durability of concrete

3. Asif Iqbal 2014-BT-CIVIL-20
Ghullam Mustafa 2014-BT-CIVIL-38

4.  Durability of concrete
 HotWeather
 Factors Affecting on concrete
 Problems During placing the Concrete
 Techniques to control concrete temperature
 Admixtures

5.  Its means that the Strength of the concrete
structure how much life of the concrete
structure .
 The resistance of concrete against the hot
and cooled weather environment.
 How to improve concrete strength by using
some admixture according to weather
condition.

6.  Hot weather is defined by ACI 305R in Any
combination of the Following
1. High AmbientTemperature
2. High concrete temperature
3. Low relative humidity
4. High wind speed
5. Solar radiations

8.  The effect of extremely hot and arid weather
on concrete strength is similar to the effect in
typical hot weather concreting.
 This may be due to the fact that precautions
to control concrete temperature are taken.

9.  The variation range of concrete temperature
between cold and hot weather conditions in
Riyadh city is about 16 C.
 More over, concrete temperature is about
86% to 95% of the ambient temperature and
an increase of the ambient temperature by
about 5oC would increase the concrete
temperature by 2.2 C.

10.  The climatic factors affecting concrete in hot
weather are high ambient temperature and
low relative humidity.
 These effects are considerably pronounced
with the increase in wind velocity

11.  The combination of hot dry weather and high
winds is the most severe conditions,
especially when placing large exposed slabs
 A higher temperature of fresh concrete will
result in rapid hydration and can lead to
accelerated setting.

12. 1. The higher temperature also leads to a
higher water demand in order to maintain
the concrete at the specified slump.
2. Quick stiffening and difficulties in handling
and finishing the concrete

13.  Loss of workability and faster setting time.
 Rapid evaporation and drying

14.  Chilled water.
 Sprinkling of aggregate.
 Shading mix materials.
 Use of Admixtures
 Use of ice during mixing

18.  Concrete admixtures are the ingredients in
concrete other than water, cement and
aggregate which are added immediately
before or during the mixture.
 Concrete admixtures are being used primarily
to ensure the quality of concrete during the
mixing, placing, transporting and curing
process and to lessen the cost of concrete
construction.

19.  The efficiency of concrete depends on some
factors, including: water content, type and
amount of cement, mixing time, and
temperature of the concrete and air.

20.  Water-reducing admixtures usually lessens
the water content needed for a concrete
mixture by an average of 5% to 10%.
Therefore, concrete structures that contain a
water-reducing admixture needs less water
to reach a required slump than untreated
concrete.

21.  Super plasticizers, are also known as high-
range water reducers (HRWR). Chemical
manufacturers in UAE say that it reduces the
water content by an average of 12% to 30%
and can be added to the concrete mixture
with a low-to-normal slump.The effect of
super plasticizers lasts only for about 30 to 60
minutes, depending on the brands and
dosage rate.

22.  Accelerating admixtures increase the
percentage of early strength development,
lessens the time needed for proper curing
and protection and speed up the start of
finishing procedures.

23.  Retarding admixtures slow down the setting
rate of the concrete.
 They are used to respond to the accelerating
effect of high weather on concrete setting. Hot
weather often causes an increase rate of
hardening which makes placing and finishing
difficult.
 Retarders keep concrete workable during the
placement process and delay the primary set of
concrete.

24.  The typical effect of concrete temperature on
its compressive strength It can be observed
that the compressive strength decreases as
them concrete temperature increases.