INTRODUCTION Plastic shrinkage cracking occurs when the concrete is in the plastic state, which is within the first 24 hours. Plastic shrinkage cracks.

Slides:



Advertisements
Similar presentations
ARC313 Building Code II. Review What is the minimum bearing pressure allowed for soils to support foundations? 75 kPa How can you tell by looking at the.
Advertisements

Subfloor Evaluation Prior to Installation Understanding the science of concrete slabs prior to installation of moisture sensitive floor covering materials.
FUNDAMENTALS OF CONCRETE Presented By: Kevin J. Brigandi Construction Services Department Manager Debra A. Nunes Construction Services.
CE-303-Lecture #1 Fundamentals of Concrete Objectives To explain the basic concepts of concrete To explain briefly the properties of freshly mixed concrete.
1 Class #27.1 Civil Engineering Materials – CIVE 2110 Concrete Material ShrinkageCreep Thermal Properties Fall 2010 Dr. Gupta Dr. Pickett.
Lecture #13 Properties of Hardening Concrete Curing.
Concrete Man made stone. constituents u mixture of aggregate and paste u paste30 to 40% u portland cement7% to 15% by Vol. u water 14% to 21% by Vol.
Lecture 2 Design of Concrete Mixes and Properties of Fresh Concrete Dr Magnus Currie ENG-1010: Reinforced Concrete Design.
Curing and Protection of Concrete
Properties of Asphalt Important properties of asphalt include: Adhesion Consistency Specific Gravity Durability Rate of curing Ductility Aging and.
WORKSHEET 4 CONCRETE. Q1 a) what are the two main properties that concrete must have? (i) strength b) how do we achieve them? by using an acceptable water.
Introduction Dr Magnus Currie From Scotland, UK MEng Civil Engineering
Learning Objectives Relevance of fresh concrete properties
Problem-solving with MATLAB Week 4: Computing volumes: cubic feet, gallons, measuring water NAME _________________________.
Civil Engineering Materials
Curing Concrete. Curing n Moisture n Temperature n Time Curing requires adequate — If any of these factors are neglected, the desired properties will.
Strength of Concrete.
Topic : MIX DESIGN OF CONCRETE Properties of concrete Submitted To: DR. AYUB ELAHI Submitted By: SOHAIB NASEER 2K9-scet-29/CIVIL M.ZAEEM FAKHAR 2K9-scet-03/CIVIL.
Development of Strength. Development of strength: development of strength after placing of concrete. Curing: It is the procedures used for promoting the.
Placing Quality Concrete
Chapter 4. Working with Silica-Fume Concrete  Conducting a Test Placement  Transporting, Placing, and Consolidating  Finishing Flatwork  Finishing.
Chapter 12 Concrete Construction Part 3 1CE 417, King Saud University.
ADMIXTURES Department of Civil Engineering,
“Properties of Concrete” Introduction
Concrete Unit 24 Carpentry and Building Construction.
Silver Oak College Of Engineering & Technology.
2009 Quality Concrete School IT’S HOT!! IT’S CHILLY!! SHRINKAGE!!
Plastic Shrinkage Cracking How to make sure it happens!
Hot-Weather Concreting. Detrimental Hot Weather Conditions  High ambient temperature  High concrete temperature  Low relative humidity  High wind.
LECTURE NOTES-CHAPTER 8 CURING OF CONCRETE
Reading a Station Model from a Weather map. Cold Fronts & Warm Fronts.
University of Sydney – Structures CONCRETE Peter Smith 1998 Concrete Making and Testing l Unique material çMade specially for each job çHandling on job.
SESSION 9 Construction Considerations. Objectives  Describe key aspects of: Prepaving operations Paving operations Postpaving operations  Understand.
CEMENT CURRING COMPOUND S-102.  Replacement Of Water Curring  Concrete Curing Product Used On Concrete Floors/Decks, Pavements, Vertical Applications,
Silica Fume Inspection
Properties of Concrete Design and Control of Concrete Mixtures – Chapter 9.
Hot Weather Concreting
Curing Definition The process of prevention of loss of moisture from fresh concrete while maintaining satisfactory temperature regime (BS 8110) Fig: The.
Hot Weather Concreting
CRACKS IN BUILDINGS: Some Remedial Measures
Concrete Man made stone.
CONCRETE TECHNOLOGY.
CONCRETE CHEMICALS & APPLICATIONS
Chemical Admixtures In Concrete
Design and Control of Concrete Mixtures CHAPTER 18
Unit 7 Review 2014 : Mrs. Knowlton.
What are Admixtures? Admixtures are the material, other than Cement
High Performance Concrete
NAFA Guide To Air Filtration
Air Masses and Fronts.
A STUDY ON HIGH PERFORMANCE CONCRETE WITH FLY ASH AND SILICA POWDER
ADMIXTURES???? Materials added to the concrete besides cement, water and aggregate. To improve the properties of the concrete required. Admixtures can.
GOALS For the classification of cracks in the wet and hardened concrete. To diagnose cracks in concrete structures and determine their types.
Interior Finishes and Detailing
إختبار وتقييم المنشآت الخرسانية
Curing
Psychrometry & Air-conditioning
Chemical Admixtures In Concrete
Journal #44 How often do you watch the weather on TV/internet? Why?
2018 Revisions to NYCDOB Code
Influences on Weather.
Then cut lines (top sheet only!)
Section 3: Gathering Weather Data
INNOVATIVE TECHNIQUES AND MATERIALS FOR PREVENTING CONCRETE SHRINKAGE CRACKING - Cleary, Lomboy, and Zhu Concrete shrinks due to reduction and movement.
Curing.
Admixtures.
Super plasticizers These are linear polymers containing sulfonic acid groups. Two major commercial formulations 1- sulfonate melamine- formaldehyde condensate;
Silica Fume and Fly ash 5 minute Flash Mohamed Wagih
Influence of properties of coarse aggregate
Then cut lines (top sheet only!)
Presentation transcript:

INTRODUCTION Plastic shrinkage cracking occurs when the concrete is in the plastic state, which is within the first 24 hours. Plastic shrinkage cracks are usually spaced 1 to 3 feet apart, are generally parallel to one another.

