Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
InspectAPedia ® Home
STRUCTURAL INSPECTIONS & DEFECTS
ADVANCED INSPECTION METHODS
AGE of a BUILDING - how to determine
ARCHITECTURE & BUILDING COMPONENT ID
BEST CONSTRUCTION PRACTICES GUIDE
BRICK FOUNDATIONS & WALLS
BRICK STRUCTURAL WALL Loose Bulged
BRICK WALL THERMAL EXPANSION CRACKS
BRICK VENEER WALL Loose, Bulged
BRICK WALL DRAINAGE WEEP HOLES
BUCKLED FOUNDATIONS due to INSULATION?
BUILDING DAMAGE ASSESSMENT & REPAIR
BUILDING SAFETY HAZARDS GUIDE
CHIMNEY INSPECTION DIAGNOSIS REPAIR
COLD POUR JOINTS, CONCRETE
COLUMNS & POSTS, DEFECTS
CONCRETE FOUNDATIONS, PRE-CAST
CONNECTORS, FASTENERS, TIES
Cracks, Checking or Splitting Beams & Log Homes
DECK & PORCH CONSTRUCTION
DECK COLLAPSE Case Study
DEFINITIONS of MOBILE HOME, DOUBLEWIDE, MODULAR, PANELIZED CONSTRUCTION
DEFINITIONS of ENGINEERED WOOD OSB LVL etc
DEW POINT TABLE - CONDENSATION POINT GUIDE
DISASTER BUILDING INSPECTION & REPAIR
EARTHQUAKE DAMAGED FOUNDATIONS
FLOOD DAMAGE ASSESSMENT, SAFETY & CLEANUP
FLOOR, ENGINEERED WOOD & LAMINATES
FLOOR FRAMING & SUBFLOOR for TILE
FOOTING & FOUNDATION DRAINS
FOOTINGS EXPOSED, Repair Methods
FOUNDATION CONSTRUCTION TYPES
FOUNDATION CONTRACTORS, ENGINEERS
FOUNDATION CRACK DICTIONARY
FOUNDATION FAILURES by MOVEMENT TYPE
FOUNDATION INSPECTION METHODS
FOUNDATION INSULATION OPTIONS
FOUNDATION MATERIALS, Age, Types
FOUNDATION REPAIR METHODS
FRAMING DAMAGE, INSPECTION, REPAIR S
FRAMING CONNECTORS & JOIST HANGERS
FRAMING MATERIALS, Age, Types
FRAMING SIZE & Spacing, Age, Types
FRAMING TABLES, SPANS for DECKS
FROST HEAVES, FOUNDATION, SLAB
GRADING, DRAINAGE & SITE WORK
GUTTERS & DOWNSPOUTS
HOUSE PARTS, DEFINITIONS
I-JOISTS, Wood Roof Floor
ROOF ICE DAM LEAKS
INSECT INFESTATION / DAMAGE
LOG HOME GUIDE
LVL Laminated Veneer Lumber, Beams
MOBILE HOMES, DOUBLEWIDES, TRAILERS
MODULAR HOME CONSTRUCTION
MOISTURE CONTROL in BUILDINGS
NOISE / SOUND DIAGNOSIS & CURE
OSB - Oriented Strand Board
PLYWOOD Roof, Wall, Floor Decks & Sheathing
PORCH CONSTRUCTION & SCREENING
PRE-CUT & KIT HOMES
Preservative-Treated Framing Lumber
RETAINING WALL DESIGNS, TYPES, DAMAGE
RETAINING WALL GUARD RAILINGS
ROT, FUNGUS, INSECT DAMAGE
SEARS KIT HOUSES
SINKHOLES, WARNING SIGNS
CONCRETE SLAB CRACK EVALUATION
CONCRETE SLAB CRACK REPAIR
STAIRS, RAILINGS, LANDINGS, RAMPS
STONE VENEER WALLS
STRAW BALE CONSTRUCTION
STRESS SKIN INSULATED PANELS
STRUCTURAL DAMAGE PROBING
STRUCTURAL WOOD ASSESSMENT
SUMP PUMPS GUIDE
TEST KITS for DUST, MOLD, PARTICLE TESTS
Thermal Expansion Cracking of Brick
THERMAL MASS in BUILDINGS
TIMBER FRAMING, ROT
TRUSS UPLIFT, ROOF
TRUSSES, Floor & Roof
WALL CONSTRUCTION BARRIER vs CAVITY
WATER BARRIERS, EXTERIOR BUILDING
WATER ENTRY in BUILDINGS
WINTERIZE A BUILDING
WOOD STRUCTURE ASSESSMENT
Concrete slab cracks at control joints: this article describes the causes, evaluation, and repair of cracks at control joints in poured concrete slabs or floors. This article series describes how to recognize and diagnose various types of foundation failure or damage, such as foundation cracks, masonry foundation crack patterns, and moving, leaning, bulging, or bowing building foundation walls.
Types of foundation cracks, crack patterns, differences in the meaning of cracks in different foundation materials, site conditions, building history, and other evidence of building movement and damage are described to assist in recognizing foundation defects and to help the inspector separate cosmetic or low-risk conditions from those likely to be important and potentially costly to repair.
Green links show where you are. © Copyright 2014 InspectApedia.com, All Rights Reserved.
Here we focus on control joints needed in poured concrete floor slabs and monolithic concrete foundations. But control joints are also required in certain masonry walls, including brick walls and in some cases concrete block walls as well as poured concrete walls. ( BRICK WALL THERMAL EXPANSION CRACKS) Separately at CONCRETE SLAB CRACK EVALUATION we catalog the different types of cracks that show up in poured concrete.
