BLOCKS AND BLOCKWORK - Elsevier.com · 2013. 12. 20. · BLOCKS AND BLOCKWORK 41 Table 2.4 Typical relationship between density and thermal conductivity for concrete blocks Nominaldensity(kg/m3)

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ing a wide choice of load-bearing capacity and levelof insulation. Manufacturers work size dimensions

BLOCKS AND

IntroductionThe variety of commercially available concrete blocksis extensive, from dense through to lightweight, offer-ing a range of load-bearing strength, sound andthermal insulation properties. Where visual blockworkis required, either internally or externally, fairfacedblocks offer a selection of textures and colours ata different visual scale compared to that associatedwith traditional brickwork. Externally, visual concrete

blockwork weathers well, provided adequate attentionis given to the quality of the material and rainwaterrun-off detailing. Blockwork has considerable eco-nomic advantages over brickwork in respect of speedof construction, particularly as the lightweight blockscan be lifted in one hand.

Whilst clay blocks are used extensively for masonryconstruction on the continent of Europe, untilrecently there had been little demand from thebuilding industry within the UK. However, bothfired and unfired-clay blocks are now commer-cially available within the UK. Gypsum blocks maybe used for internal non-load-bearing partitionsand the internal insulation of walls. Inverted rein-forced concrete T-beams with concrete or clay blockinfill is a standard form of domestic-scale floorconstruction.

Concrete paving blocks, which offer opportunitiesfor creative hard landscaping with their diversity ofform and colour, are widely used for town pedestrianprecincts and individual house driveways. Concreteinterlocking blocks with planting are used to createenvironmental walls.

LOCKWORK

Concrete blocksTYPES AND SIZES

Concrete blocks are defined as solid, cellular or hollow,as illustrated in Fig. 2.1.

Concrete blocks are manufactured to various workface dimensions in an extensive range of widths, offer-

should be indicated as length, width and height, inthat order, to BS EN 771-3: 2003 and BS 6073-2: 2008.However, the National Annex NA (informative) to BSEN 771-3: 2003 and the British Standard particularlynote that previous standard UK practice was to specifyblocks by length, height and thickness.

The standard work face size, which co-ordinatesto three courses of metric brickwork allowing for10 mm mortar joints, is 440 × 215 mm (Fig. 2.2), butthe other sizes in Table 2.1 are marketed for aes-thetic and constructional reasons. For example, narrowbands of a different colour may be used as visualfeatures within fairfaced blockwork, and foundationwall blocks are normally laid flat. The use of thin-joint masonry offers speedier construction, especiallywhen using large format blocks (Fig. 2.3), whichare approximately equivalent in size to two standardunits. However, blocks heavier than 20 kg should notbe lifted by a single person as this potentially canlead to injury. Within the 20 kg limit are 100 mmwide aircrete blocks with face dimensions 610 ×375 mm for speedy construction using the thin-jointsystem.

3 8 M A T E R I A L S F O R A R C H I T E C T S A N D B U I L D E R S

Solid

Composite - bondedComposite - insulation filled

Cellular

Fig. 2.1 Types of concrete blocks

The European Standard (BS EN 771-3: 2003)describes a wide range of aggregate concrete masonryunits incorporating either dense or lightweight aggre-gates. Under the European Standard, the minimum

Fig. 2.2 Co-ordinating sizes for blockwork

Sound absorbing - insulation filled insulation

Hollow

description for concrete blocks includes the Euro-pean Standard number and date (e.g. BS EN 771-3:

2003), the type of unit (e.g. common or facing), worksize dimensions and tolerance category, configuration(e.g. solid or with voids) and compressive strength.Also, depending on the particular end use, additionaldescription may be required. This may, as appropri-ate, include surface finish, net and gross dry density,co-ordinating size, thermal properties and moisturemovement. Tolerance limits for regular-shaped blocksare defined at four levels in Table 2.2. Compressivestrengths of concrete masonry units are classified asCategory I or Category II. Category I units have atighter control with only a 5% risk of the units notachieving the declared compressive strength.

The European Standard (BS EN 771-4: 2003)gives the specification for autoclaved aerated con-crete (AAC) masonry units. The maximum size ofunits within the standard is 1500 mm length × 600 mmwidth × 1000 mm height. The tolerance limits on thedimensions are defined in Table 2.3, and are dependenton whether the units are to be erected with standard orthin-layer mortar joints. The standard manufacturer’sdescription for AAC masonry units must include theEuropean Standard number and date (e.g. BS EN771-4: 2003), dimensions and tolerances, compressivestrength (Category I or Category II, as for concrete

B L O C K S A N D B L O C K W O R K 3 9

Table 2.1 Typical work sizes and strengths for concrete blocks to BS6073: 2008

Length(mm)

Width(mm)

Height(mm)

Aggregate concrete blocksCoursing blocks

190 90 65190 90 90215 100 65290 90 90440 90 65440 100 65440 90 140440 100 140

Standard blocks390 90 190390 100 190390 140 190390 190 190440 75 215440 90 215440 100 215440 140 215440 190 215

440 215 215

Aircrete concrete blocksCoursing blocks

215 90–150 65215 90–150 70

Standard blocks440 50–350 215610 50–350 215620 50–350 215

Notes:Not all sizes are produced by all manufacturers but other sizes may beavailable.Widths quoted by certain manufacturers include: 50, 70, 75, 100,115, 125, 130, 140, 150, 190, 200, 215, 255, 265, 275, 300 and355 mm.Foundation blocks with face sizes of typically 255 × 290, 255 × 300,310 × 350, 400 × 215, 440 × 140 or 440 × 215 mm are laidflat.Beam and block floor rectangular units are usually 100 mm thick, withface dimensions of 440 × 215, 440 × 350, 440 × 540, 610 × 350 or620 × 215 mm.Common crushing strengths to BS 6073-2: 2008 are 2.9, 3.6, 7.3, 8.7,10.4, 17.5, 22.5, 30.0 and 40.0 MPa, but some manufacturers supplyadditional intermediate strengths (e.g. 4.2 MPa).

