14 Questions to Ask a Commercial Concrete Contractor Before Hiring
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Typically, an unbroken, whole structure is the strongest version of itself.
However, due to concrete’s properties, a slab that is too large can be susceptible to cracking in certain circumstances. These circumstances include shrinkage, temperature fluctuations, and structural loads.
In construction, various types of concrete joints prevent uncontrolled cracking and maintain structural integrity. Joints allow for controlled movement, expansion, and contraction. They ultimately improve the longevity and performance of concrete structures.
This article will explore five different types of joints, how they function, and where they are commonly used.
Table of Contents
1. Expansion Joints
2. Isolation Joints
3. Control Joints
4. Construction Joints
5. Decorative Joints
Expansion joints create a flexible buffer between concrete elements.
In concrete construction, expansion joints accommodate the expansion and contraction of concrete caused by temperature fluctuations, moisture changes, and other environmental factors. They allow independent movement while maintaining the integrity of the structure.
Without these joints, the stress from expansion could lead to uncontrolled cracking, buckling, or structural failure.
Expansion joints come in many different forms. The list is as follows:
Horizontal expansion joints are best for flat or level concrete surfaces (e.g., pavements, slabs, bridge decks, floors). These joints manage movement across the horizontal plane caused by thermal changes or load stress.
Vertical expansion joints go in upright structures like walls, columns, and facades. They accommodate height-related movement due to thermal expansion, shrinkage, or settlement. These joints ensure vertical elements can expand or contract without stressing adjacent components.
As the name suggests, seismic joints can absorb and accommodate movement during seismic activity. They allow large, multidirectional movement between structural sections, preventing major damage during an earthquake. These joints often include advanced materials and components to enhance flexibility and energy dissipation.
Fire-rated expansion joints combine fire-resistant materials with movement-accommodating capabilities. They are key in fire-rated assemblies to maintain compartmentalization in the event of a fire while still allowing expansion and contraction under normal conditions.
These joints use precompressed foam or other elastomeric materials inserted into the joint gap. The compressed material expands or contracts to fill the space as the concrete moves, creating a watertight, flexible seal.
A strip seal joint includes a flexible rubber gland that spans the joint opening, held in place by steel edge retainers. These joints provide both movement accommodation and a watertight seal. They are extremely durable and suited for high-traffic areas.
Inflated or inflatable expansion joints use air-pressurized rubber components that adjust in size based on the pressure or load applied. These are typically used in specialty or dynamic applications where varying joint widths are expected.
Rubber gland joints use a thick, molded rubber component—usually in a wave or bellow shape—that absorbs lateral and longitudinal movements. These joints offer high durability and excellent sealing capabilities.
Expansion joints absorb movement caused by temperature changes, seismic activity, settlement, and vibration. This absorption power prevents cracks and structural damage.
They allow building components to expand and contract independently while maintaining weather-tight seals to block water, air, and sound infiltration.
Discover: What is a Floating Slab Foundation?
These joints are crucial where concrete slabs meet other building parts (e.g., walls, columns, footings, or utility pads).
Isolation joints are used in concrete construction to separate one structural element from another, allowing each to move independently. They prevent stress transfer that can lead to cracking or structural damage.
Unlike control or construction joints, isolation joints are not intended to manage shrinkage cracks but rather to isolate movement caused by factors like expansion, contraction, settlement, or vibration.
There are several different types of isolation joints.
These joints completely divide adjacent sections of a building, allowing independent movement.
They are essential in large structures or complexes where parts of the building may expand, contract, or settle at different rates.
Building separation joints are often wide and continuous from foundation to roof. Often, they may include fire- or seismic-rated components.
Perimeter joints go around the edges of concrete slabs where they meet walls, columns, or other fixed elements.
Their primary function is preventing bonding and allowing slab movement without stressing the adjacent structures.
They are commonly seen on slab-on-grade floors, sidewalks against buildings, or around machinery pads.
Column isolation joints are designed to decouple a column from the surrounding concrete slab.
Since columns are load-bearing and may settle differently than the slab, these joints prevent the column from restraining the slab, thereby avoiding cracking and distortion.
These joints separate different structural systems within a building. For example, separating a stair tower from the main structure or a concrete deck from a steel frame.
They allow independent movement and prevent incompatible loads from transferring between systems.
A material transition joint is necessary when two different construction materials meet, such as concrete and steel or concrete and masonry.
These joints accommodate differing expansion rates, movement tolerances, and structural behaviors, reducing the likelihood of material failure at the connection point.
Isolation joints allow adjacent structural elements to move independently, preventing cracking, spalling, and unwanted stress transfer.
They accommodate differential settlement, thermal expansion, and vibration while preventing loads from being unintentionally transferred between connected components.
This helps preserve both the structural and functional integrity of the building over time.
Several materials are commonly used in the construction of isolation joints.
Their selection is based on the type of structure, environmental conditions, and performance requirements:
(Also known as contraction joints.)
Control joints are intentionally weakened planes created in concrete and masonry elements, such as slabs, pavements, and walls, to control where cracks will occur.
These joints sit at specific intervals to guide the natural cracking process of concrete as it cures and contracts.
Concrete shrinks as it dries and expands or contracts with temperature and moisture changes. These joints help manage that movement in a controlled way.
