Unit 3 - Bricks.pdf

CCOV212 CONSTRUCTION MATERIALS Unit 1: Concrete Module Content Unit 2: Bitumen and Asphalt Unit 3: Bricks Unit 4: Steel Unit 5: Timber 1 UNIT...

CCOV212 CONSTRUCTION MATERIALS Unit 1: Concrete Module Content Unit 2: Bitumen and Asphalt Unit 3: Bricks Unit 4: Steel Unit 5: Timber 1 UNIT 3: BRICKS Introduction The term masonry is used to describe all structures produced by stacking, piling or bonding together chunks of rock, fired clay, concrete etc. to form the whole. Masonry is probably the oldest Image by flatart on Freepik Masonry dates back from ancient civilizations of the Middle East and was used widely by Romans and Greeks. Stone structures such as the Egyptian pyramids and the Great Wall of China have survived thousands of years. 2 1  The history of bricks Early cultures used mud bricks, these structures have mostly not survived. In the Bronze Age, people realized that firing (setting fire to or burning) brick-shaped clay produced greater hardness and durability. The art of burning moulded brick was well known by Roman times. The Romans used both fired clay bricks and hydraulic (lime/pozzolana) mortar and spread this technology over most of Europe. In South Africa, the very first clay bricks were fired in 1656. The Castle of Good Hope in Cape Town, built between 1666 and 1684, has withstood the Cape of Storms for over three centuries and is our oldest surviving colonial building. On 29th March 1963 the first Annual General Meeting the S.A Brick Association, was held. South African Standards: o Burnt clay masonry units is SANS 227: 2007 o Burnt clay paving units is SANS 1575: 2007 o Concrete masonry units is SANS 1215: 2008 3 Stable masonry Easily moulded The basic principle of masonry is of building stable bonded (interlocking) stacks of handleable pieces. Bricks or blocks are usually chosen or manufactured to be of size and weight to be placed by hand. Traditional masonry owes much of its strength and stability to interlocking action, weight and inertia. Mortar is a bonding agent but does not substantially contribute to strength, unless irregular shaped and sized pieces are packed apart and bonded with mortar (random rubble walls), strength is mostly derived from mass and interlocking of shapes. Mortar fills the gaps and resists the flow of air and water. Masonry may be reinforced similar to concrete. 4 2 Types of bricks and blocks Many different types, colour, texture and strength are available. Dimensions of a masonry unit = length x width x height (mm) SANS 227:2007 classifies a brick dimensions as: a length not more than 300mm, a width not more than 130mm and a height not more than 120mm. A masonry unit larger than these dimensions is classified as a block. Imperial size of solid bricks 222mm long, 106mm wide and 73mm high. Imperial clay brick weighs between 2.4kg and 3.3kg. 5 Types of bricks and blocks Special shaped bricks are manufactured for creative brickwork. Specialised bricks such as bullnoses, plinth headers or sill bricks are manufactured for their special requirements. Various types of joints are used. Joints vary between 3 to 12mm depending on the type of brick, construction method and aesthetic appearance. 6 3 Different unit forms: Unit form Description Frogged (pressed) Consists of a depression (frog) in one or both bed faces. Standard perforated One or more holes passing (extruded) through one face to the opposite face. The holes are usually vertical when placed. Highly perforated (extruded) Medium perforated (extruded) 7 Different unit forms: Unit form Description Solid (Pressed or extruded) No designed voids other than those inherent in the material. Cellular (pressed, moulded or Has one or more deep holes extruded) or depressions in one bed face which do not penetrate to the other side. Advantage of perforated bricks: Reduction in manufacturing process times Lighter Less materials Provides better bonding Better insulation against heat and noise 8 4 Clay bricks Used for different purposes – building, facing and aesthetics, floor making and paving. o Building bricks – structural material (typically strong and durable) o Facing bricks – facing and aesthetics o Flooring and paving bricks – high resistance to abrasion Properties Very durable and fire resistant – require very little maintenance. Non-combustible and poor conductors. Have moderate insulating properties – keep buildings cool in summer and warm in winter. Minimises the need for heating and cooling (heaters / air- conditioners), therefore reduced energy costs – Green Building. Compressive strength is dependent on – composition of clay, method of manufacturing and degree of firing. 