3 - Masonry materials.ppt

Masonry Materials Building Inspectors September 2024 Copyright Rod Rankine Presenter Dr. Rod GD Rankine Pr Eng.  Materials & applicable standards SANS 10400 The application of the national building regulations Part K Walling...

Masonry Materials Building Inspectors September 2024 Copyright Rod Rankine Presenter Dr. Rod GD Rankine Pr Eng.  Materials & applicable standards SANS 10400 The application of the national building regulations Part K Walling SANS 2001 CM1 Masonry walling SANS 2001 EM1 Cement plaster SANS 10249 Masonry walling Material Applicable standard Burnt clay masonry unit SANS 227 Burnt clay masonry units Concrete masonry unit SANS 1215 Concrete masonry units Cement SANS 50197- Part 1 Sand SANS 1090 Sands for plaster & mortar Brickforce SANS DPC SANS 952-1 Polymer film for damp-proofing in buildings SANS 248 Bituminous damp proof courses  Methods of manufacture of burnt clay masonry units (SANS 227) Clamp kiln (field kiln) Transverse arch kiln Tunnel kiln Show Clay Brick Association DVD on “The making of clay bricks”  Minimum strength & water absorption requirements (SANS 227) Note that SANS 227 makes no mandatory requirements regarding the maximum water absorption of burnt clay units. Concrete brick Burnt clay brick  0.46ℓ water absorbed Burnt clay brick is like a solid sponge. The pictures above show the mass of the same brick dry (LHS) and wet (RHS) after 30 minutes of soaking.  0.115ℓ of water absorbed Concrete units are not as thirsty. The photos above show the same unit before and after soaking for 30 minutes. Think of each brick soaking up or “stealing” 500mℓ of water from the mortar  A bedding mortar Burnt clay bricks should always be pre-soaked prior to laying. Even though these bricks appear dry, they are actually only surface dry. Inside they are saturated – a condition called “Saturated Surface Dry” (SSD). This garden wall fell over because the clay bricks were not pre-soaked and the mortar did not bond. The mortar was also very weak – possibly as a result of retempering.  IRREVERSABLE MOISTURE EXPANSION Kiln fresh bricks Parapet wallexpand a lot as they absorb moisture. The overall tendency is for clay bricks to expand and reinforced concrete frames to problems shrink. Moisture expansion in boundary walls. Moisture expansion in clay brick paving can cause it to lift and shear walls at their bases. Outward ratcheting of curved burnt clay infill masonry Efflorescence is caused by the migration of water through materials (from a wet surface to a dryer surface). If this water contains dissolved salts, then when it dries on the dry surface, salts are left behind. Both these bricks were left to stand in a tray containing a magnesium sulphate solution. The clay brick has suffered more severe efflorescence than the cement brick because of its permeable capillary internal structure. Crypto-efflorescence caused by a build-up of sulphate salts inside the pores and fissures of brickwork. Dissolved salts enter the pores in solution and when the water evaporates, the salts are left behind. With repeated wetting & drying cycles, the salt crystals grow and exert pressure on the brickwork causing it to rupture. Brick bonding facilitates load sharing and helps to transmit loads safely from points of application to the foundation. Unbonded Wall No load sharing Sand-cement mixes  BRICK BONDING Bricklaying Stretcher Bond Alternate layers are offset by 50%. English Bond Alternate layers are headers or stretchers. Headers are laid centered over joints between stretchers. Flemish Bond Headers and stretchers laid alternately. Headers centered over stretchers.  Size requirements for English and Flemish bonding Co lla rj oin t Just right Too short Too long To be suitable, the length of the unit must be twice the width plus the thickness of the collar joint. Cleaning mortar off clay face bricks Prevention is better than cure! Use a bucket of clean water and a stiff brush (not a wire brush) to clean off mortar BEFORE it sets. Use a dilute hydrochloric acid solution (spirits of salts) 1 part acid to 20 parts water to clean off hardened mortar. ALWAYS saturate the bricks with water first to prevent ingress of aggressive acid. Concrete masonry units (SANS 1215) Making of concrete masonry units A simple hand tamper brick mould is the cheapest and simplest way to get started in brick/block manufacturing. Quality is variable and dependent on labour. Material costs tend to be high because more cement is needed to compensate for low compaction. A sophisticated concrete brick manufacturing machine. The capital cost of these machines is high because they have the ability to exert huge compressive forces on the units