Fig. 2.3 Thin-joint masonry using large format blocks. Photographreproduced from GBG 58 by permission of BRE and courtesy of AircreteProducts Association

units) and dry density. Further description for specificpurposes may include durability, configuration (e.g.perforations or tongued and grooved jointing system)and intended use.

Table 2.2 Limit of tolerances on aggregate concrete block sizes

Tolerance category D1 D2 D3 D4

Length (mm) +3 +1 +1 +1−5 −3 −3 −3

Width (mm) +3 +1 +1 +1−5 −3 −3 −3

Height (mm) +3 ±2 ±1.5 ±1.0−5

Notes:BS 6073: 2008 states that tolerance categories D3 and D4 are intended foruse with thin-layer mortar joint systems. Therefore, most units used withinthe UK conform to tolerance categories D1 and D2.Closer tolerances may be declared by the manufacturer.

H I T
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Table 2.3 Limit of tolerances on autoclaved aerated concreteblock sizes

Standard joints of generalpurpose and lightweight mortar

Thin-layer mortar joints

GPLM TLMA TLMB

Length (mm) −5 to +3 ±3 ±1.5Width (mm) ±3 ±2 ±1.5Height (mm) −5 to +3 ±2 ±1.0

Notes:For autoclaved aerated concrete units of category TLMB, the maximumdeviation from flatness of bed faces and plane parallelism of bed faces is≤1.0 mm in each case.Closer tolerances may be declared by the manufacturer.

MANUFACTURE

Dense concrete blocks, which may be hollow, cellularor solid in form, are manufactured from natural denseaggregates including crushed granite, limestone andgravel. Medium and lightweight concrete blocks aremanufactured incorporating a wide range of aggre-gates including expanded clay, expanded blastfurnaceslag, sintered ash and pumice. Concrete is cast intomoulds, vibrated and cured. Most aerated (aircrete orautoclaved aerated concrete) blocks are formed by theaddition of aluminium powder to a fine mix of sand,lime, fly ash (pulverised fuel ash) and Portland cement.The hydrogen gas generated by the dissolution of themetal powder produces a non-interconnecting cellu-lar structure. The process is accelerated by pressuresteam curing in an autoclave (Fig. 2.4). For some prod-ucts, additional insulation is afforded by the filling ofvoids in the cellular blocks or by bonding on a layer of

Fig. 2.4 Manufacture of aerated blocks

E C T S A N D B U I L D E R S

extruded polystyrene, polyurethane or foil-faced phe-nolic foam (Fig. 2.1). Standard blocks, typically naturalgrey or buff in colour, are usually shrinkwrapped fordelivery. Different grades of blocks are usually identi-fied by scratch marks or colour codes.

PROPERTIES

Density and strength

The British Standard BS 6073-2: 2008 lists common

compressive strengths of 2.9, 3.6, 7.3, 8.7, 10.4, 17.5,22.5, 30.0, and 40.0 MPa for the range of aircreteand aggregate concrete blocks. However, the major-ity of concrete blocks fall in the range from 2.8 to30 MPa, with associated densities of 420–2200 kg/m3

and thermal conductivities from 0.10 to 1.5 W/m K at3% moisture content (Table 2.4). Drying shrinkagesare typically in the range 0.03–0.05%.

Durability

Dense concrete blocks and certain aerated lightweightblocks are resistant to freeze/thaw conditions belowdamp-proof course (DPC) level. However, somelightweight concrete blocks, with less than 7 MPacrushing strength should not be used below DPC level,except for the inner skin of cavity construction.

Fixability

Aerated and lightweight concrete blocks offer a goodbackground for fixings. For light loads, nails to a depthof 50 mm are sufficient. For heavier loads, wall plugsand proprietary fixings are necessary. These fixingsshould avoid the edges of the blocks.

D B
B L O C K S A N
Table 2.4 Typical relationship between density and thermal conductivity

Nominal density (kg/m3) 2200 2000 1800 1600 1400 1Typical thermal conductivity (W/m K) 1.5 1.2 0.83 0.63 0.47 0

Notes: Blocks of differing compositions may vary significantly from these average fig

Thermal insulation

The Building Regulations Approved Document PartL (2006 Edition) requires new dwellings (Part L1A)and other new building types (Part L2A) to be com-pliant with an overall energy and carbon performance,the Target Emission Rate (TER) based on the wholebuilding (Chapter 7, page 246). Individual U-valuesfor elements are therefore not set, except for exten-sions on existing dwellings (Part L1B) and otherexisting buildings (Part L2B) where an indicative U-value of 0.30 W/m2 K is the standard for new exposedwalls. The limiting area-weighted U-value standardfor wall elements in new buildings is 0.35 W/m2 K,but to achieve the Target Emission Rate overall, mostbuildings will require wall U-values within the range0.27–0.30 W/m2 K.

The following material combinations achieve aU-value of 0.27 W/m2 K (Fig. 2.5).