PLASIC SHRINKAGE CRACKING : THE AMERICAN CONCRETE INSTITUTE [ACI] defines plastic shrinkage cracking as the “ cracking that occurs on the surface of fresh concrete soon after it is placed and still it is in plastic’’. FIG: Plastic shrinkage cracking

HOW IT OCCURS PLASTIC SHRINKAGE CRACKS are caused by the rapid loss of water from the surface of concrete before it has set. The critical condition exist when the rate of evaporation of surface moisture exceeds the rate at which bleed water can replace it.

CAUSE FOR CRACKING

CONDITIONS THAT CAUSES HIGH EVAPORATION Wind velocity in excess of 5mph Low relative humidity High concrete temperature

FACTORS CONTRIBUTING PLASTIC SHRINKAGE CRACKING 1.Concrete strength 2.Depth of section 3.Fines content 4.Admixtures 5.Fibers 6.Surface sprays

PREDICTION OF EVAPORATION RATE : 1. By the usage of Nomograph 2. By using Formula

NOMOGRAPH : Nomo graph is a graph that relates air temperature, relative humidity and wind velocity to predict the evaporation rates for a concrete surface with bleed water.

NOMOGRAPH FOR DETERMINING THE RATE OF EVAPORATION FROM CONCRETE SURFACES

BY THE USAGE OF FORMULA METRIC UNITS: E = 5 ( [ Tc + 18]2.5 - r [ Ta+ 18 ]2.5 )(V +4)X10-6 here,E=Evaporation Rate, kg/m2/hr Tc =Concrete(watersurface)Temperature,C Ta = Air Temperature, C r = Relative Humidity (percent)/100 V = Wind Velocity, kph

EVAPORATION RATE CAUSING PLASTIC SHRINKAGE CRACKING When the evaporation rates exceed 1.0 kg/m2/hr plastic shrinkage cracks are expected. Precautionary measures are almost manitory. Some of these are erecting a wind screen, cooling the concrete, using a fogging system, and placing concrete at night

Conti…… When the evaporation rate is between 0.5 and 1.0 kg/m2/hr plastic shrinkage cracking may occur.. When the evaporation rates are 0.5 kg/m2/hr, plastic shrinkage cracks are not expected.

WHY NOMOGRAPH AND FORMULA NOT WIDELY USED 1. Contractors, Ready mix concrete companies and designers are unaware of nomograph. 2.The nomograph and equations are not easy to use 3.Unaware of how to get weather information.

COMPUTER PROGRAM Computer program makes the Nomograph and the equations easy to use. The user simply enters the air temperature, concrete temperature, relative humidity, and wind velocity.

COMPUTER PROGRAM Cont… The program will determine the evaporation rate and warn the user if precautionary methods are needed. To further emphasize the fact that some conditions may cause or might cause plastic shrinkage cracking, the answers are color coded.

COMPUTRE PROGRAM cont… The color codes are similar to a traffic light; The output is in red when plastic shrinkage cracks are expected.

COMPUTER PROGRAM Conti… The output is in yellow when the plastic shrinkage cracks can occur. The output is green is used when the plastic shrinkage cracking is not expected.

IMPACT OF PLASTIC SHRINKAGE CRACKING Plastic shrinkage cracking rarely impairs the strength of a concrete element. It will have a dramatic impact on the appearance of the concrete. Where it penetrates full depth it may lead to water penetration

WATER PENETRATION THROUGH CRACKS Figure showing water penetrating through the cracks formed due to plastic shrinkage.

REPAIR OF PLASTIC SHRINKAGE CRACKS In pre-hardened concrete: Surface vibrators can be used to close the cracks over their full depth and the surface finishing can then be completed as specified.

REPAIR contin…. Figure shows surface vibration to close the plastic shrinkage cracks

REPAIR contin… Figure showing finishing of concrete surface.

REPAIR contin.. In hardened concrete: If the cracks are not wide at the surface then it may be best to tolerate them otherwise, the cracks should be filled with a suitable proprietary filler.

HOW TO MINIMISE PLASTIC SHRINKAGE CRACKING : Erecting temporary wind breakers to reduce the wind velocity Usage of fog sprays to reduce the rate of evaporation Avoiding the usage of vapor retarders Covering the concrete with moisture retaining coverings such as polythene sheeting, building paper etc.

Contin….. Curing the concrete as soon as possible Usage of synthetic fibers Accelerating the setting time of concrete

Contin.. Figure shows the use of fog sprays

Contin.. Figure shows moisture retaining covering on concrete surfaces

CONCLUSION This paper alerts people about the impact of plastic shrinkage cracks on concrete. Makes the people realise that nomograrh and equations still exist. Computer program makes nomograph and equations easy to use.

REFERENCE 1. American Concrete Institute (ACI) Committee 308, “Guide to Curing Concrete”, ACI 308R-01, American Concrete Institute, Concrete Q & A, “Estimating Evaporation Rates to Prevent Plastic Shrinkage Cracking”, Concrete International, March Uno, P ‘Plastic Shrinkage Cracking and Evaporation Formulas’ ACI Materials Journal Vol 95, No 4, July– August, 1998, pp 365–375.