7/29/2019 Effect of Rain on Concrete Surfaces

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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 ireland.ino@cemex.com

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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