Cavity wall partially filled with insulation

102.5mm fairfaced brickworkouter leaf (e.g. λ = 0.77 W/m K)

50mm clear cavity

50mm foiled-faced polyurethanefoam (λ = 0.023 W/m K)

100mm lightweightblocks (λ = 0.15 W/m K)12.5mm plasterboardon dabs (λ = 0.16 W/m K)

Solid wall

16mm ext

215mm hilightweigh

40mm pheinsulation

9.5mm pla(λ = 0.16 W

Fig. 2.5 Typical blockwork construction achieving U-values of at least 0.27

L O C K W O R K 4 1

for concrete blocks

200 1000 900 800 750 700 600 500 460 420.36 0.27 0.24 0.20 0.19 0.17 0.15 0.12 0.11 0.10

ures and manufacturers’ data should be used.

Partially filled cavity

102.5 mm fairfaced brickwork outer leaf50 mm clear cavity50 mm foil-faced polyurethane foam (�=0.023 W/m K)100 mm lightweight blocks (�= 0.15 W/m K)12.5 mm plasterboard on dabs (�= 0.16 W/m K).

Fully filled cavity

102.5 mm fairfaced brickwork outer leaf100 mm full-fill cavity of blown mineral wool(�= 0.038 W/m K)100 mm lightweight blocks (�= 0.15 W/m K)13 mm dense plaster.

Similarly, a U-value of 0.27 W/m2 K can be achievedwith 100 mm external fairfaced blockwork as analternative to fairfaced brickwork, provided that the

Cavity wall fully filled with insulation

102.5 mm fairfaced brickworkouter leaf (e.g. λ = 0.77 W/m K)100mm full-fill cavity of blownmineral wool (λ = 0.038 W/m K)100mm lightweightblocks (λ = 0.15 W/m K)

13mm dense plaster

ernal reader

gh performancet blocks (λ = 0.11 W/m K)

nolic foam(λ = 0.023 W/m K)

sterboard/m K)

W/m2 K

H I T
necessary additional thermal resistance is furnishedby slightly increased cavity insulation. The thin-jointmortar system for inner leaf blockwork gives slightlyenhanced U-values compared to the equivalent stan-dard 10 mm joint blockwork construction.

Rendered solid wall construction can also achieve aU-value of 0.27 W/m2 K (Fig. 2.5).

Solid wall

16 mm external render215 mm high-performance lightweight blocks(�= 0.11 W/m K)50 mm lining of 9.5 mm plasterboard (�=0.16 W/m K) backed with 40 mm phenolic foaminsulation (�= 0.023 W/m K).

The following material combinations achieve aU-value of 0.20 W/m2 K. These tighter specificationsare required to achieve higher ratings in respect of theCode for Sustainable Homes.

Partially filled cavity

102.5 mm fairfaced brickwork outer leaf50 mm clear cavity

75 mm foil-faced polyurethane foam (�=0.022 W/m K)100 mm lightweight blocks (�= 0.15 W/m K)12.5 mm plasterboard on dabs (�= 0.16 W/m K).

Fully filled cavity

102.5 mm fairfaced brickwork outer leaf150 mm full-fill cavity of blown mineral wool(�= 0.038 W/m K)100 mm lightweight blocks (�= 0.15 W/m K)13 mm dense plaster.

Solid wall

16 mm external render70 mm phenolic foam insulation (�= 0.023 W/m K)215 mm high-performance lightweight blocks(�= 0.11 W/m K)12.5 mm plasterboard on dabs (�= 0.16 W/m K).

For domestic construction the appropriate RobustDetails should be used to ensure compliance withthermal and sound requirements of the Building Reg-ulations.


Phase change material blocks

Phase change materials (PCMs) incorporated into aer-ated concrete blocks offer some additional thermalstability to the internal environment by absorbingexcessive summer heat, which is then released duringthe cooler periods. This phase change at 26◦C effec-tively increases the thermal capacity of the lightweightblocks. One manufacturer colour codes the phasechange material blocks green for easy identification.The phase change material is described in Chapter 12(page 337).

Fire resistance

Concrete block construction offers good fire resistance.Solid unplastered 90 mm blocks can give up to 60 min-utes’ fire protection when used as load-bearing walls;certain 150 mm and most 215 mm solid blocks canachieve 360 minutes’ protection. Dense, lightweightand autoclaved aerated concrete blocks with less than1% organic material are automatically categorised asEuroclass A1 with respect to reaction to fire.

Sound insulation

The Building Regulations 2000 Approved Document

E (2003) recognises the need to provide adequatesound insulation both between and within dwellingsalso between rooms in hostels, hotels and residentialaccommodation. The regulations require minimumairborne sound insulation of 45Rw dB for separatingwalls and 40Rw dB for internal bedroom or WC walls.The passage of airborne sound depends on the densityand porosity of the material. The use of Robust Detailsor Pre-Completion Testing is required to demonstratecompliance. The following alternative systems shouldperform to the required airborne insulation standardfor separating walls of new build dwellings.

12.5 mm plasterboard on dabs8 mm render100 mm dense (1600–2200 kg/m3) or lightweight(1350–1600 kg/m3) blockwork75 mm clear cavity only linked by appropriate wallties100 mm dense (1600–2200 kg/m3) or lightweight(1350–1600 kg/m3) blockwork8 mm render12.5 mm plasterboard on dabs.

These alternatives perform to the required standardonly if there are no air leaks within the construction,

D B L O C K W O R K 4 3
B L O C K S A N
all joints are filled, the cavities are kept clear except forthe approved wall ties and any chasing out on oppositesides of the construction is staggered. Vertical chasesshould, in any case, not be deeper than one third of theblock thickness. Horizontal chases should be restrictedto not more than one sixth of the block thickness, dueto the potential loss of structural strength.

