8.11
Uitharding methoden
Betonelementen met een kleine oppervlakte-tot-volumeverhouding worden uitgehard door de vormen te oliën en te bevochtigen voordat het betonelement wor…
Oiling and moistening forms before pouring concrete aid in curing concrete members with a small surface-to-volume ratio.
These forms may be left in place for a specific time and wetted if made of wood, or if removed early, the concrete needs to be moistened and covered using polyethylene sheets.
A covering is suspended above freshly laid large horizontal concrete surfaces exposed to dry weather until the concrete is set, followed by wet curing.
Spraying or fogging water using a system of nozzles and ponding or flooding concrete surfaces with water facilitates wet curing.
Alternatively, covering concrete with moistened sawdust or straw or saturated moisture-retaining fabrics such as wet hessian or cotton mats that are either periodically watered or overlain with a polyethylene film ensures water-concrete contact.
Providing impervious membranes on concrete can minimize the evaporation of moisture but prevent moisture ingress. These can be made of waterproof papers, plastic sheets, or membrane-forming sealing compounds applied manually or sprayed onto damp concrete surfaces.
Curing laboratory test specimens of concrete is achieved by immersing them in water.
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Q1: Why should concrete forms be oiled and moistened before pouring?
Oiling and moistening forms before pouring concrete aids in curing concrete members with a small surface-to-volume ratio. This preparation helps prevent moisture loss from the freshly cast concrete and facilitates easier form removal. Proper form conditioning ensures better moisture retention during the critical early curing period.
Q2: What are the main methods for wet curing concrete surfaces?
Wet curing concrete is achieved through spraying or fogging water using nozzle systems or by ponding and flooding concrete surfaces with water. Alternatively, covering concrete with moistened sawdust, straw, or saturated moisture-retaining fabrics like wet hessian or cotton mats maintains water-concrete contact. These methods ensure continuous moisture availability during the curing process.
Q3: How do impervious membranes affect concrete curing?
Impervious membranes made of waterproof papers, plastic sheets, or membrane-forming sealing compounds minimize moisture evaporation from concrete surfaces. However, these membranes prevent moisture ingress and cannot replace moisture lost through self-desiccation. They are applied manually or sprayed onto damp concrete to reduce surface water loss.
Q4: What should be done if concrete forms are removed early?
If concrete forms are removed early, the concrete must be moistened and covered using polyethylene sheets to maintain moisture content. This protective covering prevents rapid evaporation and ensures adequate hydration during the critical curing phase. Early form removal requires immediate protective measures to preserve concrete quality.
Q5: How are large horizontal concrete surfaces protected during curing in dry weather?
A temporary covering is suspended above freshly laid large horizontal concrete surfaces exposed to dry weather until the concrete sets. After the concrete hardens, wet curing is initiated using spraying, fogging, or ponding methods. This staged protection prevents rapid moisture loss during the vulnerable initial setting period.
Q6: Why is immersion in water used for laboratory concrete specimens?
Immersion in water is the standard curing method for laboratory test specimens of concrete because it provides complete and uniform moisture saturation. This method ensures consistent hydration conditions and allows accurate measurement of concrete properties under controlled curing environments. Water immersion represents ideal curing conditions for standardized testing.
Q7: Can wooden forms be left in place during concrete curing?
Yes, wooden forms can be left in place for a prolonged period and periodically wetted to prevent moisture loss from the concrete. Keeping forms in place protects the concrete surface and maintains moisture content during curing. If forms are made of suitable materials, they can be an effective moisture-retention strategy.