CONCRETING: Foundations, driveways, flooring slabs
One of the most important factors in producing a good quality concrete slab is often overlooked completely within the construction industry: The curing of the newly finished slab!
In many cases the concrete contractor is employed on a labour only basis, leaving the "curing" of the slab up to the builder or owner on site.
Many times, we have seen new concrete slabs (residenital & commercial alike) "baking in the sun".
Many times, we have seen new concrete slabs (residential and If the concrete contractor is not curing the slab (as part of his contract), the building contractor must take all steps necessary to minimise the high probability that the slab will very likely crack.
The concrete contractor needs to have open dialogue with the customer (builder) and ensure the matter of curing is discussed in the planning stages so it is clear just who is responsible for this all-important process.
On-site Specialist Subcontractor - Best Practice to produce a good quality concrete slab
1. Concrete of correct slump, air content and specified strength is delivered to site in accordance with NZS 3604:2011 paragraph 4.5.2.
2. No water is added without the conditions stipulated in NZS 3109:1997 A1 paragraph 9.4.2.1 being strictly adhered to
3. Concrete is placed in accordance with NZS 3109:1997 and compacted with the use of immersion vibrators
4. Concrete is finished only after all bleed water has evaporated from the surface
5. Antivap sprays can be used (and applied more than once if necessary) to control the evaporation rate to prevent plastic shrinkage cracking
6. The curing process is started immediately finishing operations are completed
7. Joints are cut immediately (using early-entry saws) or within 12–18 hours if possible, using traditional sawcutting equipment
8. Wet curing or covering the concrete with black plastic sheeting is continued for a minimum of 7 days (unless otherwise stipulated) if a curing membrane is not used
Remember:
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Poor curing of floor slabs can reduce concrete strength by up to 50% resulting in lower strength and a greater risk of random shrinkage-induced cracking, despite control joints being saw-cut
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Effective curing will improve the durability and the abrasion resistance of the concrete
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The curing period should be at least 7 days is better. A longer period may be required, or shorter period feasible, as prescribed in NZS 3101:2006 or as intended by the designer On-site specialist subcontractor
WHERE YOU CAN GET MORE INFORMATION:
- NZ Master Concrete Placers Association Inc. (NZMCPA) – www.mcpa.org.nz
- Cement & Concrete Association of New Zealand (CCANZ) - www.ccanz.org.nz
Since this document is for general guidance only and in no way replaces the services of professional consultants on particular projects, no liability can be accepted by CCANZ or NZMCPA by its use
Suppliers - Click on those you would like to find out more about…
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- NZ Master Concrete Placers Association
- By setting and maintaining a high standard for membership, those who employ a Master Concrete Placer to carry out their contract can be assured of a professional job in all aspects of their dealings from quotation through to back-up service.
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- Concreting Services & Suppliers
- Choosing Concrete as a choice for a sustainable material of choice for the environment. By setting and maintaining a high standard for concreting, those who employ a qualified Concrete Association member to carry out their contract can be assured of a professional job in all aspects of their dealings from quotation through to back-up service.
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- License Building Practitioners - Concreting
- Licensed Building Practitioners scheme. This scheme was introduced in November 2007. From 1 March 2012 all building practitioners must be licensed in order to carry out or supervise work on homes and small medium sized apartment buldings that is critical to the integrity of the building.
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- Superform Building Systems
- The Superform Building Systems represents an exciting engineering development in New Zealand. It has been designed to conform to and comply with NZ building codes, practices and offers excellent insulation properties for projects including housing, inground basements, retaining walls, swimming pools, multistory buildings, motel units, rest homes and hotels to name a few.