Sound absorption

The majority of standard concrete blocks with hardsurfaces are highly reflective to sound, thus creatinglong reverberation times within building enclosures.Acoustic absorbing concrete blocks are manufacturedwith a slot on the exposed face which admits soundinto the central cavity (Fig. 2.1). Since the void spaceis lined with sound-absorbing fibrous filler, incidentsound is dissipated rather than reflected, significantlyreducing reverberation effects. Acoustic control blocksin fairfaced concrete are suitable for use in swimmingpools, sports halls, industrial buildings and auditoria.

SPECIALS

Most manufacturers of blocks produce a range of spe-cials to match their standard ranges. Quoins, cavity

closers, splayed cills, flush or projecting copings, lin-tel units, bullnose ends and radius blocks are generallyavailable, and other specials can be made to order (Fig.2.6). The use of specials in fairfaced blockwork cangreatly enhance visual qualities. Matching full-lengthlintels may incorporate dummy joints and should bearon to full, not cut, blocks.

FAIRFACED BLOCKS

Fairfaced concrete blocks are available in a wide rangeof colours from white, through buff, sandstone, yellow,to pink, blue, green and black. Frequently the colour isall through, although some blocks have an applied sur-face colour. Most blocks are uniform in colour, butthere is some variability with, for example, fleckedfinishes. Textures range from polished, smooth andweathered (sand- or shot-blasted) to striated and splitface (Fig. 2.7), the latter intended to give a randomvariability associated more with natural stone.

Glazed masonry units are manufactured by theapplication of a thermosetting material to one ormore faces of lightweight concrete blocks, which arethen heat-treated to cure the finish. The glazed blocksare available in an extensive range of durable brightcolours and are suitable for interior or exterior use.

Fig. 2.6 Block specials

Where required, profiled blocks to individual designscan be glazed by this system. Most manufacturers pro-duce a range of specials to co-ordinate with theirstandard fairfaced blocks, although, as with specialbricks, they may be manufactured from a differentbatch of mix, and this may give rise to slight varia-tions. In specific cases, such as individual lintel blocks,specials are made by cutting standard blocks to ensureexact colour matching.

Clay blocksFIRED-CLAY BLOCKS

Masonry clay honeycomb-insulating blocks can beused as a single skin for external load-bearingconstruction as an alternative to standard cavity con-struction. These fired-clay honeycomb blocks combinestructural strength, insulation and, when externallyrendered, moisture protection. The internal surface

H I T

hs: Co


Fig. 2.7 Split and polished architectural masonry finishes. Photograp

is normally finished directly with gypsum plas-ter. Blocks for monolithic construction are 260 mmlong × 240 mm high and either 300 or 365 mm widegiving wall U-values of 0.36 and 0.30 W/m2 K, respec-

tively, when rendered and plastered. For internal walls,blocks are 400 mm long and range in widths from 100to 125 and 150 mm. Horizontal joints require 10 mmof a lightweight mortar, but the vertical joint edges, iftongued and grooved, remain dry. The British Stan-dard (BS EN 771-1: 2003) illustrates a selection ofhigh density (HD) vertically perforated units and arange of low density (LD) fired-clay masonry units.The LD units may be vertically or horizontally perfo-rated, with butt jointing, mortar pockets or a tongueand groove system (Fig. 2.8). Special blocks are avail-able for corners, lintels, door and window openings,but individual blocks can also be cut.

Fairfaced fired-clay blocks, as illustrated in Fig. 2.9,offer an alternative to traditional brickwork. Theyare manufactured to natural, riven or textured fin-ish in a range of colours including terracotta red,ochre, buff and blue, and also to high gloss or satinfinish in strong or pastel shades. Where used asinfill, rather than load-bearing, alternative bondingis possible including stack bond. Typical work sizes,depending on the manufacturer, are 215 × 215 mm,327 × 215 mm, 327 × 140 mm, 440 × 215 mm, 390 ×240 mm, 390 × 190 mm and 490 × 190 mm withwidths of 90 and 102 mm. A standard 10 mm mor-


urtesy of Lignacite Ltd.

tar joint is appropriate, which may match or contrastwith the block colour.

UNFIRED-CLAY BLOCKS

Unfired blocks manufactured from clay and sometimesincorporating straw may be used for non-load-bearingpartition walls. Blocks (typically 500 × 250 mm and450 × 225 mm × 100 mm wide) may be tongued andgrooved or square edged, but only the horizontal jointsrequire fixing with a thin layer of cellulose-based adhe-sive or clay mortar. Blocks are easily cut to createarchitectural features, and are usually finished with askim coat of clay plaster, although they may be painteddirectly. Internal walls are sufficiently strong to sup-port shelving and other fixtures. Unfired-clay blockwalls are recyclable or biodegradable and have theadvantage of absorbing odours and stabilising internalhumidity and temperature by their natural absorp-tion and release of moisture and heat. A 100 mm thickwall gives a 45 dB sound reduction and 90 minutes’fire resistance. (The thermal conductivity of perforatedunfired-clay blocks is typically 0.24 W/m K.)

Gypsum blocksGypsum blocks are available with densities rangingfrom 600 to 1500 kg/m3 and thicknesses from 50 to


Low Density Units

High Density Units

Vertically perforatedunit

Vertically perforatedunit with mortar

pocket

Vertically perforatedunit with grip holes

Vertically perforatedunit with tongue and

groove system

Horizontally perforatedunit (for partition walls)

Horizontally perforatedunit with rendering

keyways

Horizontally perforatedunit with mortar pocket

Unit for concrete ormortar infill

Unit for masonrypanels

Solid unit Frogged unit Vertically perforated unit

Vertically perforated unit Vertically perforated unit(a)

Fig. 2.8 (a) Low-density and high-density units. Permission to reproduce extracts from BS EN 771-1: 2003 is granted by the British StandardsInstitute. (b) Hollow clay blocks in Greece. Photograph: Arthur Lyons

4 6 M A T E R I A L S F O R A R C H I T E C T S A N D B U I L D E R S

Fig. 2.8 (continued)

100 mm. The maximum thickness to BS EN 12859:2008 is 150 mm. The preferred face dimensions are666 mm in length and 500 mm in height, with a maxi-mum length of 1000 mm. Gypsum blocks are classifiedby density and water absorption.