9 Manufacturing of clay bricks Clay bricks - manufactured from a mixture of Clay (different clays produce the different colours) and other additives. Clays – silica (grains of sand), alumina, lime, iron, manganese, sulfur and phosphates in different proportions. Most clays contain traces of iron oxide which give the reddish colour. If the material is unindurated (soft and loamy), it is clay; if the rock is indurated (hardened) it is a claystone; if the rock is indurated and laminated, it is shale. Claystone Shale 10 5  Manufacturing of clay bricks Five main processes (clay and shale bricks): Obtain material Mixing Shaping Drying Firing The final composition of clay brick includes the four natural elements: earth, wind, fire and water. For facing bricks, additional work is done at the shaping stage, either by the application of coloured sand to the surface of the wet clay or by mechanical texturing of the surface. Watch: https://www.youtube.com/watch?v=GEvoXuFKSA0 and https://www.youtube.com/watch?v=kgrYIjIi28Y 11 Manufacturing of clay bricks Obtaining material and mixing: Clay is extracted from the pit, prepared and mixed dependent on the type of raw material and shaping process. Water content is controlled – material may be very wet to relatively dry (depending on shaping process) Shaping systems: Extrusion and wire- Ribbon of clay created by pushing clay through a long mould. Do cut not have frogs but may have perforations. Hand-made bricks High quality plastic clay – thrown into mould by hand (expensive) Semi-dry bricks Fine clay dust pressed repeatedly into moulds. No drying. Fairly regular in shape Pressed bricks May have one or two frogs / shaped holes (cellular) 12 6 Manufacturing of clay bricks Drying: Necessary in all cases where after forming, the brick is soft and unable to withstand the weight of other bricks when stacked for firing. All hand-made and soft-mud type bricks, as well as wire-cut bricks with high moisture content. Carried out in a series of tunnels or chambers. Temperature is regulated to control shrinkage. Firing: Undergoes complicated chemical and physical changes. Firing temperature and type of atmosphere affects the brick colour. Temperatures reach 1200 deg C inside the kiln. Four types of methods: Clamp burning, Intermittent kilns, Continuous kilns, Tunnel kilns. 13 Basic types of clay bricks Brick type Description Non-face extra bricks (NFX) Used plastered or unplastered, used under damp conditions – foundations. Non-face plaster bricks (NFP): General building work. Require plastering or Common / Stock brick tiling, also called commons, stock bricks of run- of-kiln bricks. Engineering units (E) Produced for structural or load-bearing purposes, manufactured to an agreed compressive strength. Can be above 14MPa to over 50MPa Face brick extra (FBX) Selected for durability and highest degree of conformity to size, shape and colour. Compressive strength can be greater than 50MPa. Face brick standard (FBS) Durable and uniform in size and shape Face brick aesthetic (FBA) Selected or produced for durability and aesthetic effect derived from size, shape or colour. Refer Clay Brick Technical Guide Chapter 2 14 7  NFP E 15 NFX 16 8  FBS FBA 17 Concrete bricks Controlled manufacture – mixture of cement, sand and aggregate together with additives such as colouring agents. Mixture is pressed and / or vibrated into brick-sized moulds. Moulded bricks either cured in steam chambers or in air. Regular in size and colour. Minimum strength of solid units is 7MPa. Maximum stone size is 13.2mm. Concrete Blocks Similar to concrete bricks but larger. Usually 390mm x 190mm x 90mm. Used for both internal and external walls. Plastering is recommended for extra protection against moisture. Less expensive than clay bricks and faster construction. Minimum strength for hollow blocks is 3.5Mpa. Stone size should not exceed 1/3 of the maximum hollow unit shell. 