)

05/03/2023 30

Two types of aggregates were chosen for this study:

Natural aggregates (NA)

Recycled aggregates (RA)

NA were crushed dark limestone aggregates.

RA were obtained by crushing unknown waste concrete from the recycling plant.

The RA used in this study are classified as aggregates type I, RCU95

05/03/2023 31

Properties of aggregates used

05/03/2023 32

The water absorption coefficient of each type of aggregate was defined

according to the pycnometer and hydrostatic weighing.

The recycled aggregate used in this study showed relatively fast absorption

Which is typical of high W/C ratio of initial concrete and weak paste

aggregate interface.

The table summarizes the mixture proportions, the fresh concrete properties

and the materials used in the seven mixtures.

MIX PROPORTIONING

05/03/2023 33

Properties and composition of concrete mixtures, with theoretical mixtures composed by dry aggregates and actual mixtures

Ahmed Z. Bendimerad et al (2016)

05/03/2023 34

All the mixtures were established and optimized by the Compressive packing model (CPM) and the software BETONLAB.

The initial water saturation of sand was kept constant for all the mixtures at SSD value.

The Effective water (Weff) to Equivalent Binder (Beq) ratio is less than 0.65 (Weff/Beq </= 0.65) for all the mixtures.

. The Equivalent Binder content is determined according to European standard EN 206-1:

Beq = Cement + k × Limestone Where k is the activity coefficient of limestone filler given by the standard (k = 0.25).

05/03/2023 35

The water saturation of gravel (Wgravel) is assessed from the gravel water content to water absorption (WA24) in percent (Wgravel/WA24).

All the mixtures were designed keeping the total water (Wtot) constant the additional water (Wadded) was calculated from the following

equation:

Wtot = Wadded + Waggregates + Wsp = Weff + Wabs

The packing density of aggregates (g*) was calculated according to the procedure given by the software BETONLAB to allow the calculation of the maximum paste thickness (MPT)

The packing density of a given aggregate is the ratio of the volume of solids to the bulk volume of the solid particles

[Prof WP Boshoff(2012) Plastic Shrinkage Cracking of Concrete Part 1: Guideline]

05/03/2023 36

1. Plastic shrinkage

2. Setting time

3. Elastic properties of concrete at early age

4. Tensile strength

TESTING PROCEDURES

05/03/2023 37

The tests were performed in an air-conditioned room

T 20±1°C

Relative humidity = 50±5%Started about 30–40 min after the first contact between water and

cement. Two identical moulds of size (70X70X280)mm3 is used.Plastic shrinkage developed in between concrete and mould is

measured.The concrete was cast in a plastic sheet between 2 PVC plates.Their displacement is measured without contact by 2 laser sensors.

1. PLASTIC SHRINKAGE

05/03/2023 38

Both ends of the steel mould are drilled in the centre.

The circular opening allows monitoring the movement of the reflecting plates anchored to the edges of the specimen.

Uncertainly on the plastic deformation was ±50μm/m

Cont…

Ahmed Z. Bendimerad et al (2016)

05/03/2023 39

The Vicat test was used to monitor initial and final setting time for all the mixtures.

The samples were placed in temperature controlled water (at 20ºC) to prevent mortar from drying.

The setting time is indicated by rapidly increasing penetration resistance.

The uncertainty on the setting time was ±0.5 h.

2. SETTING TIME

05/03/2023 40

The evolution of elastic properties of concrete at early age was monitored by the Fresh Concrete system.

Which measures the velocity of ultrasonic pressure (p) and shear (s) waves.

This device analyse the setting and hardening of any kind of material .

The testing device consists of a mould constituted of two polymethacrylate (PMMA) walls and held by four screws.

3. ELASTIC PROPERTIES OF CONCRETE AT EARLY AGE

05/03/2023 41

Test set up for ultrasonic monitoring device

(a) Piezoelectric sensor, (b) P-wave mould, (c) S-wave mould

Ahmed Z. Bendimerad et al (2016)

05/03/2023 42

It is equipped with an ultrasonic emitter and transducer (transmitter and receiver).

The U-shaped mould absorb the waves through the mould and travelling around the concrete specimen (concrete volume of 450 cm3).

