12) MASONRY BRICK/BLOCK/STONE Contents • Masonry materials • Types of masonry units • Manufacture of bricks and blocks • Characteristics and testing of bricks • Mortar for brickwork/masonry work • Type of construction whereby units are laid together to form a structure
• Masonry Construction =
Masonry units
+
Mortar
Masonry units : Bricks, Blocks @ Stones (Made from a variety of non-organic material) MASONRY UNIT
Block
Brick
Stone
Mixs
MASONRY STRUCTURE
DESIRABLE CHARACTERISTICS • Strength • Durability • Resistance to water, noise and fire • Aesthetic • Other special requirements e.g. blast resistance
BRICKS • Bricks are produced in many formats: solid, perforated and hollow • Typically 215 x 102 x 65 mm (length x width x height) • Made of clay, sand-cement, concrete and calcium silicate Types of bricks (shape)
Types of Clay Bricks
Three types of clay bricks: 1) Common – general use; not design to provide good finish or high strength; usually plastered, nonload bearing 2) Facing – for attractive appearance; no cracks; may or may not be load bearing; durable 3) Engineering – good strength and durability; high density; well fired (load bearing walls, retaining walls, sewers, embankments etc.)
Common Brick
Facing Brick
ENGINEERING BRICK
CLAY BRICKS Clay bricks continue to be the most important building units Raw materials are clay or shale Efficient material to use in terms of their energy consumption Strong and durable
Clay for Brick-making A variety clay composition and minerology deposited at different geological period; from soft sticky mud to shale Hence bricks are differ in their properties- colour, texture, strength, density and durability Only 30-40% of brick making clay are clay minerals Clay minerals-size less than 2 microns; the amount and particle size present in the clay affect the cohesiveness, forming characteristics, drying and firing properties of the clay Too much clay can result in high drying shrinkage; adding sand can reduce drying shrinkage Clays are hydrated aluminosilicates (predominance is silica and alumina); the main minerals are: kaolinite, Illite, montmorillonite
Other mineral present in clays are: potash (K2O), Lime (CaO), Soda (Na2O), Magnesium (MgO)
and iron (FeO, Fe2O3) Chemical analysis may be undertaken, together with minerological examination can assist in identifying the presence of chemicals and clay minerals in the raw materials
Manufacturing of clay bricks
Stiff mud process
Manufacturing Clay Bricks Clay Preparation Objectives: 1) improve homogeneity and plasticity of clay 2) control of physical and chemical properties such as shrinkage, colour and vitrification temperature 3) well prepared clay eliminate problems during the production process thereby reduces the rejection rates Process: 1) Digging, crushing, sieving, grinding, proportioning, mixing, tempering 2) Add chemicals for special purpose; eg. barium carbonate react with soluble salts producing insoluble product (expensive) MOULDING Process of giving shape to the bricks A variety of shaping methods that depends on the moisture content and consistency of the clay Semi Dry Process Moisture content @ 10% Granular consistency, pressed in 4 stages After pressing be textured or sand faced Can be fired without going through drying stage Smooth finish Stiff Plastic Process Moisture content @15% Extruded and then compacted into a mould under high pressure Many engineering bricks are made this way; clay containing large quantity of iron oxide help the fusion during firing Smooth finish
Wire Cut Process Moisture content @ 20% Extruding a column of clay through a die and cut by tensioned wire Extrusion to a size which allow dry and firing shrinkage Perforated bricks are made this way, the perforation being formed during extrusion Soft Mud Process Moisture content @ 30% Soft clay from shallow deposit Rolled in sand or sawdust and pressed manually into a mould DRYING OF BRICKS Green bricks contain a considerable amount of moisture depending on the shaping process The moisture content has to be further reduced before firing can be carried out Objectives: 1) Enable brick to be stacked higher in the kiln 2) Avoid too much shrinkage happening in the kiln which might cause the stack to become unstable 3) Enable firing temperature to be increased more rapidly Important for green bricks with high moisture content Temperature being increased while humidity progressively decreased Low rate of drying to avoid stresses that cause cracking and distortion Dried until approximately at critical moisture content (leather-hard) Sufficiently rigid and strong for handling and stacking Chamber or tunnel dryers takes 1 or 2 days, natural drying takes 6 weeks FIRING OF BRICKS Changes their physical structure and give them good mechanical properties and resistance to water Sintering of clay increases the strength and decreases the soluble salt without loss of shape Silica and alumina do not melt, they are fused together with metallic oxides THREE stages of firing: 1) 100 °C – water evaporation 2) 400 ºC – burning of carbonaceous matter 3) 900 – 1200 °C – sintering of clay Clay composition and chemical changes during firing influence the final colour of bricks Fe2 oxidation produce red colour bricks Large amount of lime produce yellowish-brown colour bricks Properties of clay bricks Physical properties • Colour • Texture • Size • Density
Engineering properties • Compressive strength • Water Absorption • Initial rate of suction • Efflorescence and soluble salt content
Colour and texture • Variety of colours : red, yellow, brown etc • Depending on mineral content and firing temperature • Variety of textures : smooth, rough, bark face etc.
