Specification Part 3 - Road & Bridge Works - Urban Administration ...

The Contractor will be required to suite his methodology for the Engineer in charge’s
approval when temperatures of concrete arc likely lo exceed 40 degrees Celsius during the work.
1713. PROTECTION AND CURING
Concreting operations shall not commence until adequate arrangements for concrete curing have
been made by the Contractor. Curing and protection of concrete shall start immediately after
compaction of the concrete to protect it from:
a) Premature drying out particularly by solar radiation and wind
b) High internal thermal gradients
c) Leaching out by rain and flowing water
d) Rapid cooling during the first few days after placing
e) Low temperature or frost
f) Vibration and impact which may disrupt the concrete and interfere with its bond to the
reinforcement Where members are of considerable size and length , with high c ement content,
accelerated curing methods may be applied, as approved by the Engineer in charge.
1713.1. Water Curing
Water for curing shall be as specified in Section 1000. Sea water shall not be used for curing.
Sea water shall not come into contact with concrete members unless it has attained adequate
strength.
Exposed surfaces of concrete shall be kept continuously in a damp or wet condition by
ponding or by covering with a layer of sacks, canvas, Hessian or similar materials and shall be
kepi constantly wet for a period of not less than 14 days from the date of placing of concrete.
1713.2. Steam Curing
Where steam curing is adopted, it shall be ensured that it is done in a suitable enclosure to
contain the live steam in order 10 minimize moisture and heat losses. The initial application of the
steam shall be after about four hours of placement of concrete to allow the initial set of the
concrete 10 take place.
Where readers are used, the waiting period before application of the steam shall be
increased to about six hours.
The steam shall be at 100 per cent relative humidity to prevent loss of moisture and to
provide excess moisture for proper hydration of the cement. The application of steam shall not he
directly on the concrete and the ambient air temperature shall increase at a rate not exceeding 5
degrees Celsius per hour until a maximum temperature of 60 degrees Celsius to 70 degrees
Celsius is reached. The maximum temperature shall be maintained until the concrete has
reached the desired strength.
When steam curing is discontinued, the ambient air temperature shall not drop at a rate
exceeding 5 degrees Celsius per hour until a temperature of about 10 degrees Celsius above the
temperature of the air 10 which the concrete will be exposed, has been reached. The concrete
shall not be exposed to temperatures below freezing for at least six days after curing.
1713.3. Curing Compounds
Curing compounds shall only be permuted in special circumstances and will require specific
approval of the Engineer in charge; Curing compounds shall not be used on any surface which
requires further finishing to be applied. All construction joints shall be moist, cured and no curing
compound will be permitted in locations where concrete surfaces are required to be bonded
together.
Curing compounds shall be continuously agitated during use. All concrete cured by this
method shall receive two applications of the curing compound. The first coat shall be applied
immediately after acceptance of concrete finish. If the surface is dry, the concrete shall be
saturated with water and curing compound applied as soon as the surface film of water