Gypsum blocks - density class:

Low density (L) 600–800 kg/m3

Medium density (M) 800–1100 kg/m3

High density (H) 1100–1500 kg/m3

Gypsum blocks - water absorption class:

H3 >5%H2 ≤5%H1 ≤2.5%

The standard BS EN 15318: 2007 details the soundinsulation properties of gypsum block partitions inrelation to wall thickness and block density. Gypsumblocks may be used as non-load-bearing partitions andinternal insulation of walls. They are assembled with

gypsum-based adhesives as specified in BS EN 12860:2001.

BlockworkFAIRFACED CONCRETE BLOCKWORK

Within fairfaced blockwork, an appropriate choice ofsize is important to both co-ordination and visualscale. Whilst blocks can be cut with a masonry cutter,the addition of small pieces of block, or the wideningof perpends over the 10 mm standard, is unaccept-able. The insertion of a thin jumper course at flooror lintel height may be a useful feature in adjustingthe coursing. Curved blockwork may be constructedfrom standard blocks, the permissible curvature beingdependent on the block size. The oversail betweenalternate courses should not normally exceed 4 mmin fairfaced work. If the internal radius is exposed,then the perpends can be maintained at 10 mm withuncut blocks, but if the external radius is exposed, theblocks will require cutting on a splay. For tighter curvesspecials will be required.

B L O C K S A N D B

Fig. 2.9 Fairfaced blockwork—IDP Offices, Glasgow. Architect: IDP.Photograph: Courtesy of Ibstock Brick Ltd.

THIN-JOINT MASONRY SYSTEMS

Thin-joint blockwork may be constructed with mor-tar joints of only 2–3 mm, provided that the aircrete orequivalent blocks have been manufactured to fine tol-erances and on-site workmanship is good. The specialrapid-setting mortar sets typically within 60 minutesand the full bond strength is achieved after only2 hours, allowing more courses to be laid each day.In the case of brick and block cavity construction, theinner leaf is built first, providing a weatherproof enclo-sure as quickly as possible. The outer skin of brickworkcan subsequently be built up, using wall ties fixed to theface, either screwed or hammered into the completedblockwork. Bed joints in thin-layer mortar blockworkdo not necessarily co-ordinate with those of the brick-work, so conventional cavity wall ties can only be usedif they are slope-tolerant.

Usually, inner leaf construction commences witha line of 440 × 215 mm standard height blocks, withnormal bedding mortar to compensate for varia-

L O C K W O R K 4 7

tions in the foundation level, followed by the larger440 or 620 mm × 430 mm high blocks, which shouldweigh less than 20 kg for repeated lifting by one oper-ative. Heavier blocks require mechanical lifting ortwo-person handling. Thin-joint mortars, consistingof polymer-modified 1 : 2 cement : sand mix withwater-retaining and workability admixtures, are fac-tory pre-mixed and require only the addition of water,preferably mixed in with an electrically powered plas-terer’s whisk. The mortar is applied manually with aserrated scoop of the appropriate width or through apumped system to achieve uniformity. Work shouldonly proceed at temperatures above 5◦C.

The main advantages of thin-joint systems over tra-ditional 10 mm joint blockwork are:

� increased productivity allowing storey-height innerleaves to be completed in one day;

� up to 10% improved thermal performance due toreduced thermal bridging by the mortar;

� improved airtightness of the construction;� the accuracy of the wall, which allows internal thin-

coat sprayed plaster finishes to be used;� higher quality of construction and less wastage of

mortar.

The acoustic properties of thin-joint mortar wallsdiffer slightly from those of walls constructed with10 mm mortar joints. Resistance to low-frequencynoise is slightly enhanced, whilst resistance to high-frequency sound is slightly reduced.

Completed thin-joint blockwork acts as a mono-lithic slab, which, if unrestrained, may crack at theweaker points, such as near openings. To avoid this,the block units should be laid dry to avoid shrinkageand bed joint reinforcement (1.5 mm thick GRP mesh)should be appropriately positioned. Larger structuresrequire movement joints at 6 m centres.

Certain extruded multi-perforated clay and calciumsilicate blocks are designed for use with thin mortarbed joints and dry interlocking vertical joints. Onesystem of clay blocks requires only horizontal propri-etary adhesive joints of 1 mm applied with a specialroller tool, as the units are ground to exact dimensionsafter firing. Blocks may be used for inner and/or outerleaf cavity construction or for solid walls. Whilst thisreduces the initial construction time, exposed sides ofthe units subsequently require plaster or cement renderto minimise heat loss by air leakage. Typical block sizesare 300 × 224 mm and 248 × 249 mm with widths of100, 140, 190 and 365 mm.

4 8 M A T E R I A L S F O R A R C H I T

than equivalent brickwork masonry. Therefore, thelocation and form of the movement joints requiresgreater design-detail consideration, to ensure that

Fig. 2.10 Selection of bonding patterns for visual blockwork

BOND

A running half-block bond is standard, but this may bereduced to a quarter bond for aesthetic reasons. Block-work may incorporate banding of concrete bricks, butbecause of differences in thermal and moisture move-ment, it is inadvisable to mix clay bricks with concreteblocks. Horizontal and vertical stack bonds and moresophisticated variations, such as basket-weave bond,may be used for infill panels within framed structures(Fig. 2.10). Such panels will require reinforcement


within alternate horizontal bed joints, to compensatefor the lack of normal bonding.