Density • Varies from 1300 – 2200 kg/m3 • Important for thermal and acoustic property of wall: – Heavier wall better sound and thermal insulation – Solid units have higher thermal conductivity Size
Dimensional tolerance (MS 76/BS 3921): • Sizes of bricks must not be outside the ranges shown in Table 1 • Must not exceed the coordinating size • Test method – overall measurement of 24 bricks Coordinating size (mm)
Work size (mm)
225 112.5 75
215 102.5 65
Overall measurement of 24 bricks Maximum (mm)
Minimum (mm)
5235 2505 1605
5085 2415 1515
Table 1: Limits of sizes (MS/BS) Test Methods for Dimension
•
Dimensional deviations : Overall measurements of 24 bricks
Compressive strength • Most important mechanical properties • Measure of quality • Use for classifying bricks • Varies in accordance to materials and manufacturing methods • Available in strengths of 5 – 100 N/mm2 Test Methods for Bricks Compressive strength • Select 10 bricks from a stack • Bricks are immersed in water for 24 hours before testing • Faces are capped between 3 mm ply sheets or packed before testing to reduce the effects of roughness, lack of plane and platen effects • Bricks loaded normal to its bed face. Tested until failure. Compressive strength is calculated as the average of 10 bricks as below:
Compressive strength =
maximum load -------------------- (N/mm²) bed face area
Compressive Machine (Tonipact) Water Absorption • Water absorption is the quantity of water that could be absorbed by the unit • Indicate porosity • Varies widely, clay units from 4.5 to 21%, calcium silicate units from 7 to 21% and concrete units from 7 to 10% • Clay bricks which absorb between 4.5 and 7.0% of their weight can be used as damp-proof course material • Highly absorptive clay bricks remove water from mortar preventing complete hydration of cement • Relation of water absorption to flexural strength of masonry • Two types of tests: 1) 24 hours cold immersion test (Partially saturated condition) 2) 5 hr. boiling test (Fully saturated condition
24 hours cold immersion test (ASTM C67) Select 5 bricks from a stack Dry bricks in the oven @110ºC for not less than 24 hrs Cool the specimen and weigh each brick (Wd) Immerse the dry bricks in clean water at 15 to 30ºC for 24 hours Remove the bricks and weigh each brick (Ws) Calculate the absorption of each brick as follows: Ws - Wd Wd
Absorption % = 100
Report the average absorption for the 10 bricks
5 hours Boiling Test • Select 10 bricks. • Heat at 110 C for not less than 48 hours – dry bricks. • When cool, weigh the bricks and record the dry mass (wd) • Then boil for 5 hours and then allow to cool naturally in the water a minimum of 16 hours and a maximum of 19 hours. • Weigh each brick and record the wet mass (ws) • Water absorption A %= 100 Ws - Wd
Wd
Classification of clay bricks according to compressive strengths and absorption (BS) Designations
Average compressive strength not less than 2
(N/mm )
Average absorption not greater than (% by weight)
Engineering A
70
4.5
Engineering B
50
7.0
Damp-proof course 1
5
4.5
Damp-proof course 2
5
7.0
Others
5
No limits
Characteristic flexural strengths and levels of water absorption (BS 5628 Pt. 1, 1985) 2
Mortar designation
Characteristic flexural strength, f N/mm kx
Plane of failure parallel to bed joints
Plane of failure perpendicular to bed joints
(i)
(ii) and (iii)
(iv)
(i)
(ii) and (iii)
(iv)
Clay bricks having a water absorption less than 7%
0.7
0.5
0.40
2.0
1.5
1.2
Between 7 % and 12 %
0.5
0.4
0.35
1.5
1.1
1.0
Over 12 %
0.4
0.3
0.25
1.1
0.9
0.8
Initial rate of suction (IRS) • The rate at which bricks absorb water from mortar during laying • Measured in kg/m2/min. For clay bricks generally range from 0.25 – 2.05 kg/min/m2 Low values < 0.25 kg/min/m2 - High values > 1.5 kg/min/m2
