Part - 5 (Specifications)
Section - 5
Block Works
Section - 5
BLOCK WORKS
5.1 SCOPE :
These specifications cover the materials, manufacture and workmanship for concrete block work and calcium silicate brickwork and associated items to be incorporated into the works.
5.2 MATERIALS :
5.2.1 Cement :
Cement shall be sulphate resisting Portland Cement complying with BS 4027: 1980 for work up to and including the structural ground slab and ordinary Portland Cement to BS 12 for work above this level.
5.2.2 Water :
Water shall conform to the requirement specified for water in the 'Concrete Work' section.
5.2.3 Aggregate :
Aggregate shall conform to the requirements specified for aggregate in the 'Concrete Work' section and shall comply with BS 882:1983.
5.2.4 Additives :
Additives to mixes for blocks and mortar shall be from approved manufacturers and shall be used strictly in accordance with the manufacturer's instructions. Additives shall only be used with the Engineer's written instructions.
5.2.5 Damp - Proof Courses :
Damp-proof courses, cavity trays and the like shall be 0.3mm PVC sheet and modified bitumen polymer compound laminate membrane of 1.8mm thickness obtained from an approved manufacturer. The membrane shall be of a type suitable for hot climates.
5.3 MANUFACTURE :
5.3.1 Concrete Blocks :
Block work shall comply with BS 6073: Part 1: 1981 Type A and with Dubai Municipality local order No. 44 of 1990.
5.3 MANUFACTURE [Cont'd]
5.3.1 Concrete Blocks [Cont'd]
Aggregate shall be so sized, graded, proportioned and thoroughly mixed in a batch mixer with such proportions of cement and water as to produce a homogeneous concrete mixture.
The recommended mix to obtain the compressive strength and finish required is as follows :
- 50 kg sulphate resisting cement
- 0.15 m³ fine aggregate (graded up to 4.8mm)
- 0.30 m³ coarse aggregate (graded up to 9.5mm).
Pre-Cast concrete blocks shall be manufactured in approved vibrating machines. If for any reason the strength requirement is not achieved, the cement shall be increased at the Contractor's own expense. The water used in the mix shall be clean and of a sufficient quantity to allow complete hydration of the cement without providing an excess when moulding.
Concrete blocks shall be hard, sound, durable, sharp, rectangular shape, clean with well defined arises free from cracks, flaws and other defects.
Concrete blocks shall be either obtained from approved local factory or manufactured on the Site. If manufactured on site, the blocks shall be press moulded in approved moulds and vibrating pressure machines with a minimum of 2,800 cycles per minute.
Closers and half blocks shall be purpose made; cut blocks shall not be used.
Blocks manufactured on the site shall be cured in the shade by being kept thoroughly moist with water applied by sprinklers or other approved means for a period of at least seven ( 7 ) days. The blocks shall be stacked on a clean and level platform free from earth or other impurities during the curing process, and shall be stacked in honeycomb fashion after curing. The blocks shall not be used prior to one ( 1 ) month after the date of manufacture, nor shall any block be used that have not been inspected and approved by the Engineer.
Concrete blocks (solid or hollow) shall be manufactured in accordance with BS 6073 : Part 1 : 1981 and in the following dimension (work sizes) :
- Height = 190mm + 1% Tolerance (200mm coordinating size)
- Length = 390mm + 1% Tolerance (400mm coordinating size)
- Width = As required + 1% Tolerance.
The thickness and work sizes of blocks shall be as indicated on the drawings and as directed in writing by the Engineer, but shall conform to 75, 90, 100, 140, 190mm work sizes. Coordinating sizes are 85, 100, 150, 200mm.
5.3 MANUFACTURE [Cont'd]
5.3.1 Concrete Blocks [Cont'd]
All Blocks shall be from approved automatic plant. Blocks from M/s. Juma Al Majid, M/s. National Block Factory and M/s. Emcon shall be used.
Minimum crushing strength on gross area for :
a) Non load bearing hollow block = 7.5 N/mm²
b) Load bearing hollow blocks = 12.50 N/mm²
c) Solid blocks = 12.50 N/mm²
d) Hurdi blocks = 3.00 N/mm².