Rather than allowing random, uncontrolled cracking, control joints encourage cracks to form at predetermined, straight-line locations that are less noticeable and more manageable.
This protects the appearance and longevity of the surface and helps preserve the concrete element’s structural integrity over time.
Keep Reading: 9 Types of Concrete Cracks (& Which Ones to Fix ASAP)
Not all control joints are the same. Below is a list of the different types.
Sawed joints are created by cutting into the hardened surface of the concrete after it has set but before it begins to crack on its own.
Timing is crucial. These cuts are typically made within 6 to 18 hours of finishing, depending on the concrete mix and weather conditions.
The saw cut forms a straight, shallow groove that acts as a stress relief point, encouraging cracks to form below the cut.
Tooled joints are formed while the concrete is still fresh by using a grooving tool to score a joint into the surface.
These commonly appear in smaller slabs, sidewalks, and decorative concrete applications. The grooved joint provides functionality and a finished appearance, often blending into the surface’s aesthetic.
Formed joints are created by placing removable wooden, plastic, or metal strips into the concrete forms before pouring.
Once the concrete sets, these strips are removed or left in place, depending on the design. Formed joints are instrumental in larger pours or precast panels and ensure consistent placement and depth of the joint.
These joints use pre-manufactured strips made from plastic, rubber, or similar materials embedded in the concrete during placement.
Pre-molded strip joints provide clean, uniform joint layouts and are often used in commercial and industrial flooring where both function and appearance are essential.
Shaped, interlocking joints, or keyway joints, serve a dual purpose. They control cracking and provide some load transfer between adjacent concrete sections.
These joints are typically cast into the bottom or side of a concrete pour using a key-shaped form. They are primarily found in construction joints between slabs.
Control joints manage the natural cracking of concrete by creating predetermined weak points where cracks can safely form.
They relieve internal stresses caused by shrinkage, temperature changes, and structural movement.
By guiding cracks to specific locations, control joints:
Related: How Long Does a Concrete Building Last? (& When It’s Time to Consider a Replacement)
Construction joints ensure structural continuity and integrity across separate pours when properly designed and detailed.
Construction joints are interfaces formed between separate concrete placements. They occur when a pour must be paused due to construction logistics, size limitations, or scheduling needs.
These joints are not a flaw in the structure but an intentional and necessary part of concrete construction.
They allow the placing of concrete to happen in stages while still forming a strong, cohesive, monolithic system once all elements are completed.
They may also serve additional purposes, such as acting as control joints or integrating features for water resistance or load transfer.
Construction joints can be built in several different ways:
These occur between successive lifts of concrete, such as between a foundation and wall, or between floor slabs poured on different days.
These joints are created when walls, columns, or other vertical elements are placed in segments rather than in one continuous pour.
Joints formed with interlocking shapes. They are typically created by embedding wood or metal forms during placement. These joints provide mechanical interlock and improve shear resistance between adjacent concrete sections.
These use steel dowels that extend across the joint to transfer loads while keeping the two concrete sections aligned and allowing for limited horizontal movement.
Joints created when the surface of the initial concrete pour is intentionally roughened before it fully hardens, enhancing the mechanical bond with the subsequent pour.
Made by placing temporary vertical formwork (i.e., bulkheads) to define the end of a concrete pour and create a clean, manageable stopping point.
Include embedded flexible materials such as PVC or rubber waterstops, which are designed to prevent water from penetrating through joints in water-retaining or water-resistant structures.
These involve preparing the existing concrete surface and applying bonding agents to ensure a strong, durable adhesion between old and new concrete during subsequent placements.
Construction joints serve several practical purposes in concrete construction:
See also: What Are “Cold Joints”? (And How Do You Prevent Them?)
These are the last on the list because they are optional and do not fulfill a specific structural purpose.
These specially designed joint systems enhance the visual appeal of concrete, masonry, tile, or other construction materials while simultaneously providing necessary movement accommodation.
Decorative joints can transform what would otherwise be purely utilitarian features into design elements that contribute to the overall aesthetic of the structure.
The list below provides ideas on how to use decorative joints in a project.
Arranged in geometric shapes, curves, or custom designs to add visual interest and guide the eye across concrete slabs, plazas, or walkways.
Use pigmented sealants, mortars, or fillers that either contrast with or complement the surrounding concrete, enhancing the appearance.
Incorporate materials like brass, aluminum, or stainless steel, offering both aesthetic appeal and functional edge protection.
Metal or plastic inserts used in terrazzo flooring separate different terrazzo mix colors while also contributing to decorative patterning.
Intentionally deepened or shaped to create shadow lines, adding dimension and texture to concrete or masonry surfaces.
Feature joint fillers with decorative aggregate materials that coordinate with exposed aggregate concrete for a cohesive and visually rich finish.
Incorporate wood, stone, or glass elements within the joint to form unique decorative bands that contrast with or accent the concrete surface.
Include embossed or patterned surfaces within the joint area, adding tactile and visual detail to enhance the overall design.
Understanding the different types of concrete joints is essential for ensuring structural integrity, durability, and performance in any construction project.
Whether accommodating movement, controlling cracks, or connecting segmented pours, each joint type serves a specific purpose that contributes to the overall success of the structure.
By selecting and correctly detailing joints, builders can create resilient and long-lasting concrete systems.
Contact FMP Construction today for your concrete construction needs. We use all the right joints in all the right places.