• • •
Necessary for bond between bricks and mortar Water tightness Critical for highly stressed masonry structures
IRS Process • Select 10 bricks • Dry bricks in the oven • When cool, weigh the bricks and record the dry mass (m1). • Then immerse the dry brick in water for 1 min. Depth of immersion is 3± 1mm • After 1 min remove the wet bricks and weigh (m2) • Calculate initial rate of suction using formula below:
IRS (kg/m²/min) = 1000(m2-m1) A A is the area of the immersed face of the brick in mm² Efflorescence and Soluble Salt Content • Efflorescence is the white deposits (salts) on brick surfaces • Salts from bricks, ground and environment • Usually occurs on new brickwork
• •
Affect appearance but often harmless Bricks exceeding the “heavy”category should be rejected
Spalling effects of bricks
Source of water
Levels of efflorescence (MS/BS) Nil
No perceptible deposit of salt
Slight
Up to 10% of the area of the face covered with a deposit of salt, but unaccompanied by powdering or flaking of the surface
Moderate
More than 10% but not more than 50% of the area of the face covered with a deposit of salts but unaccompanied by powdering or flaking of the surface
Heavy
More than 50% of the area of the face covered with a deposit of salts and/or powdering or flaking of the surface
Applications
Calcium Silicate Bricks (sand-lime) • Consists of 90-95% sand (majority passing 1.15 mm sieve) • lime (aggregate lime ratio by weight of 10 – 20 :1) • water
Manufacturing
Properties of Calcium Silicate Bricks • Size • Colour • Water absorption
• •
Strength Shrinkage
Size and Colour • Size – similar to clay bricks • Colour – Calcium silicate and are usually light grey and other paler shades
Paving Units
Water Absorption • Varies between 6 to 16 % • Absorption is less relevance for calcium silicate and concrete units Strength • Compressive strength is the criteria • Typically strength varies from 14 – 27.5 N/mm2
Compressive Strengths Classes and Requirements of Calcium Silicate (BS187) Designations
Class
Mean compressive strength of 10 2
bricks not less than (N/mm ) Load-bearing brick or facing brick
7 6 5 4 3
48.5 41.5 34.5 27.5 20.5
Facing brick or common brick
2
14.0
CONCRETE BRICK AND BLOCK
Blocks • Three main types of blocks:
Shrinkage not greater than (%) 0.040
Concrete Bricks and Blocks • Bricks are units with size not exceeding 337.5mm in length, 225mm in width and 112.5mm in height • Bigger than this are called blocks • Lengths : 400 – 600 mm • Heights : 150 – 300 mm • Thickness : 60 – 250 mm • Consists of aggregates, cement and water • May contain additives such as air entraining agents, pozzolanic material, colouring pigments
Standard blocks
Screening blocks
Manufacturing of Concrete Blocks
Manufacturing
Handling of aggregates in a plant
Block machine in operation
Properties of Concrete Blocks (BS 6073) Face size (440 215 mm)
Type Thickness (mm)
Minimum average compressive 2
strengths of unit (N/mm ) Solid
75 100
Solid or cellular or hollow
140 150 190 200 215
Glass Blocks
Stone
Most common • Limestone • Granite • Marble • Slate
7.0 – 21.0
Applications
Marble quarry
MORTAR FOR BRICKWORK MASONRY MORTAR
MORTAR
A mixture of materials for jointing masonry units Made up of sand, a binder such as cement or lime, and water The thickness of mortar in brickwork is normally 10 mm thick and should not exceed 15 mm because of high shrinkage
