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7/29/2019 Effect of Rain on Concrete Surfaces
1/1www.cemex.ie/supafoCall 01 865 8700 (ROI) 02890 616611(NI) or email [email protected] www.cemex.ie
Readymix Concrete/Aggregates/Concrete Blocks/Mortar/Admixtures
Eect o rain
on concrete
suracesRainfall during placement
of concrete can present
challenges in achieving
a quality concrete.
Potential outcomes
range from no damage to
a weakened nondurable
surface, which maybe visible immediately
or may only become
apparent with time.
Placing and fnishingI during placing and fnishing concrete is not protected rom rain and the water is not allowed to evaporate
rom the slab surace; and multiple passes o oats and trowels used to fnish the surace are made with
surace moisture in place; the energy supplied by the fnishing operations mixes the excess water into the
slab surace creating a high w/c ratio in the near surace o the concrete reducing its strength and thereore
its durability.
Ater fnishing, i the immature concrete suraces have not been protected rom rainsome o thecement paste may be washed out o the concrete, leaving a weakened surace and the possibility o related
problems in the uture. This may include dusting o the surace; an unsealed surace that will allow ar more
water to be absorbed.
Damage to the concrete surace may be readily apparent, however, i the surace strength is only slightly
aected, the long term durability o the concrete may be reduced as indicated by surace deterioration in the
orm o crazing, scaling or erosion and a reduced ability to resist cracking due to reeze-thaw cycles.
The most common consequence is normally surace scaling, resulting in a aky, layered concrete surace,
which may not become visible until the slab has being trafcked when the scale breaks or crumbles away
Concrete strength and durability below the surace are not normally aected.
Protecting concreteConcrete can be poured while it is raining and with proper timing and process, the durability o the concrete
is not aected.
In very heavy prolonged rain it is advisable to hold o pouring concrete. Water in oundation trenches, orms
or on slabs must be removed prior to commencing the pour.
Where heavy showers are orecast a plan should be in place o where the concrete pour can be broken and
poured concrete should be protected as quickly as possible to prevent damage to the surace.
Where there is a risk o light intermittent showers, concrete can be protected or short periods with sheets
o polythene in much the same manner as curing,
Once concrete has been fnished and sufciently hardened, keeping water on it during the hydration period
is benefcial. However, i ponding occurs, on the surace o the concrete, it may result in some discoloration.
Beyond that, its strength and durability should not be adversely aected by the presence o excess water.
Further advice and inormation is available rom our technical team by calling
01 865 8700 (ROI) or 02890 616611 (NI) or emailing [email protected]
Disclaimer:This is intended as general advice only and does not absolve the end user from following bestpractice or any other instructions or guidelines as set down in specifcations or directed by the Specifer/Engineer.
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