REINFORCEMENT

Blockwork will require bed-joint reinforcement aboveand below openings where it is inappropriate to dividethe blockwork up into panels, with movement jointsat the ends of the lintels. Bed-joint reinforcementwould be inserted into two bed joints above and belowsuch openings (Fig. 2.11). Cover to bed reinforcementshould be at least 25 mm on the external faces and13 mm on the internal faces. Combined vertical andhorizontal reinforcement may be incorporated intohollow blockwork in accordance with BS 5628-2: 2005,where demanded by the calculated stresses. Typical sit-uations would be within retaining basement walls, andlarge infill panels to a framed structure.

MOVEMENT CONTROL

Concrete blockwork is subject to greater movements

inevitable movements are directed to the required loca-tions and do not cause unsightly stepped cracking orfracture of individual blocks. Ideally, such movementjoints should be located at intersecting walls, or otherpoints of structural discontinuity, such as columns.Additionally, movement joints are required at changesin thickness, height or loading of walls, above andbelow wall openings, and adjacent to movement jointsin the adjoining structure (Fig. 2.12). External unrein-forced non-load-bearing concrete masonry walls witha length to height ratio of 3 : 1 or less must be separatedinto a series of panels with vertical movement-controljoints at approximately 9 m centres or more frequentlyfor masonry walls with a length to height ratio of morethan 3 : 1 (NA to BS EN 1996-2: 2006).

Wall ties should allow for differential movementbetween the leaves in cavity construction and should bespaced at 900 mm horizontally and 450 mm vertically,for 50–75 mm cavities.

MORTARS

The mortar must always be weaker than the blocks toallow for movement.


The usual mixes for standard 10 mm joints are byvolume:

cement/lime/sand 1 : 1 : 5 to 1 : 1 : 6cement/sand + plasticiser 1 : 5 to 1 : 6masonry cement/sand 1 : 4 to 1 : 5

Fig. 2.11 Reinforced blockwork

Fig. 2.12 Blockwork movement joints

Below DPC level a stronger mix is required andsulphate-resisting cement may be necessary dependingon soil conditions.

cement/sand 1 : 4cement/lime/sand 1 : 1.5 : 4.5

Where high-strength blockwork is required, stron-ger mortars may be necessary. Mortar joints should

H I T

most aggressive, DS5. Foundation blocks can be ofeither dense or appropriate lightweight concrete, thelatter providing enhanced floor edge insulation. Inter-locking foundation blocks, with a tongue and groovevertical joint, slot together with only bed-joint mor-tar being required. A handhold makes manipulatingthese blocks on site much easier than lifting stan-dard rectangular blocks. Thicknesses within the range255–355 mm are standard.

Beam and block flooringBeam and block flooring offers an alternative systemto traditional solid ground floors within domestic-scale construction (Fig. 2.13), and may also be usedfor upper storeys. Systems are described in BS EN15037 Part 1 : 2008 and Parts 2 and 3 : 2009. Beamsmay be inverted T or I in form, alternatively incorpo-


be slightly concave, rather than flush. Bucket handleand weathered or struck joints are suitable for externaluse, but recessed joints should only be used internally.Coloured mortars should be ready mixed or carefullygauged to prevent colour variations. Contraction jointsshould be finished with a bond breaker of polythenetape and flexible sealant. For expansion joints, a flexiblefiller is required, e.g. bitumen-impregnated fibreboardwith a polythene foam strip and flexible sealant. Whereblockwork is to be rendered, the mortar should beraked back to a depth of 10 mm for additional key.Masonry should not be built when the temperature isat or below 3◦C and falling or unless it is at least 1◦Cand rising (BS 5628-3: 2005).

FINISHES

Internal finishes

Plaster should be applied normally in two coats to13 mm. Blocks intended for plastering have a tex-tured surface to give a good key. Dry lining may befixed with battens or directly with adhesive dabs to theblockwork. Blockwork to be tiled should be first ren-dered with a cement/sand mix. Fairfaced blockworkmay be left plain or painted. Where standard blocks

are to be painted, the appropriate grade should beused.

Unfired-clay blocks should be finished with breath-able materials, such as clay or lime plaster, clay boards,limewash or highly vapour-permeable paint.

External finishes

External boarding or hanging tiles should be fixed tobattens, separated from the blockwork with a breathermembrane. For external rendering a spatterdash coatshould be applied initially on dense blockwork, fol-lowed by two coats of cement/lime/sand render. Thefirst 10 mm coat should be the stronger mix (e.g.1 : 1 : 6); the 5 mm second coat must be weaker (e.g.1 : 2 : 9). Cement/sand mixes are not recommended asthey are more susceptible to cracking and crazing thanmixes incorporating lime. The render should termi-nate at damp-proof course level with a drip or similarweathering detail.

FOUNDATIONS

Foundation blocks laid flat offer an alternative totrench fill or cavity masonry. Portland cement blocks


should not be used for foundations where sulphate-resisting cement mortar is specified, unless they areclassified as suitable for the particular sulphate condi-tions. Sulphate and other chemically adverse groundconditions are classified in the BRE Special Digest 1(2005) from DS1 (Design Sulphate Class 1) to the

rate partially exposed lattice girder reinforcement tobe covered within a concrete topping. The infill maybe standard 100 mm concrete blocks with a minimumtransverse crushing strength of 3.5 MPa. Insulationwill be required to achieve a U-value between 0.20

Fig. 2.13 Beam and block flooring


Fig. 2.14 Selection of concrete pavers and hard landscape to the Gateshea

and 0.25 W/m2 K. For first and subsequent floors,the infill can be full-depth solid or hollow concreteblocks or hollow clay blocks which may require a castin situ structural topping to comply with BuildingRegulations.

d Millennium Bridge. Photographs: Courtesy of Marshalls Plc.