FUNCTION OF MORTAR Joint the units together Seals any gaps to resist wind and rain penetration Take up the tolerances between building units, fill up the holes between the units REQUIREMENTS Should be able to support the weight of the brick Should not segregate, easy to spread and align the units Adhere to the vertical face of the units Should impart sufficient strength to the whole unit Should permit movement (unless this is negligible or joints are provided). When movement occurs, it should take place in the form of micro cracks within the mortar rather cracking of the bricks or blocks “mortar must not be stronger than the units it is bonding” Should be durable, resisting the penetration of water through the units Should contribute to the aesthetic appearance of the wall SAND FOR MORTAR Well graded – even distribution of particle sizes from fine to coarse. In well graded sand the void is one-third of the total volume Sand containing silt and clay should not be used which can lead to unacceptable shrinkage movement Sand lack in finer particles causes poor water retention resulting in a harsh unmanageable mortar BINDER MATERIALS Hydraulic lime From limestone contaminated with clay which gave the resulting hydraulic properties Relatively weak and slow setting Only suitable for thick wall and low stress Lime-sand mortars are obsolete ORDINARY PORTLAND CEMENT Principal binding ingredients in modern binders Cement and sand (1:3) by volume produces high strength, good durability, density and hardness For most application such properties are not required. Can be replaced with pozzolanic materials MASONRY CEMENT Premixed binder, 75% OPC, 25% inert fine mineral filler and powdered air entraining admixture On no account should masonry cement be used in place of OPC in making up the other type of mortar SULPHATE RESISTING CEMENT Sulphate Resisting Portland Cement may be used in place of OPC to combat sulphate attack where prolong wet condition are likely The soluble sulphates are either from the ground or in clay bricks The proportion of the mortar constituents are not altered
Table 15 BS 5628:Part3 Cement: Lime: sand
Masonry cement:sand
Cement:Sand with Superpl.
Increasing
Increasing
1:0 to ¼:3
-
-
Strength and
Ability to
1:1/2:4 to 4.5
1:2.5 to3.5
1:3 to 4
Improving
accommodate
1:1:5 to 6
1:4 to 5
1:5 to 6
durability
movements
1:2:8 to 9
1:5.5 to 6.5
1:7 to 8
(arrow upward)
(arrow downward)
1:3:10 to 12
1:6.5 to 7
1:8
NON-HYDRAULIC LIME Insufficient setting and hardening strength to make them as a total binder Added as a binder constituent to produce cement: lime: sand mortar Lime has good water retentive properties which give good workability characteristics and promote bonding of the Portland cement Have better resistance to rain penetration AIR-ENTRAINERS As an alternative to lime as a binder supplement, the reduced volume can be made with minute bubbles by adding air-entraining agent In powder/liquid form but must be intended for mortar Air entrainment must not exceed 12% of the volume because it reduces the bond strength At 15% or above the bonding performance is seriously impart Induces good plasticity/workability characteristics Linear Thermal Movement of Masonry unit and Mortar Coeff. Of Linear Thermal
Moisture movement and Thermal properties of Common Building Materials Material
Reversible moisture movement
Irreversible moisture movement
Coeff. Of Thermal
+- 0.5-2.5
_
4 - 70
-
_
10 - 18
Concrete
+-0.02-0.10
-(0.03-0.08)
7 - 14
Dense concrete agg. products
+-0.02-0.04
-(0.02-0.06)
6 – 12
Lightweight agg. conc.
+-0.02-0.06
-(0.02-0.06)
8 - 12
Aerated (autoclave) products
+-0.02-0.03
-(0.05-0.06)
8
Calcium silicate brick
+-0.01-0.05
-(0.01-0.04)
8 - 14
+-0.02
+(0.02-0.07)
5-8
-6
Material
Expansion (x 10 /K) Timber Fired-clay masonry units
Concrete masonry units
4-8
7 - 14
Calcium silicate masonry units
11 - 15
Mortars
11 - 13
Steel
Clay brick
-6/
Exp. (x10 K)
