Long-term concrete cracking is unavoidable, and large openings impact concrete durability [4,5]. In hot and dry areas of the world, high air temperature, wind, and low relative humidity are also known to impact durability [6], as they can cause high plastic and drying shrinkage strains in concrete [7,8,9]. ACI 224R-01 [10] attributes early-age concrete cracks to excessive evaporation due to environmental conditions prior to concrete setting. The earlier concrete cracks develop, the shorter the serviceable life of concrete is expected [11,12]. Plastic shrinkage cracks are the earliest to appear, as they occur two-three hours after casting, prior to setting. Subsequent propagation of plastic shrinkage cracks will allow ingress of water and offensive agents such as chlorides and increase the possibility of concrete deterioration and corrosion of steel rebars [13,14]. Plastic shrinkage cracks not only reduce concrete durability but are also aesthetically undesirable [15].
download need for speed world pc crack
Download File: https://shurll.com/2vKdhs
Hot weather casting is known to increase plastic shrinkage cracking [23]. It is widely accepted that plastic shrinkage starts when the evaporation rate exceeds the bleeding rate. Several studies reported that environmental conditions such as high air temperature, high wind speed, and low relative humidity have a direct effect on fresh and hardened concrete, as they also accelerate the final set time [24,25].
To examine the possibility of plastic shrinkage cracking in concrete, ASTM C1579 [28] recommends a set of environmental conditions to be applied: air temperature 36 3 C, wind speed more than 4.7 m/s, and relative humidity around 30 10%. These environmental conditions were selected based on past experimental work [28]. However, Al-Gahtani et al. [30], working in the eastern part of Saudi Arabia, known for high temperature and humidity, found that concrete is more likely to crack with and without the environmental conditions proposed by [28,31].
Nabil et al. [32] examined substrate bases of concrete (50 95 365 mm) for plastic shrinkage cracking in an environmental chamber by covering concrete with plastic sheets. The concrete mixes were exposed to a temperature of 55 C during the first 8 h after casting and 50 C until the end of the test (24 h). The relative humidity (RH) was about 10%, and the wind speed was 10 km/h during the duration of the test. As expected, it was found that covering concrete with plastic sheets was more efficient in minimizing plastic shrinkage cracking and reducing loss of water compared with non-covering. Almutairi et al. [33] did a survey to determine the causes of all early-age cracking in concrete structures in Kuwait city and concluded that the environmental conditions were the main reason for most the concrete cracking, but also high concrete temperature. It was recommended to prevent early-age cracking. The concrete temperature should be controlled by adding ice to the mixing water.
The capital of Saudi Arabia, Riyadh city, is located in the middle of Saudi Arabia. Temperatures are high in the summer, and the relative humidity is very low in both winter and summer (see Figure 2b). During the months of June to September, the air temperature, relative humidity, and wind speed are at the levels that increase the possibility of plastic shrinkage cracks, as anticipated by ASTM C1579 [28], and concreting at temperatures around 45 C is not uncommon. This (high) temperature level will be examined in this study, as well as the effect of a lower average wind speed of 3 m/s.
Figure 12, Figure 13 and Figure 14 show the evolution of the cracks for the three variable parameters: temperature, wind speed, and w/c ratio, respectively. The graphs also show the crack widths at 24 h measured both with DIP and a conventional manual optical device. The crack widths obtained for the two methods of measurement are almost identical, confirming that DIP works well. The mean difference between the two measurements was 0.113 mm.
Similarly, to what was observed for increasing temperature values, increasing wind speed causes earlier cracking to develop and eventually leads to larger crack widths. Interestingly, both the Low wind speed and Low-temperature environments, which are below the ASTM C1579 [28] recommendations, led to cracks (see Figure 13).
Again, the use of RTSF at a dosage of 30 kg/m3 prevented cracking in the specimens subjected to the Low and Medium wind speeds only, whilst 40 kg/m3 of RTSF was effective in preventing cracking at High wind speeds.
Effect of (a) temperature; (b) wind speed; and (c) w/c ratio on evaporation rate at crack initiation and time of crack initiation. * higher content of RTSF (40 kg/m3).
At low wind speeds (3 m/s), the evaporation rate reduces but the plain concrete cracks only a bit later and a bit less wide. Hence, at the ranges used, wind speed seems to play a less important role than temperature.
The CRR for the examined values of wind speed is shown in Figure 17. Again, 30 kg/m3 of RTSF eliminated cracks at low and mid-wind speeds, while 40 kg/m3 of RTSF was necessary to eliminate plastic shrinkage cracking at high wind speeds.
Sirajuddin and Gettu [84] examined the plastic shrinkage behavior of specimens exposed to a wind speed of 4.5 1 m/s and made of concrete comprising cement and fly ash and granulated blast furnace slag and reinforced with different volume fractions of four types of fiber (polypropylene, polyester fibers, polyacrylonitrile and glass fibers). The results showed that increasing the volume fraction of the different types of fibers led to a reduction in cracking by up to 60%.
When the download need for speed for pc commenced lower back inside the 90s, it become a sport approximately night time! In other words, underground racing with rapid vehicles and streaking streetlights.
Then slowly shifting towards Drift as the races got increasingly more difficult and became more acquainted with the controls. By the time you get close to crowning glory on any of the career tracks! Therefore, observed that the need for speed most wanted 2005 download pc game penalises you for shunning the flow controls. 2ff7e9595c
댓글