Construction World February 2016

CONSTRUCTION WORLD

FEBRUARY

2016

APPROPRIATE CURING AGENT

SELECTION

PRODUCTS AND SERVICES

Eddie Correia, executive vice president

of Chryso Southern Africa, says that

the duration and type of curing applied

during the setting process will play a determinant

role in enabling the concrete to achieve the

strength and durability that is required to meet

the design parameters of the structure.

Correia explains that curing is the process

in which the concrete is protected from loss

of moisture and kept within an acceptable

temperature range.

”This process is key to producing a final

product with increased strength and decreased

permeability, and is important in mitigating

cracks which allow open access for harmful

materials to bypass the low permeability

concrete near the surface and this can adversely

affect durability,” he says.

“When effective curing of concrete is applied

the amount of cement required to achieve the

given strength or durability is reduced or in some

instances can be replaced with supplementary

cementitious materials,” Correia continues.

With cement being themost energy intensive

portion of a concrete mix this reduction leads to

a cost reduction as well as a lower carbon foot-

print. In addition to this, sound curing methods

using quality products can enhance sustainability

by eliminating the need for resource intensive

conditioning treatments, particularly those that

are not compatible with the environment.

Curing methods are divided into two

phases; one prior to the initial set and these are

applied continuously during the bleeding of the

concrete. The other is after the initial set and

final surface finishing and is generally applied

before the final set.

Temperature can be an important factor

as the rate of hydration and therefore strength

development is faster at higher temperatures.

Correia says the temperature of placed and

compacted concrete should not be allowed

to fall below 5°C because this will result in

the slowing down or even halting of the hydra-

tion process with the result that the concrete

will take longer to gain strength, delaying

form or mould removal and subsequent

construction. Concrete will freeze at tempera-

tures below 2 °C.

In situations where the concrete temperature

is expected to drop below 2 °C, an air entraining

agent from the CHRYSO

Air range can be added

to protect it from freezing or thawing conditions.

Air bubbles act as a pressure relief valve allowing

moisture within the concrete to freeze and

expand into the bubbles, thereby preventing the

cracking and spalling of concrete.

Correia says that in addition to protecting

the new concrete from extremely low tempera-

tures, it is also important to reduce the tempera-

ture differential between the core and outer

surface of the concrete to an acceptable level

while the concrete is gaining strength to avoid

thermal cracking.

Protection from moisture loss due to

evaporation is easily achieved using Chryso

ProFilm 19. Correia says this is an evapora-

tion reducer that offers contractors a reliable

controlled way of preventing the rapid evapora-

tion of water. Suitable for use on fresh concrete

prior to the initial set, it produces an effective

continuous barrier film over the concrete

surface. It can be applied after compaction and

initial striking of concrete.

A range of other Chryso

Curing Agents

is available to use after the initial set and final

Concrete structures are expected to last a certain number of years

and in order to meet the expected lifespan, the concrete must be

able to withstand structural loading, fatigue, weathering, abrasion

and chemical attack.

surface finishing. These include Chryso

Cure

Acrylic, Chryso

Cure WB (wax based), Chryso

CureWP (pigmented) and Chryso

Cure HPS – all

are suitable for use on pavements and slabs. The

first three are used on columns beams and walls,

while Chryso

Cure Acrylic is most appropriate

for the top of columns, beams and walls.

Use of Chryso® Curing Agents enables con-

tractors to achieve a perfect finish

on concrete.

The duration and type of curing applied during

the setting process will play a determining role

in enabling the concrete to achieve the strength

and durability that is required to meet the

design parameters of the structure.