Every year in winter and spring alternating and spring construction, the concrete pouring most prone to cracks, many people do not understand the reasons, which do not understand, that the climate is not high temperature is not low, should not appear such Quality of concrete and concrete itself, this paper through the analysis of all aspects of geography and climate, contact the concrete itself, a feature of the concrete cracks in the cause of this season, and put forward a corresponding solution Measures for construction reference
1, the reasons for the analysis
1.1 Environmental and climate reasons
In the spring, the temperature difference between day and night is large, and the temperature of concrete pouring at different times is bigger in the same period.There are large temperature difference between concrete inside and outside, which is easy to form temperature shrinkage. The air is dry and the humidity is small (<30%). 4 to 5, in the open construction site on the floor of the larger wind, just pouring concrete surface water loss faster, easy to form a dry plastic shrinkage cracks.
1.2 Construction reasons
Construction of the blindly require a large slump to facilitate the construction, not knowing the greater the slump of the greater the probability of cracks, coupled with the construction of the light is not timely, too early to receive, or less than the number of light reception; construction conservation Not in place, after the concrete pouring does not meet the CB50204-2002 7.4.7 requirements to cover the concrete and moisturizing conservation, more likely to form shrinkage cracks. Due to investment or other reasons, the required short duration, resulting in the floor load or demolition of the mold too early, concrete pouring less than 24 hours began to hang steel pipe reinforcement and template, in the demolition of wall panels and hanging material during the shock too much or Stacking too concentrated, easy to form destructive cracks.
1.3 Raw material control aspects
In terms of materials, sand and gravel is too large, the concrete cohesive force is insufficient, the quality of the binder is unstable, especially with III grade fly ash premixed II fly ash, easy to form shrinkage cracks.
1.4 mix design aspects
In terms of mix design, the amount of cement and the amount of admixture is too high, the slump is too large, the shrinkage of coagulation is larger and the admixture is more. Concrete condensation is too long, easy to form shrinkage cracks.
2, control measures
2.1 Material Control
Coagulation enterprises to strengthen the detection of raw materials to control the control of gravel material mud content, increase the frequency of mixing materials to prevent the use of substandard raw materials
2.2 Matching ratio control
Strict control of water-cement ratio, to reduce the use of Mercury, control admixture and admixture of the mixed, the final setting time normal control in 8 ~ 12h, when the condensation time should be long under the guidance of technical personnel to strengthen the table blood conservation, appropriate delay Line and other processes to carry out; control the right slump, put an end to the map to facilitate the expansion of the slump or on-site random secondary water.
2.3 Construction control
Coagulation to meet the requirements of the construction conditions, the slump as small as possible, if the dumping of concrete on the slump is too small, by the concrete technical staff to use water-reducing agent after the dosing method, to adjust and stir even rear Can be discharged pouring. Try to avoid the concrete waiting at the site to ask too long to prevent the interval between the pouring layer is too long and the formation of cold joints, concrete construction in the construction process should be strictly enforced national standards and specifications, pouring concrete should be smooth, Early condensate, before the final condensate should be carried out before the light receiving process, the appropriate increase in the number of times the light, the final finish before the completion of light receiving work, and in the surface covered with thin film, straw bag, etc., if necessary, sprinkler curing agent, after pouring must be strictly enforced Conservation system.
Now a lot of site with a polisher in the floor to receive light, with particular attention should be carried out before and after the beginning of the initial condensate, after the final closure of the machine, or because the concrete strength is small, prone to vibration caused by micro-cracks, this crack is not easy heal.
For the beam plate (floor) after the end of the concrete pouring force should not be too early, lifting materials to lightly and scattered stacking, demolition should not be too early, demolition of the mold in the process did not just pour the site to produce too much vibration to avoid Destructive cracks.
2.4 conservation control
After the completion of pouring must strictly implement the maintenance system, in time on the concrete surface covered with plastic film, straw bags, etc., the conditions permit the spraying of conservation agents recommended for conservation, timely watering and curing, curing time shall not be less than 7d, Admixtures or hangings required for the concrete, moisture conservation shall not be less than 14d, so that the concrete can be a good early conservation, to prevent the occurrence of early cracks and other quality problems.
3, the conclusion
(1) strict control of raw materials quality Star off, the use of raw materials meet the requirements;
(2) the choice of quality and stability of the admixture and good admixture, control the amount;
(3) concrete mix ratio design is reasonable, using low water gray (glue) ratio;
(4) control the construction of concrete pouring all aspects of the time, the timing of light, the number of timely coverage;
(5) high-strength coagulation after pouring moisture conservation measures.
From:mobile concrete batching plant