What is a concrete slab control joint & why do we need control joints in concrete?
A control joint controls where and how a shrinkage crack appears in poured concrete, and it allows for thermal expansion or contraction without additional damage. Without a control joint, cracks in concrete floors, walls, or ceilings appear at stress points in uneven, diagonal, or other patterns in locations where they may be unsightly or may cause damage such as cracks in ceramic tile or other floor coverings, or may be traced to leaks.
How much does concrete shrink as it cures? How much does concrete move in response to temperature changes?
Because concrete shrinks as it cures (about 1/16 inch for each 10 liner feet or by other sources, about .66 inches per 100 feet), and because there may also be some expansion and contraction of poured concrete in response to temperature (about 0.25 inches per 100 feet per 25 degF temperature change, with a maximum of about 0.5" per 100 feet) and moisture changes in its environment, a large solid slab of poured concrete for a floor or slab is likely to crack.
Control joints, called "relief joints" by some builders and more loosely speaking, "expansion joints" by others, are built into a well-designed poured concrete slab so that the occurrence of more random, ugly cracks is less likely.
Remember that concrete shrinkage itself is a normal process. If a pour and control joints are perfect, cracks caused by concrete shrinkage will not be noticeable - they'll occur inside the control joints (as we show below), or if a slab shrinks perfectly with no internal cracks, you'll see a gap opening around the perimeter of the slab where it abuts the foundation walls.
Description of the concrete curing process
During the concrete curing process, a chemical process called hydration, concrete hardens, using some of the water molecules in its original content.
Concrete typically takes 28 days to reach its design strength; a considerable portion of concrete shrinkage is going to occur during this interval, particularly during the first week or less.
Even though the concrete's design strength is reached in about a month, concrete continues to harden for days or weeks after that point too.
What do control joints or "expansion joints" look like?
A control joint is a gap, usually formed in a straight line, placed at intervals to control where and how cracks will occur in poured concrete. When you see a "crack" or joint that is formed in a straight line, dividing poured concrete into sections, most likely it's a control joint. Concrete control joints may also be cut by a power saw if they were omitted during the original pour.
In the photo at left is a tooled control joint in a concrete floor slab.
A concrete control joint that was formed during the pour or placement of the concrete usually is tooled to round the upper edges of either side of the joint, and the joint extends some depth into the concrete, or in some cases (such as sidewalks and some floors) the control joint may extend through the full depth or thickness of the concrete. Full-depth control joints are normally filled with a flexible material.
The photograph at page top and the photo just above where Andy is walking away from the camera show expansion joints in a garage floor slab in Arizona.
Even in a climate where we do not anticipate freezing, control joints are needed to prevent random shrinkage cracks that would otherwise occur in a large concrete floor slab pour like this one. Notice that we do not see other cracks in this slab.
Control joints are likely to appear as straight lines at regular intervals across a poured concrete slab (if they were used in the construction of the slab) such as we show in the sketch below, at the lines marked (G) at 4' intervals or larger depending on the concrete materials and slab design used.
Close-up Photos Reveal Concrete Shrinkage Cracks Within the Control Joint
No FAQs have been posted for this page. Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Search the InspectApedia website
For detailed information about foundation repair methods, including repairs to various kinds of cracks in concrete, see:
The frost heaving forces developed under a 1 ft. (30.5 cm) diameter steel plate were measured in the field throughout one winter. The steel plate was fixed at the ground surface with a rock-anchored reaction frame. heave gauges and thermocouples were installed at various depths to determine the position and temperature of the active heaving zone. The general trend was for the surface force to increase as the winter progressed. when the frost line approached the maximum depth the force was in excess of 30,000 lb (13,608 KG). Estimates of the heaving pressure at the frost line ranged from 7 to 12 psi (0.49 to 0.84 KG/cm) square during this period. The variation of surface heaving force was closely associated with weather conditions. Warming trends resulting in a temperature increase of the frozen layer caused the forces to decline.
Leda clay slopes in the Ottawa valley are vulnerable to catastrophic landslides. More than 250 landslides, historical and ancient, large and small, have been identified within 60 km of Ottawa. Some of these landslides caused deaths, injuries, and property damage, and their impact extended far beyond the site of the original failure. In spectacular flowslides, the sediment underlying large areas of flat land adjacent to unstable slopes liquefies. The debris may flow up to several kilometres, damming rivers and causing flooding, siltation, and water-quality problems or damaging infrastructure. Geologists and geotechnical engineers can identify potential landslide areas, and appropriate land-use zoning and protective engineering works can reduce the risk to property and people.
Deposits of Leda clay, a potentially unstable material, underlie extensive areas of the Ottawa-Gatineau region. Leda clay is composed of clay- and silt-sized particles of bedrock that were finely ground by glaciers and washed into the Champlain Sea. As the particles settled through the salty water, they were attracted to one another and formed loose clusters that fell to the seafloor. The resulting sediment had a loose but strong framework that was capable of retaining a large amount of water. Following the retreat of the sea, the salts that originally contributed to the bonding of the particles were slowly removed (leached) by fresh water filtering through the ground. If sufficiently disturbed, the leached Leda clay, a weak but water-rich sediment, may liquefy and become a 'quick clay'. Trigger disturbances include river erosion, increases in pore-water pressure (especially during periods of high rainfall or rapid snowmelt), earthquakes, and human activities such as excavation and construction.
After an initial failure removes the stiffer, weathered crust, the sensitive clay liquefies and collapses, flowing away from the scar. Failures continue in a domino-like fashion, rapidly eating back into the flat land lying behind the failed slope. The flowing mud may raft intact pieces of the stiffer surface material for great distances.