Name: masonry wall joints for temperature and moisture
Uploaded: 2024-09-12T16:16:29.000Z
Duration: 1 min 19 s
Channel: JoVE

Considera un muro di mattoni esposto a pioggia continua; il mattone assorbe l'umidità e tende ad espandersi leggermente. In assenza di spazio per espandersi, si sviluppano sollecitazioni di compressione nella parete, portando alla formazione di crepe nella parete.
Per consentire l'espansione nella muratura deve essere prevista un'apertura continua nel muro, chiamata giunto di dilatazione. 
Nel caso di un muro in muratura di calcestruzzo di nuova costruzione, man mano che la malta si asciuga, il muro subisce un ritiro, che induce sollecitazioni di trazione.
Se queste sollecitazioni superano la resistenza alla trazione del muro, compaiono crepe da ritiro.
Queste crepe casuali possono essere confinate lungo un giunto di controllo, un giunto debole creato intenzionalmente che corre continuamente lungo il muro.
I giunti di dilatazione e di controllo sono forniti nei punti in cui le pareti intersecano una colonna o un'apertura e nelle posizioni in cui la parete cambia direzione, altezza e spessore.
I giunti verticali sono integrati nelle pareti quando vengono posati i mattoni. Questi giunti sono spesso riempiti con un'asta di supporto e sigillati con sigillanti elastici per giunti per evitare che l'umidità e l'aria entrino nella stanza.

espansione e contrazione nelle pareti in muratura

Le pareti in muratura sono soggette a una leggera espansione e contrazione a causa delle variazioni di temperatura e umidità. Il movimento termico nella muratura è relativamente semplice da misurare e pianificare. D'altro canto, il movimento dell'umidità rappresenta una sfida maggiore. Le unità di muratura in argilla di nuova fabbricazione in genere assorbono acqua e si espandono nel tempo in normali condizioni ambientali. Al contrario, nuove unità di muratura in calcestruzzo tendono a restringersi poiché perdono l'umidità in eccesso acquisita durante il processo di produzione.

Per adattarsi a questi movimenti senza danneggiare la struttura, gli edifici devono incorporare tipi specifici di giunti. I giunti di dilatazione sono fondamentali in quanto sono progettati per aprirsi o chiudersi, consentendo al materiale di espandersi o contrarsi in risposta alle variazioni di umidità e temperatura. Questi giunti sono spesso sigillati con materiali flessibili per impedire l'infiltrazione di aria e acqua. I giunti di controllo, un'altra caratteristica essenziale, sono intenzionalmente incorporati come piani di debolezza all'interno della muratura. Questi giunti sono progettati per aprirsi e gestire il restringimento, in particolare durante la fase iniziale di stagionatura della muratura.

Sia i giunti di dilatazione che quelli di controllo devono essere posizionati strategicamente nella struttura. Comunemente, essi vengono posizionati in punti di discontinuità geometrica come angoli, cambiamenti nell'altezza o nella larghezza del muro e vicino alle aperture.

Espansione e contrazione nelle pareti in muratura

Considera un muro di mattoni esposto a pioggia continua; Il mattone assorbe l'umidità e tende ad espandersi leggermente. In assenza di spazio per l'espansione, ...

expansion-and-contraction-in-masonry-walls

Education

Didattica

JoVE Core

Civil Engineering

Ingegneria Civile

Unit 1

Unità 1

Masonry

Muratura

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

Expansion and Contraction in Masonry Walls

masonry wall joints for temperature and moisture

Masonry walls change size slightly as temperature and moisture change. Builders account for this movement so the wall does not crack or shift out of place. Thermal movement is usually easy to measure and plan for. Moisture movement is harder to predict.

New clay masonry units often absorb water and expand over time in normal outdoor conditions. New concrete masonry units behave differently. They usually shrink as they lose extra moisture gained during production. These opposite changes make joint design an important part of masonry construction.

Expansion joints give masonry room to open or close as the material expands or contracts. These joints are often sealed with flexible materials so air and water cannot get in. Control joints are another key feature. A control joint is a planned line of weakness in the masonry. It helps manage shrinkage, especially during the early curing stage.

Both expansion joints and control joints must be placed carefully. Common locations include corners, changes in wall height or width, and areas near openings. These points are called geometric discontinuities because the wall shape changes there. Proper joint placement helps protect the structure as the masonry moves.

Masonry Wall Joints for Temperature and Moisture

masonry-wall-joints-for-temperature-and-moisture

composite masonry walls

Bonding and Materials in Composite Masonry

Composite masonry walls use two or more wythes, or vertical layers, of masonry to form one unified wall. The wythes may use the same material or different masonry materials. They are joined to work together as a single structure. These wythes can be bonded in several ways. Builders may use mortar-filled collar joints, grouted spaces, or rigid metal ties with reinforcement. Masonry header units can also connect the layers, but this method is rare. Metal ties are often preferred because they...

masonry cavity walls

Masonry Cavity Walls and Moisture Control

Masonry cavity walls use two wythes, or layers, with a hollow space between them. The outer and inner wythes are linked only by corrosion-resistant metal ties. This design helps manage water and improve wall performance. When rainwater passes through the outer wythe, it moves down through the cavity. Flashing catches the water and directs it toward weep holes, where it can leave the wall. The inner wythe often has damp-proofing on the cavity side. This layer also works as an air barrier. The...

masonry loadbearing walls

How Masonry Walls Support Buildings

Masonry load-bearing walls support floors and roofs and carry those loads down to the foundation. They are built from brick, stone, or concrete masonry units. These walls rely on compressive strength, which means they can resist pushes from above very well. Masonry walls may be reinforced or unreinforced, depending on the building needs. They carry dead loads and live loads while using working stresses that stay below the materials' ultimate strength. That safety margin helps the structure...