8” thick solid blockwork shall be provided below all external tie beams from foundation level. Also 8” thick solid block work to be provided wherever floor level changes, as advised by consultant.
Thickness of solid block to be increased to that equal to the tie beam, if the tie beam thickness is more than 8”. Minimum thickness of solid block work shall be 8”.
Mortar for block shall be 1:3 ratio using SRC/OPC appropriately.
All blocks to be thoroughly cured before placing in position.
All concrete and block junctions to have G.I. hold-fasts for every alternative layer (i.e. at 16” c/c). Size of hold fast 300 x 30 x 3mm thick.
All junctions between concrete and blockwork shall have 8” wide approved expanded metallath on both sides for plaster, stainless steel metal lath to be used for external plaster and GI for internal plaster.
Hollow concrete blocks shall comply with the following requirements :
a) The density of the concrete blocks shall not be less than 1,500 kg/m³ but shall not exceed 2160 kg/m3.
b) The Compressive Strength at twenty eight ( 28 ) days shall be 70 kg/cm² for non-load bearing walls and 100 kg/cm² for load bearing walls, expressed as force per unit of net cross sectional area.
c) The water absorption shall be 20% or less of dry weight.
d) The design of the cavities and webs of the hollow concrete blocks shall be submitted to the Engineer prior to manufacture. The thickness of the face shell and of the membrane of solid portions shall not be less than thirty five ( 35 ) mm. The total volume of the cavities shall not exceed 50% of the volume of the block.
5.3.2 Samples :
Samples of all types and sizes of blocks to be used shall be submitted for the written approval of the Engineer.
5.3 MANUFACTURE [Cont'd]
5.3.3 Mortar :
Mortar shall be prepared with the addition of the minimum quantity of clean water for workability.
Cement and sand mortar (1:3) mix shall be composed of one part ordinary Portland Cement to three parts of sand by volume for works above damp proof course level and mortar mix for below damp proof course shall be one part sulphate resisting cement to three parts of sand.
The ingredients for mortar shall be measured in proper clean gauge boxes and the mixing shall be carried out by means of an approved mechanical batch mixer.
Mortars shall be used within thirty ( 30 ) minutes of mixing. Hardened mortars shall not be used in the work and shall, upon the request of the Engineer, be immediately removed from the site.
5.4 WORKMANSHIP :
5.4.1 Block Work :
The block work workmanship shall comply in general with the recommendations of BS 5628 Part 1:1978 (1985) & BS 5628 Part 2: 1985.
All block work shall be set out and built to the respective dimensions, thickness and heights shown on the Drawings or as instructed in writing by the Engineer.
All walls and partitions, where shown on the Drawings without indicating the type of the block to be used, shall be built in hollow concrete blocks, unless otherwise directed in writing by the Engineer.
The blocks shall be wall soaked before being used and the tops of walls left off shall be wetted before work is recommenced. All blocks shall be well buttered with mortar before being laid and all joints shall be thoroughly flushed up as the work proceeds. All joints shall be uniform and shall not exceed 10mm. Block work shall be carried up in a uniform manner no more than six courses being built in any one day without the prior permission of the Engineer. Any wall left at different levels must be raked back. All perpends, quoins, internal and external angles, etc. shall be kept strictly true and square and the whole properly bonded together and leveled round. All block work shall be plumbed vertically.
The surface of the walls and partitions prepared for rendering shall have the joints raked out 20mm from the face of the wall to form key for the plaster.
All block walls shall be bonded to adjacent reinforced concrete structures by means of galvanized mild steel cramps at every third course, complying in all respects with BS 1243: latest edition. The ties shall be minimum 200mm long one end bent and shot fired into the reinforced concrete and the remainder set into the block wall.
5.4 WORKMANSHIP [Cont'd]
5.4.1 Block Work [Cont'd]
Partitions shall be bonded to main walls by toothing at every third course to a depth of not less than 100mm.