The following material combination achieves aU-value of 0.20 W/m2 K:

18 mm particleboard (�= 0.13 W/m K)100 mm continuous insulation (�= 0.030 W/m K)

H I T
100 mm concrete block (�= 0.46 W/m K)dense concrete inverted T-beam at 515 mm centres(�= 1.65 W/m K)under-floor ventilated space.

Landscape blockworkBLOCK PAVING

Concrete block paving units are manufactured to awide range of designs as illustrated in Fig. 2.14. Blocksmay be of standard brick form (200 × 100 mm) tothicknesses of 60, 80 or 100 mm depending on theanticipated loading. Alternative designs include tum-bled blocks, which emulate granite setts, and variousinterlocking forms giving designs based on polygo-nal and curvilinear forms. Colours range from red,brindle, buff, brown, charcoal and grey through tosilver and white, with smooth, textured or simulatedstone finishes. For most designs, a range of kerbblocks, drainage channels, edging and other accessoryunits are available. Concrete paving blocks are usuallylaid on a compacted sub-base with 50 mm of sharpsand. Blocks are frequently nibbed to create a nar-row joint to be filled with kiln-dried sand. For the

wider joints that occur between the simulated stonesetts a coarser grit can be used to prevent loss by winderosion.

Physical properties, including water absorption,freeze/thaw resistance, abrasion resistance and toler-ances on size, are categorised in BS EN 1338: 2003.Guidance on the design and construction of pavementsfor a range of applications is given in BS 7533 Parts1–13 inclusive. The types of tactile paving surfaces –blister, rib and groove – are defined and coded in thestandard DD CEN/TS 15209: 2008.

Sustainable urban drainage systems (SUDS) aredesigned to reduce the environmental impact of imper-meable hard landscaping surfaces which create rapidrainwater run-off. With permeable surfaces, includingnibbed blocks, the rainwater permeates through thespacing and is dispersed by natural drainage into theunderlying soil, or may be collected through rainwaterharvesting systems for further use.

Where the appearance of grass is required, but withthe traffic-bearing properties of a concrete block pave-ment, a selection of porous (hollow) blocks is availablewhich can be filled with soil and seeded to give therequired effect. Different block depths and sub-basescan be specified according to the anticipated traffic


loading. Sulphate-resisting blocks are available if dic-tated by the soil conditions.

EARTH-RETAINING BLOCKWORK

A range of precast-cellular concrete-interlockingblocks is manufactured for the construction of dry-bed retaining walls. Soil is placed in the pockets ofeach successive course to allow for planting. The rear isbackfilled with granular material to allow for drainage.The size of the block determines the maximum con-struction height, but over 20 m can be achieved withvery deep units. A face angle of 15◦ to 22◦ is typical toensure stability, but other gradients are possible withthe appropriate block systems. Limited wall curvatureis possible without cutting the standard blocks. Thesystems are used both for earth retention and to formacoustic barriers.

ReferencesFURTHER READING

British Cement Association. 2005: BCA guide to mate-rials for masonry mortar. Camberley: BCA.

Concrete Block Association. 2006: Aggregate concreteblocks. Part L. Thermal insulation from April 2006.Guidance for designers and users. Leicester: CBA.Concrete Block Association. 2007: Aggregate concreteblocks. Aggregate block sustainability. Data Sheet 16.Leicester: CBA.Concrete Society. 2007: External in-situ concretepaving. Technical Report No. 66. Camberley: The Con-crete Society.Hugues, T., Greilich, K. and Peter, C. 2004: Buildingwith large clay blocks. Details, products, built examples.Basel: Birkhäuser.Robust Details. 2007: Robust details handbook. 3rd ed.Milton Keynes: Robust Details Ltd.

STANDARDS

BS 743: 1970 Materials for damp-proof courses.BS 5628 Code of practice for use of masonry:

Part 1: 2005 Structural use of unreinforcedmasonry.Part 2: 2005 Structural use of reinforced and pre-stressed masonry.Part 3: 2005 Materials and components, designand workmanship.

D B
B L O C K S A N
BS 5977 Lintels:Part 1: 1981 Method for assessment of load.

BS 6073 Precast concrete masonry units:Part 2: 2008 Guide for specifying precast concretemasonry units.

BS 6100 Glossary of building and civil engineeringterms:

Part 0: 2002 Introduction.Part 1: 2004 General terms.Part 6: 2008 Construction parts.

BS 6398: 1983 Specification for bitumen damp-proofcourses for masonry.BS 6515: 1984 Specification for polyethylene damp-proof courses for masonry.BS 7533 Pavements constructed with clay, naturalstone or concrete pavers:

Part 3: 2005 Code of practice for laying precastconcrete paving blocks and clay pavers for flexiblepavements.Part 4: 2006 Code of practice for the constructionof pavements of precast concrete flags or naturalstone slabs.Part 6: 1999 Code of practice for laying naturalstone, precast concrete and clay kerb units.

BS 8000 Workmanship on building sites:

Part 3: 2001 Code of practice for masonry.

BS 8103 Structural design of low-rise buildings:Part 2: 2005 Code of practice for masonry wallsfor housing.

BS 8215: 1991 Code of practice for design and instal-lation of damp-proof courses in masonry construc-tion.BS EN 413-1: 2004 Masonry cement. Composition,specifications and conformity criteria.BS EN 771 Specification for masonry units:

Part 1: 2003 Clay masonry units.Part 3: 2003 Aggregate concrete masonry units.Part 4: 2003 Autoclaved aerated concrete masonryunits.Part 5: 2003 Manufactured stone masonry units.