A pulse signal is generated (800 V with a pulse width of 2.5 μs) at selected regular intervals.

The ultrasonic longitudinal compression waves are then transmitted through the concrete sample.

The signal is received by an ultrasonic receiver after travelling through the sample and sent back to the data acquisition card (DAQ card).

The software automatically calculates the time it takes for the wave to travel from the transmitter to the receiver and deduces the velocity.

05/03/2023 43

.The evolution of dynamic properties (Poisson’s ratio ʋdyn, shear modulus Gdyn and elastic modulus Edyn in MPa) was obtained as a function of the velocity of the compression waves and the shear waves using the following equations:

05/03/2023 44

Tensile strength of concrete was determined from direct tensile tests.

The load is applied horizontally by an electric displacement-controlled actuator.

The load cell is placed between the actuator and the mobile part of the mould.

The dog bone shaped mould actually comprises two halves with curved transitions to a central part with reduced constant section, 100 mm high, 100 mm long, and 105 mm wide.

The inner face of the mould is covered with PTFE and protected with thin polyethylene sheets during the test.

The two parts of the mould are linked to the frame and the load cell by spherical pin connections.

4. TENSILE STRENGTH

05/03/2023 45

The stress was deduced from the measured load and the cross section (100 X

105 mm2).

The concrete specimen was cast in the steel mould just after mixing then

vibrated in one layer.

An external frame was placed on the plate to avoid displacements of the two

halves of the mould due to the vibration and pressure of fresh concrete.

The specimen was covered until testing with a polyethylene sheet to avoid

drying

The average difference between two strength values at the same age was 6%.

05/03/2023 46

Direct tensile testing machine:

1: Steel mould, 2: Concrete specimen, 3:Spherical pin connection, 4: Electric actuator, 5: Load cell, 6: LVDT2.

05/03/2023 47

Mould used for direct tensile tests

05/03/2023 48

1. Analysis of early age behavior and correlations

2. Effect of the water saturation of recycled aggregates

3. Effect of the recycled aggregates substitution

4. Early age cracking risk of recycled concrete

STUDY ON EXPERIMENTAL RESULTS

05/03/2023 49

The results of plastic shrinkage showed a good repeatability.

The curves presenting are relates to concrete 0RS-100RG-70SSD.

ANALYSIS OF EARLY AGE BEHAVIOUR AND CORRELATIONS

05/03/2023 50

Deformation (strain) evolution and its time derivative

05/03/2023 51

Initial and final setting time

05/03/2023 52

Evolution of elastic properties at early age

05/03/202353

Schematic timeline of early age parameters

05/03/202354

Correlation between plastic shrinkage and rate of water absorption.

EFFECT OF THE WATER SATURATION OF RECYCLED AGGREGATES

05/03/2023 55

EFFECT OF THE RECYCLED AGGREGATES SUBSTITUTION

Effect of substitution rate on plastic shrinkage

05/03/2023 56

Effect of substitution rate of recycled aggregate on MPT

05/03/2023 57

Young’s modulus vs. hydration degree

α (t) = Q (t) / Qmax

Edyn (α) = a X E28d (1-exp-bxα(t))

05/03/2023 58

This is the comparison of shrinkage induced cracking sensitivity of different conventional and recycled concrete at early age.

Plastic shrinkage generates restraining stresses.

σ (t) = ε (t) X E (t)

Where: ε(t) is plastic shrinkage strain, E(t) is Young modulus evolution and σ(t) is the estimated stress produced by total restraint. The value of σ(t) at 24 h is noted ’S’.The concrete tensile strength noted as ‘R’.In this study the cracking sensitivity of recycled concrete at early

age, based on comparing the S/R ratio of the different mixtures.

EARLY AGE CRACKING RISK OF RECYCLED CONCRETE

05/03/2023 59

Influence of initial water saturation of RG on early age properties

05/03/2023 60

Initial water saturation of RG (%) on cracking sensitivity

The cracking sensitivity is assumed to increase with the S/R ratio.

05/03/2023 61

Influence of substitution rate of RG on early age properties.