Cavity walls shall be built raising the skins of block work at a similar rate and incorporating wall ties at 900mm horizontal centers and 600mm vertical centers spaced diagonally.
Cavities shall be kept clear of mortar droppings and the inside faces of block work shall be pointed as necessary for correct application of insulation.
All walls and partitions shall be properly cured by sprinkling water for a period of not less than three ( 3 ) days after completion of laying the course.
Walls and partitions terminating against soffits of beams or slabs shall be tightly wedged with temporary metal wedges after mortar in bed joints has attained its initial set, and the joint packed with bitumen impregnated building board strips of appropriate thickness (10, 12, 18mm) with the temporary wedges withdrawn.
Special block shall be fitted next to the reinforced concrete structure, door and window jambs and sills, and to form chases for the ends of door and window lintels. If hollow blocks at any built-in fixtures, e.g., door and window frames, apertures, louvers, etc., they shall be filled with grade 15 concrete and where shown reinforced.
Where block work is described as fair faced, selected hard, sharp, clean blocks shall be used with well-defined arises and perfect rectangular shape. Joints shall be finished off with neat flush pointing, taking care to keep mortar from adhering to any part of the block.
Block work over lintels shall be reinforced with two layers of expanded metal mesh reinforcement well bedded in mortar and 150mm longer at each end than the lintel.
5.4.2 Fire Stop Products :
Fire resistant products for fire stops shall be of the appropriate type suitable for the specific application as specified hereunder.
The product shall be capable of stopping the passage of fire, smoke and water through fire rated wall, floor and ceiling penetrations, claddings and expansion joints for the specific designed fire ratings of the adjacent areas. The product shall exhibit the minimum designed fire resistant properties when tested as per BS 476:Part 20:1987 and shall be approved by the Engineer. Necessary certificates to establish the above shall be produced by the Contractor to the Engineer.
The products shall be obtained from an approved, established and proven firm and shall be applied by experienced personnel strictly in accordance with the written instructions of the manufacturer and to the approval of the Engineer.
5.4 WORKMANSHIP [Cont'd]
5.4.2 Fire Stop Products [Cont'd]
Mild steel selves appropriate for the size of the cable/pipe passing through it, with the least annular space around them shall be provided in the walls, floors and ceilings. Alternatively, similar openings to those of the sleeves may be provided in concrete. The size of the openings shall be minimum recommended by the product manufacturer.
The following products shall be provided as appropriate for the situation and as detailed on the Drawings and to the approval of the Engineer :
a) Silicone sealant : Silicone sealant shall be an elastic fire rated silicone sealant, fire tested to BS 476:Part 20:1987 and approved by the Engineer.
b) Mastic : Mastic shall be as intumescent, graphite based mastic with expansion pressure of minimum 7 bar and fire tested to BS 476: Part 20:1987 and approved by the Engineer.
c) Light Weight Mortar : Mortar shall be light weight and fire resistant with vermiculite additive. Lightweight mortar shall be used always in conjunction with and intumescent putty as specified below. The mortar shall be fire tested to BS 476: Part 20:1987 and approved by the Engineer.
d) Intumescent Putty : Intumescent putty shall be a putty based on graphite and shall have a 7 bar expansion pressure and shall be tested to BS 476: Part 20:1987 and approved by the Engineer.
e) Backing foam : Backing foam shall be a one component, ready to use, polyurethane based adhesive expanding sprayed foam. It shall be fire tested to BS 476: Part 20:1987 and exhibit one hour integrity rating.
f) Mineral Wool / Rock Wool : Rock wool / mineral wool for fire stop applications shall be of minimum 45 kg/m³ density.
The recommended treatments for various applications shall be as follows in keeping with the recommendations of the manufacturer of the product and shall be read in conjunction with the typical details, detailed on the drawings.
Junction of block walls terminating against soffits of beams and slabs shall be treated as follows :
1) For one hour fire rating : The block wall shall be built so that the gap between the top of the wall and the soffit of slab / beam is a minimum of 10mm.The gap shall then be wedged using steel wedges and shall be packed with fire resistant backing foam for the entire thickness of the wall.