BS EN 772 Methods of test for masonry units:Part 1: 2000 Determination of compressivestrength.

BS EN 845 Specification for ancillary componentsfor masonry:

Part 1: 2003 Ties, tension straps, hangers andbrackets.Part 2: 2003 Lintels.Part 3: 2003 Bed joint reinforcement of steel mesh-work.

L O C K W O R K 5 3

BS EN 934 Admixtures for concrete, mortar andgrout:

Part 1: 2008 Common requirements.Part 2: 2001 Concrete admixtures. Definitions,requirements, conformity, marking and labelling.

BS EN 998-2: 2003 Specification for mortar formasonry. Masonry mortar.BS EN 1338: 2003 Concrete paving blocks. Require-ments and test methods.BS EN 1745: 2002 Masonry and masonry products.Methods for determining design thermal values.BS EN 1806: 2006 Chimneys. Clay/ceramic flueblocks for single wall chimneys.BS EN 1858: 2003 Chimneys. Components. Con-crete flue blocks.BS EN 1996 Eurocode 6: Design of masonry struc-tures:

Part 1.1: 2005 General rules for reinforced andunreinforced masonry.Part 1.2: 2005 Structural fire design.Part 2: 2006 Design considerations, selection ofmaterials and execution of masonry.Part 3: 2006 Simplified calculation methods forunreinforced masonry structures.

BS EN 12859: 2008 Gypsum blocks. Definitions,

requirements and test methods.BS EN 12860: 2001 Gypsum based adhesives for gyp-sum blocks. Definitions.BS EN 13139: 2002 Aggregates for mortar.BS EN ISO 14683: 2007 Thermal bridges in buildingconstruction. Linear thermal transmittance. Simpli-fied methods and default values.BS EN 14909: 2006 Flexible sheets for waterproofing.Plastic and rubber damp proof courses. Definitionsand characteristics.BS EN 15037 Precast concrete products. Beam-and-block floor systems:

Part 1: 2008 Beams.Part 2: 2009 Concrete blocks.Part 3: 2009 Clay blocks.

DD CEN/TS 15209: 2008 Tactile paving surface indi-cators produced from concrete, clay and stone.BS EN 15254 Extended application of results fromfire resistance tests. Nonloadbearing walls:

Part 2: 2009 Masonry and gypsum blocks.BS EN 15318: 2007 Design and application of gyp-sum blocks.BS EN 15435: 2008 Precast concrete products. Nor-mal weight and lightweight concrete shuttering blocks.Product properties and performance.

H I T
PD CEN/TR 15728: 2008 Design and use of in-serts for lifting and handling of precast concrete ele-ments.DD 140-2: 1987 Wall ties. Recommendations fordesign of wall ties.

BUILDING RESEARCH ESTABLISHMENTPUBLICATIONS

BRE Special digests

BRE SD1: 2005 Concrete in aggressive ground.BRE SD4: 2007 Masonry walls and beam and blockfloors. U-values and building regulations.

BRE Digests

BRE Digest 432: 1998 Aircrete: thin joint mortar sys-tem.BRE Digest 460: 2001 Bricks, blocks and masonrymade from aggregate concrete (Parts 1 and 2).BRE Digest 461: 2001 Corrosion of metal compo-nents in walls.BRE Digest 468: 2002 AAC ‘aircrete’ blocks andmasonry.BRE Digest 487: 2004 Structural fire engineeringdesign. Part 4. Materials behaviour: Masonry.

BRE Good building guides

BRE GBG 44: 2000 Insulating masonry cavity walls(Parts 1 and 2).BRE GBG 50: 2002 Insulating solid masonry walls.BRE GBG 54: 2003 Construction site communica-tion. Part 2. Masonry.BRE GBG 58: 2003 Thin layer masonry mortar.


BRE GBG 62: 2004 Retro-installation of bed jointreinforcement in masonry.BRE GBG 66: 2005 Building masonry with lime-based bedding mortars.BRE GBG 67: 2006 Achieving airtightness (Parts 1,2, and 3).BRE GBG 68: 2006 Installing thermal insulation(Parts 1 and 2).

BRE Information papers

BRE IP 14/98 Blocks with recycled aggregate. Beam-

and-block floors.BRE IP 1/99 Untied cavity party walls. Structuralperformance when using AAC blockwork.BRE IP 7/05 Aircrete tongue and grooved blockmasonry.BRE IP 1/06 Assessing the effects of thermal bridgingat junctions and around openings.BRE IP 8/08 Determining the minimal thermal resis-tance of cavity closers.

ADVISORY ORGANISATIONS

Aircrete Products Association, 4th floor, 60 CharlesStreet, Leicester LE1 1FB, UK (0116 253 6161).British Concrete Masonry Association, Grove CrescentHouse, 18 Grove Place, Bedford MK40 3JJ, UK (01234353745).Concrete Block Association, 60 Charles Street, Leices-ter LE1 1FB, UK (0116 253 6161).Concrete Society, Riverside House, 4 Meadows Busi-ness Park, Station Approach, Blackwater, Camberley,Surrey GU14 9AB, UK (01276 607140).Mortar Industry Association, Gillingham House, 38-44 Gillingham Street, London SW1V 1HU, UK (0207963 8000).

Documents

BLOCKS AND BLOCKWORK - Elsevier.com · 2013. 12. 20. · BLOCKS AND BLOCKWORK 41 Table 2.4 Typical relationship between density and thermal conductivity for concrete blocks Nominaldensity(kg/m3)