masonry curtain walls

Masonry Curtain Walls and Support Systems

Masonry curtain walls use brick or stone veneer as an exterior cladding system. The veneer is supported by the building structure, so the wall can be both attractive and functional. Two main construction methods are used for these walls. One method builds the masonry units in place through traditional layering. The other uses prefabricated panels that are assembled on the ground and then lifted into position. In traditional construction, steel shelf angles attached to the spandrel beam carry...

posttensioned masonry walls

How Masonry Walls Gain Extra Strength

Post-tensioned masonry walls gain extra strength from high-strength steel rods or flexible tendons. These tensioning elements are anchored to the foundation and run vertically through the wall. In some walls, they sit inside the cores of the masonry units. In others, they are placed between the masonry wythes, or layers. The wall is built first with the tensioning elements already in place. After the mortar cures fully, the wall is tightened. Steel rods are tensioned by turning nuts against...

cavity drainage and flashings in masonry walls

cavity-drainage-and-flashings-in-masonry-walls

Moisture Control in Masonry Cavity Walls

Masonry cavity walls use a gap between two wythes, or wall layers, to help control moisture. The cavity is usually at least 2 inches wide, and it may contain insulation. Even with insulation, a clear space of at least 1 inch is kept so water can drain away. Some walls also use a continuous drainage mat to reduce the needed space while still moving moisture out. Weep holes are another key part of cavity drainage. These openings sit at the base of the cavity and let collected water escape. They...

thermal insulation in masonry walls

Masonry Wall Insulation Options

Masonry wall insulation can be placed on the outside, inside the wall, or on the interior surface. The best choice depends on the climate, the building design, and whether the wall is being built new or retrofitted. In hot, dry climates, masonry can help smooth indoor temperatures by absorbing heat during the day and releasing it at night. In many other climates, extra insulation is needed to improve thermal resistance. One common exterior method is an Exterior Insulation and Finish System, or...

expansion and contraction in masonry walls

Masonry walls change size slightly as temperature and moisture change. Builders account for this movement so the wall does not crack or shift out of place. Thermal movement is usually easy to measure and plan for. Moisture movement is harder to predict. New clay masonry units often absorb water and expand over time in normal outdoor conditions. New concrete masonry units behave differently. They usually shrink as they lose extra moisture gained during production. These opposite changes make...

movement joints in buildings

How Buildings Handle Structural Movement

Buildings are designed to handle movement from temperature changes, moisture changes, and structural deflection. If these changes are ignored, they can cause visible damage or even unsafe conditions. Movement joints give building materials room to move without creating distress. Working joints are the simplest type. They are placed during construction and help materials cope with change as the building goes up. Shingled roofs and wood bevel siding are common examples because they can move with...

types of building separation joints

Building Joints for Movement and Stability

Building separation joints help large or complex buildings move in a controlled way. They split a structure into smaller, separate units. This reduces stress when the building shifts under different forces. The joints are grouped into three main types: volume-change joints, settlement joints, and seismic separation joints. Volume-change joints handle expansion and contraction caused by temperature changes and moisture changes. They are placed where the building mass has discontinuities,...

efflorescence in masonry

Stopping White Salt Crystals on Masonry

Efflorescence is the white, fluffy crystal layer that can form on masonry walls. It happens when water-soluble salts in brick, stone, concrete, or mortar are dissolved by water and carried to the surface. When the water evaporates, the salts are left behind as a powdery deposit. New efflorescence is often seen soon after construction. In many cases, it can be cleaned with water and a brush. It may also fade over time as rain leaches salts out of the masonry surface. If efflorescence appears...

mortar joint deterioration in masonry

Repairing Damaged Mortar Joints in Masonry

Mortar joints in masonry can break down when water collects in them and freezes. The repeated freezing and thawing makes the water expand and shrink. That process creates cracks in the joints and can spread damage over time. As the mortar worsens, pieces may spall, or break off from the joint surface. Loose masonry units can follow, and the wall becomes weaker. Damaged joints also let moisture move into the wall, which adds to the problem. Good construction helps protect mortar joints. Using...

masonry in cold and hot weather conditions

masonry-in-cold-and-hot-weather-conditions

Protecting Mortar During Weather Changes

Masonry work changes in cold and hot weather because mortar must stay at the right temperature and moisture level. If mortar freezes before it cures, its strength and watertightness can drop. For proper hydration and curing, mortar should stay between 60°F and 80°F. When the weather is below 40°F, the water used for mortar must be heated. The water should not exceed 120°F, because very hot water can reduce compressive strength and bond strength. Masonry units and sand should also stay dry and...

masonry paving

Masonry Paving Materials and Base Layers

Masonry paving uses bricks, stones, and concrete masonry units to create durable walking and driving surfaces. These materials are selected for their shape, color, strength, and resistance to abrasion and weathering. Masonry units can be used in different paving setups depending on the site and the load they must carry. Some paving systems are installed dry on a thin sand layer over a gravel base. Others are set in mortar or asphalt on a concrete slab. For areas with heavy vehicular loads, a...

key terms and concepts

Learn how expansion joints and control joints help masonry walls handle temperature and moisture changes, including clay and concrete unit movement.

Masonry Wall Joints for Temperature and Moisture | JoVE K12

JoVE Core Civil Engineering provides a foundational exploration of essential construction materials in civil engineering, focusing on bricks, stones, steel, wood, and concrete through easy-to-understand animated videos. This collection covers the properties, manufacturing processes, and practical applications of these materials. Additionally, the accompanied science-in-action videos demonstrate the research experiments performed in laboratories.

civil engineering

Masonry Wall Joints for Temperature and Moisture

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