05/03/2023 62

Influence of substitution rate of RS on early age properties

05/03/2023 63

Influence of substitution rate of RG on cracking sensitivity

05/03/2023 64

Influence of substitution rate of RS on cracking sensitivity

05/03/2023 65

RECYCLED CONCRETE AGGREGATE BENEFITS

1. Cost Savings

2. Eco Friendly

3. Versatility

4. Durability

5. Create additional business opportunities.

6. Save Energy

7. Job Opportunities

8. Market is Wide

RECYCLED AGGREGATE –ADVANTAGES AND DISADVANTAGES

05/03/2023 66

Use of recycled aggregate in different countries

V. Radonjanin, et al (2007).

05/03/2023 67

Lack of Specification and Guidelines

It requires more land, special equipment, and machineries etc.

Plastic shrinkage cracking

The duration of procurement of materials may affect life cycle of

project

DISADVANTAGES OF RECYCLED AGGREGATE

05/03/2023 68

1. Moisten subgrades and forms to prevent absorption.

2. Reduce the temperature of the concrete by

a. Precooling aggregate with water.

b. Cooling the cement.

c. Using chipped ice to cool mixing water.

d. Shading aggregates, water tanks, and lines.

3. Avoid over mixing.

4. Place concrete early in the morning or late afternoon.

5. Construct temporary walls to reduce wind velocity.

6. Provide sunshades for concrete.

7. Reduce time between placing and start of curing by working efficiently during construction.

8. Use evaporation retardant (usually polymers).

HOW TO MINIMIZE PLASTIC SHRINKAGE?

05/03/2023 69

Concrete is a heterogeneous material, it shows variations in the plastic shrinkage rate with time.

The initial setting takes more duration (6 hours) than the normal (opc) concrete (30 minutes), it may be due to the addition of super plasticizers. But it has no long term effect on mechanical properties.

The shear modulus is proportional to the time, i.e. the evolution of mechanical properties are acceptable.

Insufficient curing results in higher plastic shrinkage.

The recycled aggregate show lower elastic modulus than natural aggregates. (Hence flexural strength and tensile strength will be lesser).

CONCLUSION

05/03/2023 70

CONCLUSIONThe development of hydration strongly affects the evolution of the young

modulus.

The W/C ratio and MPT has influence on the plastic shrinkage cracking risk in recycled aggregate concrete.

Due to the addition of recycled aggregate there is no considerable change in mechanical strength variations in the concrete mix; the major problems are occurred in the characteristics like workability, setting time etc.

Recycled aggregate is a convenient construction material. The plastic shrinkage cracking risk can be easily avoided by the use of suitable measures like

a. Moisten subgrades and forms to prevent absorption.

b. Provide sunshades for concrete

05/03/2023 71

1. Ahmed Z. Bendimerad, Emmanuel Rozière, Ahmed Loukili.,(2016) “Plastic shrinkage and cracking risk of recycled aggregates concrete” Construction and Building Materials Volume 127, Published by Elsevier

2. Akansha Tiwari ., (2015-sep),“Recycled Concrete Aggregates” International Research Journal of Engineering and Technology (IRJET)- Volume: 02 Issue: 06

3. D. Jevtić, D. Zakić, A. Savić,(2009) “Specific properties of recycled aggregate concrete production technology” Materijali i konstrukcije, Vol. 52−1 p 52−62.

4. Emma Boghossian a, Leon D. Wegner b,(2008)” Use of flax fibres to reduce plastic shrinkage cracking in concrete” Cement & Concrete Composites Elsevier Ltd.

5. Jeongsoo Nam 1, Gyuyong Kim 2,, Jaechul Yoo 2, Gyeongcheol Choe 2, Hongseop Kim 2, Hyeonggil Choi 3 and Youngduck Kim 4., (2016)“ Effectiveness of Fiber Reinforcement on the Mechanical Properties and Shrinkage Cracking of Recycled Fine Aggregate Concrete”,pp: 9, 131; doi:10.3390/ma9030131

6. Mirjana Malesev, Vlastimir Radonjanin, Gordana Broćeta., (2014) “properties of recycled aggregate concrete” Original scientific papers, V−2

7. Mr. Tushar R Sonawane1,Prof. Dr. Sunil S. Pimplikar2 ., , (2014)“Use of Recycled Aggregate Concrete” IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE)

References

05/03/2023 72Thank you

Civil engineers