together with strong vibration. Consequently, a very dry mix can be used which allows for large reductions in cement content (compared to simple hand-operated machines). Use of waste by-products from other industries, as aggregates, in the production of concrete masonry units and the associated problems that can result. Throughout the world, policy makers are putting pressure on brick manufacturers to use industrial waste products including coal power station bunker ash (top left), metallurgical slag (top right) and crushed burnt clay brick (bottom left as aggregates to make concrete bricks. Provided these materials are used responsibly, together with good quality controls and regular testing, good and competent bricks can be manufactured. However, when these controls are absent, disasters often follow. Deleterious expansion of brickwork caused by the use of metallurgical slag as aggregate from the BOF furnace at Arcelor Mittal’s Vanderbijl works. Free lime (calcium oxide) and magnesium oxide react with water (hydration) to form much more voluminous calcium hydroxide and magnesium hydroxide long after the masonry has been built. This can cause severe expansion and fragmentation of bricks. This wall was stripped of plaster and replastered in November 2007. The new plaster was reinforced with chicken mesh to combat future plaster cracking. This is what the wall looked like 4 months later. The chicken wire had ruptured – see insert. As a result of deleterious expansion, the brickwork in these gable ends now has zero tensile strength and is at risk of collapsing if there is a strong wind storm. Internally, ceramic tiles crack, rainwater enters dwellings and aggravates the problem promoting the growth of mould and destroying finishes. Long-term deleterious expansion problem is demonstrated here in this autoclave test (accelerated test). Brick fragments (from cracked walls) are coated with lime wash (insert) and put into an autoclave (pressure cooker) for about 4 hours at 120 0C. A popout caused by a metallic nodule containing iron. Unsound materials such as bits of unburnt coal, iron pyrites and metallic slag nodules can expand when they get wet. When they do so, they cause the surface to spall and some staining can result.  Let the buyer beware! Many manufacturers of concrete masonry units create the impression that they produce bricks in accordance with SANS 1215 and when pressed, will sometimes show customers test certificates such as the one shown on the left (which was supplied by the SABS itself – a well-trusted organisation). However, this does not necessarily mean that the product complies with SANS 1215 – only that one aspect does (compressive strength in this case). The words “PARTIAL TEST” stamped across the page are the laboratories means of indicating this. Not all labs are so conscientious or honest. Should bricks purchased under such circumstances subsequently be found to be defective, the builder has little recourse – even via the NHBRC.  Maturation of concrete units The NHBRC Home Builders Manual and SANS 2001 – CM1 require concrete units to be left to mature for a period of at least 21 days (unless proven to have a shrinkage of < 0,06%) before they are used. This is to prevent problems that could otherwise result from early drying shrinkage. Rate of drying shrinkage Time 21 days Concrete units should always be laid dry. In rainy weather, plastic sheets should be used to cover stacks and keep them dry If concrete units are laid wet like this, they are temporarily swollen and when they dry, they will shrink resulting in cracking. Hollow units should always be laid upside-down relative to their direction of casting - as shown above. The taper should face pointed side downwards. This is to afford the mason a larger area on which to spread the mortar. Mortar should only be applied to the inner and outer shells of the blocks (including buttering of the ends) – as shown on the right. Mortar should never be applied to the webs of the blocks. This is to prevent ingress of moisture from outside.  Building with standard modular units (SANS 993) Basic block dimensions (390 x 190 x 190). Together with a standard 10mm mortar joint, this gives a module of 400 x 200 x 200mm. Show video of the Catamaran reinforced masonry hotel construction in San Diego.  The issue of brickforce (bed-joint reinforcing) The provision of brickforce in horizontal bedding joints is not a mandatory requirement of any national standard including SANS 10400 The application of the national building regulations, SANS 2001-CM1: Masonry walling, SABS 0249: Masonry walling or the South African NHBRC (National Home Building Registration Councils) Home Building Manuals. According to SABS 0249, such “reinforcement for non-structural purposes, such as crack control, should be specified by the designer”.  