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How Can Concrete Survive The 40-Degree Summer?

Thomas Huang posted this article in June 30, 2020

In summer, the temperature is high, the humidity is low, and the drying is fast. The newly poured concrete may have adverse effects such as faster setting speed and lower strength. At this time, special care needs to be taken when pouring concrete. It is necessary to correctly analyze the causes of adverse factors, and then take effective technical measures to eliminate the adverse factors or minimize them.
(1) The adverse effects of hot weather on concrete
When the temperature of the concrete increases, in order to maintain the slump required for the pouring operation, the water consumption of the concrete should be increased. At the same time, the temperature rises and the slump loss rate of the concrete mixture is accelerated, so that sometimes when the concrete is transported from the mixing station to the construction site, water needs to be added to the concrete mixture again. Both of these conditions increase the water consumption of the concrete, which in turn leads to increased shrinkage and reduced strength. Because higher temperatures accelerate the setting, the transportation of concrete will become more difficult. When the humidity is low or the wind speed is high, the amount of water loss is greater. If the concrete needs air entrainment, the high temperature will make the gas content more difficult to control. Since the high temperature will reduce the gas content, the amount of air-entraining agent should be increased. Even if the amount of cement is used to compensate for the increase in water consumption, the quality of hardened concrete may still be adversely affected. The early strength of concrete cured at a higher temperature increases faster, but the strength that may be achieved at 28 days will decrease accordingly. In order to improve the quality of concrete pouring in hot climates, make detailed construction plans and ensure implementation. Through careful selection of raw materials and construction methods for the preparation of concrete, some adverse effects can also be reduced. In addition, during concrete construction, measures should be taken to improve the quality of summer construction.
(2) Measures in the process of concrete mixing, transportation and unloading
When mixing concrete, measures should be taken to control the temperature of the concrete. By controlling the temperature of the concrete to control the additional water volume, the slump loss rate is reduced, and the plastic shrinkage cracking is reduced. At this stage, the following measures can be taken:
(1) Reduce the amount of cement by using water reducer or replacing cement with fly ash. At the same time, increase the aggregate particle size if the pouring conditions permit.
(2) If the concrete mixture needs to be transported over a long distance, the retarder can be used to control the setting time, but the correct dosage of the retarder should be ensured, which is especially important for underwater concrete engineering.
(3) If higher slump is required, high efficiency water reducer should be used. The high slump produced by some superplasticizers can be maintained for 2 hours. The superplasticizer can also reduce the friction between the aggregate particles during the mixing process and slow down the heat accumulation in the mixing drum of the transport mixer.
(4) Sprinkle water into the aggregate pile to promote evaporative cooling to reduce the temperature of the concrete; if wetting with cold water (such as groundwater or well water), the cooling effect will be better, especially when the humidity is high.
(5) When the concrete is to be transported for a long distance in seasons with high temperature and high humidity, the delayed mixing of the transport mixer can be considered so that it will still be in the mixing state when it reaches the construction site.
(6) When possible, plans should be made to avoid pouring concrete at the maximum daily temperature. Under dry conditions, the concrete poured at night is relatively less affected by wind and temperature.
(7) In addition to adding mixing water according to the design amount to adjust the specified slump, no additional mixing water should be added on the construction site
(3) Treatment measures for pouring concrete in summer
(1) The final strength of concrete poured in a hot climate will be reduced, and the influencing factors are: ① the temperature of the concrete is higher; ② the setting and early strength increase faster; ③ the water consumption increases under the same slump requirements.
Treatment measures: ①Sprinkle water on the aggregate pile to cool the aggregate through the evaporation of water; ②Add a retarder to the concrete; ③Use ice to replace part of the mixing water if necessary; ④Add fly ash to regulate the heat Impact of climate; ⑤ Properly increase the amount of cement in each cubic meter of concrete.
(2) The hot climate lowers the air content of the concrete, thereby causing some adverse effects on the concrete. The main reasons are: ① the durability of hardened concrete becomes worse; ② the workability of concrete mixture decreases; ③ the amount of mixing decreases.
Treatment measures:
① Always check the air content of the concrete mixture; ② Increase the amount of air-entraining agent.
(4) Construction measures during the rainy season
(1) Construction site: form a good drainage system for the construction site and living area according to the terrain to ensure smooth flow of water and no accumulation of water.
(2) Reinforcement engineering: ① Rainproof and drainage work should be done in the steel processing site. The raw material of the steel and the processed steel should be covered with plastic cloth to prevent the rain from corroding the steel. The steel storage site is all hardened with fine stone concrete. Put the steel bar on the concrete pier of 250mm×300mm to prevent the water from soaking and the soil from contaminating the steel bar. ② Rebars should be piled up neatly and covered with plastic cloth for protection when it rains. Organize the construction progress of the steel bar project during construction, and try to use rain-free weather for construction.
(3) Concrete engineering: ① During the rainy season construction, get in touch with the meteorological department to formulate a short-term weather forecast. Before the concrete is poured, the weather forecast should be known in time, and the construction should be organized on sunny days. If it rains when the concrete is poured, measures should be taken to cover it with plastic cloth to prevent the newly poured concrete from being washed by rain. Concrete must be poured because of the engineering rush, and shelter measures should be taken. ②Because of the use of commercial concrete, the commercial concrete mixing station is required to adjust the construction mix ratio according to the sand and stone moisture content before the opening, strictly control the slump of the commercial concrete, and meet the construction requirements during the rainy period. Concrete pouring is strictly prohibited during heavy rain. ③When the concrete has not reached the initial setting, if it rains, it should be covered with plastic cloth in time to prevent rain.
(5) Maintenance of mechanical and electrical equipment and material stacking
(1) The large-scale electromechanical equipment placed in the open air should be protected from rain and moisture, and the mechanical bolts and bearing parts should be regularly lubricated and rotated to prevent corrosion. All electromechanical equipment must be installed with anti-leakage protectors.
(2) Electromechanical equipment that is relatively fixed at the construction site, such as an electric welding machine, must be set up with a rain shed or a motor and a protective cover, and it is not allowed to be wrapped with plastic cloth. Its electrical equipment must have reliable grounding measures. The wire and rubber line should be checked for aging, damage, and substandard rubber line should be replaced and repaired to prevent leakage accidents.
(3) Various high and low voltage lines on site should be checked whether they meet the requirements of safe operation regulations. Ordinary rubber lines and ordinary plastic lines are not allowed to be dragged anywhere.
(4) Electrical switches for mechanical and electrical equipment of various machines shall be provided with rain and moisture proof facilities.
(5) After rain, conduct patrol inspections on various electromechanical equipment, temporary lines, etc. If signs of electrical leakage occur, immediate danger warnings should be marked and repaired and repaired in a timely manner. If there are serious safety hazards, stop working immediately.
(6) Temporary construction projects and others
(1) Before the rainy season, the houses under construction should be inspected and repaired to prevent rain leakage, electricity leakage and other unsafe factors. Before thunderstorms, explain to workers that they should not approach the shelf or the area within 10m around overhead wires during thunderstorms to avoid lightning strikes.
(2) After the rain, high-altitude workers should wear rubber-soled shoes, pay attention to anti-skid.
(3) Purchase a diesel generator and submersible pump to prevent the water in the basement from being discharged out of the site in a timely manner when there is a power failure during the rainy season.

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