18 9 19 Concrete bricks and blocks Advantages Disadvantages Ingredients are readily available Generally require plastering and painting No heating process – more economical May be subject to water seepage over time Can be cast to any shape Requires internal reinforcement when using hollow concrete blocks especially in areas subject to earthquakes Free from flaws and defects due to Large blocks are heavy and difficult to quality control handle Generally strong due to strength of Plumbing issues – pipe leaks etc. are aggregates more difficult and expensive to repair- blocks have to be cut open for this purpose. Continues to cure after manufacture Price can vary depending on region, cement costs and availability. High durability Can withstand high temperatures and non-combustible 20 10 Building with Bricks Sides or wider surfaces are called Stretchers or Stretcher faces Ends or narrow surfaces are called Headers or Header faces Top and bottom surfaces are called Beds A Perpend is a vertical joint between any two bricks and is usually—but not always—filled with mortar 21 Building with bricks: Functions of mortar Four Functions: Bonds the units together and seals the spaces between Compensates for dimensional variations in the units Bonds to reinforcing steel causing it to act as an integral part of the wall Provides a decorative effect by creating shadows or colour lines Joints falls into two classes: Trowelled or Tooled Trowelled: excess mortar is struck off and the joint is finished with a trowel Tooled: a special tool is used to compress and shape the joint 22 11 Building with bricks: Classes of mortar Class I Highly stressed masonry, for use in multi-story loadbearing buildings or reinforced masonry. Class II Used for normal loadbearing applications, as well as parapets, retaining structures, freestanding walls and walls exposed to damp conditions. Building lime can be added to cement to improve workability, impermeability and adhesion. Lime must not be used to replace the cement in the mix. Do not use lime with masonry cement. 23 Mortar strength requirements and mix proportions Mortar Minimum required Quantities of material required per m3 of mortar (not class compressive strength including wastage) at 28 days (MPa) Prelim lab tests Common 50kg Sand m3 Masonry 50kg Sand cement bags 32.5 or cement bags m3 42.5 22.5x I 14.5 10 1.25 13.5 1.15 II 7 7 1.35 10 1.25 Typical cement:sand ratio for mortar is 1:3 24 12 Building with bricks: Brick Ties and Brick reinforcing 25 Building with bricks: Bonding patterns 1. Stretcher bond 2. English bond 3. Flemish bond 4. Stacked bond 26 13 Building with Bricks: Brick Bonding 1. Stability is key – lay in a recognized pattern / bond 2. The bond also affects the appearance 3. Vertical joints for loadbearing walls must not extend into the next brick course – sometimes bricks need to be cut to ensure this. 4. Cut bricks should not be less than half a brick length 5. Laps must not be less than a quarter of the brick length 27 Bonding patterns 1. Stretcher bond Longer side facing the outside wall – used for half brick walls and cavity walls Half brick wall Cavity wall with wall ties – plan and section 28 14 Bonding patterns 2. English bond A very strong bond – alternative courses of stretchers and headers. Used for one brick walls Plan: Plan: Course 1, 3, 5 Course 2, 4, 6 29 Bonding patterns 3. Flemish bond Alternative headers and stretchers in each course. Not as strong as the English bond Plan: Plan: Course 1, 3, 5 Course 2, 4, 6 30 15 Bonding patterns 4. Stacked bond Can be used for non-load bearing walls Common to include brick reinforcing to increase load strength Used mostly for aesthetic purposes Plan: Course 1, 2, 3 etc 31 Properties of bricks Water absorption The % increase in the weight of a dry brick when it is saturated Compressive strength The mean of 10 crushing tests in which a falling load is divided by the gross area of the brick. Frost resistance Determined by their pore structure (the percentage of fine pores in the brick). Bricks with low porosity and lower water absorption better suited for harsh environments (for e.g. engineering bricks). Soluble salt content May cause efflorescence – powdery deposits on the surface of the brick, forms with water ingress, when the water evaporates it takes the salt to the surface. Thermal movement Bricks expand when warm and shrink when cooled. Expansion of the brickwork as a whole must be considered. Moisture movement Clay bricks expand on cooling from the kiln – some water molecules re-attach. This is non-reversible unless re-fired. 32 16