The function of brickforce “Where it is impractical to subdivide a wall. Shrinkage cracking may be controlled by the use of horizontal joint reinforcement which will improve the distribution of stresses throughout the wall.” Source – A Technical Guide to Good House Construction – 1989, pg. 21 Hot dip galvanized 5.6 mm diameter hard-drawn ribbed steel makes far superior bed-joint reinforcing. Crimped wire ties should have a minimum diameter of 3.15 mm (± 0.1 mm) and they should be fabricated from pre-galvanized with a minimum galvanizing thickness of 450 g/m2. The best way to fill a collar joint – add lots of water to the same mortar until the consistency of this porridge – then pour it from a cut-open cooldrink bottle.  Mortar will not stick to DPC DPC Bricks are highly permeable and ‘wick’ water by capillarity. To prevent rising damp, superstructure brickwork must be built on top of a Damp Proof Coarse (DPC). This is an infill masonry wall built upon a suspended RC slab in a multi-storey building. Should it have been built on a DPC? Omitting the DPC or putting it in the wrong place can result in severe rising damp! There is no limit to how high rising damp will climb. Capillary forces are huge. Free standing walls should not be built on a DPC. They will blow over! A house can be built on a DPC because the intersecting walls provide stability. This structure was damaged by high winds before the roof was installed. Complete collapse of the walls was prevented only because of the intersecting walls.  DPC Poor parapet detailing. Mortar is weak in tension and will not adhere to DPC. Can you suggest a better detail? This is called a structural crack because it goes right through the load- bearing masonry. The other side of the same wall. Can you see the crack?  A thought for the day Does the mortar between the bricks hold them together or keep them apart ? ‘A stone must never touch the ones above or below,’ Tom replied. ‘That’s what the mortar’s for.’ ‘Why must they not touch?’ ‘It causes cracks.’ Tom stood upright to explain. ‘If you tread on a slate roof, your foot will go through it; but if you put a plank across the roof, you can walk on it without damaging the slates. The plank spreads the weight, and that’s what the mortar does.’ Ken Follett The Pillars of the Earth Mortar – choice of materials ‘Building sand’ is sold throughout South Africa for bricklaying. In Gauteng, it typically contains up to 30% sub 75µm fines. In the Western Cape, it is virtually deficient of such fines. Don’t use highly extended cements (like CEM III) Hydrated builders lime can be used to improve workability and water-retention. It is particularly beneficial for use with sands lacking in fines. Do NOT use lime-wash or agricultural lime. Only use builders hydrated lime complying with SABS 523. Do NOT use lime-wash or agricultural lime. Note that class III mortar is no longer permitted. Why are masonry cement mixes richer?  Mortar (good practice) Sift building sand to remove lumps Mix thoroughly Small batches: use in 2 hours max No retempering (adding water and remixing to restore workability) Thin joints (the thinner the joint the stronger the brickwork) Pre-soak burnt clay bricks but lay concrete units dry Is this mortar adequately mixed? Is the mixing method correct? Note sand clod lumps! The solution to sand clods and lumps  The effect of retempering on the compressive strength of mortar Delay after Compressive Percentage of mixing (hours) strength at 7 original days (MPa) strength 0 12.5 100 2 10.3 82 4 9.3 74 6 7.8 62 7 6.8 54 S. Crosswell, PCI Tip No. 133A, June 1995. 1:6 sand-cement mix by dry mass using Klipheuwel sand and OPC ex De Hoek. Ambient temperature at time of mixing approx 200C  8mm round ruling tool Ideal shape for water resistance Raking tool to remove excess mortar from bed joint  SANS 2001-CM1 requirements of sand for mortar Shall contain no organic material (produced by animal or plant activities) Shall contain no particles retained on a sieve of 5mm nominal aperture size. When 2.5 kg of cement is mixed with 12,5kg of air-dry sand, the mixture shall not require more than 3.0ℓ of water to be added to reach a consistency suitable for the laying of masonry units. Note that poor sand which requires more than 3.0ℓ of water in the above test can often be improved by blending with a coarser sand. One solution would be to design an upstand reinforced concrete beam. This would stiffen the slab edge. It could even be clad in brickwork. Relationship between slab thickness & deflections is not linear The end The end