Manufacture

Dense concrete blocks, which may be hollow, cellular or solid in form are manufactured from natural dense aggregates including crushed granite, limestone and gravel. Medium and lightweight concrete blocks are manufactured incorporating a wide range of aggregates including expanded clay, expanded blast furnace slag, sintered ash and pumice. Concrete is cast into moulds, vibrated and cured. Most aerated (aircrete or autoclaved aerated concrete) blocks are formed by the addition of aluminium powder to a fine mix of sand, lime, fly ash (pulverised-fuel ash) and Portland cement. The hydrogen gas generated by

Table 2.1 A range of standard work sizes for concrete blocks

Length (mm)

Height (mm)

Coursing blocks

215

40

215

65

215

70

215

100

Wall blocks

440

140

440

215

440

430

540

440

610

140

610

215

610

270

620

215

620

300

620

430

Floor blocks

440

215

440

350

540

440

610

350

620

215

620

540

Foundation blocks

440

140

440

215

620

140

620

215

Only a selection of thicknesses are produced by most manufacturers within the range 50 to 350 mm.

Generally available thicknesses are: 70, 75, 100, 1 1 5, 125, 130, 140, 1 50, 1 75, 190, 200, 21 5, 250, 255, 265, 275, 280 and 300 mm.

the dissolution of the metal powder produces a non-interconnecting cellular structure. The process is accelerated by pressure steam curing in an autoclave (Fig. 2.4). For some products, additional insulation is afforded by the filling of voids in the cellular blocks or by bonding on a layer of extruded polystyrene, polyurethane or foil-faced phenolic foam (Fig. 2.1). Standard blocks, typically natural grey or buff in colour, are usually shrink-wrapped for delivery. Different grades of blocks are usually identified by scratch marks or colour codes.

Fig. 2.3 Thin-joint masonry using large format blocks. Photograph reproduced from GBG 58 by permission of BRE and courtesy of Aircrete Products Association

Table 2.2 Limit of tolerances on block sizes

Tolerance category

Table 2.2 Limit of tolerances on block sizes

Length (mm)

+ 3

+1 +1

-5

-3 -3

Width (mm)

+ 3

+1 +1

-5

-3 -3

Height (mm)

+ 3

+2 +1.5

-5

-2 -1.5

Table 2.3

Limit of tolerances on

autoclaved aerated concrete

block sizes

Standard joints

Thin layer mortar joints

TLMA TLMB

Length (mm)

-5 to +3

±3 ±3

Width (mm)

-5 to +3

±2 ±1

Height (mm)

±3

±2 ±2

Fig. 2.4 Manufacture of aerated blocks
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